About

Kenneth Brentner is a faculty member in Penn State's Department of Aerospace Engineering, which has a distinguished record of research excellence and scholarship. The department's research spans traditional disciplines associated with aeronautics and astronautics, with particular strengths in rotorcraft and aero-acoustics. The department is also expanding into new areas driven by increasing computational power for design, analysis, and on-board autonomy, as well as addressing industry challenges such as sustainable aviation and the growth of space systems. Brentner's work is part of a broader departmental effort that includes leading research centers like the Vertical Lift and Rotorcraft Center of Excellence and involvement in large, multidisciplinary research initiatives supported by agencies such as NASA, NSF, and DoD. The faculty, including Brentner, have received numerous awards and honors, including society fellowships, distinguished society elections, and prestigious awards like the AIAA Aero Acoustics Award and the Collier Trophy, reflecting their significant contributions to aerospace research and innovation.

Research topics

• Computer Science
• Engineering
• Acoustics
• Telecommunications
• Physics
• Electrical engineering
• Aerospace engineering
• Aeronautics
• Optics
• Structural engineering
• Mechanics
• Mechanical engineering

Selected publications

• Predictions and Measurements of Noise Control via Synchrophasing for a Fixed Wing Distributed Electric Propulsion Aircraft in Free Flight

  2026-05-20

  articleSenior author

  Tonal noise is often a dominant component of multirotor and distributed electric propulsion (DEP) aircraft noise, with discrete tones occurring at the harmonics of the blade-passing frequency. Synchrophasing offers a potential noise-control strategy by prescribing relative blade azimuth positions among rotors to produce constructive or destructive acoustic interference at selected observer regions. This paper investigates synchrophasing for a fixed-wing DEP aircraft with eight wing-mounted propellers. Phase combinations are computed from isolated-rotor acoustic pressure histories predicted using the Penn State Noise Prediction System (PSU-NPS) and optimized to minimize or maximize noise levels over the target observer regions. Predicted loading distributions show weak rotor-rotor aerodynamic interaction, supporting the use of similar acoustic pulse shapes among rotors. A far-field assessment confirms that the planned 100 ft flight-test altitude exceeds the estimated far-field onset for all cases. Predicted sound exposure level footprints and lower-hemisphere overall sound pressure level projections show that synchrophasing redistributes acoustic energy, reducing noise by up to 10 dB in targeted regions while producing spatially dependent changes in the surrounding acoustic field. Results for propellers with different blade pitch (10 x 10 and 10 x 6) and rotational speeds show similar directivity patterns—but different noise levels—for the same phase combinations. These results demonstrate the potential of synchrophasing for directional control of the tonal noise of fixed-wing DEP aircraft.

  PublisherDOI

• Beats of rotor broadband noise modulation in unmanned aerial vehicles

  The Journal of the Acoustical Society of America · 2025-10-01

  article

  Rotor broadband noise modulation with the blade passage frequency (BPF) is known to be significant for human perception of wind turbine and helicopter noise. Psychoacoustic studies of unmanned aerial vehicles (UAVs) in the literature have found the sound quality metric of fluctuation strength to be potentially important, despite this metric capturing perception of modulation frequencies much lower than typical UAV BPFs. This presentation shows that a possible cause for this low frequency modulation is beats of amplitude modulated (AM) broadband noise (BBN) created by small BPF differences between rotors, similar to tonal beats. Beats of AM BBN were observed in measurements of two small UAV rotors set to the same BPF, resulting in BPF differences between 0.8–1.8 Hz, < 0.3% of the BPF setpoint. These BPF differences lie in the modulation frequency range relevant for fluctuation strength. Although beats of AM BBN can be heard, the beat frequency is not a modulation frequency of the sound pressure level time history, but its envelope. Therefore, noise analysis should consider beats of broadband noise modulation by computing this envelope.

  PublisherDOI

• Broadband noise modulation of multirotor aircraft

  The Journal of the Acoustical Society of America · 2025-02-01 · 8 citations

  article

  Rotor broadband noise is typically analyzed over time scales encompassing multiple rotor periods. However, modulation of broadband noise levels with the blade passage frequency has been shown to be significant for human perception of wind turbine and helicopter noise. In contrast, broadband noise modulation has not been extensively studied for aircraft with many rotors, such as unmanned aerial vehicles (UAVs) or advanced air mobility aircraft. In this work, significant broadband noise modulation was measured in flight tests and anechoic chamber experiments of hexacopter UAVs. The amplitude of this modulation depended on the azimuthal phase offsets between rotors, demonstrating the potential for synchrophasing control to reduce broadband noise modulation, analogous to synchrophasing control of tonal noise. If rotors are not synchronized, as in typical flight, the azimuthal phase offsets between rotors vary with time. This variation was found to follow a uniform random distribution, resulting in modulation depth also varying randomly with time. The probability distribution of modulation depth was computed using offset copies of the modulation of a single rotor. These results contribute understanding to how the broadband noise modulation of rotors sum together, and showed that this modulation is likely to be significant in flight.

