Momentum Transfer in Turbulent Separated Flow Past a Rectangular Cavity

1966 ◽  
Vol 33 (3) ◽  
pp. 641-646 ◽  
Author(s):  
R. L. Haugen ◽  
A. M. Dhanak
Keyword(s):  
Boundary Layer ◽  
Momentum Transfer ◽  
Separated Flow ◽  
Flow Region ◽  
Eddy Diffusion ◽  
Rectangular Cavity ◽  
Width Ratio ◽  
Transfer Rates ◽  
Turbulent Momentum ◽  
Vortex Patterns

This paper presents results of an analytical and experimental investigation aimed at describing the turbulent momentum transfer mechanism in the separated-flow region of a rectangular cavity facing an oncoming turbulent boundary layer. A flow model of the mixing region in the slot postulated on the basis of eddy diffusion in free jets gives values of velocities and drag in good agreement with the measurements. The results further point to the significant effects exerted by the oncoming boundary layer on transfer rates from the slot. Flow-visualization pictures show some interesting vortex patterns inside the cavity when height-to-width ratio is varied between values of 1 and 3.

Base Heat Transfer in Two-Dimensional Subsonic Fully Separated Flows

1971 ◽  
Vol 93 (4) ◽  
pp. 342-348 ◽  
Author(s):  
John W. Mitchell
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Experimental Investigation ◽  
Vortex Shedding ◽  
Separated Flow ◽  
Flow Region ◽  
Separated Flows ◽  
Two Dimensional ◽  
Layer Behavior ◽  
Low Speed Wind Tunnel

An experimental investigation of the heat transfer from the base of a two-dimensional wedge-shaped body to the separated-flow region was conducted in a low-speed wind tunnel. The Stanton number has been determined as a function of Reynolds number for two geometries that are representative of heat-exchanger surfaces. The heat transfer is found to be comparable in magnitude to that for attached flows. An analysis based on the mechanisms of vortex shedding and boundary-layer behavior is developed. The analysis agrees fairly well with the data and indicates the parameters governing base heat transfer.

Physics of unsteady blunt-fin-induced shock wave/turbulent boundary layer interactions

1994 ◽  
Vol 273 ◽  
pp. 375-409 ◽  
Author(s):  
Leon Brusniak ◽  
David S. Dolling
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Time History ◽  
Separated Flow ◽  
Flow Region ◽  
Horseshoe Vortex ◽  
Wall Pressure ◽  
Pressure Measurements ◽  
Separation Shock ◽  
Pressure Distributions

Fluctuating wall-pressure measurements have been made on the centreline upstream of a blunt fin in a Mach 5 turbulent boundary layer. By examining the ensemble-averaged wall-pressure distributions for different separation shock foot positions, it has been shown that local fluctuating wall-pressure measurements are due to a distinct pressure distribution, [weierp ]i, which undergoes a stretching and flattening effect as its upstream boundary translates aperiodically between the upstream-influence and separation lines. The locations of the maxima and minima in the wall-pressure standard deviation can be accurately predicted using this distribution, providing quantitative confirmation of the model. This model also explains the observed cross-correlations and ensemble-average measurements within the interaction. Using the [weierp ]i model, wall-pressure signals from under the separated flow region were used to reproduce the position–time history of the separation shock foot. The unsteady behaviour of the primary horseshoe vortex and its relation to the unsteady separation shock is also described. The practical implications are that it may be possible to predict some of the unsteady aspects of the flowfield using mean wall-pressure distributions obtained from either computations or experiments; also, to minimize the fluctuating loads caused by the unsteadiness, flow control methods should focus on reducing the magnitude of the [weierp ]i gradient (∂[weierp ]i/∂x).

A study of the turbulent separated-flow region occurring at a compression corner in supersonic flow

1965 ◽  
Vol 22 (3) ◽  
pp. 481-505 ◽  
Author(s):  
H. McDonald
Keyword(s):  
Boundary Layer ◽  
Single Layer ◽  
Separated Flow ◽  
Flow Region ◽  
Initial Boundary ◽  
Base Pressure ◽  
Layer Model ◽  
Compression Corner ◽  
Shock Configuration ◽  
Turbulent Separated Flow

The turbulent separated-flow region occurring at a compression corner under certain circumstances at supersonic speed has been examined in the light of recent improvements to base pressure theory (McDonald 1964). This base pressure theory is further extended from what could be termed a single-layer model of the re-attaching boundary layer to a two-layer model, thus enabling the inviscid shock configuration which occurs at the corner to be determined. Application of this analysis to some experimental results indicates a substantial measure of agreement.While this analysis has been framed for estimating the scale of the corner interaction, the extension can of course be applied to increase the range of initial boundary-layer thicknesses to which McDonald's analysis is applicable. An example of such an application is shown to be in good agreement with experiment.

