Assessment of transition modeling for the unsteady performance of a pump-jet propulsor in model scale

The generally adopted strategy to investigate the flow on a pump-jet propulsor (PJP) is in model scale, but the flow is often overestimated as full turbulence in numerical prediction. The effects of transition modeling on the flow around PJP are unknown, which is a potential cause of the obvious deviations of numerical results to experimental data. So, this work presents an assessment of these effects. The unsteady fully turbulent flow field around the duct is firstly analyzed based on discussing the effects of mesh density and unsteady calculation. Then, the turbulence inlet quantities, cross-flow, and free-stream edge location are considered to estimate their effects on predicting transition and thus performance. Finally, a comparative investigation on the effects of transition modeling is implemented. Results indicate that transition modeling has significant effects on predicting PJP performance, and the flow details on PJP surface are very sensitive to the transition modeling approach. Unsteady prediction is essential for obtaining the performance and transition. An intense interaction between the tip clearance leakage flow and duct trailing edge wake exists near the duct trailing edge and results in more prominent components of pressure in the low-frequency band. The turbulent viscosity ratio of inlet is very significant for predicting the transition location. The pressure component and friction component of forces change obviously in the prediction when considering the transition, and the friction component demonstrates the relatively considerable change. The rotor shows a significant fluctuation of force in the axial direction while the duct has the equivalent fluctuation of side force. The fluctuation degree of force is slightly increased when considering the transition.