scholarly journals Interference due to walls of a wind-tunnel

1933 ◽  
Vol 142 (846) ◽  
pp. 308-320 ◽  
Keyword(s):  
Wind Tunnel ◽  
Approximate Method ◽  
Practical Importance ◽  
Approximate Theory ◽  
Interference Factor ◽  
Rigid Boundary ◽  
Free Surfaces ◽  
Free Jet ◽  
Exact Theory ◽  
Trailing Vortices

This paper arose out of a discussion with Mr. Glauert on the validity of certain results on wind-tunnel interference given in a recent paper by Theodorsen, and I am greatly indebted to him for several very valuable suggestions. In his paper Theodorsen investigated, on the lines of the approximate theory laid down by Glauert, the interference factors due to rectangular tunnels in the following five conditions: (1) tunnel entirely enclosed; (2) free jet; (3) horizontal boundaries only, the vertical sides being free surfaces; (4) vertical boundaries only, the horizontal sides being free surfaces; (5) bottom boundary only, the remaining sides being free surfaces. Apart from one or two minor errors, Theodorsen's paper has to face a more serious objection on the score that the approximate method employed is not always valid. This objection to the approximate method was raised rather briefly in a previous paper, but at that time all the cases discussed, using the approximate method, were those due to Glauert, and they were such that the approximate method did not come into conflict with the exact theory. The more complicated method was, however, of some practical importance as it enabled additional refinements to be introduced into tire numerical evaluation of the interference factors, and it enabled Glauert to show that there is an appreciable drop in the interference factor in the Duplex Tunnel (height/breadth equal to one half) as the span of the aerofoil increases. Some of the cases discussed by Theodorsen are such that they must be considered according to the exact theory. The crux of the matter is as follows:— The basis of the theory of wind-tunnel interference is due to Prandtl, and he investigated several cases himself. On the assumption that trailing vortices spring from the aerofoil and extend downstream without distortion, Prandtl showed that the whole problem can be converted into one dealing with the flow in a transverse section of the wake far behind the aerofoil, the necessary boundary conditions being that the velocity potential is constant over the surface of the free jet, and the stream function constant over the rigid boundary. The theory was extended by Glauert and others, and applied particularly to the case of the small aerofoil in a rectangular tunnel. When the aerofoil is very small the exact distribution of vorticity is not of extreme importance as, to a first approximation, they all give the same result.

scholarly journals The aerofoil in a wind tunnel of elliptic section

1933 ◽  
Vol 140 (842) ◽  
pp. 579-604 ◽  
Keyword(s):  
Boundary Condition ◽  
Wind Tunnel ◽  
Uniform Distribution ◽  
Rectangular Channel ◽  
Circular Section ◽  
Free Jet ◽  
Free Air ◽  
Trailing Vortices ◽  
Elliptic Section ◽  
Lift And Drag

The lift and drag experienced by an aerofoil in a wind tunnel differ from the lift and drag experienced by the same aerofoil under free air conditions. These differences, which are the induced effects due to the walls of the enclosure, can be determined by the aid of general considerations laid down by Prandtl. In a closed tunnel, that is, a tunnel with rigid walls, the necessary boundary condition is that the velocity normal to the walls shall be zero. In an open tunnel, or free jet, the condition is that the pressure is constant over the boundary. Assuming that trailing vortices spring from the aerofoil and extend downstream without distortion, Prandtl has shown that the problem can be converted into one dealing with the flow in a section of the wake far behind the aerofoil, the necessary boundary condition being that the velocity potential is constant over the trace of the open tunnel. Prandtl ( loc. cit .) himself has investigated the interference experienced by an aerofoil in a tunnel of circular section for an elliptic distribution of lift across the span. Glauert, to whom a considerable extension of the theory is due, found approximate values of the induced drag in a rectangular tunnel when the span of the aerofoil is indefinitely small. Terazawa modified Glauert’s method and obtained the exact solution for an aerofoil with uniform distribution of circulation in a rectangular channel. Rosenhead obtained exact results for uniform and elliptic distributions both in circular and rectangular tunnels. More recently, in connection with the building of a wind tunnel of elliptic section, Glauert was led to reconsider the general problem of wind tunnel interference, and his conclusions are embodied in three valuable papers. In the first of these he pointed out that the problem discussed by previous investigators is that in which the lift distribution is prescribed to be the same as that in free air, and the aerofoil is twisted in the tunnel to a position in which this distribution is maintained. In general, if the aerofoil is not twisted in this way, there is a change in the distribution of circulation. If this change is taken into account, Glauert has shown for a tunnel of circular section “that the formulæ derived from the assumption of elliptic distribution of lift are sufficiently accurate for all conventional shapes of aerofoil, but that those derived from the assumption of a uniform distribution over-estimate the effect of increasing span of the aerofoil.”

