A Study of Rough-wall Turbulent Boundary-layer Flows Including Effect of Stagnation Heating PDF Download
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Author: Peeush K. Bishnoi
Publisher:
ISBN:
Category :
Languages : en
Pages : 232
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Book Description
Author: Peeush K. Bishnoi
Publisher:
ISBN:
Category :
Languages : en
Pages : 232
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Book Description
Author: P. M. Ligrani
Publisher:
ISBN:
Category : Frictional resistance (Hydrodynamics)
Languages : en
Pages : 272
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Book Description
Thick, fully rough, and transitionally rough turbulent boundary layers were studied in order to investigate the differences between fully rough and transitionally rough behavior and to observe how downstream development affects these flows as the boundary layers become very thick. Measurements included Stanton numbers, skin friction coefficients, mean temperature and velocity profiles, Reynolds stress tensor component profiles, and spectra of the longitudinal velocity fluctuations. Predictions of wall heat transfer, wall shear, and mean profiles were made using a mixing-length and turbulent Prandtl number closure scheme which accounted for the effects of wall roughness in the boundary layer equations. The turbulent layers were artificially thickened using an array of solid obstacles which produced a two-dimensional equilibrium flow field with properties representative of natural bounday layers, at least up to the level of the turbulent correlations on a smooth wall, and to the level of the spectra of longitudinal velocity fluctuations on a rough wall. A rough-wall boundary layer environment was provided in which all measurements of lower order than the turbulence correlations could be discussed regarding the influence of roughness, and considered to have properties representative of natural behavior. (Author).
Author: C. K. Liu
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 171
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Book Description
Experimental data are presented on flow structure, mean, and fluctuating velocities in turbulent boundary layers over a family of flat surfaces with transverse roughness elements made of square bars of variable spacing. All flows were incompressible and had zero streamwise pressure gradient. The flow structures are described for surfaces extending from hydraulically smooth to fully rough. A distinct flow pattern is observed in the wall region for each of four cases: smooth, skimming, wake-interference and isolated-roughness flow. Maximum roughness was observed with a ratio of gap to bar width of approximately 11. The most obvious effect of an increase in surface roughness is the distinct increase of turbulence production and the concomittant increase in the value of eddy viscosity. It is shown that this increase in eddy viscosity increases the total thickness of the layer in the same way that an increase in molecular viscosity would do in a laminar layer. The normalization of eddy viscosity for the outer portion of the layer as suggested by Clauser is found to apply to the rough surfaces studied. (Author).
Author: Stanford University. Thermosciences Division. Thermosciences Division
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 342
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Book Description
The turbulent boundary on a deterministic rough wall has been examined for the cases of isothermal and non-isothermal, zero pressure gradient flows with and without transpiration. Both the transitionally rough and the fully rough.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Experimental studies are being conducted to examine the stagnation region heating in transitional flow over blunt nose tips; and the effects of surface roughness on the heat transfer and skin friction to hypersonic re-entry vehicles. Measurements have been made of the distribution of heat transfer and skin friction over sharp and blunted cones to a range of incidences for surface roughness of 0, 10 and 15 mils. These studies have been conducted at a local Mach number of 11.7 and Reynolds numbers based on model length of 30 x million, giving roughness Reynolds numbers from transitional to fully rough over the models. New calorimeter and thin film instrumentation was developed expressly for the rough wall heating measurements. The measurements indicated that while the roughness-induced augmentations in heat transfer and skin friction were less than would be predicted using theories based on low speed data for low R sub k's, close to the nose tip significantly larger augmentation factors were observed. The current studies suggest that significant compressibility effects may be present in hypersonic turbulent boundary layers over rough walls. The models and highly detailed heat transfer and pressure instrumentation have been completed for the stagnation point heating studies. A new and novel throat valve has been developed to eliminate the frangible mylar diaphragm which can cause particles and disturbances during flow establishment in the shock tunnel. The experimental studies are now in progress.
Author: Walid Chakroun
Publisher:
ISBN:
Category : Acceleration waves
Languages : en
Pages : 410
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Book Description
Author: Michael E. Tauber
Publisher:
ISBN:
Category : Aerodynamic heating
Languages : en
Pages : 44
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Book Description
Author: Tuncer Cebeci
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 430
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Book Description
Author: A. F. Mills
Publisher:
ISBN:
Category :
Languages : en
Pages : 120
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Book Description
The influence of wall roughness on the alteration of the characteristics of the turbulent boundary layer to produce increased heat transfer and skin friction during re-entry is examined. Attention is restricted to roughness heights which are small compared with the boundary layer thickness. It is shown that rough wall transfer rates can be calculated almost as reliably as for smooth walls provided that the geometry of the roughness is known. In this regard it is pointed out that models of roughness effects for use in finite-difference boundary layer calculation procedures should be in the form of drag coefficients and sub-layer Stanton numbers to be applied as 'slip' values at a characteristic roughness height; use of mixing length models of turbulent transport with nonzero wall values is shown to have serious shortcomings. The effect of heat conduction through roughness elements is demonstrated and the implications with respect to the validity of existing sub-layer Stanton number correlations are discussed. A thorough review of the pertinent literature is included with the view towards making this report a self contained treatment of the subject.
Author: Joseph G. Marvin
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 60
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Book Description
Equilibrium convective heat transfer in several real gases was investigated. The gases considered were air, nitrogen, hydrogen, carbon dioxide, and argon. Solutions to the similar form of the boundary-layer equations were obtained for flight velocities to 30,000 ft/sec for a range of parameters sufficient to define the effects of pressure level, pressure gradient, boundary-layer-edge velocity, and wall temperature. Results are presented for stagnation-point heating and for the heating-rate distribution. For the range of parameters investigated the wall heat transfer depended on the transport properties near the wall and precise evaluation of properties in the high-energy portions of the boundary layer was not needed. A correlation of the solutions to the boundary-layer equations was obtained which depended only on the low temperature properties of the gases. This result can be used to evaluate the heat transfer in gases other than those considered. The largest stagnation-point heat transfer at a constant flight velocity was obtained for argon followed successively by carbon dioxide, air, nitrogen, and hydrogen. The blunt-body heating-rate distribution was found to depend mainly on the inviscid flow field. For each gas, correlation equations of boundary-layer thermodynamic and transport properties as a function of enthalpy are given for a wide range of pressures to a maximum enthalpy of 18,000 Btu/lb.
