Air Compressor Methodology
OpenFOAM® methodology for the designing air compressors
In November 2010 we have received the request on providing the methodology and Best-Practice settings for CFD simulations of flow in a big air compressor using OpenFOAM® software. The whole methodology creation process of cfd simulation of compressor later became a part of the Turbomachinery CFD package. The main task was to calculate the compressor characteristics.
Another requirements on the methodology were: to be able to simulate cases using periodicity (single rotor blade, single stator blade); importing external meshes different for rotor and stator; automatic evaluation of results; user friendly control.
The customer also wanted to switch to OpenFOAM® to avoid the costs associated with the purchase of the licenses of commercial software.
The flow simulation conditions were following:
- Compressible Flow
- Turbulent Flow
- Steady State
- Both Subsonic and Transonic
- Ideal Gas
- Sunderland Viscosity
To solve this case we had to create the new OpenFOAM® solver to be able to capture all the different computational meshes and make the meshes communicate each other. The solver is based on rhoSimpleFoam and is optimized for effective simulating of compressors. We have employed the multiregioning approach, which means each of the model regions are computed separately and regions communicate over the interfaces. This approach gives us a chance to use a wide range of CFD methods.
Another big deal for this case was threating the interface between rotor and stator meshes. Due to the different number of blades the interfaces are not of equal size. Our engineers have implemented special “Mixing Plane” boundary conditions for OpenFOAM® to solve this effect. At the interface, each variable is first averaged into certain number of radial (axial) intervals and then applied to the corresponding boundary.
The simulation run process is fully automated. The user sets a few parameters in the run script and make the case run. When the computation is finished another script evaluates all the results. As a result one obtains an extensive database of engineering results for the tested compressor data.
Altogether there were necessary to do many modifications (solvers, function objects, boundary conditions) to adapt OpenFOAM® methodology for the turbomachinery problems. Finally, we have introduced OpenFOAM® Best-Practice methodology of CFD simulations of air compressors. The methodology gives good agreement with customers measurement data.
Please contact us for further information.