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Your search keyword '"Knight, D. A."' showing total 11 results
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11 results on '"Knight, D. A."'

2. Self-sustained oscillations of lift and drag forces, heat fluxes, and flowfield parameters over supersonic bodies under asymmetrical energy deposition.

Author

Azarova, O. A., Knight, D. D., and Kravchenko, O. V.

Subjects
*DRAG force, *LIFT (Aerodynamics), *HEAT flux, *NAVIER-Stokes equations, *OSCILLATIONS
Abstract

This paper examines the effect of an asymmetrical energy source impact on the flow around supersonic aerodynamic bodies in a viscous heat-conducting gas (air) at Mach 2.5. The simulations are based on the Navier–Stokes equations with temperature-dependent viscosity and thermal conductivity. The dynamics of density, pressure, temperature, and heat fluxes were analyzed. Specific emphasis is placed on the effects of viscosity and thermal conductivity. Self-sustained oscillations of the flow parameters, lift and drag forces, and heat fluxes were obtained and studied. The mechanism of these oscillations was established, and the conditions of their presence in a flow in relation to the energy source characteristics and location were researched. Possible approaches for elimination of these oscillations were discussed. [ABSTRACT FROM AUTHOR]

Published
2023
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5. Investigation of a hypersonic crossing shock wave/turbulent boundary layer interaction

Author

Narayanswami, N, Knight, D. D, and Horstman, C. C

Subjects
Aerodynamics
Abstract

A combined theoretical and experimental study is presented for the interaction between crossing shock waves generated by (10 deg, 10 deg) sharp fins and a flat plate turbulent boundary layer at Mach 8.3. The theoretical model is the full 3D mean compressible Reynolds-averaged Navier-Stokes (RANS) equations incorporating the algebraic turbulent eddy viscosity model of Baldwin and Lomax (1978). A grid refinement study indicated that adequate resolution of the flow field has been achieved. Computed results agree well with experiment for surface pressure and surface flow patterns and for pitot pressure and yaw angle profiles in the flow field. The computations, however, significantly overpredict surface heat transfer. Analysis of the computed flow field results indicates the formation of complex streamline and wave structures within the interaction region.

Published
1993
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10. Numerical characterization of high-temperature filament interaction with blunt cylinder at Mach 3.

Author

Golbabaei-Asl, M. and Knight, D.

Subjects
*DRAG (Hydrodynamics), *SEDIMENTATION & deposition, *FLOW control (Data transmission systems), *NUMERICAL analysis, *COMPUTER simulation of gas flow
Abstract

Energy deposition is a robust technique for various high-speed flow control applications including drag reduction. A numerical study of energy deposition is performed for perfect gas flow approaching a blunt cylinder at Mach 3. The energy deposition is simulated by a high-temperature filament injected instantaneously in front of the cylinder. The effect of important dimensionless parameters is studied to characterize the drag modification. The results indicate a saturation effect on maximum drag reduction at higher magnitudes of energy deposition. The computations reveal that the discharge location of the filament does not significantly impact the drag. A phenomenological examination of the interaction is performed. The effectiveness and efficiency of the filament on drag reduction are investigated. A one-dimensional analytical approach is studied to describe the numerical results. [ABSTRACT FROM AUTHOR]

Published
2014
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11. Effect of energy addition on MR $\rightarrow$ RR transition

Author

Yan, H., Adelgren, R., Elliott, G., Knight, D., and Beutner, T.

Abstract

A combined computational and experimental study was performed to investigate the effect of a single laser energy pulse on the transition from a Mach Reflection (MR) to a Regular Reflection (RR) in the Dual Solution Domain (DSD). The freestream Mach number is 3.45 and two oblique shock waves are formed by two symmetric $22^\circ$ wedges. These conditions correspond to a point midway within the DSD wherein either an MR or an RR is possible. A steady MR was first obtained experimentally and numerically, then a single laser pulse was deposited above the horizontal center plane. In the experiment, the laser beam was focused resulting in a deposition volume of approximately 3 mm 3, while in the simulation, the laser pulse was modeled as an initial variation of the temperature and pressure using Gaussian profile. A grid refinement study was conducted to assess the accuracy of the numerical simulations. For the steady MR, the simulation showed the variation of Mach stem height along the span due to side effects. The predicted spanwise averaged Mach stem height was 1.96 mm within 2% of the experimental value of 2 mm. The experiment showed that the Mach stem height decreased to 30% of its original height due to the interaction with the thermal spot generated by the laser pulse and then returned to its original height by $300\;\mu$s. That the Mach stem returned to its original height was most likely due to freestream turbulence in the wind tunnel. The numerical simulation successfully predicted the reverse transition from a stable MR to a stable RR and the stable RR persisted across the span. This study showed the capability of a laser energy pulse to control the reverse transition of MR $\rightarrow$ RR within the Dual Solution Domain.

Published
2003
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