About

Dr. Nathan Webb is a research assistant professor at The Ohio State University’s Aerospace Research Center within the College of Engineering. He earned his Ph.D. in Mechanical Engineering from Ohio State in 2013, with a dissertation focused on the control of shock wave-boundary layer interactions using localized arc filament plasma actuators. Over nearly 18 years of research activities, Dr. Webb has contributed to projects supported by organizations such as AFOSR, AFRL, ARO, ONR, LLNL, UCAH/JHTO, FAA, and ODOT. His research encompasses plasma-based flow control, hypersonic flows and flow control, UAS fluid dynamics and acoustics, unsteady flows, and high-speed air-breathing propulsion. He has disseminated his work through numerous conference presentations and 46 papers, including 12 journal publications. Dr. Webb actively mentors graduate and undergraduate students and is engaged in service to the aerospace community through AIAA technical committees. He was recognized as an Associate Fellow of the American Institute of Aeronautics and Astronautics for his outstanding contributions to active flow control using plasma actuators in flows relevant to various aerospace applications, including supersonic and hypersonic flight.

Research topics

• Physics
• Mechanics
• Acoustics
• Optics
• Engineering
• Aerospace engineering
• Electrical engineering

Selected publications

• Active Control of Acoustics in a Supersonic Circular Jet

  2026-01-08 · 1 citations

  article

  The acoustics of a supersonic circular jet were studied using active flow control over a limited frequency band. The nozzle was designed using the Method of Characteristics with a design Mach number of 1.52 and an exit diameter of 1 inch. The results presented in this paper were obtained at the Gas and Dynamics Laboratory at the Ohio State University. The baseline acoustics were analyzed for two flow regimes, overexpanded and ideally expanded, and a variety of excitation parameters, varying frequency and azimuthal mode, were applied to investigate the jet’s response. For the ideally expanded case it was found that when exciting at a frequency within the jet column mode (JCM), the jet responded for all azimuthal modes investigated (m = 0 , 1 , 3. 1), but with the strongest response occurring at the jet’s natural azimuthal mode (m = 1). For the weakly screeching overexpanded case, when exciting at screech frequency, the screech is reinforced when exciting at the jet’s natural mode and is disrupted when other modes were used. For both cases, when exciting at a frequency higher than the JCM, a weak response was produced for the ideally expanded case, with minimal variations between excitation modes. However, for the overexpanded case, the control was able to further disrupt the screech, with a larger impact when exciting at the jet’s nondominant azimuthal modes.

  PublisherDOI

• The Effect of Micro-Cavity Actuator Geometry on Dynamic Stall Control Authority

  2026-01-08

  articleSenior author

  The effectiveness of a micro-cavity resonator is experimentally investigated on a dynamically pitching NACA 0012 airfoil as a means of dynamic stall control. The micro-cavity is positioned and dimensioned to excite self-induced resonant oscillations during the deep stall period to prevent laminar separation bubble bursting. Two physical airfoils were manufactured (aluminum and 3D printed resin), both with a micro-cavity. Wind tunnel testing at M = 0.20 – 0.25, k = 0.039 – 0.049 and Re = 6.8 – 8.35 ×〖10〗^5 revealed that the resin (plastic) micro-cavity airfoil significantly improved aerodynamic performance. Lift hysteresis was reduced by up to 68.3% and positive aerodynamic damping was generated. By comparison, the micro-cavity on the aluminum airfoil delivered only 41 - 56% lift hysteresis reduction with intermittent effective control. To investigate this discrepancy, cavity chordwise position, corner sharpness, L/D ratio, and Mach number effects were considered. Scans of each cavity revealed a significant difference in L/D, which resulted in different predicted resonant tones. Previous studies of cavity L/D’s effect on pressure fluctuations show that deeper cavities exhibit a strong periodic component, whereas shallow cavities are more random in character. Thus, the current work suggests that stronger periodicity may be more important in LSB stabilization than targeting specific resonant tones centered about the exact LSB receptivity range.

  PublisherDOI

• The Ohio State University Large-Area Reflected Shock Tunnel: Overview and Characterization

  2026-01-08

  article

  The Large Area Reflected Shock Tunnel at The Ohio State University Aerospace Research Center has been recommissioned and characterized to provide a large-scale university platform for experimental hypersonics research and testing. This paper documents the facility charac- teristics, operational envelopes, and flow quality. The facility features a 45-in diameter nozzle attached to a 9-ft diameter test cabin, enabling operation as a free jet. The current operational capability with air as a driver gas includes Mach numbers of 6, 7 and 8, with stagnation enthalpies up to approximately 2.2 MJ kg^−1 and unit Reynolds numbers ranging from 0.1 to 100 ×10^6 m^−1. The use of a helium driver extends the achievable enthalpy to approximately 7.8 MJ kg^−1 and permits operation to Mach 12+. LARS can be operated in either reflected shock or blowdown modes with typical run times of a few tens of ms and 150ms, respectively. Characterization measurements with a pitot-probe rake indicate mean flow uniformity of approximately 1% and freestream noise levels near 2% with spectral content that is consistent with other conventional hypersonic tunnels.

