Laminar-Turbulent Transition in Axial Compressor Disc Boundary Layers

In gas turbine high-pressure compressor (HPC) cavities unsteady buoyancy and rotational effects generate oscillating Ekman layers. The laminar-turbulent transition of these oscillating boundary layers strongly influences heat transfer within the cavity, yet the underlying mechanisms remain poorly understood. Performing direct numerical simulations (DNS) of the full cavity flow is currently infeasible due to the extremely high computational cost, while detailed experimental investigation is also highly challenging. To address this challenge, the present study investigates a simplified oscillating disc configuration that produces unsteady disc boundary layers as observed in compressor cavities under engine-like conditions. Using a spectral element-Fourier CFD solver, oscillatory Ekman layers are simulated under controlled conditions to resolve the transition between laminar and turbulent flow. The study examines the influence of oscillation amplitude, frequency, and both rotational and local Reynolds numbers on boundary layer transition. Depending on the imposed conditions, the results reveal intermittent laminar and turbulent boundary layers with complex temporal evolution. Disc shear stresses correlate well with laminar and turbulent Ekman layer solutions. These results highlight the significance of transition in modelling heat transfer at high Reynolds number engine conditions.