The author does this simulation to demonstrate his ability of using ANSYS when he applies for a hydraulic engineer job at Atlas Copco AB,Örebro. Due to the limitation of computation time, a case with the simple motion of piston is simulated.
Situation —Transient flow in a piston chamber.
An axis drives a piston to compress the fluid in the chamber so that fluid can flow out from the exit to drive a drill. The piston is moving at speed of 1.25 m/s to the right direction. Then it stops for a while. The inertia of the fluid continues to drive fluid out at the outlet. This causes low pressure before the piston. A reflective wave occurs to drive fluid back to balance the pressure wave.
The model is built in ANSYS 6.1. The grid and boundary condition are shown in Figure 1. The flow is turbulent so the turbulent model (kepsilon model) is used.
The flow condition when the piston is moving is shown in Figure 2 (velocity vector), 3 (turbulent energy) and 4 (turbulent energy dissipation rate). These pictures can be understood as the initial condition of the transient flow.
Then the piston stops for a while and transient flow occurs. This is simulated. A part of the convergence history is shown in Figure 5. The velocity vector change is shown in the following figures 6-10 for different time points. The turbulent energy and dissipation rate are not shown.
The author can use the existing CFD tool at Atlas Copco AB to develop and improve the product design.
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