About

Turbulence is everywhere around us. It critically affects the performance of planes, helicopters, ships, submarines, trains, cars, rockets, and more. But due to our limited understanding of turbulent dynamics, our prediction of the behavior of these technologies, especially in unsteady conditions

Research topics

• Physics
• Mechanics
• Materials science
• Computer Science
• Meteorology
• Database

Selected publications

• Flow Characterization over a Modified Boeing Bump

  2026-01-08

  articleSenior author

  This experimental study characterized the flow over a modified Boeing bump at Reynolds numbers based on bump height (Re_ℎ) ranging from 1.3 × 10^4 to 8.8 × 10^4. Removable inserts are included to make the facility adaptable for future flow control approaches. For now, the inserts are employed to incorporate different sensor arrays. High-frequency pressure and wall shear stress measurements are conducted on the upstream and downstream sides of the bump, while oil flow visualization is performed on the downstream side to capture the three-dimensional surface flow topology and identify flow features. Pressure measurements show lower mean values downstream of the bump than the upstream side indicating flow separation. Skin friction measurements supported the pressure results, showing larger values of wall shear stress in the upstream region. Additionally, the skin friction coefficient (��_�� ) decreases with increasing ����_ℎ accordingly to literature data with larger uncertainty at lower freestream conditions. Oil flow visualization captures flow separation on the bump. Spectral analysis of pressure data in the downstream region shows periodic motions in the separated flow. Correlation between the different measurements techniques and surface flow visualization were observed. They will serve for informing future experiments that will focus on integrating metamaterial for mitigation of flow separation.

  PublisherDOI

• Intrinsic phase-based proper orthogonal decomposition (IPhaB POD): a method for physically interpretable modes in near-periodic systems

  Journal of Fluid Mechanics · 2025-01-09 · 3 citations

  articleOpen accessSenior author

  Fluid dynamics systems driven by dominant, near-periodic dynamics are common across wakes, jets, rotating machinery and high-speed flows. Traditional modal decomposition techniques have been used to gain insight into these flows, but can require many modes to represent key physical processes. With the aim of generating modes that intuitively convey the underlying physical mechanisms, we propose an intrinsic phase-based proper orthogonal decomposition (IPhaB POD) method, which creates energetically ranked modes that evolve along a characteristic cycle of the dominant near-periodic dynamics. Our proposed formulation is set in the time domain, which is particularly useful in cases where the cyclical content is imperfectly periodic. We formally derive IPhaB POD within a POD framework that therefore inherits the energetically ranked decomposition and optimal low-rank representation inherent to POD. As part of this derivation, a dynamical systems representation is utilized, facilitating a definition of phase within the system's near-periodic cycle in the time domain. An expectation operator and inner product are also constructed relative to this definition of phase in a manner that allows for the various cycles within the data to demonstrate imperfect periodicity. The formulation is tested on two sample problems: a simple, low Reynolds number aerofoil wake, and a complex, high-speed pulsating shock wave problem. The method is compared to space-only POD, spectral POD (SPOD) and cyclostationary SPOD. The method is shown to better isolate the dominant, near-periodic global dynamics in a time-varying IPhaB mean, and isolate the tethered, local-in-phase dynamics in a series of time-varying modes.

  PublisherOA PDFDOI

• Poster: Turbulent Boundary Layer Separation over a Gaussian Bump

  2025-11-23

  articleOpen accessSenior author
  PublisherDOI

• Statistics of a Turbulent Boundary Layer Under a Favorable-Adverse Pressure Gradient

  2025-01-03

  articleSenior author

  A statically deformable ceiling was used at the Turbulence Dynamic Research facility at the University of Illinois at Urbana-Champaign. This facility was used to impose static spatially varying pressure gradients in a favorable-adverse (FAPG) arrangement. This study focuses on the FPG region of this flowfield which experiences a rapid spatial variation of its pressure gradient over 6.2��. Non-time-resolved particle imaging velocimetry data were captured for 6 pressure gradients and 6 Reynolds numbers. This manuscript focuses on ������ = 953 and four pressure gradient cases that have maximum acceleration parameters of �������� E+6 = 0, 2.43, 4.77, and 5.97. The Reynolds stresses and turbulent kinetic energy of the boundary layer were investigated. The results were analyzed for the occurrence of relaminarization and it was concluded that no relaminarization occurred in any of the cases. The Reynolds stresses showed behavior suggestive of an internal layer, including knee points in ��′��′. However, no conclusive evidence was found to support this hypothesis.

