Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.

A Computational Analysis of Thermochemical Studies in the LENS Facilities

Abstract: A review has been presented detailing the comparisons between numerical prediction and experimental data collected in the LENS facilities for a program focusing on thermochemical modeling of the flow in the reflected shock tunnel facility at high enthalpy. Comparisons have been provided for several studies made in the LENS-I facility including fundamental laser diode measurements of freestream nitric oxide concentration, temperature, and velocity; measurements on a two-dimensional cylinder; and measurements of laminar shock-wave/boundary layer interaction on a double cone geometry. The freestream velocity of the facility is found to be predicted to an accuracy of 2.5% or better for well-tailored conditions at all enthalpy levels, but the static temperature is significantly over-predicted for high enthalpy flows. Despite this, good agreement is obtained with all measurements for a two-dimensional cylinder. For the double cone model, the effect of vibration-dissociation coupling with the T-TV and CVDV models has been investigated. The choice of coupling model has impact for the lower enthalpy case, but in the high enthalpy case, it is unclear whether the discrepancy with the measurements is attributable to the coupling in the interaction region or the understanding of the freestream conditions.

Nonlinear receptivity to oblique vortical modes in flow past an elliptic leading edge

Abstract: Nonlinear boundary-layer receptivity to pairs of unsteady oblique freestream vortical modes is studied in direct numerical simulation of flow over a flat plate with an elliptic leading edge. The freestream is perturbed by three types of oblique Fourier modes, differing in the magnitude of the three vorticity components. The vortical modes excite steady boundary-layer streaks. The associated receptivity mechanism, described in detail, is quadratic in the forcing amplitude. Elliptic leading edges with two different aspect ratios are considered. We find that – and explain why – the streak amplitudes in nonlinear receptivity are largely unaffected by the leading-edge bluntness for the types of external disturbances studied. As linear receptivity is the predominant mechanism at low forcing frequencies, the nonlinear mechanism comes into play when high-frequency vortices are present in the freestream. Nonlinear receptivity is therefore expected to contribute to the excitation of boundary-layer streaks by freest...

Influence of Nonequilibrium Kinetics on Heat Transfer and Diffusion near Re-Entering Body

Abstract: The heat transfer and diffusion near the surface of a space vehicle under re-entry conditions are studied on the basis of the kinetic theory of gases. The influence of the nonequilibrium kinetics in an (N 2 , N) mixture on the transport properties of the flow is investigated. The nonequilibrium vibrational distributions in the boundary layer near the surface of the re-entering body have been obtained in the state-to-state approach and Inserted in the transport kinetic theory code. As a result, the total heat flux, thermal conductivity, and all diffusion coefficients are calculated under different conditions in the freestream and on the surface. The effects of various energy exchanges, vibrational nonequilibrium, dissociation, and recombination on the heat transfer and diffusion are examined

Simultaneous Infrared And Pressure Measurements Of Crossflow Instability Modes For HIFiRE 5 (POSTPRINT)

Abstract: A 2:1 elliptic cone model was tested in a Mach-6 quiet wind tunnel with both low and elevated freestream noise levels. Simultaneous measurements were made using an infrared camera and 22 pressure sensors mounted flush with the model surface. Infrared measurements confirmed the presence of stationary crossflow vortices in quiet flow. This is the first time infrared imaging has identified stationary crossflow vortices in a quiet wind tunnel. Power spectral densities of the signals from the pressure transducers also revealed the presence of traveling crossflow waves much farther upstream than had previously been measured. Stationary crossflow wavelengths and traveling crossflow wave properties matched those measured on a previous model of the same geometry. Neither stationary nor traveling crossflow vortices were observed in noisy flow, even though the boundary layer was seen to transition from laminar to turbulent as the freestream Reynolds number was increased. The primary transition mechanism in noisy flow is unknown.

Supersonic Shock Wave Turbulent Boundary-Layer Interactions

Abstract: Results are presented of an experimental investigation of shock wave turbulent boundary-layer interactions in supersonic flow. The experiments were conducted at a freestream Mach number of 2.96 and over a boundarylayer Reynolds number range of 10 5 to 10 6. Surface static pressure measurements, oil flow photographs, and interferograms were obtained to define the length of separation and the incipient separation angles for 1) twodimensional compression corner and 2) planar shock wave interactions with a turbulent boundary layer. The tests were conducted in a high unit Reynolds number freestream on a long flat plate with a turbulent boundarylayer thickness in the interaction region of from 0.12 to 0.18 in. Direct comparisons were made between the compression corner and incident shock wave interactions to determine the effects of configuration on turbulent boundary-layer separation. For both configurations the length of the separated region was found to decrease and the incipient separation angle to increase with increasing Reynolds number. For constant Reynolds number, the overall pressure rise for incipient separation was approximately the same for the compression corner interaction and the incident shock wave interaction. Turbulent boundary-layer separation was found to be of the "free interaction" type whereby the separation angle and pressure distribution through separation were independent of Reynolds number, overall pressure rise, and configuration. fo Nomenclature skin friction coefficient at beginning of interaction freestream Mach number pressurepressure freestream pressure Reynolds number based on freestream condition and boundary-layer thickness at beginning of interaction . span °f shock generator stagnation temperature wall temperature axial distance from flat plate leading edge axial location of center of interaction axial distance from flat plate/ramp hinge line to shock generator leading edge axial location of separation point axial offset distance vertical distance between flat plate and shock generator leading edge effective incipient separation corner angle compression ramp angle shock generator angle boundary-layer thickness at beginning of interaction