The Effect of Slot Height and Slot-Turbulence Intensity on the Effectiveness of the Uniform Density, Two-Dimensional Wall Jet

1968 ◽  
Vol 90 (4) ◽  
pp. 469-475 ◽  
Author(s):  
S. C. Kacker ◽  
J. H. Whitelaw
Keyword(s):  
Turbulence Intensity ◽  
Free Stream ◽  
Velocity Ratio ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Uniform Density ◽  
Wall Jet ◽  
Two Dimensional ◽  
Significant Parameter

This paper presents measurements of the impervious-wall effectiveness of a two-dimensional wall jet obtained using a constant value of lip thickness, 0.032 in. and four slot heights, viz., 0.5, 0.25, 0.132, and 0.074 in. The measurements are in the range of slot-to-free-stream velocity ratio 0.288⩽u¯C/uG⩽2.66 and clearly demonstrate that, in the region where the velocity ratio is close to unity, the effectiveness is greatly dependent upon the slot height. The reason for this dependence is investigated and additional measurements are presented to show that the influence of the slot turbulence intensity on the effectiveness is small. It is concluded that the ratio of slot lip thickness to slot height is the most significant parameter and that the effect of an increase in this ratio is to decrease the effectiveness.

Unsteady laminar boundary layers in a compressible stagnation flow

1975 ◽  
Vol 70 (3) ◽  
pp. 561-572 ◽  
Author(s):  
C. S. Vimala ◽  
G. Nath
Keyword(s):  
Free Stream ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Compressible Boundary Layer ◽  
Two Dimensional ◽  
Stagnation Flow ◽  
Laminar Boundary Layers ◽  
Implicit Finite Difference ◽  
Layer Flow ◽  
Heat Transfer Parameter

The unsteady laminar compressible boundary-layer flow in the immediate vicinity of a two-dimensional stagnation point due to an incident stream whose velocity varies arbitrarily with time is considered. The governing partial differential equations, involving both time and the independent similarity variable, are transformed into new co-ordinates with finite ranges by means of a transformation which maps an infinite interval into a finite one. The resulting equations are solved by converting them into a matrix equation through the application of implicit finite-difference formulae. Computations have been carried out for two particular unsteady free-stream velocity distributions: (i) a constantly accelerating stream and (ii) a fluctuating stream. The results show that in the former case both the skin-friction and the heat-transfer parameter increase steadily with time after a certain instant, while in the latter they oscillate, thus responding to the fluctuations in the free-stream velocity.

On the unsteady behaviour of cavity flow over a two-dimensional wall-mounted fence

2019 ◽  
Vol 874 ◽  
pp. 483-525 ◽  
Author(s):  
Luka Barbaca ◽  
Bryce W. Pearce ◽  
Harish Ganesh ◽  
Steven L. Ceccio ◽  
Paul A. Brandner
Keyword(s):  
High Speed ◽  
Single Phase ◽  
Free Stream ◽  
Free Stream Velocity ◽  
Small Scale ◽  
Stream Velocity ◽  
Phase Flow ◽  
Two Dimensional ◽  
Single Phase Flow ◽  
Dynamic Surface

The topology and unsteady behaviour of ventilated and natural cavity flows over a two-dimensional (2-D) wall-mounted fence are investigated for fixed length cavities with varying free-stream velocity using high-speed and still imaging, X-ray densitometry and dynamic surface pressure measurement in two experimental facilities. Cavities in both ventilated and natural flows were found to have a re-entrant jet closure, but not to exhibit large-scale oscillations, yet the irregular small-scale shedding at the cavity closure. Small-scale cavity break-up was associated with a high-frequency broadband peak in the wall pressure spectra, found to be governed by the overlying turbulent boundary layer characteristics, similar to observations from single-phase flow over a forward-facing step. A low-frequency peak reflecting the oscillations in size of the re-entrant jet region, analogous to ‘flapping’ motion in single-phase flow, was found to be modulated by gravity effects (i.e. a Froude number dependence). Likewise, a significant change in cavity behaviour was observed as the flow underwent transition analogous to the transition from sub- to super-critical regime in open-channel flow. Differences in wake topology were examined using shadowgraphy and proper orthogonal decomposition, from which it was found that the size and number of shed structures increased with an increase in free-stream velocity for the ventilated case, while remaining nominally constant in naturally cavitating flow due to condensation of vaporous structures.

