Freestream

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

Supersonic Flow over a Shallow Open Rectangular Cavity

Abstract: An experimental investigation was conducted on a supersonic flow at a freestream Mach number of 2 over a shallow open cavity, including the effects of adding streamwise serrated edges. These flows have relevance to weapons bays and airframe gaps on high-speed aircraft. The measurements consisted of single-shot and time-resolved schlieren visualization, as well as unsteady pressure spectra. The length-to-depth ratio of the cavity was 8. The tests conducted at different Reynolds numbers with the baseline cavity (straight leading and trailing edges) showed that increasing the Reynolds number increases the root-mean-square pressure inside the cavity. The addition of serrations to the cavity leading or trailing edge did not show any significant effect on the separating shear layer nor in controlling the oscillations of the shear layer. There was also no noticeable effect on the overall sound pressure levels inside the cavity. A new expression for calculating shallow-cavity resonant frequencies applicable at su...

Suppression of the unsteady vortex wakes of a circular cylinder pair by a doublet-like counter-rotation

Abstract: The present investigation examines the suppression of unsteady, two-dimensional wake instabilities of a pair of identical circular cylinders, placed side-by-side normal to freestream at a low Reynolds number of 150. It is found that when the cylinders are counter-rotated, unsteady vortex wakes can be completely suppressed. At fast enough rotational speeds, a virtual elliptic body is produced by a closed streamline, strongly resembling a doublet potential flow. Copyright © 2009 John Wiley & Sons, Ltd.

Role of data uncertainties in identifying the logarithmic region of turbulent boundary layers

Abstract: Composite expansions based on the log-law and the power-law were used to generate synthetic velocity profiles of zero pressure gradient turbulent boundary layers (TBLs) in the range of Reynolds number $$800 \le Re_{\theta } \le 860{,}000,$$ based on displacement thickness and freestream velocity. Several artificial errors were added to the velocity profiles to simulate typical measurement uncertainties. The effects of the simulated errors were studied by extracting log-law and power-law parameters from all these pseudo-experimental profiles. Various techniques were used to establish a measure of the deviations in the overlap region. When parameters extracted for the log-law and the power-law are associated with similar levels of deviations with respect to their expected values, we consider that the profile leads to ambiguous conclusions. This ambiguity was observed up to $$Re_{\theta }=16{,}000$$ for a 4 % dispersion in the velocity measurements, up to $$Re_{\theta }=8.6 \times 10^{5}$$ for a 400 $$\upmu$$ m uncertainty in probe position (in air flow at atmospheric pressure), and up to $$Re_{\theta }=32{,}000$$ for 3 % uncertainty in the determination of $$u_{\tau }.$$ In addition, a new method for the determination of the log-law limits is proposed. The results clearly serve as a further note for caution when identifying either a log or a power-law in TBLs. Together with a number of available studies in the literature, the present results can be seen as a additional reconfirmation of the log-law.

Flowfield near a Mulitiport Injector Array in a Supersonic Flow

Abstract: Experiments were performed to study the effects of toe-in angle on the exterior ports of a three-hole, lowdownstream-angleinjector array in a supersonic e ow. The three jetswere arranged e ush with the test section e oor so that the interference between the three plumes and the main e ow would instill vortical motions. Three different cone gurations were tested involving three, 30 deg downstream angled, round injection holes in a row with sonic air and helium injection into a Mach 3.0 air cross stream. The two exterior holes of the row injector were set at toe-in angles of 0, 15, and 30 deg. The primary qualitative observations were nanoshadowgraphs and surface oil e ow visualization. A novel vertical plate e ow visualization concept was also tested. Aerothermodynamic probe measurementswereperformedata downstream location with heated airinjection to assessthetotalpressurelosses and mixing potential of the e ow. Results showed improved mixing and core penetration with an increase of jet momentum and toe-in angle. The observed oblique shock angle also increased with jet to freestream momentum ratio and toe-in angle, but the integrated total pressure losses associated with the injector shock structure were minimized with the 15 degree toe-in array injector.