ORCID Number
0000-0003-2371-5001
Date of Award
Fall 12-2025
Access Type
Dissertation - Open Access
Degree Name
Doctor of Philosophy in Aerospace Engineering
Department
Aerospace Engineering
Committee Chair
R.R. Mankbadi
Committee Chair Email
mankbadr@erau.edu
First Committee Member
Vladimir V. Golubev
First Committee Member Email
golubd1b@erau.edu
Second Committee Member
Anastasios S. Lyrintzis
Second Committee Member Email
lyrintzi@erau.edu
Third Committee Member
William MacKunis
Third Committee Member Email
mackuniw@erau.edu
Fourth Committee Member
Samuel Afari
Fourth Committee Member Email
afaris@cadence.com
College Dean
James W. Gregory
Abstract
Urban Air Mobility (UAM) vehicles operate in complex, unsteady aerodynamic environments where wake interactions, gust and turbulence significantly affect both performance and noise generation. Understanding these mechanisms is critical for developing quieter and more efficient eVTOL systems that meet future community noise and certification requirements. This dissertation focuses on the high-fidelity numerical investigation of propeller noise in three representative unsteady loading scenarios: (i) transition (tilt) flight, (ii) edgewise inflow, and (iii) wake–propeller interaction. Each case emphasizes different physical mechanisms that dominate noise generation in UAM operations. Hybrid turbulence-resolving approaches—Detached Eddy Simulation (DES) and Delayed Detached Eddy Simulation (DDES)—are coupled with the Ffowcs–Williams and Hawkings (FW–H) acoustic analogy to capture both unsteady flow dynamics and far-field sound radiation.
The first part focuses on the investigation to transition (tilt) flight conditions, where both blade–vortex interaction (BVI) and blade–wake interaction (BWI) mechanisms are also dominant. This section explores the application of the Overset mesh method for propeller simulations in OpenFOAM and compares its performance against the Arbitrary Mesh Interface (AMI) approach in OpenFOAM. While AMI has been extensively validated for rotor acoustics, it is limited in handling large relative motions and interacting components. The Overset method, by contrast, provides greater flexibility for simulating complex transition kinematics through dynamic overlapping grids. However, its effectiveness for aeroacoustic prediction in OpenFOAM has not been previously demonstrated.
To address this gap, a comparative study was conducted for a Joby-scaled five-bladed propeller at an 80° tilt angle without a fairing, representative of a transition-flight condition. Aerodynamic and acoustic analyses were performed using a hybrid DDES coupled with the FW–H formulation. The results show that the Overset method predicts thrust and torque coefficients in closer agreement with experimental data and resolves stronger leading-edge vortices compared to AMI. Both approaches successfully capture leading-edge vortex shedding (LEVS), BVI, and BWI mechanisms. However, the Overset grid exhibits higher BBN levels due to increased vortex intensity and interpolation-induced disturbances, whereas the AMI method provides smoother near-field pressure distributions and clearer tonal responses. In the far field, AMI achieves better tonal agreement with experiments, while Overset demonstrates improved broadband resolution. Overall, the study highlights the complementary strengths of both approaches and underscores the potential of Overset grids for future UAM aeroacoustic simulations involving complex motion and component interaction.
The second part focuses on edgewise flow conditions, representing crosswind or transition phases typical of tilt-rotor and multirotor UAM configurations. A Joby-scaled five-bladed propeller is simulated using DES and the FW–H equation to evaluate physics-based permeable-surface strategies for far-field noise prediction. Various surface configurations—including open-end, closed-end, and end-cap–averaged geometries—are assessed to determine their effects on acoustic accuracy. Comparisons with experimental measurements show that open-ended surfaces significantly underpredict downstream noise due to vortex leakage, whereas closed-end configurations improve prediction accuracy, with 97 % of microphones within 10 dB of the data (compared to 33 % for open-ended). Two correction strategies—JetEnd and SPODEnd—are tested to mitigate spurious low-frequency end-cap noise. Both yield nearly identical results, differing by less than 2.3 dB, indicating that a single end cap is sufficient for accurate prediction. Theoretical analysis and SPOD-based flow decomposition confirm that the proposed convective-spacing model accurately captures the spacing between dominant pressure-fluctuation structures near the propeller tip. This validates the physical basis for end-cap spacing and demonstrates that JetEnd provides a reliable and efficient correction method. Remaining discrepancies for smaller surfaces highlight the need for improved lateral boundary treatments to prevent side-edge vortex contamination. These results collectively establish a validated framework for applying permeable-surface FW–H formulations to UAM propeller noise prediction under edgewise conditions.
The third part of this study extends the investigation to the wake–propeller interaction noise generated by the ingestion of a circular-cylinder wake. The configuration models the effect of a coherent upstream disturbance convected into the propeller disk at a freestream velocity of 20 m/s. The DES-based flow solution captures the unsteady aerodynamic structures within the wake and their interaction with the rotating blades. Coupled FW–H acoustic analysis reveals that wake ingestion leads to strong unsteady blade loading, which decreases thrust and torque while intensifying the hub vortex and promoting complex interactions with tip and trailing-edge vortices. These effects increase vorticity and flow separation in impacted regions. The resulting unsteadiness enhances both tonal and broadband noise components. The Spectral Proper Orthogonal Decomposition (SPOD) analysis shows that tonal noise is dominated by periodic BVI, whereas broadband noise arises from turbulence–wake interactions and the breakdown of coherent structures. The findings confirm that wake ingestion and vortex coupling are key contributors to UAM propeller broadband noise and performance degradation.
Overall, this dissertation advances the understanding of the complex aerodynamic and aeroacoustic mechanisms associated with transition flight, edgewise, and wake ingestion in UAM propellers. The results demonstrate that hybrid LES–URANS methods such as DES and DDES, combined with the FW–H formulation, provide a robust foundation for predicting tonal and broadband noise across a range of unsteady loading conditions. The proposed permeable-surface strategy, end-cap correction model, and AMI-based simulation framework collectively form a scalable methodology for accurate and efficient noise prediction in future UAM design and certification processes.
Scholarly Commons Citation
Hua, Jie, "Propeller Noise Prediction of an Urban Air Mobility Vehicle in Urban Environment" (2025). Doctoral Dissertations and Master's Theses. 936.
https://commons.erau.edu/edt/936
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