Origin and Characteristics of the Spray Patterns Generated by Planing Hulls

2011 ◽  
Vol 27 (02) ◽  
pp. 63-83
Author(s):  
Daniel Savitsky ◽  
Michael Morabito†
Keyword(s):  
Free Stream ◽  
Experimental Studies ◽  
Leading Edge ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Maximum Height ◽  
Two Dimensional ◽  
Swept Wing ◽  
Analytical Treatment ◽  
Stagnation Line

Analytical and experimental studies were made of the origin and characteristics of the two distinctly different appearing spray patterns associated with prismatic planing hulls. It was found that these two spray patterns, identified as "whisker spray" and "main spray," are a consequence of the same basic hydrodynamic flow phenomenon and transform seamlessly from one into the other. Similar to the analytical treatment developed for swept-wing aircraft, where the oncoming free stream velocity is divided into components normal to and along the leading edge of the swept wing, the free stream velocity for the planing surface is divided into components normal to and along the stagnation line. Combining this orientation of velocity components with the results of analytical studies of Wagner (Uber stoss-und gleitoorgauge an der oberflache von flussiglaseiten. Z.f.a.M.M., 2, 4, 1932) for two-dimensional planing of infinitely long flat planing surfaces with those of Green (The gliding of a flat plate on a stream of finite depth, Proceedings of the Cambridge Philosophical Society, 31, 1935) for planing of a two-dimensional, finite length surface, explains the origin and characteristics of both the whisker and main spray patterns. It is shown that the main spray originates in a small local area at the intersection of the stagnation line with the chine. Relatively simplistic equations that define the three-dimensional location of the spray apex are developed, and the results presented in three graphs. An illustrative example is presented that demonstrates the ease of application of the method to define the main spray geometry of a typical planing craft. Model tests were conducted to define the maximum height of the main spray and its lateral and longitudinal positions relative to the hull as a function of deadrise angle, trim angle, and speed coefficient. These data substantiate the analytical results.

On the Indeterminateness of the Boundary Conditions for the Mixing of Two Parallel Streams

1960 ◽  
Vol 27 (3) ◽  
pp. 390-392 ◽  
Author(s):  
K. T. Yen
Keyword(s):  
Boundary Conditions ◽  
Free Stream ◽  
Velocity Ratio ◽  
Interface Velocity ◽  
Numerical Data ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Lower Velocity ◽  
Parallel Streams

Results obtained from a study of the indeterminateness of the boundary conditions for laminar “free” mixing of two parallel streams under constant pressure are presented in this paper. A method is given for the determination of the interface velocity, the location of the interface in the mixing region, and the transverse force acting on the dividing wall as a consequence of the mixing. Based on available numerical data, calculations have been made for two free-stream velocity ratios, 0.5 and 0. It is shown that values of interface velocity obtained here differ appreciably from those obtained using other proposed boundary conditions (the third condition). In addition, for a free-stream velocity ratio of 0.5 the interface deflects toward the higher velocity stream, while for a zero free-stream velocity ratio it deflects toward the zero (lower) velocity stream.

scholarly journals Boundary-Layer Type Solutions for Initial Platelet Activation and Deposition

2002 ◽  
Vol 4 (2) ◽  
pp. 95-108 ◽  
Author(s):  
T. David ◽  
P. G. de Groot ◽  
P. G. Walker
Keyword(s):  
Platelet Activation ◽  
Peclet Number ◽  
Free Stream ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Bulk Fluid ◽  
Péclet Number ◽  
Activated Platelets ◽  
Activation Rate ◽  
Initial Adhesion

This paper presents, on the basis of high Peclet number, a mathematical model for the activation and initial adhesion of flowing platelets onto a surface. In contrast to past work, the model is applicable to general 2D and axi-symmetric flows where the wall shear stress is knowna priori. Results indicate that for high activation reaction rates there exist two layers, one containing only activated platelets and the other both activated and non-activated platelets. Fundamental relationships are proposed between the adhesion rate of platelets to the surface and the characteristic parameters of Peclet number and Reynolds number. Activation in the bulk fluid (blood) is characterised by the Damkohler number, which is a function of activation rate and the free-stream velocity. It is shown that, as the free-stream velocity varies, there exists a maximum of activated platelet flux to the wall for particular values of the velocity. These values, at which the maximum occur, are themselves functions of the platelet activation rate. As the free-stream velocity increases the activation of platelets ceases altogether and adhesion is reduced to a very small value strengthening the hypothesis of the correlation between atherogenesis/thrombogenesis and areas of low shear.

Free-Stream Turbulence From a Circular Wall Jet on a Flat Plate Heat Transfer and Boundary Layer Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 78-86 ◽  
Author(s):  
R. MacMullin ◽  
W. Elrod ◽  
R. Rivir
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Flow Characteristics ◽  
Surface Profile ◽  
Constant Heat Flux ◽  
Length Scale ◽  
Wall Jet ◽  
Reynolds Analogy ◽  
Free Stream Turbulence

The effects of the longitudinal turbulence intensity parameter of free-stream turbulence (FST) on heat transfer were studied using the aggressive flow characteristics of a circular tangential wall jet over a constant heat flux surface. Profile measurements of velocity, temperature, integral length scale, and spectra were obtained at downstream locations (2 to 20 x/D) and turbulence intensities (7 to 18 percent). The results indicated that the Stanton number (St) and friction factor (Cf) increased with increasing turbulence intensity. The Reynolds analogy factor (2St/Cf) increased up to turbulence intensities of 12 percent, then became constant, and decreased after 15 percent. This factor was also found to be dependent on the Reynolds number (Rex) and plate configuration. The influence of length scale, as found by previous researchers, was inconclusive at the conditions tested.

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