Multi-Stage Axial Compressor

Multi-Stage Axial Compressor CFD Simulation, ANSYS Fluent Tutorial

Description

An axial compressor is a gas compressor capable of continuously pressurizing gas, using a rotating, airfoil-based design in which the working fluid flows primarily parallel to the axis of rotation. Axial compressors consist of both rotating and stationary components: a central drum, driven by a shaft and supported by bearings within a stationary tubular casing, carries rows of airfoils alternating between the drum and the casing.

A pair consisting of one row of rotating airfoils (blades/rotors) followed by one row of stationary airfoils (vanes/stators) forms a stage. The rotating blades accelerate the fluid in both the axial and circumferential directions, while the stationary vanes convert this increased kinetic energy into static pressure through diffusion, redirecting the flow to prepare it for the next stage's rotor. The cross-sectional area between the rotor drum and casing progressively narrows along the flow direction, maintaining an optimal Mach number as the fluid compresses.

This project models a compressor with 4 stages (2 rotors, 2 stators), each featuring 120 blades, representing a high-performance, high-pressure compressor under realistic operating conditions. The 3D geometry was designed in ANSYS BladeGen, with the domain defined by a mass flow inlet and a pressure outlet. The domain was meshed in TurboGrid using an unstructured grid totaling 11,430 elements.

Methodology

The simulation used a pressure-based solver, with turbulence modeled using the k-omega SST model, run at the compressor's operational point with a mass flow rate of 110 kg/s. Compressor rotation was modeled using the MRF method, with each stage rotating at 10,000 rpm, and the Turbo Workflow module was used to streamline the overall compressor modeling process.

Conclusion

The Mach number contour clearly shows how flow speed changes through each passage, dropping progressively at each stage, while the pressure contour shows pressure rising correspondingly after each stage, yielding an overall pressure ratio of 4 across the full compressor.

The velocity triangles generated by the rotating rotors are clearly visible in the results, and the pressure contour on the blades reveals regions of flow stagnation and separation throughout the system. Using the software's workflow efficiency calculation, the compressor's overall efficiency was determined to be 20%, with the corresponding pressure drop also reflected in the pressure contour results.