Enhancing the Resolution of Blade Tip Vortices in Hover with High-Order WENO Scheme and Hybrid RANS–LES Methods

Abstract

The accurate prediction of blade tip vortices continues to be challenging for the investigation of rotor aerodynamics. In the current work, the blade tip vortex system of a Caradonna–Tung rotor in the hovering state is simulated on account of the framework of a high-order WENO scheme and hybrid RANS/LES method progressively. With the RANS method based on a fifth-order WENO–Roe scheme, the spatial resolution of wake age and capture the accuracy of tip vortices are improved significantly. However, the unsteadiness of the vortex system fails to be distinguished. Then, the DDES and IDDES methods, coupled with a fifth-order WENO–Roe scheme, are implemented to further enhance the resolution of the spatial turbulence. Compared with RANS, the improvement of spatial resolution is reflected in both the statistical and transient results with DDES. The identifiable vortex core distributions can be predicted at older wake ages. The asymmetrical characteristic of blade tip vortices is revealed along with the release of fluctuation while the predicted distribution of velocity profiles in the vortex core is enhanced. With the application of IDDES, the secondary turbulent structures are captured around the primary vortex core of blade tip vortices while the complex behaviors of the vortices are observed. However, the statistics of the averaged flow field are similar to DDES.

IDDES Investigation of Rotor Blade Tip Vortices in Hovering State with Tip Slots

“…Both of the b tip vortex systems describe a helicoidal pattern. Based on the current spatial resoluti method, the rotor tip vortices of the baseline blade develop to the wake age of fou revolutions, which is close to the previous result[26] with the same method. Comp to the baseline blade, it is observed that the wake age of slotted blade lasted for only revolutions, which indicates the remarkable attenuation of vorticity strength.…”

“…Other numerical methodologies are consistent with the RANS simulation. The capability of the method has been verified via a variety of cases about helicopter fuselage and rotating blade flow fields [25,26], where how a particular numerical scheme is affected by diffusion has been discussed in detail correspondingly.…”

“…The time step size is set as a rotor rotation of ∆ϕ = 0.25 deg per physical time step with 25 subiterations, which is in consistent with Ref. [26] and is enough to fulfill the demand for convergence and robustness.…”

“…Compared to RANS, with the rapid activation of WMLES mode in the focused region, the resolution of transient turbulent structures of blade tip vortices is significantly enhanced through IDDES. The behaviors of secondary turbulent structures of vortex worms around the blade tip vortices are successfully predicted, including the interactions and pairing of adjacent vortices [26]. IDDES successfully predicts the secondary turbulence structure near the tip vortex (the so−called "vortex worms") [16].…”

Combination of Advanced Actuator Line/Disk Model and High-Order Unstructured Finite Volume Solver for Helicopter Rotors

“…Figure 20 shows comparisons of the ALM results of blade tip vortex evolution in vertical and radial directions, where z/R and r/R represent the vertical position and the radial position. The full CFD results of the simulation with the RANS method based on a fifth-order WENO-Roe scheme [36] were adopted as a reference for comparison. It can be found that the ALM with the third-order solver (ALM3), due to lower numerical dissipation, predicts a better agreement with the experimental results for the vortex age up to 360 • .…”