Hỏi về mô phỏng dòng chảy trong van

Discussion in 'CAE & CÁC PHẦN MỀM MÔ PHỎNG' started by Persious, Mar 1, 2018.

  1. umy

    umy Well-Known Member

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    - Mấy cô cậu đào tạo ủy quyền ANSYS ở VN thâu tiền, mà không giải thích cho học viên hiểu được sao ? Tôi phải đổ vỏ sò, tư vấn chùa cho cái bọn nầy à ??:p

    - Hỏi các đào tạo nầy (thường là vị "TS" có được hổ trợ rộng nhiều TL của Ansys bên Mỹ , nhưng ko có chiều sâu qua các áp dụng trong thực tế ! đỉnh cao nghề nghiệp :rolleyes:);
    Cho biết trong trường hợp thực tế nào ?? thì dùng mô hình nào Viscous hoặc Turbulent ? và chọn RB k-epsilon hoặc k-omega để thích hợp !!> Mời các Cô Cậu ấy vào Dđ MesLab nầy thảo luận, trao đổi và đưa TL lên thêm. Bớt quản cáo gió nhiều quá !:cool:
    Xem thêm k-epsilon or k-omega for turbulence models (tùy thuộc Reynolds)
    Fluent Inc. (2002). 2. Turbulence models. A turbulence model is a computational procedure to close the system of mean flow equations
    www.bakker.org/dartmouth06/engs150/10-rans.ppt


    - Tích lủy trong mềm là kiến thức cao hằng 100 năm! Áp dung cho chuyên ngành dòng chảy nầy rất rộng, số chuyên gia giao tiếp trao đổi làm việc với công ty tôi ở Âu Mỹ thường là Master trở lên, chuyên gia có >10 năm chuyên nghề. >>
    - Cho SV giỏi như cậu Persious muốn hiểu được phải cố gắn qua bằng KS, ra ngoài học thêm Master và vào kỹ nghệ làm khoãng 5 đến 10 năm nghề.

    - Đi ngang về tắc như ở VN có thể tự tìm hiểu thêm: hiểu biết được khi nào phải tính dòng chảy cho cái gì: tính ứng suất thay đổi gia tăng theo thời gian! thêm (Gió động, Biển động trong Offshore), Nhiệt độ thay đổi rất lớn trong lảnh vưc Hạt nhân nguyên tử (Kernspalten), Hội tụ hạt nhân (Kernfusion)...Tính phi cơ của Boeing, Airbus ...
    Thí dụ; Tại sao Fatigue Turbin phản lực cho phi cơ mỹ sống lâu gấp 3 lần hơn nga !! của trung quốc chưa đạt đúng mực được ... Có Áp dụng thực tế thì mới hiểu thêm được cho từng bài toán, chứ không thể nào giải thích qua loa cho giống nòi thánh gió "hiểu" được !:D
     
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  2. umy

    umy Well-Known Member

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    Xem thêm về lối chọn mô hình, chia mạng cho dòng chảy qua Comsol Blog (Thử so sánh đưa TL của Solidwork, Hyperwork ...)
    1- Lý thuyết sâu rộng của Fluent về k-epsilon, k-omega có cho ở bài #5
    2- Giãi thích của CFX:
    https://www.sharcnet.ca/Software/Ansys/16.2.3/en-us/help/cfx_thry/i1302321.html
    3- Trích: COMSOL BLOG:
    https://www.comsol.com/multiphysics/mesh-refinement
    Which Turbulence Model Should I Choose for My CFD Application?
    [​IMG] Walter Frei July 6, 2017
    [​IMG] [​IMG] [​IMG] [​IMG]
    The COMSOL Multiphysics® software offers several different formulations for solving turbulent flow problems: the L-VEL, algebraic yPlus, Spalart-Allmaras, k-ε, k-ω, low Reynolds number k-ε, SST, and v2-f turbulence models. These formulations are available in the CFD Module, and the L-VEL, algebraic yPlus, k-ε, and low Reynolds number k-ε models are also available in the Heat Transfer Module. In this blog post, learn why to use these various turbulence models, how to choose between them, and how to use them efficiently.
    This post was originally published in 2013. It has since been updated to include all of the turbulence models currently available with the CFD Module as of version 5.3 of the COMSOL® software.
    Introduction to Turbulence Modeling
    Let’s start by considering the fluid flow over a flat plate, as shown in the figure below. The uniform velocity profile hits the leading edge of the flat plate, and a laminar boundary layer begins to develop. The flow in this region is very predictable. After some distance, small chaotic oscillations begin to develop in the boundary layer and the flow begins to transition to turbulence, eventually becoming fully turbulent.

