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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 paper, the authors measured the heat transfer from a short uniform heat flux strip beneath a turbulent boundary layer with and without freestream turbulence using a liquid crystal imaging technique.
Abstract: The heat transfer from a short uniform heat flux strip beneath a turbulent boundary layer with and without freestream turbulence was measured using a liquid crystal imaging technique. Data were taken for freestream turbulence intensities on the order of 12% and at momentum thickness Reynolds numbers on the order of 1,000 and 2,000 for the turbulent and steady freestreams respectively. Heat transfer enhancement due to the presence of freestream turbulence was measured in terms of the ratio of the average St on the heated strip for the turbulent freestream case to the steady freestream case. Compared to the baseline case of a uniformly heated surface upstream of the strip, the heat transfer enhancement decreased by 20%. The temperature distribution measured on and around the heated strip represented a kernel solution that was used by means of superposition to predict the heat transfer for any arbitrarily specified thermal boundary condition given the same flowfield. Predictions are compared against correlations and numerical predictions as well as data from the literature. The details and practical applications of this approach to handling heat transfer with non-uniform thermal boundary conditions are presented.

21 citations

Journal ArticleDOI
TL;DR: In this paper, an unsteady Reynolds-averaged Navier-Stokes (URANS) strategy is applied to the problem of wake-induced transition at high freestream turbulence on the suction side of two blades representative of those used in low-pressure turbines.
Abstract: An unsteady Reynolds-averaged Navier-Stokes (URANS) strategy is applied to the problem of wake-induced transition at high freestream turbulence on the suction side of two blades representative of those used in low-pressure turbines. Experimentally, the blades are arranged in high-aspect-ratio linear cascades, with upstream circular bars generating passing wakes, and two-dimensional flow conditions are, thus, assumed. The strategy combines an explicit algebraic Reynolds-stress turbulence model with transition-specific modifications targeted at capturing the effects of high freestream turbulence and of pretransitional laminar fluctuations. Close attention is paid to numerical accuracy, and grids of up to 140,000 cells are used in combination with 800 time steps per pitchwise traverse to resolve small-scale features in the blade boundary layers that are associated with the unsteady interaction. The computational results demonstrate that the combined model returns a good representation of the response of the suction-side boundary layer to the passing wakes in both blades. Specifically, in the boundary layer of one of the two blades, the wakes are observed to cause a periodic upstream shift in the transition onset and, thus, correspondingly periodic attachment and calming. In the other, no separation occurs, and the wakes are shown to produce a significant periodic reduction in shape factor and increase in skin friction in the blade boundary layer, again as a consequence of the upstream shift in the transition location.

21 citations

01 Mar 1972
TL;DR: In this paper, photographic data were obtained for the transverse injection of water and isopropyl alcohol from a flat plate into airstreams having Mach numbers of 162 and 272 Jet/freestream dynamic pressure ratio, jet Reynolds and Weber numbers, and freestream Reynolds number were varied.
Abstract: : Photographic data were obtained for the transverse injection of water and isopropyl alcohol from a flat-plate into airstreams having Mach numbers of 162 and 272 Jet/freestream dynamic pressure ratio, jet Reynolds and Weber numbers, and freestream Reynolds number were varied Improved empirical equations for jet penetration and width were developed and substantiated for two sets of test conditions by detailed flowfield mapping 50 jet diameters downstream using pitot-pressure, cone-static-pressure, and heated sampling probes An improved theoretical analysis was obtained

21 citations

Journal ArticleDOI
TL;DR: In this paper, the wake of asymmetric bluff bodies was measured using particle imaging velocimetry, laser Doppler anemometry, load cell, hotwire, and flow visualization techniques at Re=2600-8500 based on the freestream velocity and the characteristic height of the bluff bodies.
Abstract: The wake of asymmetric bluff bodies was experimentally measured using particle imaging velocimetry, laser Doppler anemometry, load cell, hotwire, and flow visualization techniques at Re=2600–8500 based on the freestream velocity and the characteristic height of the bluff bodies. Asymmetry is produced by rounding some corners of a square cylinder and leaving others unrounded. It is found that, with increasing corner radius, the flow reversal region is expanded, and the vortex formation length is prolonged. Accordingly, the vortex shedding frequency increases and the base pressure rises, resulting in a reduction in the mean drag as well as the fluctuating drag and lift. It is further found that, while the asymmetric cross section of the cylinder causes the wake centerline to shift toward the sharp corner side of the bluff body, the wake remains globally symmetric about the shifted centerline. The near wake of asymmetric bluff bodies is characterized in detail, including the Reynolds stresses, characteristic velocity, and length scale, and is further compared with that of the symmetric ones.

21 citations

Journal ArticleDOI
TL;DR: In this article, the effect of mainstream turbulence on heat transfer from a cylinder was investigated and the results showed that in the Reynolds number range 5000-35 000 increases in freestream turbulence intensity of 10 per cent result in improvements of heat transfer at the rear of the cylinder of up to 100 per cent.

21 citations


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