Multi-Stage Axial Gas Turbine

Multi-Stage Axial Gas Turbine CFD Simulation, ANSYS Fluent Training

Description

An axial turbine is a turbine in which the working fluid flows parallel to the shaft, as opposed to radial turbines, where fluid moves around the shaft (as in a watermill). Structurally similar to an axial compressor, an axial turbine operates in reverse, converting the flow of a fluid into rotating mechanical energy rather than adding energy to the fluid.

A set of static guide vanes, or nozzle vanes, accelerates and imparts swirl to the fluid, directing it toward the next row of turbine blades mounted on the rotor. Axial-flow turbines are the most widely used type for compressible fluid applications, with their gas turbine implementation emerging as a direct outgrowth of earlier steam turbine technology. As gas turbine inlet temperatures have trended progressively higher in recent years, various cooling schemes have become essential, and axial-flow turbines are now designed with a high work factor to reduce fuel consumption and turbine noise. Turbine blade and vane cooling technology has advanced substantially — from early air and steam cooling methods to modern blade structures engineered to eliminate both transverse and linear grain boundaries, enabling operation at very high temperatures.

This project models a turbine with 4 stages (2 rotors, 2 stators), each featuring 130 blades, representing a high-performance, high-pressure turbine 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 12,182 elements.

Methodology

The simulation used a pressure-based solver, with turbulence modeled using the k-omega SST model, run at the turbine's operational point with a mass flow rate of 520 kg/s. Turbine rotation was modeled using the MRF method, with each stage rotating at 6000 rpm, and the Turbo Workflow module was used to streamline the overall turbine modeling process.

Conclusion

The Mach number contour clearly shows flow speed increasing progressively through each stage's passages, while the pressure contour shows a corresponding pressure drop after each stage, yielding an overall pressure ratio of 0.8 across the full turbine.

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 turbine's overall efficiency was determined to be 18%, consistent with the expected performance behavior of a multi-stage axial turbine operating under these conditions.