    [​IMG]

    The transition between these three regions can be defined in terms of the Reynolds number, [​IMG], where [​IMG] is the fluid density; [​IMG] is the velocity; [​IMG] is the characteristic length (in this case, the distance from the leading edge); and [​IMG] is the fluid’s dynamic viscosity. We will assume that the fluid is Newtonian, meaning that the viscous stress is directly proportional, with the dynamic viscosity as the constant of proportionality, to the shear rate. This is true, or very nearly so, for a wide range of fluids of engineering importance, such as air or water. Density can vary with respect to pressure, although it is here assumed that the fluid is only weakly compressible, meaning that the Mach number is less than about 0.3. The weakly compressible flow option for the fluid flow interfaces in COMSOL Multiphysics neglects the influence of pressure waves on the flow and pressure fields.
    In the laminar regime, the fluid flow can be completely predicted by solving Navier-Stokes equations, which gives the velocity and the pressure fields. Let us first assume that the velocity field does not vary with time. An example of this is outlined in The Blasius Boundary Layer tutorial model. As the flow begins to transition to turbulence, oscillations appear in the flow, despite the fact that the inlet flow rate does not vary with time. It is then no longer possible to assume that the flow is invariant with time. In this case, it is necessary to solve the time-dependent Navier-Stokes equations, and the mesh used must be fine enough to resolve the size of the smallest eddies in the flow. Such a situation is demonstrated in the Flow Past a Cylinder tutorial model. Note that the flow is unsteady, but still laminar in this model. Steady-state and time-dependent laminar flow problems do not require any modules and can be solved with COMSOL Multiphysics alone.

    [​IMG]

    As the flow rate — and thus also the Reynolds number — increases, the flow field exhibits small eddies and the spatial and temporal scales of the oscillations become so small that it is computationally unfeasible to resolve them using the Navier-Stokes equations, at least for most practical cases. In this flow regime, we can use a Reynolds-averaged Navier-Stokes (RANS) formulation, which is based on the observation that the flow field (u) over time contains small, local oscillations (u’) and can be treated in a time-averaged sense (U). For one- and two-equation models, additional transport equations are introduced for turbulence variables, such as the turbulence kinetic energy (k in k-ε and k-ω).

    In algebraic models, algebraic equations that depend on the velocity field — and, in some cases, on the distance from the walls — are introduced in order to describe the turbulence intensity. From the estimates for the turbulence variables, an eddy viscosity that adds to the molecular viscosity of the fluid is calculated. The momentum that would be transferred by the small eddies is instead translated to a viscous transport. Turbulence dissipation usually dominates over viscous dissipation everywhere, except for in the viscous sublayer close to solid walls. Here, the turbulence model has to continuously reduce the turbulence level, such as in low Reynolds number models. Or, new boundary conditions have to be computed using wall functions.

    Low Reynolds Number Models
    The term “low Reynolds number model” sounds like a contradiction, since flows can only be turbulent if the Reynolds number is high enough. The notation “low Reynolds number” does not refer to the flow on a global scale, but to the region close to the wall where viscous effects dominate; i.e., the viscous sublayer in the figure above. A low Reynolds number model is a model that correctly reproduces the limiting behaviors of various flow quantities as the distance to the wall approaches zero. So, a low Reynolds number model must, for example, predict that k~y2 as y→0. Correct limiting behavior means that the turbulence model can be used to model the whole boundary layer, including the viscous sublayer and the buffer layer.

    Most ω-based models are low Reynolds number models by construction. But the standard k-ε model and other commonly encountered k-ε models are not low Reynolds number models. Some of them can, however, be supplemented with so-called damping functions that give the correct limiting behavior. They are then known as low Reynolds number k-ε models.

    Low Reynolds number models often give a very accurate description of the boundary layer. The sharp gradients close to walls do, however, require very high mesh resolutions and that, in turn, means that the high accuracy comes at a high computational cost. This is why alternative methods to model the flow close to walls are often employed for industrial applications.

    Wall Functions
    The turbulent flow near a flat wall can be divided into four regions. At the wall, the fluid velocity is zero, and in a thin layer above this, the flow velocity is linear with distance from the wall. This region is called the viscous sublayer, or laminar sublayer. Further away from the wall is a region called the buffer layer. In the buffer region, turbulence stresses begin to dominate over viscous stresses and it eventually connects to a region where the flow is fully turbulent and the average flow velocity is related to the log of the distance to the wall. This is known as the log-law region. Even further away from the wall, the flow transitions to the free-stream region. The viscous and buffer layers are very thin and if the distance to the end of the buffer layer is [​IMG], then the log-law region will extend about [​IMG] away from the wall.

    [​IMG]

    It is possible to use a RANS model to compute the flow field in all four of these regions. However, since the thickness of the buffer layer is so small, it can be advantageous to use an approximation in this region. Wall functions ignore the flow field in the buffer region and analytically compute a nonzero fluid velocity at the wall. By using a wall function formulation, you assume an analytic solution for the flow in the viscous layer and the resultant models will have significantly lower computational requirements. This is a very useful approach for many practical engineering applications.

    [​IMG]

    If you need a level of accuracy beyond what the wall function formulations provide, then you will want to consider a turbulence model that solves the entire flow regime as described for the low Reynolds number models above. For example, you may want to compute lift and drag on an object or compute the heat transfer between the fluid and the wall.

    Automatic Wall Treatment
    The automatic wall treatment functionality, which is new in COMSOL Multiphysics version 5.3, combines benefits from both wall functions and low Reynolds number models. Automatic wall treatment adapts the formulation to the mesh available in the model so that you get both robustness and accuracy. For instance, for a coarse boundary layer mesh, the feature will utilize a robust wall function formulation. However, for a dense boundary layer mesh, the automatic wall treatment will use a low Reynolds number formulation to resolve the velocity profile completely to the wall.

