Bài tập Mô phỏng Piston cho nhóm KS Ôtô với Ansys-CFX
http://automotiveenginesgroup3.blogspot.com/#!
kích thước và mô hình vật liệu có trong links !
A- Transient Thermal Analysis of Piston
The piston, which is one of the most important components of an engine, works at temperatures around 2000oC
1- Chia Mạng lưới Solid cho Mô Hình Píston
Figure 1 CAD model of Piston
2- Nhiệt tác dụng
Temperature difference = 1912-200 = 1712oC
Area of heat transfer = 7022 mm2
Figure 3 Convective Heat Transfer Surfaces
Hence the heat transfer coefficient has been calculated and it is 0.249W/mm2
Temperature Profile of the piston cylinder:
Figure 4 Temperature Profile
This the mesh generated which was further used for the thermal analysis of the piston
Figure 6 Temperature profile of piston at maximum temperature (combustion)
3- Truyền nhiệt:
The temperature below the rings can be observed to be around 200C. This can be explained by the heat transfer from the piston to the ambient surroundings making its temperature equal to that of surroundings i.e. 200C
Figure 7 Total Heat Flux Profile
The profile of heat flux from the cylinder shows that the highest heat transfer takes place from the crown region and the piston rings region.
This supports the earlier result of temperature profile, from which we have stated that flanks will be at minimum temperature.
From this study, we can conclude that the generated stresses, temperatures are well within the limiting design parameters.
Video link: References:
B- Transient Structural Analysis of Piston
4- Constraints: Điều kiện biên !
Figure 3: Fixed supports
5- Loading: tác dụng Nhiệt và Gia tốc động thay đổi Theo thời gian
Figure 4: Loading on the piston
Dynamic loading Profile
Figure 5: Dynamic Loading profile
Acceleration profile:
Figure 6: Acceleration (mm/s2) vs time
6- Simulation Results: >>
Kết quả bài tính: Ứng Suất và Chuyển vị tối đa ở một thời điểm cho tổng thể và cục bộ
Equivalent (Von- Mises) stress Distribution:
Figure 7: Equivalent (Von-Mises) stress distribution after 20 time-steps
Total Deformation:
Figure 8: Total Deformation
Interpretation:
- Stress concentration:
The stresses generated in the piston are higher near the pin hole due to high stress concentration factor. More specifically, the region on the top of the pin hole should have the highest stress. This can be explained by observing the causes of the upward and downward strokes of the piston. During its upward stroke, the connecting rod, due to rotational inertia of the crankshaft, pushes the pin upwards and during its downward stroke the pressure inside the combustion chamber pushes the piston down. Hence, the top region of the pinhole is always the critical region. It is highly probable that the crack initiation takes place at this region.
- Stress distribution around the pin hole:
As observed, the stresses around the pinhole are not uniform with top region being the most stressed and the bottom region, the least stressed.
Lower stress region
- Total deformation:
The largest total deformation is observed at the bottom portion of the piston skirt, at the regions far away from the supports (pin hole).
This result can be attributed to two reasons.
- The region is situated far away from the support, making its deformation higher. The situation can be visualized as a cantilever beam with uniform loading.
- The bottom portion of the skirt has less material than that of the crown
- Region of high deformation
Videolink:
References:
- http://umpir.ump.edu.my/1750/1/Zarul_Shazwan_Zullkafli_(_CD_5096_).pdf
- http://mea.pucminas.br/palma/fca-art2.pdf
- http://www.miata.net/garage/KnowYourCar/S11_Piston.html
- http://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston and Piston Rings.htm