Verification of Radially Continuous Actuator-Based Models for Rotors in Hover

This study models flow around isolated and side-by-side three-bladed propellers in (IGE) and out of ground effect (OGE) using actuator-based techniques of varying fidelity. Actuator techniques model propellers using momentum sources distributed over the disk in actuator disk method (ADM) or distributed over moving lines in actuator line method (ALM) to reduce computational cost compared to blade-resolved DDES simulations. The lowest fidelity ADM method is observed to reasonably predict thrust with the use of a tip loss model to control runaway thrust at the tip while not resolving flow features such as blade-bound vortices and helical tip vortices at a fraction of the cost of BR-DDES (1/100). The coarser ALM model resolves these features but still requires a tip loss model to control runaway thrust at 1/10th the cost of BR-DDES. Finally, the finer ALM model used in this study accurately captures blade-related features and further predicts the tip loss trend from first principles at 1/3rd the cost of BRDDES. Demonstrating the efficacy of these techniques for a commonly encountered flow scenario - side-by-side rotors at 2.5R hub separation are simulated where turbulent fountaining flow is observed between the rotors which eliminates the thrust increase normally seen IGE, a feature captured by both ADM and ALM techniques. However, only ALM captures the impulsive 3-per-rev thrust loading seen in BR-DDES.