Centrifugal Compressor with CFD Simulation by ANSYS Fluent
The present problem is to simulate a centrifugal compressor with a diffuser using ANSYS Fluent software.
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The present problem is to simulate a centrifugal compressor with a diffuser using ANSYS Fluent software. 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. To simplify and reduce the computational cost, and due to the compressor’s symmetrical structure and the geometric similarity of the compressor blades, only one of the blades is modeled.
Each blade’s geometric model consists of two parts, including inblock (connected to input) and 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 frame motion technique is used to define this 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.
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.
Centrifugal Compressor Geometry & Mesh
The present model is designed in three dimensions using Design Modeler software. The model is a centrifugal compressor with blades and a diffuser. Since the model’s geometric shape has symmetrical geometry around its central axis, only one compressor blade has been modeled to reduce the computational cost, and the periodic boundary condition has been used on both sides of each blade.
We carry out the model’s meshing using ANSYS Meshing software, and the mesh type is unstructured. The element number is 303600. The following figure shows the mesh.
Centrifugal Compressor CFD Simulation
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The simulation is steady.
- The gravity effect on the fluid is ignored.
The following table represents a summary of the defining steps of the problem and its solution:
|near wall treatment||standard wall functions|
|gauge total pressure||0 pascal|
|total temperature||300 K|
|gauge pressure||0 pascal|
|wall motion||moving wall|
|type of motion||rotational|
|rotational speed||0 rad.s-1|
|heat flux||0 W.m-2|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|momentum||second order upwind|
|density||second order upwind|
|turbulent kinetic energy||first order upwind|
|turbulent dissipation rate||first order upwind|
|energy||second order upwind|
Results & Discussions
At the end of the solution process, two-dimensional contours related to pressure and stress are obtained on the compressor blade surface. Three-dimensional contours related to pressure, temperature, velocity, and turbulent kinetic energy have been obtained on the compressor blade. 3D velocity vectors have also been obtained.
There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.