Rampressor

Rampressor, ANSYS Fluent CFD Simulation Training

Description

This project simulates air compression inside a Rampressor using ANSYS Fluent — a distinctive type of supersonic compressor rotor capable of achieving high pressure ratios through ramjet-style supersonic shock wave compression.

The operating principle relies on gas flow passing between a fixed outer housing and an angled inner surface, or "ramp." As this inner ramp surface rotates relative to the fixed outer body, it progressively narrows or widens the gas passage. This changing cross-section triggers shock wave formation and alters the local Mach number, ultimately compressing the gas.

In this simulation, the Rampressor's inner wall rotates about its central (z) axis at 40,000 rpm, modeled using the frame motion technique: the shroud wall itself is assigned zero rotational velocity, while the surrounding computational region containing the rotating ramp is assigned the full 40,000 rpm rotational speed within the frame motion setup. Given the compressive nature of the device, pressure boundary conditions were applied at the inlet and outlet, set to relative pressures of 104,600 Pa and 350,000 Pa respectively. Since the internal airflow is fully compressible, a density-based solver was used throughout.

Geometry & Mesh

The 3D geometry was designed in Design Modeler as a three-dimensional ring structure, with the sides defined as inlet and outlet sections. The outer wall was defined as static, while the inner wall — featuring several angled ramp surfaces — was defined as rotating.

The domain was meshed in ANSYS Meshing using an unstructured grid totaling 1,785,931 elements.

Methodology

Several assumptions were applied to the simulation: a density-based solver was used, the flow was treated as steady-state, and gravitational effects were excluded.

Key simulation settings included:

• Viscous model: Standard k-epsilon with standard wall functions; energy equation enabled

• Boundary conditions: Pressure inlet at 104,600 Pa gauge total pressure and 300 K total temperature; pressure outlet at 350,000 Pa gauge pressure; shroud and inner wall defined as rotating walls with 0 rpm assigned directly to the wall motion (rotation handled via the frame motion region) and zero heat flux

• Solution methods: Implicit formulation, with first-order upwind schemes applied to flow, turbulent kinetic energy, and turbulent dissipation rate

• Initialization: Hybrid method

Conclusion

Results include 2D and 3D contours of pressure, velocity, density, temperature, and Mach number. The results show a clear pressure increase at the Rampressor outlet, along with elevated Mach numbers in the gap between the ramp surfaces and the surrounding equipment body — consistent with the shock-compression mechanism driving this device's operation.