    Going from a low Reynolds number formulation to a wall function formulation is a smooth transition. The software blends the two formulations in the boundary elements. Then, the software calculates the wall distance of the boundary elements’ grid points (this is in viscous units given by a liftoff). The combined formulations are then used for the boundary conditions.

    All turbulence models in COMSOL Multiphysics, except the k-ε model, support automatic wall treatment. This means that the low Reynolds number models can be used for industrial applications and that their low Reynolds number modeling capability is only invoked when the mesh is fine enough.

    About the Various Turbulence Models
    The eight RANS turbulence models differ in how they model the flow close to walls, the number of additional variables solved for, and what these variables represent. All of these models augment the Navier-Stokes equations with an additional turbulence eddy viscosity term, but they differ in how it is computed.

    L-VEL and yPlus
    The L-VEL and algebraic yPlus turbulence models compute the eddy viscosity using algebraic expressions based only on the local fluid velocity and the distance to the closest wall. They do not solve any additional transport equations. These models solve for the flow everywhere and are the most robust and least computationally intensive of the eight turbulence models. While they are generally the least accurate models, they do provide good approximations for internal flow, especially in electronic cooling applications.

    Spalart-Allmaras
    The Spalart-Allmaras model adds a single additional variable for an undamped kinematic eddy viscosity. It is a low Reynolds number model and can resolve the entire flow field down to the solid wall. The model was originally developed for aerodynamics applications and is advantageous in that it is relatively robust and has moderate resolution requirements. Experience shows that this model does not accurately compute fields that exhibit shear flow, separated flow, or decaying turbulence. Its advantage is that it is quite stable and shows good convergence.

    k-ε
    The k-ε model solves for two variables: k, the turbulence kinetic energy; and ε (epsilon), the rate of dissipation of turbulence kinetic energy. Wall functions are used in this model, so the flow in the buffer region is not simulated. The k-ε model has historically been very popular for industrial applications due to its good convergence rate and relatively low memory requirements. It does not very accurately compute flow fields that exhibit adverse pressure gradients, strong curvature to the flow, or jet flow. It does perform well for external flow problems around complex geometries. For example, the k-ε model can be used to solve for the airflow around a bluff body.

    The turbulence models listed below are all more nonlinear than the k-ε model and they can often be difficult to converge unless a good initial guess is provided. The k-ε model can be used to provide a good initial guess. Just solve the model using the k-ε model and then use the new Generate New Turbulence Interface functionality, available in the CFD Module with COMSOL Multiphysics version 5.3.

    k-ω
    The k-ω model is similar to the k-ε model, but it solves for ω (omega) — the specific rate of dissipation of kinetic energy. It is a low Reynolds number model, but it can also be used in conjunction with wall functions. It is more nonlinear, and thereby more difficult to converge than the k-ε model, and it is quite sensitive to the initial guess of the solution. The k-ω model is useful in many cases where the k-ε model is not accurate, such as internal flows, flows that exhibit strong curvature, separated flows, and jets. A good example of internal flow is flow through a pipe bend.

    Low Reynolds Number k-ε
    The low Reynolds number k-ε model is similar to the k-ε model, but does not need wall functions: it can solve for the flow everywhere. It is a logical extension of the k-ε model and shares many of its advantages, but generally requires a denser mesh; not only at walls, but everywhere its low Reynolds number properties kick in and dampen the turbulence. It can sometimes be useful to use the k-ε model to first compute a good initial condition for solving the low Reynolds number k-ε model. An alternative way is to use the automatic wall treatment and start with a coarse boundary layer mesh to get wall functions and then refine the boundary layer at the interesting walls to get the low Reynolds number models.

    The low Reynolds number k-ε model can compute lift and drag forces and heat fluxes can be modeled with higher accuracy compared to the k-ε model. It has also shown to predict separation and reattachment quite well for a number of cases.

    SST
    The SST model is a combination of the k-ε model in the free stream and the k-ω model near the walls. It is a low Reynolds number model and kind of the “go to” model for industrial applications. It has similar resolution requirements to the k-ω model and the low Reynolds number k-ε model, but its formulation eliminates some weaknesses displayed by pure k-ω and k-ε models. In a tutorial model example, the SST model solves for flow over a NACA 0012 Airfoil. The results are shown to compare well with experimental data.

    v2-f
    Close to wall boundaries, the fluctuations of the velocity are usually much larger in the parallel directions to the wall in comparison with the direction perpendicular to the wall. The velocity fluctuations are said to be anisotropic. Further away from the wall, the fluctuations are of the same magnitude in all directions. The velocity fluctuations become isotropic.

    The v2-f turbulence model describes the anisotropy of the turbulence intensity in the turbulent boundary layer using two new equations, in addition to the two equations for turbulence kinetic energy (k) and dissipation rate (ε). The first equation describes the transport of turbulent velocity fluctuations normal to the streamlines. The second equation accounts for nonlocal effects such as the wall-induced damping of the redistribution of turbulence kinetic energy between the normal and parallel directions.

    You should use this model for enclosed flows over curved surfaces, for example, to model cyclones.

    Meshing Considerations for CFD Problems
    Solving for any kind of fluid flow problem — laminar or turbulent — is computationally intensive. Relatively fine meshes are required and there are many variables to solve for. Ideally, you would have a very fast computer with many gigabytes of RAM to solve such problems, but simulations can still take hours or days for larger 3D models. Therefore, we want to use as simple a mesh as possible, while still capturing all of the details of the flow.