Flutter of Supercavitating Hydrofoils-Comparison of Theory and Experiment

1972 ◽  
Vol 16 (03) ◽  
pp. 153-166
Author(s):  
Charles C. S. Song
Keyword(s):  
Leading Edge ◽  
Experimental Program ◽  
Finite Width ◽  
Free Surfaces ◽  
First Order ◽  
Free Jet ◽  
Analytical Work ◽  
Proper Interpretation ◽  
First Order Perturbation ◽  
Good Agreement

Unsteady flow due to harmonic oscillations of a two-dimensional supercavitating flat-plate hydrofoil in a free jet of finite width has been analyzed using first-order perturbation theory. The hydrodynamic loading coefficients thus obtained were used to study the hydroelastic instabilities: flutter and divergence. In conjunction with the analytical work, an experimental program was carried out using a free-jet water tunnel. Special attention was given to the influence of the free surfaces and the point of separation on the critical flutter speed. With proper interpretation of the location of the separation point near the leading edge, the theory and the experimental data were shown to be in fairly good agreement.

scholarly journals The effect of wind tunnel interference on the characteristics of an aerofoil

1930 ◽  
Vol 129 (809) ◽  
pp. 135-145 ◽  
Keyword(s):  
Wind Tunnel ◽  
Uniform Distribution ◽  
Infinite Series ◽  
Rectangular Channel ◽  
Approximate Expression ◽  
Point Of View ◽  
Approximate Methods ◽  
Free Jet ◽  
Drag And Lift ◽  
Lift And Drag

The effect of the walls of the enclosure on the measured values of the lift and drag experienced by an aerofoil is quite appreciable and it has been known for a considerable time that correction must be applied to wind tunnel result before they can be applied to free air conditions. Prandtl* investigated the effect on an aerofoil in a free jet or circular tube both in the case where there is a uniform lift distribution, and in the case where there is an elliptic distribution of circulation. The elliptic distribution is of importance because it gives the minimum drag for a given lift. Glauert by means of an approximate method found the induced drag and lift in a rectangular channel when there is a uniform distribution of lift. Terazawa modified Glauert’s method and obtained the exact solution for an aerofoil with uniform distribution of circulation in a rectangular channel. It is The object of this note to extend these results and to obtain the induces drag and lift in a rectangular channel when there is an elliptic distribution of lift. In addition, the discussion of Prandtl is briefly gone through because Prandtl’s results are usually given as the first few terms of an infinite series, and it has not been noticed that the result can be obtained exactly. Glauert’s work on the effect of plane barries is briefly re-examined because, in his analysis, approximate expression were summed over an infinite series of points, and at first glance it appeared that this would introduce some error of the same order as the result. In this note the summation is carried out rigorously and the approximations to the actual values. The small divergences from Glauert’s result obtained by Terazawa in two numerical cases are, in effect, the result of a slightly more accurate approximation. From the practical point of view the results of this paper add little to what is known already, for the major corrections are given by the results of the approximate methods, but this note should fill in some small gaps in the theory of wind tunnel interference.

The Prediction of Aerofoil Pressure Distributions for Sub-Critical Viscous Flows

1970 ◽  
Vol 21 (3) ◽  
pp. 291-302 ◽  
Author(s):  
R. C. Lock ◽  
P. G. Wilby ◽  
B. J. Powell
Keyword(s):  
Boundary Layer ◽  
Approximate Method ◽  
Iterative Procedure ◽  
Viscous Flows ◽  
Order Theory ◽  
Second Order ◽  
Experimental Results ◽  
Inviscid Flows ◽  
Exact Theory ◽  
Pressure Distributions

SummaryThe paper first describes an approximate method for calculating inviscid flows round arbitrary aerofoils at sub-critical Mach numbers, based on second-order theory with empirical improvements to give better agreement with exact theory; several comparisons are shown. This method is then used as the basis of an iterative procedure for calculating the effect of the boundary layer on the surface pressures and overall forces; several comparisons are given with recent experimental results.

scholarly journals Experimental investigation of free jet pulsations in the wind tunnel with an open test section

2018 ◽  
Author(s):  
S. A. Baranov ◽  
N. I. Batura ◽  
G. G. Gadzhimagomedov ◽  
D. S. Sboev
Keyword(s):  
Experimental Investigation ◽  
Wind Tunnel ◽  
Test Section ◽  
Free Jet ◽  
Open Test

Development and use of a vane device for boundary-layer measurements

1959 ◽  
Vol 6 (1) ◽  
pp. 97-112 ◽  
Author(s):  
J. G. Burns ◽  
W. H. J. Childs ◽  
A. A. Nicol ◽  
M. A. S. Ross
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Boundary Layers ◽  
Free Stream ◽  
Neutral Curve ◽  
Approximate Theory ◽  
Electrical System ◽  
Natural Oscillations ◽  
Free Stream Turbulence ◽  
Tollmien Schlichting

A hinged vane and a sensitive electrical system for recording the motion of the vane have been developed for the observation of fluctuating y-components of velocity in boundary layers. An approximate theory of the natural oscillations of such vanes is presented and experimentally verified. Using vanes as resonant detectors, meassurements have been made of oscillations injected into the laminar boundary layer on a flat plate in a wind tunnel with 0·3% free-stream turbulence. Points on the neutral Tollmien-Schlichting curve have thereby been obtained which lie close to the theoretical neutral curve.

The aerodynamic forces on an oscillating aerofoil in a free jet

1955 ◽  
Vol 229 (1177) ◽  
pp. 235-250 ◽  
Keyword(s):  
Wind Tunnel ◽  
Incompressible Fluid ◽  
Classical Theory ◽  
Direct Application ◽  
Two Dimensional ◽  
Aerodynamic Forces ◽  
Small Oscillations ◽  
Free Jet ◽  
Inviscid Incompressible Fluid ◽  
Wind Tunnel Measurements

The forces acting on an aerofoil placed centrally in a two-dimensional jet of inviscid incompressible fluid are calculated exactly for the case when the aerofoil is performing small oscillations about its mean position. The theory is a generalization of the classical theory due to Theodorsen and others for an oscillating aerofoil in an infinite stream. The results, which are expressed in terms of a ‘generalized Theodorsen function’, have a direct application to the correction of open-jet wind-tunnel measurements on oscillating aerofoils.

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