Topic
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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TL;DR: In this paper, a fast response, total pressure probe was used with a periodically sampling and averaging data acquisition system to study the unsteady total pressure field in an axial-flow turbomachine.
Abstract: A fast-response, total-pressure probe was used with a periodically sampling and averaging data acquisition system to study the unsteady total-pressure field in an axial-flow turbomachine. Periodically unsteady total-pressure data were used to demonstrate some of the ways in which turbomachine blade wake transport and interaction influences the energy transfer involved. Observed trends of periodic variations in local total-pressure values could be explained in terms of the details of energy transfer associated with the different kinds of fluid particles (freestream, wake segment, blade surface boundary layer, mixed) moving through a blade row.
29 citations
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04 Jan 2011TL;DR: Aero-optical measurements of a zero-pressure gradient, supersonic boundary layer along the test section wall at M = 2.0 were performed using a Malley probe.
Abstract: Aero-optical measurements of a zero-pressure-gradient, supersonic boundary layer along the test section wall at M=2.0 were performed using a Malley probe. The Malley probe captured both the amplitude of optical distortions and the convective speed. The convective speed of the optically-active structures inside the supersonic boundary layer was found to be 0.84 of the freestream speed. The deflection-angle spectra were found to collapse with the local displacement thickness. The streamwise correlation function for the supersonic boundary layer revealed the presence of a pseudo-periodic structure with the typical size of 1.5 of the local boundary-layer thickness. A new model was developed to describe aero- optical effects of both the subsonic and the supersonic boundary layers. Finally, this new model and several other theoretical scalings were tested in the attempt to collapse both subsonic and supersonic boundary layer aero-optical results.
29 citations
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TL;DR: In this paper, the effects of using sulfur hexafluoride, SF 6, as a substitute for air were investigated and it was shown that the shock location calculated for SF 6 is vastly different from that in air and moves progressively forward on the airfoil as the freestream pressure is increased and real gas effects become more pronounced.
Abstract: Numerical study is presented that investigates effects of using sulfur hexafluoride, SF 6 , as a substitute for air. Inviscid results for airfoils indicate that for transonic cases the shock location calculated for SF 6 is vastly different from that in air and moves progressively forward on the airfoil as the freestream pressure is increased and real gas effects become more pronounced.
29 citations
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TL;DR: In this article, the stability and convolution of the interface between the freestream and recirculating/wake core regions in an axisymmetric, separated supersonic flow were studied using planar imaging.
Abstract: The steadiness and convolution of the interface between the freestream and recirculating/wake core regions in an axisymmetric, separated supersonic flow were studied using planar imaging. Five regions along the shear layer/wake boundary were investigated in detail to quantify the effects that key phenomena, such as the recompression and reattachment processes, have on the development of large-scale unsteady motions and interfacial convolution. These studies show that flapping motions, when viewed from the side, generally increase in magnitude, in relation to the local shear layer thickness, with downstream distance, except at the mean reattachment point, where they are slightly suppressed. When viewed from the end, the area-based (pulsing) fluctuations increase monotonically downstream as a percentage of the local area, whereas the position-based (flapping) motions show pronounced peaks in magnitude in the recompression region and in the developing wake. The interface convolution increases monotonically with downstream distance in both the side- and end-view orientations
28 citations
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04 Jan 2011TL;DR: In this paper, the authors investigated the linear development of the wave packet by pulsing the ∞ow with a low amplitude (0:001% of the freestream velocity) and identified the dominant waves within the resulting wave packet as two-dimensional second mode disturbance waves.
Abstract: Direct Numerical Simulations (DNS) were performed to investigate transition initiated by a localized disturbance in a hypersonic ∞at{plate boundary layer. In order to model a natural transition scenario, the boundary{layer was forced by a short duration (localized) pulse through a hole on the ∞at{plate. The pulse disturbance developed into a threedimensional wave packet which consisted of a wide range of disturbance frequencies and wave numbers. First, the linear development of the wave packet was studied by pulsing the ∞ow with a low amplitude (0:001% of the freestream velocity). The dominant waves within the resulting wave packet were identifled as two-dimensional second mode disturbance waves. Hence the wall{pressure disturbance spectrum exhibited a maximum at the spanwise mode number k = 0. The spectrum broadened in downstream direction and the lower frequency flrst mode oblique waves were also identifled in the spectrum. However, the peak amplitude remained at k = 0 which shifted to lower frequencies in the downstream direction. In order to investigate the nonlinear transition regime, the ∞ow was pulsed with a higher amplitude disturbance (5% of the freestream velocity). The developing wave packet grows linearly at flrst before reaching the nonlinear regime. The wall pressure disturbance spectrum conflrmed that the wave packet developed linearly at flrst. The response of the ∞ow to the high amplitude pulse disturbance indicated the presence of a fundamental resonance mechanism. Lower amplitude secondary peaks were also identifled in the disturbance wave spectrum at approximately half the frequency of the high amplitude frequency band, which would be an indication of a subharmonic resonance mechanism. The disturbance spectrum indicates however, that fundamental resonance is much stronger than subharmonic resonance.
28 citations