  PublisherDOI

• Turbulent boundary layers under spatially and temporally varying pressure gradients

  Journal of Fluid Mechanics · 2025-05-10 · 2 citations

  articleOpen accessSenior author

  The spatiotemporal dynamics of a turbulent boundary layer subjected to an unsteady pressure gradient are studied. A dynamic sequence of favourable to adverse pressure gradients (FAPGs) is imposed by deforming a section of the wind tunnel ceiling, transitioning the pressure gradient from zero to a strong FAPG within 0.07 s. At the end of the transient, the acceleration parameter is $K$ = $6 \times 10^{-6}$ in the favourable pressure gradient (FPG) region and $K$ = $-4.8 \times 10^{-6}$ in the adverse pressure gradient (APG) region. The resulting unsteady response of the boundary layer is compared with equivalent steady pressure gradient cases in terms of turbulent statistics and coherent structures. While the steady FAPG effects, as shown by Parthasarathy & Saxton-Fox (2023), caused upstream stabilisation in the FPG, a milder APG response downstream, and the formation of an internal layer, the unsteady case presented in this paper shows a reduced stabilisation in the FPG region, a stronger APG response and a weaker internal layer. This altered response is hypothesised to stem from the different spatiotemporal pressure gradient histories experienced by turbulent structures when the pressure gradient changes at a time scale comparable to their convection.

  PublisherDOI

• Signature of Pressure Gradient History on Wall Shear Stress in Turbulent Boundary Layers

  ArXiv.org · 2025-07-01

  preprintOpen accessSenior author

  Our experiments evaluate the presence of history effects on wall shear stress in turbulent boundary layers (TBLs) subjected to five sequences of favorable and adverse pressure gradients (FAPGs) of increasing strength. Steady but spatially varying FAPGs are imposed on a flat plate using a deformable convex false ceiling. An array of three one-dimensional capacitive probes, positioned in the adverse pressure gradient (APG) region downstream of the favorable pressure gradient (FPG), enables direct and high-frequency measurements of wall shear stress. We first characterize the sensor performance under canonical zero pressure gradient (ZPG) conditions across a range of Reynolds numbers. With increasing FAPG strength, a non-monotonic increase in skin friction and a reduction in normalized wall shear stress fluctuations are observed, indicating long-lasting upstream FPG influence within the downstream APG region. These effects are more pronounced at lower Reynolds numbers. Additionally, the influence of large-scale structures in FAPG on wall shear stress is studied through coherence spectrum, two points cross-correlation, and convection velocity.

  PublisherOA PDFDOI

• One-Way Coupling of Surface Vibration and Kármán Vortex Street Instability

  2025-07-16 · 1 citations

  article

  Among the wide range of passive flow control methods, the application of subsurface phononic materials (psubs) represents a promising avenue for passive aerodynamic performance improvement. The alignment of phononic materials’ unique frequency-dependent dynamic characteristics with the spectral scales of fluid instability modes has demonstrated opportunities for interaction, which can dampen or amplify energetic modes of the flow. However, the dynamic and spectral parameters driving such an interaction are still not well understood and a generalized design framework for phononic materials for passive flow control has yet to be established. The experiments performed in this study seek to provide insight into the key parameters governing effective fluid-structure interaction to inform the design of phononic materials for such a purpose. In this study, we experimentally characterized the one-way coupling between a prescribed vibrating surface and the Kármán vortex street instability, and systematically varied the frequency, bandwidth, and amplitude of surface motion to determine their influences on the resultant flow. Wind tunnel experiments conducted on the flow produced by a 2D cylinder and a shaker integrated into the nearby wall demonstrated that under certain surface vibration conditions, the vortex shedding process was biased to match in both frequency and phase to the surface oscillation. Narrowband surface excitation at frequencies near the mean vortex shedding frequency produced observable modifications to the spectral characteristics of the vortex shedding process, including a sustainment of circulation strength in the cylinder wake. Modal analysis confirmed the one-way coupling between the vibrating surface and the fluid instability; this one-way coupling organized vortex shedding process and did not superimpose additional dominant spatial modes. This system proved to be highly sensitive to surface vibration over a range of surface displacement amplitudes, suggesting a promising pathway for leveraging small-amplitude surface displacements from passive materials to successfully interact with fluid instabilities. Indeed, the identification of these vital criteria will help to lay necessary groundwork for a phononic material design methodology in the field of flow control.

