scholarly journals An Experimental Investigation of Nozzle-Exit Boundary Layers of Highly Heated Free Jets

1992 ◽  
Vol 114 (2) ◽  
pp. 469-475
Author(s):  
J. Lepicovsky
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Laminar Boundary Layer ◽  
Nozzle Exit ◽  
Total Pressure ◽  
Free Jets ◽  
Exit Boundary ◽  
Mach Numbers

An experimental investigation of the effects of nozzle operating conditions on the development of nozzle-exit boundary layers of highly heated air free jets is reported in this paper. The total pressure measurements in the nozzle-exit boundary layer were obtained at a range of jet Mach numbers from 0.1 to 0.97 and jet total temperatures up to 900 K. The analysis of results shows that the nozzle-exit laminar boundary-layer development depends only on the nozzle-exit Reynolds number. For the nozzle-exit turbulent boundary layer, however, it appears that the effects of the jet total temperature on the boundary-layer integral characteristics are independent from the effect of the nozzle-exit Reynolds number. This surprising finding has not yet been reported. Further, laminar boundary-layer profiles were compared with the Pohlhausen solution for a flat-wall converging channel and an acceptable agreement was found only for low Reynolds numbers. For turbulent boundary layers, the dependence of the shape factor on relative Mach numbers at a distance of one momentum thickness from the nozzle wall resembles Spence’s prediction. Finally, the calculated total pressure loss coefficient was found to depend on the nozzle-exit Reynolds number for the laminar nozzle-exit boundary layer, while for the turbulent exit boundary layer this coefficient appears to be constant.

scholarly journals An Experimental Investigation of Nozzle-Exit Boundary Layers of Highly Heated Free Jets

1990 ◽  
Author(s):  
J. Lepicovsky
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Laminar Boundary Layer ◽  
Nozzle Exit ◽  
Total Pressure ◽  
Free Jets ◽  
Exit Boundary ◽  
Mach Numbers

An experimental investigation of the effects of nozzle operating conditions on the development of nozzle-exit boundary layers of highly heated air free jets is reported in this paper. The total pressure measurements in the nozzle-exit boundary layer were obtained at a range of jet Mach numbers from 0.1 to 0.97 and jet total temperatures up to 900 K. The analysis of results shows that the nozzle-exit laminar boundary-layer development depends only on the nozzle-exit Reynolds number. For the nozzle-exit turbulent boundary layer, however, it appears that the effects of the jet total temperature on the boundary-layer integral characteristics are independent from the effect of the nozzle-exit Reynolds number. This surprizing finding has not yet been reported. Further, laminar boundary-layer profiles were compared with the Pohlhausen solution for a flat-wall converging channel and an acceptable agreement was found only for low Reynolds numbers. For turbulent boundary layers, the dependence of the shape factor on relative Mach numbers at a distance of one momentum thickness from the nozzle wall resembles Spence’s prediction. Finally, the calculated total pressure loss coefficient was found to depend on the nozzle-exit Reynolds number for the laminar nozzle-exit boundary layer, while for the turbulent exit boundary layer this coefficient appears to be constant.

Decreasing the Side Wall Contamination in Wind Tunnels

1983 ◽  
Vol 105 (4) ◽  
pp. 435-438 ◽  
Author(s):  
T. Motohashi ◽  
R. F. Blackwelder
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Laminar Boundary Layer ◽  
Three Dimensional ◽  
Side Wall ◽  
Wind Tunnels ◽  
Turbulent Fluid ◽  
Side Walls ◽  
Suction Slot

To study boundary layers in the transitional Reynolds number regime, the useful spanwise and streamwise extent of wind tunnels is often limited by turbulent fluid emanating from the side walls. Some or all of the turbulent fluid can be removed by sucking fluid out at the corners, as suggested by Amini [1]. It is shown that by optimizing the suction slot width, the side wall contamination can be dramatically decreased without a concomitant three-dimensional distortion of the laminar boundary layer.

A Theoretical Investigation of the Maximum-Lift Coefficient

1935 ◽  
Vol 2 (1) ◽  
pp. A21-A27
Author(s):  
Th. von Kármán ◽  
Clark B. Millikan
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Velocity Distribution ◽  
Theoretical Investigation ◽  
Laminar Boundary Layer ◽  
Lift Coefficient ◽  
Boundary Layer Theory ◽  
First Approximation ◽  
Transition Points

Abstract In the present paper the application of a laminar boundary-layer theory, previously developed by the authors, to the problem of the maximum-lift coefficient of airfoils is discussed. The calculations are carried through in detail for a first approximation, called a single-roof profile, to the potential velocity distribution over the upper surface of an airfoil. The results indicate a large variation in Clmax with turbulence but the quantitative dependence on Reynolds’ number and turbulence is not satisfactory. The calculations are then repeated for a so-called double-roof profile which approximates to the flow over the upper surface of an N.A.C.A. 2412 airfoil. These results are compared with those obtained from an experimental investigation on the same airfoil. The agreement is considered to indicate that for moderate values of R and Clmax the phenomenon of the maximum-lift coefficient is controlled by a contest between the separation and transition points of the laminar boundary layer over the nose of the airfoil. The difficulties involved in extending the theory to larger values of R, or to airfoils whose Cl vs. α curves are not approximately linear up to the stall, are mentioned.

