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Freestream

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


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Journal ArticleDOI
TL;DR: In this article, a transverse jet discharging into a supersonic nozzle was investigated to clarify the details of the flow and the penetration and turning of the secondary jet is governed by the dynamics of the shock structure occurring in the freeexpansion plume and it is not a simple function of jet momentum.
Abstract: The present experimental study of a transverse jet discharging into a supersonic nozzle was undertaken to clarify the details of the flow. Results of wall and impact pressure measurements throughout the core of the interaction field, as well as flow visualization tests, are reported for 11 tests differing as systematically as possible by the injected mass rate, injection station Mach number, and primary to secondary stagnation pressure ratio. These measurements are used in an effort to reconstruct the true structure of the flow and suggest the following characteristic features of it. The penetration and turning of the secondary (supersonic) jet is governed by the dynamics of the shock structure occurring in the free-expansion plume and it is not a simple function of jet momentum. The mixing region downstream of injection contains a "horseshoe" vortex separating the inner (jet) flow from the outer (freestream) flow near the nozzle wall. The entire interaction region is enveloped by a nearly ogival shock, the gross properties of which, to the first approximation, depend (nonlinearly) on the injected momentum, the freestream pressure, and the freestream velocity at the injection station.

39 citations

Proceedings ArticleDOI
05 Jun 2006
TL;DR: In this paper, a simplified analysis technique has been used based on energy accounting to freeze specified portions of the chemical or vibrational energy during the expansion process in the nozzle, which results in increased shock standoff distance that better matches the measured shock shape.
Abstract: The conditions for a typical run from the MSL phase two study of transition that was performed in the LENS facility have been analyzed to understand the sensitivity to the freestream conditions of the facility. A simplified analysis technique has been used based on energy accounting to freeze specified portions of the chemical or vibrational energy during the expansion process in the nozzle. The effect of freezing this energy results in increased shock standoff distance that better matches the measured shock shape. Based on several cases, it was found that freezing approximately 42% of the total enthalpy of the flow in the vibration mode results in the best agreement with the measured shock shape. This modified condition also results in significantly better agreement with the measured surface heat transfer at the stagnation point and with the measured pressure at the shoulders of the model. Based on this adjusted freestream condition, the surface heat transfer data shows behavior generally consistent with fully-catalytic recombination on the cold wall. This behavior is consistent with previous results obtained in shock tunnel facilities in carbon dioxide, air, and nitrogen. Although the mechanism causing this frozen energy in the flow has not been identified, the sensitivity of the transition onset point of the flowfield to this phenomenon has been estimated to be less than 10% based on a simple transition criterion.

39 citations

Journal ArticleDOI
TL;DR: In this article, measurements were obtained during the course of a series of flow quality improvements to a small stand-alone wind tunnel that has been modified for boundary-layer transition studies.
Abstract: Measurements are presented that were obtained during the course of a series of flow quality improvements to a small stand-alone wind tunnel that has been modified for boundary-layer transition studies. The objective of establishing a Blasius boundary layer with a high degree of spanwise uniformity has been frustrated by the persistence of Klebanoff modes, i.e., weak streamwise vortices within the layer. The vortices originate at the leading edge and appear to be caused by almost immeasurably small nonuniformities in the freestream introduced by the wind-tunnel screens. The vortices cause a spanwise thickening and thinning of the layer. Contours of the background unsteadiness in a spanwise plane through the layer show locally concentrated regions with elevated levels that are associated with the vortices. These contours are used as a sensitive indicator for the flow quality improvements. Although far from forming a complete parametric study, the observations should act as a valuable guide for others. For example, spanwise variations in the porosity of the screens were discovered by traversing each screen between a laser and a photo detector. Significant improvement in the spanwise uniformity of the layer was obtained by sorting the screens based on these results

39 citations

Journal ArticleDOI
TL;DR: In this article, an investigation of dynamic stall on a pitching NACA 0012 aspect ratio 4 wing is performed by means of high-fidelity wall-resolved large-eddy simulations.
Abstract: An investigation of dynamic stall on a pitching NACA 0012 aspect ratio 4 wing is performed by means of high-fidelity wall-resolved large-eddy simulations. The flow parameters are freestream Mach nu...

39 citations

Proceedings ArticleDOI
08 Jan 2007
TL;DR: In this paper, the authors report on freestream velocity measurements for a number of flows for velocities ranging from 2,060 m/s to 5,350 m /s.
Abstract: velocity measurements This work reports on freestream velocity measurements for a number of flows for velocities from 2,060 m/s to 5,350 m/s The measured velocity was compared to facility calculations that are based on the measured shock speed in the driven tube and measured reservoir conditions The calculations agree with the velocity measurements up to 10 MJ/kg At higher enthalpies the calculations under predict the actual velocity of the flow However, the velocity measurement provides a new capability to operate the tunnel in non-tailored mode to obtain velocities greater than 5,300 m/s for at least 2 milliseconds of steady flow Under most circumstances the LENS I and LENS II shock tunnels produce fully-duplicated conditions for various flight trajectories in the upper atmosphere At high enthalpy some of the dissociated products are frozen during the expansion into the test section, so non equilibrium chemistry models have been developed to predict the Nitric Oxide (NO) concentration in the free stream gas Since the presence of this contaminant in the flow changes the nature of the test gas, however slightly, computational fluid dynamic (CFD) calculations are used to compensate for these effects 2 The actual concentration of the gas must be known Also it is very desirable to measure the free stream velocity since it is a direct measure of the gas kinetic energy and thus connected to the total enthalpy of the flow, a basic operating parameter of the facility At CUBRC we have constructed a continuous wave Quantum

39 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023195
2022350
2021108
2020113
201986
2018118