Experimental Study of the Fence Wake Manipulation Using Pulsating Jet

2009 ◽  
Author(s):  
In-Su Kang ◽  
Young-Ho Choi ◽  
Chel-Woo Park ◽  
Hyoung-Bum Kim
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Separation Bubble ◽  
Water Channel ◽  
Separated Flow ◽  
Flow Region ◽  
Velocity Fields ◽  
Circulating Water ◽  
Pulsating Jet ◽  
Upstream Flow

In this study, we experimentally investigated the effect of rear-located pulsating jet to reduce the separated flow region behind the vertical fence. The separation bubble behind the fence is the representative feature of fence wake. Control of fence wake can be used for various purposes such as the reduction of drag, increasing or decreasing the mixing, etc. The vertical fence was submerged in the turbulent boundary layer in the circulating water channel. Reynolds number based on the fence height and upstream flow velocity was 3000. The parameters used for controlling the pulsating jet included the frequency, jet speed and distance between the fence and slit nozzle. In addition, we investigated the effect of continuous jet on the fence wake. Phase averaged DPIV method was applied to measure the instantaneous velocity fields around the fence. And the obtained results were compared with those of uncontrolled fence flow. The obtained results quantitatively show the decrease of reattachment region brought by the pulsating jet. And the specific jet condition which were effective to reduce the separation bubble behind the fence were found.

Heat Transfer in Turbulent Boundary-Layer Separation Over a Surface Cavity

1967 ◽  
Vol 89 (4) ◽  
pp. 335-340 ◽  
Author(s):  
R. L. Haugen ◽  
A. M. Dhanak
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Analytical Study ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Eddy Diffusion ◽  
Uniform Heat Flux ◽  
Surface Cavity ◽  
Good Agreement

An experimental and analytical study is presented in this paper describing heat transfer in the region of separated flow over a two-dimensional rectangular cavity (of variable depth-width ratios) facing an oncoming turbulent boundary layer of variable thickness. The analysis, based on a prescription of eddy diffusion in the mixing region, predicts a heat transfer correlation, in terms of the foregoing variables, resulting in good agreement with the data. Experiments were performed with conditions of uniform temperature and uniform heat flux at the cavity walls and revealed no substantial difference between the two methods on the final correlation.

Transient Performance of Separated Flows: Experimental Characterization of Flow Detachment Dynamics

2019 ◽  
Author(s):  
J. Saavedra ◽  
G. Paniagua
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
Separated Flow ◽  
Flow Region ◽  
Separated Flows ◽  
Wall Region ◽  
Flow Conditions ◽  
Flow Acceleration ◽  
Test Article ◽  
Near Wall

Abstract The operation of compact power units at low Reynolds environments is constrained by the boundary layer detachment in the low pressure turbines stages. Flow separation is prompt by the lack of momentum on the near wall region when exposed to adverse pressure gradients. Transient flow conditions or periodic flow perturbations induced to the near wall flow may delay or prevent the flow detachment. The present investigation experimentally analyzes the behavior of separated flows based on ad-hoc wall mounted hump. The test article mimics the performance of the aft portion of the suction side of a low pressure turbine where flow separation occurs at low Reynolds and fully attached flow takes place at high Reynolds. The inception of separated flow under sudden flow release was investigated in a linear wind tunnel. The extension of the separated region and its transient development was monitored through surface pressure and temperature measurements and hotwire traverses. The inlet flow conditions to the test article were interrogated with total pressure, total temperature and hotwire traverses. A fast opening valve upstream of the settling chamber was sequentially actuated at low frequency to study the behavior of the recirculation bubble under sudden flow acceleration. Due to the sudden flow release, the near wall region overcomes the adverse pressure gradient. As the flow acceleration dilutes the boundary layer detaches and the separated flow region grows in the stream-wise direction. The comparison of the experimental results with 2D and 3D transient Computational Fluid Dynamic simulations demonstrates the ability of Unsteady Reynolds Average Navier-Stokes models to predict the dynamics of this phenomenon. However, CFD over-predicts the extension of the recirculated flow region. The integration of this research towards future control strategies will enable efficient operation of turbine-hybrid systems operating at high power.

scholarly journals The Behaviour of the Normal Fluctuation Terms in the Case of Attached or Detached Turbulent Boundary Layers

1984 ◽  
Author(s):  
G. A. Gerolymos ◽  
Y. N. Kallas ◽  
K. D. Papailiou
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Turbulent Boundary Layer ◽  
Boundary Layers ◽  
Separated Flow ◽  
Flow Region ◽  
Boundary Layer Separation ◽  
Turbulent Boundary Layers ◽  
Mean Flow ◽  
Boundary Layer Interaction

The turbulent normal fluctuation terms have been found from measurements to be very important, when approaching separation, inside the separated flow region, as well as, in the region where a shock wave interacts with a turbulent boundary layer. In the present work correlations are developped on the basis of available experimental results, which relate the normal fluctuation terms, appearing in integral formulations for turbulent boundary layer calculation methods, to mean flow quantities. These correlations are valid, as far as compressible attached or separated turbulent boundary layers are concerned, as well as in the case of a shock wave/turbulent boundary layer interaction which leads to boundary layer separation. Furthermore, correlations are developed for the maxima of the velocity fluctuation terms.

ON A BOUNDARY LAYER IN A SEPARATED FLOW REGION

2017 ◽  
Vol 48 (6) ◽  
pp. 493-504
Author(s):  
Georgy Lvovich Korolev ◽  
Victor Vladimirovich Sychev
Keyword(s):  
Boundary Layer ◽  
Separated Flow ◽  
Flow Region

Characteristics of a separated flow past a semicircular leading-edge airfoil model under different imposed pressure gradient

2021 ◽  
pp. 095441002110212
Author(s):  
K Anand ◽  
KT Ganesh
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Particle Image ◽  
Separation Bubble ◽  
Separated Flow ◽  
Leading Edge ◽  
Field Measurements ◽  
Bench Mark ◽  
Image Velocimetry

The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.

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