XXII.The lift and drag of a rectangular wing spanning a free jet of circular section

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.”

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

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1930.0147 ◽

1930 ◽

Vol 129 (809) ◽

pp. 135-145 ◽

Cited By ~ 10

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.

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Production and STEM examination of controlled-size silver clusters

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075488 ◽

1983 ◽

Vol 41 ◽

pp. 338-339

Author(s):

M. A. Listvan ◽

R. P. Andres

Keyword(s):

Cluster Size ◽

Metal Clusters ◽

Experimental Parameter ◽

Carbon Films ◽

Metal Species ◽

Silver Clusters ◽

Free Jet ◽

Size Dependent ◽

Cluster Properties ◽

Controllable Size

Knowledge of the function and structure of small metal clusters is one goal of research in catalysis. One important experimental parameter is cluster size. Ideally, one would like to produce metal clusters of regulated size in order to characterize size-dependent cluster properties.A source has been developed which is capable of producing microscopic metal clusters of controllable size (in the range 5-500 atoms) This source, the Multiple Expansion Cluster Source, with a Free Jet Deceleration Filter (MECS/FJDF) operates as follows. The bulk metal is heated in an oven to give controlled concentrations of monomer and dimer which were expanded sonically. These metal species were quenched and condensed in He and filtered to produce areosol particles of a controlled size as verified by mass spectrometer measurements. The clusters were caught on pre-mounted, clean carbon films. The grids were then transferred in air for microscopic examination. MECS/FJDF was used to produce two different sizes of silver clusters for this study: nominally Ag6 and Ag50.

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