Advisor: Dr. JVR Prasad

Milestone: PhD Thesis Final Examination (Defense)

Degree Program: Aerospace Engineering

Title: Development of a Velocity Potential-Based Finite State Model for Analyzing Rotor in Ground Effect

Abstract: Accurate prediction of rotor induced velocities near the ground is important for rotorcraft performance, handling qualities, and control. Existing finite-state formulations for ground-effect analysis have not explicitly enforced the non-penetration of flow boundary condition at the ground because of limitations in computing induced velocities below the rotor within the wake. This research develops a velocity potential-based finite-state model (VPBFSM) that uses a dual-rotor formulation with adjoint variables to impose the non-penetration of flow boundary condition. The main rotor is represented as an upper lifting rotor through pressure discontinuities, while the ground is represented as a lower non-lifting rotor through distributed mass sources. An algebraic relation is developed to determine the ground mass-source strengths in terms of rotor loading required to enforce the non-penetration of flow boundary condition at the ground. The model is then applied to full, inclined, and partial ground effect and is evaluated through comparisons with analytical, experimental, and higher-fidelity free-wake results. For full ground effect, the predicted average rotor inflow agrees with the Hayden model with an approximate relative error of 0.006, while normalized induced-torque predictions agree with experimental measurements to approximately 3% for most cases above ground. Corresponding induced-torque comparisons for inclined and partial ground effect show errors of approximately 2% and 1%, respectively. The VPBFSM is further extended to dynamic and moving-ground conditions by accounting for wake-propagation delay and time-varying rotor-ground geometry. Finally, the quasi-steady and dynamic VPBFSM formulations are coupled with a simplified single-degree-of-freedom vertical vehicle model. Both formulations predict recovery to a new hover equilibrium in ground effect as the reduction in induced inflow allows rotor thrust to recover. Overall, the developed VPBFSM provides a reduced-order framework for predicting rotor inflow and vehicle response across full, inclined, partial, dynamic, and moving ground-effect conditions, with potential application to real-time flight simulations.

Date and time: 2026-10-22, 11:00 AM to 1:30 PM

Location: MK-317

Committee:
Dr. JVR Prasad (advisor), School of Aerospace Engineering
Dr. Lakshmi Sankar, School of Aerospace Engineering
Juergen Rauleder, School of Aerospace Engineering
David Peters, Washington University in St. Louis
Umberto Saetti, Politecnico di Milano
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