About TTRG

About our Research

Our group investigates the physics of laminar–turbulent transition and turbulent shear flows, combining carefully designed experiments with advanced data analysis and numerical simulations. We focus on understanding underlying mechanisms and developing tools and strategies that help predict, control, or quantify complex turbulent flows relevant to aerospace applications as well as non-aerospace applications.

Laminar–turbulent transition and control

We study boundary-layer transition in subsonic flows and develop control strategies to delay or modify the transition process. Our work uses two low-speed, low-turbulence wind tunnels for measurements in transitional boundary layers, supported by hot-wire/hot-film anemometry, particle image velocimetry (PIV), and unsteady pressure measurements. We complement experiments with time–frequency analysis, proper orthogonal decomposition (POD), and stability analyses to extract coherent features and quantify transition dynamics.

Behavior of Turbulent Spots near Transition onset

Turbulent spots are localized regions of chaotic motion that emerge within an otherwise laminar boundary layer. Near the onset of transition, these spots play a critical role in dictating how smooth flow evolves into turbulence. Their growth, interaction, and eventual merging determine the spatial and temporal characteristics of the transition process. By studying the dynamics of turbulent spots—such as their initiation, spreading mechanisms, and influence on surrounding laminar flow—we gain deeper insight into the physics of boundary layer instability and the pathways to turbulence. This understanding is essential for advancing flow control strategies and improving aerodynamic performance in engineering applications.

Turbulent flow control (LEBU)

Large eddy break-up (LEBU) devices have been explored as a method to reduce skin-friction drag in turbulent boundary layers (TBLs). We perform wind-tunnel experiments on a flat-plate TBL perturbed by a LEBU placed near the edge of the logarithmic layer, using PIV and hot-wire measurements to characterize the altered flow. Results show changes in wall-normal velocity gradients and Reynolds shear stress not only near the device but also close to the wall, indicating an influence on the near-wall turbulence cycle; an internal layer forms over the LEBU and introduces synthetic large scales within the TBL (typically about three times the boundary-layer thickness). POD of PIV fields is used to compare dominant energetic modes with and without the device and to understand how LEBU acts as a scale manipulator in a complex turbulent environment.

Wavelet based detector for intermittent signals

Intermittent transitional velocity signals are non-stationary and require analysis methods that retain both time and frequency information. We use wavelet transforms to identify broadband high-frequency activity associated with turbulent spots and to formulate an intermittency factor that quantifies the stage of transition. Recent results show that wavelet-transform-based approaches can estimate intermittency more accurately than several previously used methods.

Turbulent jets

We analyze vorticity and scalar transport in canonical turbulent jets and perturbed jet flows using direct numerical simulation (DNS). For canonical jets, we interpret the flow using vorticity fluxes and coherent structures, including evidence of hairpin-like structures in the outer region that contribute to Reynolds-stress generation. We also study off-source heated jets that mimic cumulus clouds where latent heat release occurs above ground level, and we develop scaling approaches that allow meaningful comparisons across different heating parameters reported in the literature.

Linear stability of channel flows

We investigate how channel flows and wall-bounded shear layers respond to small disturbances—whether perturbations amplify and lead to turbulence or decay back to laminar flow. This provides insight into transition mechanisms and helps identify flow parameters that promote or suppress disturbance growth. Our work combines stability analysis with numerical solutions of the governing equations for incompressible flows.

Energy cascade in wall turbulence

We study the turbulence energy cascade in wall-bounded flows in real space using a band-pass-filter-based multi-scale analysis and Lagrangian particle tracking applied to DNS-generated flow fields. The multi-scale framework enables calculation of inter-scale energy and enstrophy transfer and enstrophy generation due to stretching, supporting studies of scale locality and how cascade behavior depends on shear and Reynolds number. We also explore cascade inhomogeneity and its possible causal links to small-scale intermittency, and we characterize structural morphology using Minkowski functionals as a novel quantitative descriptor. In parallel, Lagrangian particle tracking is used to examine cascade dynamics from the viewpoint of fluid particles that transport mass, momentum, and energy across scales.

Needle probe for unsteady pressure measurements

Unsteady pressure fluctuations in turbulent flows can impose fluctuating loads on aerospace vehicles, trigger structural vibrations, and generate acoustic noise that may affect sensitive payloads. Measuring static pressure fluctuations within a turbulent flow is challenging, so we developed a dedicated needle probe for time-resolved unsteady pressure measurements. The probe has a sharp nose followed by a tube with four circumferential pinholes (0.3 mm diameter) connected to a transducer housed in a larger tube; pressure fluctuations enter through the pinholes and are measured by the transducer, and the probe is dynamically calibrated over the frequency range of interest to correct acoustic effects. We validate the probe by measuring pressure fluctuations in a fully developed turbulent boundary layer and use it for aerospace-relevant measurements such as fluctuating pressure in the wake of a wing.

Wall-pressure fluctuations on launch vehicles

Turbulent boundary layers on launch-vehicle surfaces generate unsteady wall-pressure fluctuations that can adversely affect payloads. Surface protuberances such as ribs, wedges, and joints can further modify local pressure-fluctuation levels. We study these effects using a flat-plate setup with different protuberances placed upstream of a flush-mounted wall-pressure probe; the probe senses pressure fluctuations downstream through a 0.3 mm pinhole connected to a transducer, and it is dynamically calibrated over the frequency range of interest to correct acoustic effects.

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