    Referring back to the figure at the top of this blog post, we can observe that for the flat plate (and for most flow problems), the velocity field changes quite slowly in the direction tangential to the wall, but quite rapidly in the normal direction, especially if we consider the buffer layer region. This observation motivates the use of a boundary layer mesh. Boundary layer meshes (which are the default mesh type on walls when using our physics-based meshing) insert thin rectangles in 2D or triangular prisms in 3D at the walls. These high-aspect-ratio elements will do a good job of resolving the variations in the flow speed normal to the boundary, while reducing the number of calculation points in the direction tangential to the boundary.

    [​IMG]
    The boundary layer mesh (magenta) around an airfoil and the surrounding triangular mesh (cyan) for a 2D mesh.

    [​IMG]
    The boundary layer mesh (magenta) around a bluff body and the surrounding tetrahedral mesh (cyan) for a 3D volumetric mesh.

    Evaluating the Results of Your Turbulence Model
    Once you’ve used one of these turbulence models to solve your flow simulation, you will want to verify that the solution is accurate. Of course, as you do with any finite element model, you can simply run it with finer and finer meshes and observe how the solution changes with increasing mesh refinement. Once the solution does not change to within a value you find acceptable, your simulation can be considered converged with respect to the mesh. However, there are additional values you need to check when modeling turbulence.

    When using wall function formulations, you will want to check the wall resolution viscous units (this plot is generated by default). This value tells you how far into the boundary layer your computational domain starts and should not be too large. You should consider refining your mesh in the wall normal direction if there are regions where the wall resolution exceeds several hundred. The second variable that you should check when using wall functions is the wall liftoff (in length units). This variable is related to the assumed thickness of the viscous layer and should be small relative to the surrounding dimensions of the geometry. If it is not, then you should refine the mesh in these regions as well.

    [​IMG]
    The maximum wall liftoff in viscous units is less than 100, so there is no need to refine the boundary layer mesh.

    When solving a model using low Reynolds number wall treatment, check the dimensionless distance to cell center (also generated by default). This value should be of order unity everywhere for the algebraic models and less than 0.5 for all two-equation models and the v2-f model. If it is not, then refine the mesh in these regions.

    Concluding Thoughts
    In this blog post, we have discussed the various turbulence models available in COMSOL Multiphysics, highlighting when and why you should use each one of them. The real strength of the COMSOL® software is when you want to combine your fluid flow simulations with other physics, such as finding stresses on a solar panel in high winds, forced convection modeling in a heat exchanger, or mass transfer in a mixer, among other possibilities.

    Contact COMSOL to Evaluate the Software
    If you are interested in using the COMSOL® software for your CFD and multiphysics simulations, or if you have a question that isn’t addressed here, please contact us.
     
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  3. umy

    umy Well-Known Member

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    Luận văn Th.S ở Queen' Uni bên Canada, dùng Ansys CFD Fluent tính Gió động cho Buiding, có so sánh chọn lựa với nhiều mô hình lý tưởng !
    Xem và lưu trử cho các bạn nào làm ĐATN về dòng chảy nầy.
    An Evaluation of Turbulence Models for the Numerical Study of Forced and Natural Convective Flow in Atria
    https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/OKQ/TC-OKQ-1884.pdf
     
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  4. Persious

    Persious Active Member Staff Member

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    Cháu cảm ơn bác Umy đã mất công tìm giúp những phần kiến thức vô giá mà cũng khó tìm này ạ, cháu sẽ lưu lại và nghiên cứu kỹ :)
     
  5. Persious

    Persious Active Member Staff Member

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    Gần đây cháu cũng tự tìm được một vài tài liệu về các mô hình rối (Turbulent Model) trong ANSYS, nên cháu đăng lên đây để nếu ai có quan tâm và thắc mắc thì mọi người cũng trao đổi thêm ạ. Tiện cũng share luôn phần Technical Reference bên SolidWorks Flow Simulation, để tham khảo thêm cách giải thích của hãng đó, cháu cũng chưa đọc hết ạ.
    1. ANSYS Fluent V2F Turbulence Model Manual 15.0
    https://drive.google.com/file/d/1T_UprhGSYneOV91oO-zm7CmXXgSqlWZY/view?usp=sharing
    2. Lecture 7: Turbulence Modeling Introduction
    https://drive.google.com/file/d/1hV-JfM1LjwHoyUiHCzjjRQjuLBYO_kIG/view?usp=sharing
    3. SolidWorks Flow Simulation 2012 Technical Reference
    https://drive.google.com/file/d/12rf6Jke_ipMnJzUHEod-xWQtVhb3oby8/view?usp=sharing
    4. SolidWorks Flow Simulation 2012 Solving Engineering Tasks
    https://drive.google.com/file/d/1_10hSicBNEncZk5tkR7BezMG3GBLSxNo/view?usp=sharing
    5. Turbulence Models - Documentations ANSYS
    http://www.afs.enea.it/project/neptunius/docs/fluent/html/th/node330.htm
    6. Turbulence Modeling - ANSYS Fluent Advanced Course
    https://drive.google.com/file/d/1y742EOjRjOYDlaCJYNGPp3igJUExEwUQ/view
    Vẫn mong bác Umy có kinh nghiệm lâu năm cho ý kiến ạ, cháu hiểu biết có hạn nên không thể tìm được nhiều phần hay hơn nữa ạ:)
     