  PublisherDOI

• Parallelization of Rotor Noise Prediction

  2025-07-16

  articleSenior author

  Accurate and efficient rotor noise prediction is critical for the design and operation of electric Vertical Takeoff and Landing (eVTOL) aircraft within Advanced Air Mobility (AAM) frameworks. These multi-rotor vehicles introduce complex aerodynamic interactions and increased computational demands for acoustic analysis, especially across full flight trajectories and multiple observer locations. A parallel computing approach to Farassat’s Formulation 1A of the Ffowcs Williams-Hawkings (FW-H) equation is developed. The algorithm exploits the linearity of the FW-H equation to parallelize calculations across observers, time, and source surfaces using the Message Passing Interface (MPI). Performance results show significant reductions in runtime without compromising accuracy, enabling scalable noise prediction for modern eVTOL configurations and flight path planning.

  PublisherDOI

• Aeroacoustic Predictions of Propeller-Wing-Flap Aerodynamic Interactions Using High and Medium Fidelity Simulations

  2025-01-03 · 3 citations

  articleSenior author

  This paper presents a numerical study of aerodynamic noise for propeller-wing-flap configurations. High-fidelity computational fluid dynamics and a medium-fidelity viscous vortex particle method (VVPM) are employed to predict the acoustics of a Clark-Y three-bladed propeller mounted on a tapered half-span wing with a NACA 0015 airfoil. The numerical simulations encompass various thrust conditions, angles of attack (AoA), flap angles, single and dual flap configurations, as well as single and dual propeller configurations. Results indicate that propeller noise dominates at lower harmonic frequencies, while the nacelle contributes predominantly at higher frequencies. Flap deflections do not significantly affect low-frequency tonal noise but increase high-frequency broadband noise. Noise levels increase with AoA, and the first blade passage frequency (BPF) exhibits a positive correlation with thrust. The dual-propeller configuration significantly amplifies tonal noise due to flow interactions between the two propellers. Additionally, trailing-edge noise from propeller blades contributes to significant broadband noise in the high-frequency range. Medium-fidelity predictions align well with high-fidelity results for the first three BPFs especially when a flap is deployed. However, the medium-fidelity model shows a phase lag in the acoustic pressure and the underprediction of wing loading noise. This comprehensive investigation of flap deflections, angles of attack, and thrust conditions highlights the importance of accurate aeroacoustic modeling for future vertical lift concepts and advanced rotorcraft designs.

  PublisherDOI

• Noncompactness corrections to the Brooks, Pope, and Marcolini self-noise model for small rotor noise prediction

  The Journal of the Acoustical Society of America · 2025-12-01 · 1 citations

  article

  Accurate prediction of high-frequency broadband noise is essential for assessing the environmental impact of small uncrewed aerial systems (sUAS). The widely adopted Brooks, Pope, and Marcolini (BPM) airfoil self-noise model has been validated for rotorcraft and wind turbine applications but shows limitations for sUAS-scale rotors, partly due to its assumption of acoustic compactness (chord smaller than the wavelength of sound). This paper introduces a modification to the BPM model to account for noncompactness by incorporating an alternative directivity function and an exact numerical formulation based on Amiet's aeroacoustic transfer function (non-dimensional radiation integral). The modified models were applied to predict the noise from a hexacopter hovering at 20 and 40 feet and compared with outdoor measurements from a ground microphone grid. For all ground microphones, the median A-weighted SPL prediction error with the original BPM model was reduced from 8.7 dBA to 1.0 dBA at 20 feet and from 2.7 dBA to 1.8 dBA at 40 feet using the modified formulation. The modified models also showed substantially improved one-third octave spectral agreement, demonstrating the importance of noncompactness corrections for accurate sUAS trailing edge broadband noise prediction using the BPM model.

  PublisherDOI

• THE EXACT CALCULATION OF QUADRUPOLE SOURCES FOR SOME INCOMPRESSIBLE FLOWS

  2024-05-03

  articleOpen access1st authorCorresponding

  This paper is concerned with the application of the acoustic analogy of Lighthill to the acoustic and aerodynamic problems associated with moving bodies. The Ffowcs Williams-Hawkings equation, which is an interpretation of the acoustic analogy for sound generation by moving bodies, manipulates the source terms into surface and volume sources. Quite often in practice the volume sources, or quadrupoles, are neglected for various reasons. Recently, Farassat, Long and others have attempted to use the FW-H equation with the quadrupole source and neglected to solve for the surface pressure on the body. The purpose of this paper is to examine the contribution of the quadrupole source to the acoustic pressure and body surface pressure for some problems for which the exact solution is known. The inviscid, incompressible, 2-D flow, calculated using the velocity potential, is used to calculate the individual contributions of the various surface and volume source terms in the FW-H equation. The relative importance of each of the sources is then assessed.

