Multistage Compressor with 2 Rotor and 2 Stator rows
The present problem is to simulate the airflow inside a four-row multistage compressor (axial flow compressor) using ANSYS Fluent software.
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The present problem simulates the airflow inside a four-row multistage compressor using ANSYS Fluent software. The compressor designed in this simulation is of axial type and consists of four rows, including two rows of stator and two rows of the rotor. In general, axial flow compressors are compressors whose airflow is parallel to the axis of rotation. Axial compressors consist of two main parts, which include the rotor and the stator. The compressor consists of a series of rows with airfoil cross-sections, which are called rotor and stator. Rotors are rows connected to the central shaft and rotate around the central axis of the compressor at a very high speed.
Stators, on the other hand, are rows that are fixed and without rotation. The primary function of rotors is to apply torque to the airflow and accelerate the air through rotational motion. The primary function of stators is to increase the air pressure and prevent its spiral movement around the longitudinal axis by equalizing the current parallel to the longitudinal axis of the compressor. In other words, the stators convert the increased kinetic energy inside the compressor into static pressure and change the direction of air movement so that the airflow is ready to enter the next rotor. In this simulation, two areas called stators and two areas called rotors are distinguished.
The stator section is static, and all its walls are defined as static. However, the rotor section is defined as moving using the frame motion method, and all the walls related to this section are also movable. Therefore, for the airflow in the rotor area, a rotational motion with a rotational speed of 25,000 rpm is defined.
Multistage Compressor Geometry & Mesh
The present model is designed in three dimensions using Design Modeler software. The model includes two rows of the rotor and two rows of the stator. Each row of stator or rotor consists of 22 blades with an airfoil cross-section. The rotor blades have deflection, but the stator blades are horizontal and without deflection. Due to the perfectly symmetrical structure of this geometry and to reduce the computational cost, only one blade of each row of stator and rotor has been designed, and the periodic boundary condition has been used for its lateral surfaces.
We carry out the model’s meshing using ANSYS Meshing software, and the mesh type is unstructured. The element number is 972354. The following figure shows the mesh.
Multistage Compressor CFD Simulation
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The simulation is unsteady.
- 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 function|
|gauge total pressure||0 atm|
|gauge pressure||0 atm|
|Walls of Rotor||Wall|
|wall motion||moving wall|
|Walls of Stator||Wall|
|wall motion||stationary wall|
|momentum||second order upwind|
|turbulent kinetic energy||first order upwind|
|turbulent dissipation rate||first order upwind|
|gauge pressure||0.995 atm|
|y-velocity & z-velocity||0 m.s-1|
Results & Discussions
At the end of the solution process, two-dimensional and three-dimensional contours related to pressure, velocity, turbulence kinetic energy, and pressure gradient are obtained. Also, the airflow lines inside the compressor are obtained in three dimensions. Also, pressure and wall tension contours have been obtained on the body of the blades and the central part of the rotor and stator. The pictures show that in the direction of horizontal movement of airflow parallel to the central axis of the compressor, the airflow pressure increases.
There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.