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  6. umy

    umy Well-Known Member

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    Đọc so sánh các TL và dùng đầu óc sáng suốt có chất xám kiễm lại, mới trưởng thành được!. ;)
    Lể phép nhưng không ngu dại tin hết mọi thứ ! Đừng tôn suy cá nhân tôi quá có thể ... lầm lạc !
    Lối tôn suy "cá nhân tuyệt đối một chiều" nầy đã làm CAE trong nước VN chậm lại, thất bại nhiều ngành nghề CAE ... "ổn định đến 99 năm" thì khó ngoi đầu lên với người !:D:mad:
     
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  7. Persious

    Persious Active Member Staff Member

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    Hì hì, cháu cũng chọn lọc những tài liệu cần thiết 1 phần dựa vào kinh nghiệm của bác, nhiều cái khác do cháu tự mò ra được thôi ạ, chứ cũng không phải là suy tôn bác quá đâu:(. Nhưng '' Tiên học lễ, hậu học văn'' , thế hệ sau luôn luôn tiếp thu ý kiến (một cách chọn lọc không phải là thụ động) từ thế hệ trước thì từ đó mới có thể khá hơn được ạ :D
    Tuổi trẻ không bao giờ ngần ngại khó khăn, nhưng cũng phải thật khiêm nhường.:)
     
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  8. Persious

    Persious Active Member Staff Member

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    Lộ trình (tham khảo) cho người mới làm về CFD. (Source : Simscale)
    -
    Bao gồm nhiều link tài liệu về cơ học chất lỏng, âm học, khí động học, nhiệt động học, mô hình rối, dòng chảy, truyền nhiệt .....
    https://www.simscale.com/blog/2016/11/best-fluid-mechanics-books/
    Looking for a Fluid Mechanics Book? Here’s a List!
    [​IMG]
    WRITTEN BY

    Ajay Harish

    UPDATED ON

    March 14th, 2018

    APPROX READING TIME

    7-Minute Read

    BlogCFDLooking for a Fluid Mechanics Book? Here’s a List!
    98
    Fluid mechanics is a vast subject and addresses issues related to the mechanical behavior of fluids. Fluids, in general, can mean both liquids and gasses. Fluid mechanics has a wide range of applications, from mechanical and aerospace engineering to geophysics and biomechanics. It is difficult to find real-world cases that are not influenced by fluid flows. There is no single fluid mechanics book that covers the topic in full but herewith is a list to aid the study of this topic.

    This article discusses fluid mechanics books and the relevant literature pertaining to different areas of CFD that would be of interest to learners. Starting from basic thermodynamics and dimensional analysis, the article continues to address sources related to incompressible and compressible flows, viscous flows and boundary layers, acoustics, turbomachinery, and eventually turbulence.

    Dimensional Analysis and Mathematical Preliminaries
    Dimensional analysis is a mathematical technique that is commonly used in fluid mechanics to study the influence of parameters on the flow. Dimensional analysis is used to build relationships between several variables.

    One of the very common non-dimensional numbers is the Reynolds number, which quantifies the ratio between inertial and viscous forces prevalent in the flow. For example, when designing large structures in aerospace and aeronautical applications, it is impossible to build real-scale models during the design phase. Hence, reduced scale models are used to simulate the same turbulence effects (or Reynolds number flow).

    One of the classics is the fluid mechanics book titled “Dimensional analysis” by Bridgeman P W. However, the book is quite old and shows inconsistencies with present notation. An alternate reference is “Similarity and Dimensional Methods in Mechanics” by L. I. Sedov. For the uninitiated, any fluid mechanics book should provide a brief overview of dimensional analysis to begin and which provides a suitable quick read to understand the topic in brevity.

    In addition, a basic understanding of vector calculus goes a long way to an easier comprehension of mechanics. Some beginner references include:

    General Fluid Mechanics Book List
    [​IMG]
    Airflow analysis of a compressor with SimScale (turbulent and compressible flow)
    Once the basics of dimensional analysis and the rationale for non-dimensional numbers have been established, an appropriate foundation exists to move into the area of general fluid dynamics.

    An Introduction to Fluid Dynamics” by G. K. Batchelor remains a classic fluid mechanics book that addresses the theories of this field in an elegant manner. Though published in 1960’s, this timeless classic still holds a reader’s attention.

    Physical Fluid Dynamics” by D. J. Tritton provides an excellent rendition of fluid mechanics related issues from the perspective of an engineer. This is a strongly recommended read for mechanical and aerospace engineers who are interested in understanding fluid mechanics.

    For those who are more mathematically inclined, “Fluid Mechanics” by L. D. Landau and E. M. Lifshitz is a perfect treatise on fluid mechanics. The latest reprint also includes a chapter on computational fluid dynamics and introduces simple computational methodologies for simple flows.

    Incompressible and inviscid flows, or commonly known as potential flows, are ordinarily used in design processes. Though simple, they provide an excellent estimate regarding the flow parameters. Most often, like in pipe flows, fluid velocity is small enough that there is no change in density. Thus, they can be considered as incompressible in nature. “Incompressible Flow” by R. L. Panton discusses various matters related to primarily incompressible fluids.

