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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: The lift and drag characteristics and associated flow fields over the suction surface of an NACA 0015 airfoil with an aspect ratio of 2.9 were obtained at a Reynolds number of 250,000 for conditions both with and without freestream turbulence (FST).
Abstract: The lift and drag characteristics and associated flowfields over the suction surface of an NACA 0015 airfoil with an aspect ratio of 2.9 were obtained at a Reynolds number of 250,000 for conditions both with and without freestream turbulence (FST).

93 citations

01 Dec 1996
TL;DR: In this paper, the influence of freestream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and turbulence intensity was studied in simulated film cooling.
Abstract: Hot-wire anemometry of simulated film cooling was used to study the influence of freestream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and turbulence intensity. Measurements were made in the zone where the coolant and freestream flows mix. Flow from one row of film cooling holes with a streamwise injection of 35{degree} and no lateral injection and with a coolant- to-freestream flow velocity ratio of 1.0 was investigated under freestream turbulence levels of 0.5 and 12%. Coolant-to-freestream density ratio was unity. Two length-to-diameter ratios for the film cooling holes, 2.3 and 7.0, are tested. Results show that under low freestream turbulence conditions, pronounced differences exist in the flowfield between L/D=7.0 and 2.3; the differences are less prominent at high freestream turbulence intensities. Generally, short-L/D injection results in ``jetting`` of the coolant further into the freestream flow and enhanced mixing. Other changes in the flowfield attributable to a rise in freestream turbulence intensity to engine- representative conditions are documented. 15 figs, 2 tabs, refs.

93 citations

Proceedings ArticleDOI
01 Jan 2008
TL;DR: In this paper, the authors investigated the behavior of the Menter shear-stress transport (SST) and Spalart-Allmaras (SA) turbulence models at low Reynolds numbers and under conditions conducive to relaminarization.
Abstract: The behaviors of the widely-used Spalart-Allmaras (SA) and Menter shear-stress transport (SST) turbulence models at low Reynolds numbers and under conditions conducive to relaminarization are documented. The flows used in the investigation include 2-D zero pressure gradient flow over a flat plate from subsonic to hypersonic Mach numbers, 2-D airfoil flow from subsonic to supersonic Mach numbers, 2-D subsonic sink-flow, and 3-D subsonic flow over an infinite swept wing (particularly its leading-edge region). Both models exhibit a range over which they behave 'transitionally' in the sense that the flow is neither laminar nor fully turbulent, but these behaviors are different: the SST model typically has a well-defined transition location, whereas the SA model does not. Both models are predisposed to delayed activation of turbulence with increasing freestream Mach number. Also, both models can be made to achieve earlier activation of turbulence by increasing their freestream levels, but too high a level can disturb the turbulent solution behavior. The technique of maintaining freestream levels of turbulence without decay in the SST model, introduced elsewhere, is shown here to be useful in reducing grid-dependence of the model's transitional behavior. Both models are demonstrated to be incapable of predicting relaminarization; eddy viscosities remain weakly turbulent in accelerating or laterally-strained boundary layers for which experiment and direct simulations indicate turbulence suppression. The main conclusion is that these models are intended for fully turbulent high Reynolds number computations, and using them for transitional (e.g., low Reynolds number) or relaminarizing flows is not appropriate.

92 citations

Journal ArticleDOI
TL;DR: In this article, the effects of fine scale turbulence were represented by a two-equation (k-e) closure model that included a generalized formulation, low Reynolds number terms, and a compressibility correction.
Abstract: Steady flowfields resulting from slot injection at the surface of a flat plate in a freestream with a Mach number of 3.7 and a unit Reynolds number of 5.83 x 10 6 /m were simulated numerically by integration of the time-dependent compressible mass-averaged Navier-Stokes equations. Effects of fine scale turbulence were represented by a two-equation (k-e) closure model that included a generalized formulation, low Reynolds number terms, and a compressibility correction

91 citations

Journal ArticleDOI
TL;DR: In this paper, an Euler analysis procedure for predicting the unstart tolerance of supersonic inlets was developed and used to analyze inlet unstart behavior, and the results showed that both increases and decreases in temperature or velocity will unstart the inlet, whereas only pressure decreases will cause it to close.
Abstract: The objective of this article is to report progress toward the development of an Euler analysis procedure for predicting the unstart tolerance of supersonic inlets. As an aid to understanding boundary condition issues, a one-dimensional, linear-analysis procedure was developed and used to analyze inlet unstart behavior. Using these results as a guide, an Euler analysis procedure was extended through the addition of a new bleed boundary condition, a new compressor face boundary condition, and an engine demand model for the simulation of unsteady inlet flows caused by freestream flow disturbances. Five unstart conditions were identified with the Euler analysis of the axisymmetric inlet for both 20- and 90-deg throat bleed configurations. Results show that both increases and decreases in temperature or velocity will unstart the inlet, whereas only pressure decreases will unstart the inlet. It was also found that 90-deg throat bleed improves the unstart tolerance relative to 20-deg throat bleed for freestream pressure decreases, temperature increases, and changes in velocity.

91 citations


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