Analysis of limiting streamlines in vaned diffusers with different vane inlet angles by multi-color oil-film technique

Abstract

In industrial turbopump design, numerical analysis using the Reynolds-averaged Navier-Stokes equations is often used because it is less expensive in terms of computation. However, a major challenge is that the results do not exactly match the real internal flow, as turbulence models are applied in the calculations. This gap becomes especially important when dealing with complex flow phenomena, where understanding the differences between actual behavior and numerical results can help create better design guidelines. In this study, the critical flow lines were visualized using a multi-color oil-film technique for two vaned diffusers with different vane inlet angles, both of which are known to cause diffuser rotating stall (DRS). The visualization showed that in the model with a smaller vane inlet angle, rotation occurred immediately after stalling, while in the model with a larger vane inlet angle, rotation did not occur despite stalling. This suggests that the internal flow leading to DRS varies depending on the diffuser model.