    For less experienced readers, some topics include control volume equations, differential equations, Eulerian and Lagrangian formulations, Reynolds transport theorem, analysis of stress and strain, Newtonian fluid, Navier-Stokes equations, vorticity equation, and energy theorems.

    For an example of how fluid dynamics can be applied in industrial applications, you can download this free white paper on how to optimize HVAC system designs with cloud-based CFD simulation.



    Fluid Dynamics In [​IMG]


    Compressible Fluid Flow
    For many mechanical and aerospace engineering applications, the fluid speeds are much larger and comparable to the speed of sound. In these applications, the fluid density changes cannot be neglected and thus need to be treated as compressible in nature.

    Modern Compressible Flow: With Historical Perspective” by J. D. Anderson has been a well-renowned fluid mechanics book that is prescribed in most graduate courses in fluid mechanics. The book is aimed at engineers and professionals and provides a balanced outlook between traditional methods and modern computer techniques. Another regularly used reference book is “Compressible Fluid Dynamics” by P. A. Thompson. Thompson also provides an even approach that is most suitable for applied researchers and professionals.

    The book “Elements of Gasdynamics” by H. A. Liepmann and A. Roshko. Liepmann and Roshko remains a timeless exemplary. Their practical Caltech experience with aeronautical testing is evident in this text. Nevertheless, the book requires a good working knowledge of calculus and basic physics.

    [​IMG]
    CFD simulation of compressible flow over an airfoil with SimScale
    Some topics in this topic for newer readers are as follows:

    • Quasi 1-D flow: Shock waves, flows with friction, flows with heat addition, Mollier diagram, the fundamental derivative of gas dynamics, nozzles, subsonic and supersonic flow, choking total pressure, stagnation pressure, static pressure.
    • 1-D unsteady flow: Riemann invariants, characteristics expansion waves, shock waves, Rayleigh line, shock adiabat or Hugoniot weak shock and strong shock limits, acoustics contact surfaces, shock tubes, detonation, flames
    • 2-D steady flow: Characteristics, Prandtl-Meyer expansion fan, flow around corners (interior and exterior), the formation of shock waves, polar diagrams, Mach waves, Crocco’s theorem, moving sources, acoustic solution
    Viscous Flows and Boundary Layers
    All fluids are viscous in nature and consequently exhibit some frictional behavior. When fluids flow, the neighboring layers of fluids are moving at slightly different velocities and this causes a frictional resistance that is more commonly known as viscosity. The velocity gradient is referred to as strain rate. Some fluids — known as Newtonian fluids — show a linear dependence between strain rate and viscous force. The constant of proportionality here is often referred to as the coefficient of viscosity. In contrast, non-Newtonian fluids, such as blood and emulsions, demonstrate a more complicated nonlinear behavior.

    There are several fluid dynamics books in this regard but three stand out and are generally used in most universities and by professionals:

    While the books by F. M. White and H. Schlichting are more up-to-date, the fluid mechanics book by Sherman is slightly harder to find. Nevertheless, all are exceptional to get an insight into viscous flows.

    Acoustics, Aerodynamics, and Rotating Flows
    [​IMG]
    CFD analysis of a centrifugal pump carried out with SimScale
    Some tertiary or specialized topics that are needed for a thorough understanding of fluid flows include acoustics, aerodynamics, and rotating flows. Though each topic caters to a different audience, they are all specialized topics for advanced readers and hence clustered here.

    Books that provide an interesting overview of acoustics include:

    Aerodynamics in itself is a vast area but some interesting preliminary reads include:

    Rotating flows are commonly seen in turbomachinery and a starting reference would be “Rotating Fluids in Engineering and Science” by J. P. Vanyo.

    Turbulence
    [​IMG]
    Turbulent Flow over a House with SimScale
    An undisputed book on the understanding of turbulence is the book on “Turbulent Flows” by Stephen B. Pope. An alternative for readers who would prefer slightly different notations is “Turbulence: An Introduction for Scientists and Engineers” by P. Davidson. Both these books are excellent for the use of engineers, scientists, mathematicians, and hobbyists alike.

    Thermodynamics and Data Tables
    Thermodynamics forms the basis of all mechanics. As a beginner, it can be confusing to understand how the two are related. However, one needs to understand that mechanics deal with the motion of bodies and all objects are made of smaller particles that are governed by the laws of thermodynamics.

    It would not be wrong to say that mechanics is a derivative of thermodynamics. Some important references to get started with thermodynamics are:

    Some important data tables needed for calculations include:

    Conclusion
    This list of the best fluid mechanics books can help with the understanding of all areas of fluid dynamics, including compressible flows, viscous flows, turbulence, aerodynamics, acoustics and thermodynamics. If you’d like to learn how to put your knowledge into practice, watch the recording of this free webinar on Formula One aerodynamics with Torbjörn Larsson.

    Discover the benefits of cloud-based CFD simulation by creating a free account on the SimScale platform, no credit card required.
     
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  9. umy

    umy Well-Known Member

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  10. umy

    umy Well-Known Member

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  11. umy

    umy Well-Known Member

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    ** Tài Liệu FSI - ở ĐH Kassel bên Đức >> Chuyên nhiều về Lý thuyết "cao siêu" của các GS-TS !o_O!