  PublisherDOI

• Active Far-Field Noise Control of a Supersonic Rectangular Single Jet

  2025-07-16 · 1 citations

  article

  The far-field acoustics of a supersonic rectangular single jet (SRSJ) were studied, and the flow was subjected to active flow control by plasma actuators. The nozzle design is similar to those used in previous twin jet experiments by our group in the Gas Dynamics and Turbulence Laboratory at The Ohio State University. It is a converging-diverging nozzle with a design Mach number of 1.50, an aspect ratio of 2, and features a biconic inner contour. The far-field noise of the baseline jet was characterized from equivalent jet Mach numbers (Mj) 1.30-1.70, then a wide variety of excitation frequencies and modes were explored at strongly screeching Mj = 1.40 (Case 1) and weakly screeching Mj = 1.50 (Case 2) to observe their effect on the jet acoustics. Excitation near the peak shear layer mode frequency (Ste ~ 1.50) produced significant noise reduction across all polar angles. In Case 1, over 2.5 dB of reduction around the peak far-field noise angle was observed, and in Case 2, the reduction was more modest (up to 1.7 dB) and occurred at higher polar angles.

  PublisherDOI

• Effect of Geometry on Control Authority of Plasma-Based Active Flow Control for Subsonic Jet Thrust Vectoring

  2025-07-16

  articleSenior author

  Thrust vectoring, the controlled deflection of a jet to alter the angle of developed thrust, is currently implemented using complex, heavy, variable geometry nozzles to obtain hyper-maneuverability and vertical take-off/landing capabilities. Localized Arc-Filament Plasma Actuators (LAFPAs) azimuthally distributed at the jet exit have shown the ability to induce pressure asymmetries on a fixed-geometry “reaction surface” which curves away from the jet axis. It was also shown with PIV that these asymmetric pressure distributions correspond to jet deflections. This work investigates the effect of reaction surface geometry on the LAFPAs’ ability to induce pressure asymmetries over the reaction surface. Multiple reaction surfaces were 3D printed to independently vary the reaction surface length and backward facing step height. The effect of control at various excitation frequencies was documented using an array of static pressure taps embedded in each reaction surface. The 1 mm and 0.85 mm step heights were the most effective, inducing the highest magnitudes of pressure asymmetries at lower and higher Ste, while larger step heights resulted in audible resonance that likely competed with the LAFPAs’ ability to alter the development of the coherent structures. The longest tested reaction surface produces greater changes in pressure asymmetry with respect to the baseline and a much more abrupt change (as excitation frequency increases) between significant pressure asymmetry directed toward and away from the active LAFPAs.

  PublisherDOI

• Active Control of Coherent Structures in an Overexpanded Supersonic Rectangular Jet

  2025-01-03 · 1 citations

  article

  A new supersonic rectangular single jet was designed and installed at the Gas Dynamics and Turbulence Laboratory at The Ohio State University. The geometry is of similar design as previous twin jet experiments. The converging-diverging nozzle is biconic with a design Mach number of 1.50 and an aspect ratio of 2. Planar laser-sheet imaging was performed on the jet in the overexpanded regime, focusing on a fully expanded jet Mach number of 1.40. Phase-locked images were taken to directly visualize the coherent structures within the jet. Localized arc-filament plasma actuators (LAFPAs) were utilized to generate thermal perturbations to excite the Kelvin-Helmholtz instability in the shear layers of the jet. The baseline jet exhibited a flapping behavior but responded to the LAFPA excitation for all excitation modes and frequencies assessed. At excitation frequencies above the natural screech frequency, the excitation was able to switch the azimuthal mode of the jet to a symmetric mode. The size and wavelength of the coherent structures decreased as the excitation frequency increased, as expected, until they were too small to be resolved and visualized with the imaging setup at the highest tested frequency. By significantly modifying the coherent structures within the jet, and thus their entrainment and mixing characteristics, the overall phase-averaged jet behavior was significantly altered, revealing the nonlinear nature of the processes involving active flow control of the jet.

  PublisherDOI

• Active Flow Control in a Supersonic Rectangular Jet

  2025-07-16 · 1 citations

  article

  This paper summarizes the results of high-speed schlieren experiments on a supersonic rectangular jet of sharp throated design. The rectangular nozzle is of aspect ratio two and has a design Mach number of 1.50. A strongly screeching overexpanded case as well as the weakly screeching nozzle design case are investigated. LAFPA based excitation is used to explore the inherent physics of the jet as well as to control the generation and development of coherent structures (CS). The baseline jet displays a screech signature with a natural flapping mode behavior. LAFPA excitation at the screech frequency is able to reinforce the natural behavior or shift some energy towards another azimuthal pattern, depending on the excitation mode employed. Exciting the jet at a frequency above the natural screech produces smaller CS in an azimuthal mode reflecting that of the excitation. The smaller structures entrain less ambient air resulting in thinner shear layers and a lengthened jet core. The excitation is able to disrupt the natural screech loop when the jet is screeching weakly (operated at the design condition), resulting in the LAFPA introduced structures dominating the flow.

