Ph.D. Defense
Aishwerya S. Gahlot
(Advisor: Prof. Lakshmi N. Sankar)
"Physics-Based Models for Rotor Aerodynamics under Adverse Weather"
Wednesday, July 9
9.00 a.m. EDT
Montgomery Knight 317
Meeting ID: 265 926 206 291
Passcode: vP2Dm9Bj
Abstract
As the demand for next-generation air mobility systems grows across both civilian and military domains, their reliable operation under a range of environmental conditions becomes essential. Vertical lift systems, including multirotors, eVTOLs, and other compact rotorcrafts (drones), offer unique operational flexibility due to their ability to take off and land vertically, hover, and perform various tasks. However, these systems are particularly vulnerable to adverse weather conditions such as rain and icing, where even minimal accumulation of water or ice on lifting and non-lifting surfaces can lead to significant aerodynamic performance degradation.
This dissertation develops and benchmarks integrated high-fidelity and low-fidelity computational frameworks to analyze aerodynamic degradation caused by rain and ice accretion on rotor systems. The emphasis is on delivering robust, physics-informed predictive tools that support early-stage design, performance evaluation, and operational planning for modern rotorcraft.
To address existing modeling gaps, a modular modeling framework for high-fidelity and computationally efficient low-fidelity methods, is developed to assess the impact of rain and icing on various rotor configurations. The investigation begins with rain effects, enhancing 2-D and 3-D unsteady viscous flow analyses with a tightly coupled water droplet transport model to simulate droplet collection and interaction with the airflow over rotors. This coupled solver is applied to multiple rotor configurations: including a single main rotor (S-76), coaxial (Harrington rotor-1), tandem rotor (Sweet), and a notional quadrotor, under hover and forward flight conditions. The model accounts for the drag force imposed by the airstream on water droplets and the subsequent reaction forces exerted by the droplets on the airflow. This approach is found to be better suited for assessing adverse effects of rain and icing conditions on multirotor configurations with nonlinear wake interactions, eliminating the needs for airfoil drag polars, tip loss models, and empirical compressibility corrections.
For icing scenarios, both high- and low-fidelity approaches are employed to simulate ice accretion and assess performance degradation. Case studies include a two-bladed teetering tail rotor, an 81% scaled version of the Bell APT70 drone rotor tested at Université du Québec à Montréal (UQAM), and a NASA eVTOL propeller configuration. Results from the low-fidelity blade element momentum theory (BEMT) approach are benchmarked against high-fidelity Navier-Stokes simulations and compared with experimental data from NASA and UQAM. Simulations show good agreement for rime ice accretion, while discrepancies for glaze ice highlight the limitations of existing roughness and transition models. Sensitivity analyses confirm that environmental variables, such as droplet size, liquid water content, and temperature, play a dominant role in shaping ice morphology and aerodynamic penalties.
This work advances physics-based modeling capabilities for predicting the effects of adverse weather on vertical lift air mobility systems. The resulting tools and insights support the design and certification of next-generation rotorcraft capable of safe and resilient operation in adverse weather conditions.
Committee
- Dr. Lakshmi Sankar (Advisor) - Daniel Guggenheim School of Aerospace Engineering
- Dr. Jonnalagadda V. R. Prasad - Daniel Guggenheim School of Aerospace Engineering
- Dr. Juergen Rauleder - Daniel Guggenheim School of Aerospace Engineering
- Dr. Elizabeth Qian - Daniel Guggenheim School of Aerospace Engineering and Computational Science and Engineering
- Dr. Suhas Jain - George W. Woodruff School of Mechanical Engineering
- Dr. Konstantinos Kanistras - Aerodynamics Chief Project, Leonardo Helicopters