    International Workshop on FLUID-STRUCTURE ITERACTION 276Pages
    Theory, numerics and Applications - Uni Kassel 2009
    http://www.uni-kassel.de/upress/online/frei/978-3-89958-666-4.volltext.frei.pdf

    Lưu Ý:
    nhận xét sự khác biệt như thể nào
    - Chất Lỏng (Fluid) và thể Khí (Area) ?
    - Structure là Vách cứng hay vách đàn hồi ?
    - môi trường khí lỏng trong khung structure hay khối cứng bay lội trong khí nước ?

    Dùng lý thuyết trong ấy làm LV nghiên cứu cao cấp được lắm -

    Xem thêm để biết ở ĐH "người ta" phát triển đến đâu rồi.
    Hiểu được tí nào thì tốt, ko hiểu cũng chẵng sao cả ;)
    _______________________________________
    Quê nhà, Ta tắm Ao ta.
    Dù trong, dù đục Ao nhà cũng vậy thôi!:rolleyes:
     
  12. umy

    umy Well-Known Member

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    https://meslab.org/threads/blog-mo-phong-va-thiet-ke-cad-cae-engineering.51574/page-11#post-243041

    - Thú vị khi xem các bài tập trong sách, so sánh với vài kết quả tính mô phỏng và thí nghiệm ở Windtunnel.

    - Áp dụngđược thực tiển gì ở VN chưa ? để chế tạo phi cơ cho VN trong tương lai ?? tiết kiệm cả mấy tỉ U$ đấy nhỉ !!
    - SV, KS trẻ ... mà hiểu được sách nầy, lên đứng bụt giãng bài cho các thầy ở ĐH được. !:rolleyes:!
    _____________________________________
    Nếu là đam mê thực sự, cố gắn hoàn tất học trình ĐH... phải xuất ngoại mới có cơ hôi thực hiện mộng cao.
    Bây giờ cứ trao dồi thêm kiến thức, nhưng đừng làm "thánh gió VN" !

    Xem thêm:
    TL nhỏ
    https://ruag.picturepark.com/Go/9em80sSl/V/12544/1?Purgechache
    Website:
    https://aerodynamics.ruag.com/en/aerodynamics/simulation-analysis
     
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  13. Duc Dinh

    Duc Dinh Member

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    Bác Umy, cháu sinh năm 1987, độ tuổi được xem là khá già ở VN, cháu chưa biết tiếng Đức. Cháu có thể chuẩn bị tiếng Đức rồi qua đó được không bác.
     
  14. umy

    umy Well-Known Member

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    Hỏi:
    Trích: Học từ xa Ansys Fluent
    https://meslab.org/threads/hoc-tu-xa-ansys-fluent.39986/
    Đáp: (Dựa theo chương trình Cỏrnell University)
    https://www.facebook.com/groups/vudse/
    Quang Lê Đặng hat seinen Beitrag geteilt.
    21. Februar um 03:21
    Tôi xin phép admin cho đăng bài này.
    Sau nhiều lần mở thử những khóa học CFD cho sinh viên thì hôm nay tôi mới tự tin mở những khóa học chính thức cho những bạn nào cần update kiến thức về CFD. Khóa học sẽ được tổ chức online và free đến tất cả mọi người, miễn là muốn học hỏi thêm về CFD.
    Bạn nào quan tâm có thể join group và comment để đăng ký học và có thêm thông tin về khóa học.
    Tôi cũng welcome các anh chị có kiến thức và kỹ năng join course và góp ý để course ngày càng hoàn thiện hơn.
    Cám ơn các bạn đã đọc thông tin

    [​IMG]
    ‎Quang Lê Đặng‎ an CFD For Engineering
    20. Februar um 20:04

    Online Computational Fluid Dynamics (CFD) course
    Starting date: flexible date (please contact us)
    Fee: Free
    Description: This course is suitable for
    - Engineers and students who want to learn CFD (physical phenomenon, numerical method,etc) and learn how to use CFD commercial software following our materials (below).
    - A group of students with specific problems who need advice and consultant.
    - We also encourage students would like to study CFD using openFOAM to contact us
    We are welcome all students and engineers to apply this course. Please leave comment and we will contact you, thank you.
    Material:
    We are using material from
    https://confluence.cornell.edu/…/SI…/FLUENT+Learning+Modules
    https://confluence.cornell.edu/display/SIMULATION/FLUENT+Learning+Modules
     
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  15. umy

    umy Well-Known Member

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    TL nhỏ dành cho cậu Persious và Anh Duc Dinh và các bạn trẻ có quan tâm vào nghề nầy.
    Introduction to Computational Fluid Dynamics 25 Trang
    http://www.mathematik.uni-dortmund.de/~kuzmin/cfdintro/lecture1.pdf
    Chú ý đến những thí dụ áp dụng CFD trong thực tiển !
    ** Examples of CFD applications trang 5 và 6


    - thêm các thí dụ thực tiển khác CAE >> CFD có khá nhiều trong đây:
    The Colorful Fluid Mixing Gallery
    http://www.bakker.org/
     
