Search Results (3)

In the realm of marine science and engineering, hydrofoils play a pivotal role in the efficiency and performance of marine turbines and water-jet pumps. In this investigation, the boundary layer characteristics of an NACA0009 hydrofoil with a blunt trailing edge are focused on. The effectiveness of both the two-equation gamma theta (γ-Re_θt) transition model and the one-equation intermittency (γ) transition model in forecasting boundary layer behavior is evaluated. When considering natural transition, these two models outperform the shear stress transport two-equation (SST k-ω) turbulence model, notably enhancing the accuracy of predicting boundary layer flow distribution for chord-length Reynolds numbers (Re_L) below 1.6 × 10⁶. However, as Re_L increases, both transition models deviate from experimental values, particularly when Re_L is greater than 2 × 10⁶. The results indicate that the laminar separation bubble (LSB) is sensitive to changes in angles of attack (AOA) and Re_L, with its formation observed at AOA greater than 2°. The dimensions of the LSB, including the initiation and reattachment points, are found to contract as Re_L increases while maintaining a constant AOA. Conversely, an increase in AOA at similar Re_L values leads to a reduced size of the LSB. The findings are essential for the design and performance optimization of water-jet pumps, particularly in predicting and flow separation and transition phenomena. Full article

The influence of the ratio of dimple depth-to-print diameter ($\lambda$) on the highly loaded compressor cascade NACA0065-K48 is investigated based on the Reynolds-averaged Navier–Stokes (RANS) method. Simulations are conducted with a validated shear-stress transportation (SST) turbulence model coupled with the Gamma-Theta ($\mathsf{\gamma }-{\mathrm{Re}}_{\mathsf{\theta }}$) transition model at the inlet Mach number of 0.7. At 5~25% of the axial chord on the suction surface, four rows of dimples are arranged in parallel, and the dimples’ spacing is 4 mm. Moreover, there are five kinds of $\lambda$, ranging from 0.125 to 0.875, which determine the pressed arc of a spherical dimple. Three flow regimes (diffuser–confuser flow, tornado-like vortex and horseshoe vortex) with the same topological structure are observed in these dimples, which affect the flow and performance of the cascade by changing the energy distribution. The distribution of turbulent kinetic energy (TKE) reflects the disturbance of the tornado-like vortex in the inferior arc dimples ($\lambda =0.375$) intensely, whereas the disturbance of the horseshoe vortex in superior arc dimples ($\lambda =0.625, 0.875$) is relatively weak. Numerical results indicate that the loss of the corner separation can be reduced with a dimples array, which is mainly related to the vertical climbing of the lateral flow that delays the starting point of the corner separation and weakens the mixing process. However, the loss in the wake of the dimpled cascades increases, which is caused by the thickened boundary layer induced by the high turbulent vortices. The dimpled cascade with $\lambda =0.625$ can achieve the most significant loss reduction (13.47%), while ensuring the pressurization capacity. Full article

This paper presents the effect of the tip shape of a wind turbine blade on aerodynamic forces, including the effects of separation, transition and stall. A National Renewable Energy Laboratory (NREL) Phase-VI wind turbine blade was used, in which the shape of the tip was modified to a pointed tip. Computational fluid dynamics (CFD) simulations were employed for the analysis and the results were compared with the original NREL blade CFD and experimental data using ANSYS CFX (Ansys Inc., Delaware, PA, USA). To predict the separation and separation-induced transition on both near wall and far away, the shear-stress-transport (SST) Gamma-Theta turbulent model was used. The stall onset of a 20° angle of attack and its effects were also analyzed and presented. The value of torque with the pointed tip blade was found to be 3%–8% higher than the original NREL blade showing the benefit of the pointed tip. Normal force coefficient is lower at the tip for the pointed tip blade, which results in lower deformation of the blade. It was found that the pointed-tip blade is more efficient in terms of generating torque than the original NREL Phase-VI blade in the dynamic stall region of 10–15 m/s wind speeds. Full article