Centrifugal Compressor ANSYS Fluent CFD Simulation Tutorial

This simulation is about a Centrifugal Compressor ANSYS Fluent CFD Simulation with a diffuser. We perform this CFD project and investigate it by CFD analysis.

One of the most widely used compressors in the industry is the centrifugal type compressor. This compressor uses positive pressure while using centrifugal force to compress the gas. With the compressor impellers' rotation, low-pressure air is sucked from the central axis and its pressure increases.

This compressed air then exits radially from the diffuser section around the compressor. Only one of the blades is modeled to simplify and reduce the computational cost due to the compressor's symmetrical structure and the geometric similarity of the compressor blades.

Each blade's geometric model consists of an in block (connected to input) and a passage (connected to output). Two covers, called hub and shroud, are placed on either side of each blade; So that the blades are located in the space between the two covers.

The compressor blade rotates around its central axis (z-axis) at a rotational speed of 800 rpm. The cause of the diffuser in the air path leaving each blade is the increase in air pressure. When the fluid exits the central part of the compressor, it has kinetic energy and potential.

Since the amount of pressure changes in the passing fluid is inversely related to the square of the fluid velocity (according to the Bernoulli relation), it should be tried to reduce the compressor blades' output velocity to increase the amount of outlet fluid pressure.

This increase in pressure helps to increase the working efficiency of the compressor. Therefore, a diffuser is used in the compressor; Because the cross-section of the fluid passage increases, and with increasing the cross-sectional area of ​​the passage, the passage velocity decreases, and finally, as the fluid velocity decreases, the outlet fluid pressure increases.

The present model is designed in two dimensions using Design Modeler software. The model is then meshed by ANSYS Meshing software. The model mesh is unstructured, and 303600 cells have been created.

Centrifugal Compressor Method

In this simulation, the rotational movement must be defined for the fluid around the compressor blade. In cell zone conditions, the Frame Motion method is used to define rotational motion.

This means that it is assumed that the blade, as a boundary, has a rotational movement with a velocity of 0 rpm, and the circumference of the passage (passage) and the wall attached to it (hub) has a rotational velocity in the section frame motion at a speed of 800 rpm.

Centrifugal Compressor Conclusion

After simulation, two-dimensional contours of pressure and stress are obtained on the compressor blade surface. Three-dimensional contours of pressure, temperature, velocity, and turbulent kinetic energy have been obtained on the compressor blade. 3D velocity vectors have also been obtained.

The fluid's pathlines clearly show the compressor's centrifugal nature, as the fluid flow from the central part radially outwards. Also, the changes in pressure and speed around the blade are well shown, which are caused by the rotational movement of the compressor.