Effects of nozzle exit boundary-layer conditions on excitability of heated free jets

AIAA Journal ◽  
1989 ◽  
Vol 27 (6) ◽  
pp. 712-718 ◽  
Author(s):  
J. Lepicovsky ◽  
W. H. Brown
Keyword(s):  
Boundary Layer ◽  
Nozzle Exit ◽  
Free Jets ◽  
Exit Boundary

Effect of Length on Compressor Inter-Stage Duct Performance

2007 ◽  
Author(s):  
C. Ortiz Duen˜as ◽  
R. J. Miller ◽  
H. P. Hodson ◽  
J. P. Longley
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Design Methodology ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Stagnation Pressure ◽  
Computational Investigation ◽  
Physical Mechanisms

This paper describes the effect of reducing the length of a plain S-shaped compressor inter-stage duct on its performance. The investigation is aimed at understanding the physical mechanisms that determine the flow within these ducts and to assess the effect of these mechanisms in the overall duct performance. An experimental and computational investigation on the development of the boundary layers and loss generation within a datum duct (100% length) was performed. These results were used to design two S-shaped ducts with 74%, and 64% duct length of those currently used as inter-stage ducts. The duct designs were optimised for minimum stagnation pressure loss using a one degree-of-freedom design methodology. Using the duct with lengths 100%, 74% and 64% of current inter-stage ducts, an experimental investigation on the effect of duct length on the development of the boundary layers and loss generated was performed. As the duct length was reduced the loss increases mainly due to boundary layer separation. The size of the separations was found to be strongly dependant on Reynolds number. The results show that at the Reynolds numbers tested relaminarization of the boundary layer may have occurred upstream of separation.

An example of steady laminar flow at large Reynolds number

1960 ◽  
Vol 9 (4) ◽  
pp. 593-602 ◽  
Author(s):  
Iam Proudman
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Tangential Velocity ◽  
Fluid Flows ◽  
The Other ◽  
Large Reynolds Number ◽  
Rotational Flows ◽  
Flow Domain ◽  
Source Of Information

The purpose of this note is to describe a particular class of steady fluid flows, for which the techniques of classical hydrodynamics and boundary-layer theory determine uniquely the asymptotic flow for large Reynolds number for each of a continuously varied set of boundary conditions. The flows involve viscous layers in the interior of the flow domain, as well as boundary layers, and the investigation is unusual in that the position and structure of all the viscous layers are determined uniquely. The note is intended to be an illustration of the principles that lead to this determination, not a source of information of practical value.The flows take place in a two-dimensional channel with porous walls through which fluid is uniformly injected or extracted. When fluid is extracted through both walls there are boundary layers on both walls and the flow outside these layers is irrotational. When fluid is extracted through one wall and injected through the other, there is a boundary layer only on the former wall and the inviscid rotational flow outside this layer satisfies the no-slip condition on the other wall. When fluid is injected through both walls there are no boundary layers, but there is a viscous layer in the interior of the channel, across which the second derivative of the tangential velocity is discontinous, and the position of this layer is determined by the requirement that the inviscid rotational flows on either side of it must satisfy the no-slip conditions on the walls.

Aero-optics of subsonic turbulent boundary layers

2012 ◽  
Vol 696 ◽  
pp. 122-151 ◽  
Author(s):  
Kan Wang ◽  
Meng Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Dominant Role ◽  
Elevation Angle ◽  
Turbulent Boundary Layers ◽  
Density Field ◽  
Small Scale ◽  
Number Range ◽  
Scale Turbulence

AbstractCompressible large-eddy simulations are carried out to study the aero-optical distortions caused by Mach 0.5 flat-plate turbulent boundary layers at Reynolds numbers of ${\mathit{Re}}_{\theta } = 875$, 1770 and 3550, based on momentum thickness. The fluctuations of refractive index are calculated from the density field, and wavefront distortions of an optical beam traversing the boundary layer are computed based on geometric optics. The effects of aperture size, small-scale turbulence, different flow regions and beam elevation angle are examined and the underlying flow physics is analysed. It is found that the level of optical distortion decreases with increasing Reynolds number within the Reynolds-number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role, followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analysed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton’s linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.

scholarly journals Experimental Investigation of Tandem Blade Cascades With Double-Circular ARC Profiles

1985 ◽  
Author(s):  
Wu Guochuan ◽  
Zhuang Biaonan ◽  
Guo Bingheng
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Mach Number ◽  
Total Pressure ◽  
Incidence Angle ◽  
Axial Direction ◽  
Geometrical Parameters ◽  
Optimal Conditions ◽  
Turning Angle ◽  
Circular Arc

24 double circular are tandem blade cascades of three different chord-ratios were investigated under different displacements in peripheral and axial direction. The inlet Mach number was 0.3. The Reynolds number based on blade chord was 2.7×105. The characteristics of the tandem blade cascades, such as the dependence of turning angle and coefficient of total pressure loss on incidence angle were obtained. The ranges of main geometrical parameters under optimal conditions were recommended.

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