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Current Research of Dr. Thomas Corke

Dr. Corke conducts his research in the Hessert Laboratory for Aerospace Research.

Numerical Study of Receptivity to Sound on a Parabolic Leading Edge

Use of a numerical approach to study the receptivity of the boundary layer flow over a slender body with a leading edge of finite radius of curvature to small streamwise velocity fluctuations of a given frequency. The body of interest is a parabola in order to exclude jumps in curvature, which occur on finite thickness flat plates with elliptic leading edges used by others. The infinitesimally thin flat plate is contained as the limiting solution for the parabola as the nose radius of curvature goes to zero. We also use parabolic coordinates as a means of reducing spurious receptivity that might occur through nonuniformities of the body contour and the numerical grid. For the solution, the unsteady flow field is decomposed into the mean flow plus a small periodic oscillation. These are solved separately. A normal-mode form is used for the perturbation flow which then removes time from the problem. We then solve for the spatial amplitude of perturbation field subject to the free-stream oscillation. This has a distinct advantage over traditional approaches which solve for the mean flow and small unsteady fluctuations together.

Instabilities and Transition to Turbulence on Elliptic Cones at Mach 8

This experiment utilizes the Mach 8 Variable Density Tunnel (M8VDT) at NASA Langley Research Center to study instabilities leading to transition to turbulence on cones with an elliptic cross-section. The nozzle of the M8VDT is a "quiet" design to minimize acoustic disturbances. The cone is designed to fit completely within the quiet zone region. It also is designed to be placed at angles of attack of up to 5 degrees. Flow measurements are made with a hot-wire velocity sensor which is carried on a 3-D traversing mechanism mounted on a sting behind the model. The experiments focus on following the downstream development of the instability modes in order to make comparisons to linear theory, and to document the nonlinear mechanisms which ultimately lead to transition to turbulence.

MEMS and Flow Control for Aircraft Engines

This work involves the use of an azimuthal array of plasma actuators at the exit of a high Mach number axisymmetric jet to control the unsteady initial condition of instability modes leading to sound. The array fo actuators follows a design used by Corke & Cavalieri (1995) in exciting instability modes in a jet at Mach 0.85. The methodology follows that of Corke & Kusek (1993) and Corke & Ahn (1996) to excite combinations of axisymmetric and helical modes through a feed-back resonance. The objective here is to combine these techniques in order to investigate the effect of different helical mode wave angles on the acoustic characteristics of a round jet. The guiding precept is a theoretical dependence of the frequency of acoustic disturbances on the helical mode wave angle. The results with well controlled boundary and initial conditions are intended to provide a data base for numerical calculations, and lead to approaches for reducing acoustic levels and/or favorably altering acoustic dispersion.

Free-stream Turbulence Level Measurements by Leading-edge Stability Methods

This involves the development of a method for the indirect measurement of free-stream turbulence levels which will be suitable for use in cryogenic wind tunnels such as the National Transonic Facility (NTF) at NASA Langley Research Center. The approach is based on measuring the amplitude of Klebanoff modes which are known to develop through the interaction of turbulent scales and a leading edge. The advantages of this approach are that these modes occur at low frequencies and therefore do not require high frequency response (delicate) sensors, that their amplitude grows as the square-root of the distance from the leading edge, making it possible to have a relatively short model. Furthermore, it is known that the most amplified Klebanoff mode is not sensitive to its spanwise wave length so that the spanwise spacing of sensors can be determined a priori. Finally these modes are probably not sensitive to the level of acoustic disturbances so that they will directly reflect the level of vortical fluctuations in the tunnel. In conjunction with this we propose to develop a numerical (DNS) model for a vortex impinging on a leading edge. This will be based on our previous work on modeling acoustic receptivity for parabolic and elliptic leading edges.

Separation Control for Rotocraft using a Glow-Discharge Flat Array

This involves the development of a "flat-array plasma actuator" as an unsteady electrostatic pump which is designed to energize the low momentum fluid in a separated flow and cause reattachment. This has the advantages of having a very high frequency band-width, high energy density, and no moving parts. The applications for this are primarily directed towards helicopter which includes: suppressing advancing stall of rotors. Controlling flow separations on multifaced surfaces which are designed for a low radar (stealth) signature, and controlling separations in bends of internal air-inlet flows.