  PublisherDOI

• Propeller Wake Dynamics with Vortex Attenuation Using Circulation Theory

  AIAA Journal · 2025-10-01

  article

  Owing to Helmholtz’s vortex theorems and Kelvin’s circulation theorem, the formation of coherent vortex structures in the wake of a rotating wing is directly attributable to radial gradients in lift production. To mitigate these features, a constrained optimization problem was formulated to attenuate radial gradients in the bound circulation of a rotary wing, local to the propeller tip region. Prototypes of baseline and circulation-optimized propellers were tested in a wind-tunnel environment to verify design thrust characteristics and assess propeller wake flow physics. Phase-averaged stereoscopic particle image velocimetry data were acquired to obtain the wake velocity profiles across a range of wake phase angles. The baseline wake demonstrated typical coherent tip vortex roll-up behavior, resulting in a strong double-helix wake, in direct contrast to the vortex-attenuated propeller, which featured a distributed sheet of wake vorticity arranged in a conical spiral pattern. Additionally, the wake vorticity of the vortex-attenuated propeller dissipated faster than the baseline configuration. The propulsive wake of the baseline configuration behaved as expected with a uniform axial flow distribution, whereas the vortex-attenuated configuration demonstrated significantly higher axial velocities near the axis of rotation due to the axial velocity profile produced by the blade circulation distribution of this propeller configuration.

  PublisherDOI

• Supporting Graduate Women in Engineering: The Approach and Findings of a Year-Long Program at UIUC

  2024-02-07

  articleOpen accessSenior author

  Her Ph.D. research is focused on understanding the effects of spatially-and temporallyvarying

  PublisherOA PDFDOI

• Spectral Analysis of a Cylinder Wake Interacting with Coherent Structures in a Turbulent Boundary Layer

  2024-01-04

  articleSenior author

  The spectral and spatial behavior of the wake of a small cylinder immersed in a turbulent boundary layer at different wall-normal heights is studied and compared to a canonical turbulent boundary layer. Time-resolved particle image velocimetry measurements were taken downstream of the position where the cylinder is immersed. Measurements were also taken in of the unperturbed turbulent boundary layer in the same region without the cylinder for the same freestream velocity. The pre-multiplied energy spectra was computed for the seven cases and compared. Changes to the spectral content of the wake and of the boundary layer were observed for cases where the cylinder was nearer to the wall, while little interaction was observed for cases with the cylinder outside of the boundary layer thickness. Spectral proper orthogonal decomposition modes were calculated at wavelengths relevant to the wake vortex shedding and to the energetic turbulent structures and modifications to the modes were observed for cases with strong interaction. Vortex detection methods were used to visualize the wake and suggested that both a breakdown of periodicity of the vortex spacing and an overall spatial meandering of the wake may be responsible for the spectral modifications observed.

  PublisherDOI

Recent grants

• Uncovering the self-sustaining cycle in the outer region of turbulent boundary layers

  NSF · $355k · 2021–2024

Frequent coauthors

• Beverley McKeon

  Stanford University

  17 shared

• Aadhy Parthasarathy

  University of Illinois Urbana-Champaign

  7 shared

• Aadhy Parthasarathy

  University of Illinois Urbana-Champaign

  6 shared

• Marcus Hultmark

  Princeton University

  6 shared

• Liuyang Ding

  Guangdong Pharmaceutical University

  6 shared

• Alexander J. Smits

  Princeton University

  6 shared

• Akhileshwar Borra

  6 shared

• Scott T. M. Dawson

  Illinois Institute of Technology

  5 shared

Labs

• Saxton-Fox Group @ UIUCPI

Education

• Doctor of Philosophy, Department of Mechanical and Civil Engineering

  California Institute of Technology

• Masters of Science, Department of Mechanical and Civil Engineering

  California Institute of Technology

  2013

• Bachelors of Science, Mechanical Engineering

  Massachusetts Institute of Technology

  2012

Awards & honors

• Alumni Awards and Endowments
• Alumni Loyalty Award
• Outstanding Recent Alumni Award