  PublisherOA PDFDOI

• Aerodynamic Analysis of Propeller-Wing-Flap Configurations Using High-Fidelity Computational Fluid Dynamics

  2024-07-27 · 1 citations

  articleSenior author

  This paper analyzes the aerodynamics of propeller-wing-flap configurations using high-fidelity computational fluid dynamics. The study examines two configurations, featuring one or two 3-bladed propellers with Clark-Y airfoil sections mounted on a tapered half-span wing with a NACA 0015 airfoil section, at three different propeller thrust conditions. The findings indicate that the highest thrust condition produced the most significant increase in lift for the propeller-wing system with a flap at angles of attack (AoA) of 0 and 30 degrees. A notable rise in the pressure coefficient around the flap placement contributed to the overall lift increase. Visual representations of pressure coefficient fluctuations on the wing surface provide detailed insights into the influence of the propeller's potential flow and wake on wing aerodynamics. However, at 60 degrees AoA, prominent flow separation and spanwise flow resulted in a decrease in sectional lift, especially when a flap is deployed. The use of double flaps did not provide additional aerodynamic benefits for the configuration considered. The introduction of two propellers further increased lift across the entire wing, significantly enhancing the flow interactions between the propellers and the wing. Blade vortex interactions occurred between the overlapping propellers, and the propeller tip vortices interacted with the wing tip vortex, potentially becoming a significant noise source. Overall, this paper provides comprehensive insights into the complex aerodynamic interactions in propeller-wing-flap configurations, highlighting the conditions under which different configurations perform optimally in terms of wing aerodynamics.

  PublisherDOI

• Time-varying broadband noise of multirotor aircraft

  Proceedings of meetings on acoustics · 2024-01-01 · 3 citations

  articleOpen access

  Rotor broadband noise is typically analyzed over time scales encompassing multiple rotor periods. However, modulation of broadband noise levels with the blade passage frequency has been shown to be significant for human perception of wind turbine and helicopter noise. Time-varying broadband noise has not been extensively studied for aircraft with many rotors, such as unmanned aerial vehicles (UAVs) or advanced air mobility aircraft. In this work, significant broadband noise modulation was measured in flight and anechoic chamber tests of hexacopter UAVs. Envelope analysis showed that the modulation depth depends on the azimuthal phasing between rotors, demonstrating the potential for synchrophasing control to reduce broadband noise modulation. If rotors are not synchronized, as in typical flight, the phasing between rotors varies with time. This phase variation followed a uniform random distribution, resulting in modulation depth also varying randomly with time. The probability distribution of modulation depth was computed using offset copies of the modulation of a single rotor. These results contribute understanding to how the noise modulation of rotors sum together, demonstrating that broadband noise modulation is likely to be significant in flight.

  PublisherOA PDFDOI

• Multirotor broadband noise modulation

  The Journal of the Acoustical Society of America · 2024-03-01 · 1 citations

  article

  Rotor broadband noise spectra are typically analyzed over time scales on the order of one or more rotor periods. However, modulation of the broadband noise spectrum with the blade passage frequency (BPF) has been shown to be significant for noise levels and perception of wind turbines and helicopters. In contrast, time-varying broadband noise has not been extensively studied for aircraft with many rotors, such as unmanned aerial vehicles (UAVs) or advanced air mobility aircraft. In this work, significant broadband noise modulation was measured in flight and anechoic chamber tests of hexacopter UAVs at various observer angles. This modulation is aperiodic with the BPF such that the modulation amplitude varies substantially between blade passages, even when the BPFs are controlled to be nearly constant between all rotors at all times. Furthermore, the azimuthal phasing between rotors greatly affects the measured modulation, such that the modulation of multiple rotors may be less than or greater than for a single rotor, depending on the phase offsets. The effects of phase variations on acoustic interactions between rotors is studied by comparing the sum of the modulation of individual rotors to the modulation of those rotors operating simultaneously. This is done not only using measurements, but also noise predictions made using PSU-WOPWOP. These results contribute understanding to how the noise modulation of rotors sum together, including the resulting directivity and aperiodicity.

  PublisherDOI

Frequent coauthors

• Philip J. Morris

  Pennsylvania State University

  34 shared

• Seongkyu Lee

  University of California, Davis

  25 shared

• Joseph F. Horn

  Pennsylvania State University

  15 shared

• F. Farassat

  Langley Research Center

  14 shared

• Leonard V. Lopes

  Langley Research Center

  12 shared

• Eric Greenwood

  12 shared

• David P. Lockard

  Langley Research Center

  11 shared

• Kalki Sharma

  9 shared

Labs

• Vertical Lift and Rotorcraft Center of Excellence (VLRCOE)PI

Education

• Doctor of Philosophy / Acoustics, Engineering

  University of Cambridge

  1991

Awards & honors

• AIAA Aero Acoustics Award (3)
• AIAA Sperry Award (2)
• AIAA Applied Aerodynamics Award
• Am Astronautical Society Brouwer Award
• AIAA de Florez Award in Flight Simulation