  PublisherDOI

• An Experimental Investigation of Dynamic Stall Control with a Leading-Edge Microcavity Actuator

  2025-07-16 · 1 citations

  article

  The effectiveness of a micro-cavity near the leading-edge of sinusoidally pitching NACA 0012 airfoil is experimentally investigated as a means of dynamic stall control. The micro-cavity is sized and positioned to excite resonant oscillations during deep stall and thus collapse the leading-edge separation bubble. Wind tunnel testing focused on freestream conditions of M = 0.20 – 0.25, Re = 6.8 – 8.35 x 〖10〗^5, and reduced frequency, k = 0.039 - 0.049. Micro-cavity results at M = 0.20 and 0.25 showed improved lift, reduced hysteresis, and earlier downstroke flow reattachment relative to the uncontrolled airfoil. Normal and axial force contours revealed the presence of intermittent pitching cycles of beneficial control, which were increasingly present in the downstroke portions of M = 0.25 flow. These events, which are indicative of effective micro-cavity control, were separated and conditionally averaged to reveal significant (up to 56%) reductions in hysteresis and a transition from negative to positive aerodynamic damping. This study offers the first experimental verification of the micro-cavity actuator for dynamic stall control.

  PublisherDOI

• Hybrid Active-Passive Flow and Acoustic Control in Supersonic Rectangular Twin Jets

  2024-05-30

  article

  The near-field (NF) acoustics of supersonic rectangular twin jets (SRTJ) under active flow control were studied. The nozzles had a design Mach number of 1.50 and an aspect ratio of 2, operated at an overexpanded condition (Mj = 1.30). While previous works used all installed actuators to excite the flow, this work offers a preliminary look at the effect of actuation patterns with only some of the actuators active, which could significantly reduce the power required for this already very low power active control technique. The actuation patterns in this work explored two aspects of the physics that can reduce the NF overall sound pressure level (OASPL): destructive interference between the jets and the three-dimensionality of coherent structures in each jet shear layer. The best performance among the new cases took advantage of both effects to achieve OASPL reductions up to 4.5 dB. Although an actuation pattern using the full set of actuators (as in the previous work) gave the best reduction in OASPL as expected, significant benefits can still be achieved with a reduced number of actuators (i.e., with approximately 67% actuator power savings).

  PublisherDOI

• Active control of flow and near-field pressure fluctuations in heated supersonic rectangular twin jets

  Journal of Fluid Mechanics · 2024-04-03 · 12 citations

  articleOpen access

  Heated supersonic rectangular twin jets (SRTJ) with a total temperature ratio of 2, using nozzles of design Mach number 1.5 and aspect ratio 2, were investigated in flow regimes from overexpanded to the design condition ( M j = 1.3–1.5). This work complements our recently published work in unheated SRTJ using the same experimental facility (Samimy et al. , J. Fluid Mech , vol. 959, 2023, A13). Localized arc filament plasma actuators (LAFPAs) were used to excite the natural instabilities in the jets, thereby controlling the flow and acoustics. The results show that the jets were coupled primarily out-of-phase in overexpanded cases, that the coupling had significant effects on the near-field (NF) pressure fluctuations, and that these fluctuations were considerably higher for in-phase than for out-of-phase coupled cases. The results also revealed that the far-field (FF) overall sound pressure level is significantly higher on the minor axis plane of the SRTJ and that the onset of Mach wave radiation contributes to the increased acoustic radiation at the peak noise direction. The LAFPAs successfully controlled the coupling and were able to reduce the NF pressure fluctuations by 10 dB. However, only 1 to 2 dB FF noise reduction at the peak noise radiation direction was achieved. The overall trends of the baseline results and response of the flow to excitation are qualitatively similar in unheated and heated cases, but the details are significantly different.

  PublisherOA PDFDOI

Frequent coauthors

• Mo Samimy

  The Ohio State University

  41 shared

• Ata Esfahani

  The Ohio State University

  7 shared

• David Castañeda

  Universidad del Valle

  7 shared

• Ata Ghassemi Isfahani

  The Ohio State University

  6 shared

• R. Leahy

  The Ohio State University

  6 shared

• Karli Katterle

  The Ohio State University

  4 shared

• Christopher J. Clifford

  United States Air Force Research Laboratory

  4 shared

• Nicole Whiting

  Honda (United States)

  3 shared

Education

• PhD, Mechanical and Aerospace Engineering

  The Ohio State University

Awards & honors

• Associate Fellow of the American Institute of Aeronautics an…