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  16. umy

    umy Well-Known Member

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    Trích bài hay VUDSE:
    [​IMG] Nhã Nguyễn
    Lựa chọn mô hình rối cho bài toán CFD là một vấn đề không đơn giản cho người học cũng như kỹ sư CFD.
    • Nếu là bài toán mới, không kế thừa được kinh nghiệm thì phải tự làm thực nghiệm.
    • Có kết quả thực nghiệm rồi, phải làm sao chọn turbulent model cho phù hợp giữa số và thực nghiệm. Và các mô hình rối tích hợp sẵn trong các phần mềm không phải vạn năng với mọi tình huống.
    Mới đây, mô hình rối GEKO của Fluent được cải tiến uyển chuyển hơn với 6 thông số tùy chỉnh, kỹ sư CFD có thể l...inh hoạt điều chỉnh các thông số này để kết quả số phù hợp với thực nghiệm.

    https://www.ansys.com/blog/how-to-define-a-turbulent-flow-equation-for-cfd-modeling?utm_source=facebook&utm_medium=social&utm_campaign=pf_edu&utm_content=blogpost_03.13.19&fbclid=IwAR0iqUcjiOjLXMLfjsuqV2ZLZCMLDAxf_-KVCkBwtwxQqEI8tENKvGKfPbE
    Mehr anzeigen
    [​IMG]
    ansys.com
    How to Define Your Own Turbulent Flow Equation for CFD Modeling
    Generalized k-omega offers custom CFD modeling to fit your particular turbulent flow.

    Cậu Persious và Anh Duc Dinh làm ơn, tìm hiểu và giải thích tiếng Việt thêm với điều kiện k-ε (K-Epsilon) và SST là gì ? có ảnh hưởng khác nhau thế nào vào kết quả ? cho dòng chảy rối Turbulent Flow.
     
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  17. Persious

    Persious Active Member Staff Member

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    Cháu cảm ơn bác Umy ạ, nhưng tài liệu của bác cho mọi người bị thiếu, may cháu có đủ bộ lecture CFD này, để cháu đăng full lên cho mọi người ai quan tâm thì tham khảo!
    https://drive.google.com/drive/folders/18oVuXSNnVLBik0qQtFGuiAtc3n7oDAQS?usp=sharing
     
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  18. umy

    umy Well-Known Member

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    Persious sưu tầm được trọn bộ bài giãng CFD của ĐH kỹ thuật Dortmund , Khoa ứng dụng toán số bên Đức>> Rất hay!:):)
    Cho những thành viên giỏi như Persious biết tìm toài, tự học thêm... và anh Duc Dinh có thể xem thêm:
    1) một số mềm, tự viết trong ĐH để nghiên cứu được phổ biến.
    http://www.featflow.de/en/index.html
    2) Có vài Luận văn hay trong khoa toán số được đưa ra
    http://www.mathematik.tu-dortmund.de/lsiii/cms/en/schriften.html

    Xem lướt qua, lựa chọn lại những TL nào áp dụng được trong thực tế thì lưu giử (-khoãng 2% có hữu ích!)
     
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  19. umy

    umy Well-Known Member

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    A) Bài học và Tài liệu về CFD ở Thuy Điển ! Có hướng dẩn lập trình với FORTRAN.
    Có thể xem thêm để mở rộng kiến thức và tra cứu thêm các BC cần thiết khi thực hiện các bài tính loại nầy.

    Chalmers University of Technology
    Department of Applied Mecahnics
    Division of Fluid Dynamics
    How to use an in-House Fortran source code - CFD Sweden
    LES & DES 3 day COURSE

    Large-Eddy Simulation (LES) and Detached-Eddy Simulations (DES)
    1. LES of the hill flow [6]. Periodic boundary conditions in streamwise and spanwise directions.


      [​IMG]


    2. DES of the hump flow [6]. Synthetic inlet fluctuations at the inlet [7-9]. Periodic boundary conditions spanwise direction. On a 624x108x64 mesh the CPU time is 20 seconds per time step on a standard PC [14].

      [​IMG] matlab files

      [​IMG]

    http://www.cfd-sweden.se/calc-les/index.html

    Lecture Notes Ch2-Ch9
    http://www.tfd.chalmers.se/~lada/comp_fluid_dynamics/lecture_notes.html

    calc-les.pdf 44Pages
    http://www.tfd.chalmers.se/~lada/postscript_files/calc-les.pdf

    Sách hay: solids-and-fluids_turbulent-flow_turbulence-modelling.pdf 535Pages
    http://www.tfd.chalmers.se/~lada/po...luids_turbulent-flow_turbulence-modelling.pdf

    B) Cho thêm bạn nào muốn dùng nhanh ngôn ngữ Fortran 90 để lập trình trong mềm CFD
    990 Source Codes in Fortran90
    http://people.sc.fsu.edu/~jburkardt/f_src/f_src.html

    ... một bức tranh rõ ràng về cách code > Material on CFD Fortran Coding

    http://cfd2012.com/fortran90.html

    C) Books about writing a cfd code in Fortran


    1. S.Patankar - Numerical Heat Transfer and Fluid Flow
    2. J.H.Ferziger, M.Peric - Computational Methods for Fluidd Dynamics
    3. H.K.Versteeg, W.Malalasekera - An Introduction to Computational Fluid Dynamics
    There are many other good references, but people use these for incompressible viscous flow with Finite Volume Method.
     
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  20. Persious

    Persious Active Member Staff Member

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    Last edited: Aug 3, 2019
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