The paper reproduces the results of an earlier report on the vortex theory of windmills and follows that theory through to establish the aerodynamic design procedure for a horizontal axis windmill. The results are shown to differ considerably from those given in a recent paper by Griffith and the differences are explained. The main conclusion is that, when full allowance is made for the drag of the blades, hub and tip losses, and losses due to interference with the support tower, the power output coefficient or efficiency of a horizontal axis windmill cannot exceed 30 to 35 per cent, as compared to an ideal efficiency of 59 per cent.

It has been found that the addition of a whirl velocity component to an otherwise axial flow in a conical diffuser can lead to improvements in static pressure recovery and in efficiency, according to a restricted definition. Diffusers of total conical angle 10, 20 and 30 deg. were tested in detail; improvements were evident only in the last two, which would otherwise have suffered from flow separation problems caused by their relatively large divergence angles. The agency for improvement seems to be a beneficial redistribution of axial velocities.

An alternative method is described for solving the problem of a three-dimensional jet-flapped wing with a high aspect-ratio. This method is similar to the lifting-line theory of Kerney6 or Tokuda7, but differs in that the method of matched asymptotic expansions is applied to an integral equation, derived from the lifting surface theory, rather than a partial differential equation. The advantage of the present method over those used previously is that the necessary outer solutions are obtained directly; it is not necessary to rely upon physical insight or considerable ingenuity. The final results are different from those obtained by the previous authors; it is shown that the present result is correct, by noting some errors in the earlier theories.

This paper presents a theoretical study of the confluence of three shock waves in three-dimensional flow. A suitable transformation reduces the problem to that of a planar confluence point for which the theory already exists. Expressions relating the two flows are developed and successfully applied to an experimentally observed intersection. It is found that the three-dimensional flow can have an entirely supersonic downstream flow, unlike its two-dimensional counterpart, and that the flows in the two downstream regions need not be parallel.

A panel method for solving potential flow problems of arbitrary geometry is presented. It is very easy to apply and should be very quick to run. Unlike most other panel methods this one does not require a specification of the vorticity distribution in advance, but obtains it as part of the solution. The method is applied to three test cases chosen for their difficult and varied nature.

This paper reports experimental results for the performance of a freely hinged door between two incompressible air flows of different total pressures and different velocities. The apparatus used is a laboratory idealisation of the tertiary door system for an aircraft propulsion nozzle. The governing parameters are identified and the performance is presented in terms of the equilibrium door angle and the relative magnitude of the mass flow admitted. Three doors of different shapes were used and results are also presented for a plain opening. The main aerodynamic parameters are shown to be the velocity ratio and a non-dimensional pressure difference across the door. The shape of the downstream door jamb is found to have a considerable influence on the operation of the door at low angles. Removal of the door results in a lower entry mass flow over most of the operating range. It is shown that the mass flow ratio can be predicted quite well from the measured door angles by means of a simple theory.

The behaviour of a plane jet issuing in the neighbourhood of a plane wall has been studied experimentally. Such arrangements may find application in jet augmented flaps for STOL aircraft development. The essential features of this configuration are the gap between the wall and the jet nozzle, permitting entrainment of secondary flow, and the inclination of the plane wall with respect to the nozzle axis.

Measurements of velocity profiles, wall static pressure distributions and turbulence intensities reveal the presence of extensive regions of low pressure over the wall, strong pressure gradients resulting in the highly curved flow, a fair degree of self-preservation of the mean velocities, but no particularly unusual features observed in the turbulence quantities. The size of the gap, the wall angle and the wall length all influence the reattachment location, and limits of gap, angle and length for which reattachment occurs are shown. The sub-ambient static pressure regions give rise to significant forces on the wall; these forces are primarily due to the entrainment feature.

It is often assumed that the precise initial conditions exert no influence on the downstream flow development of two-dimensional wakes. A brief investigation of the wakes behind four different bodies shows the lasting influence of upstream history in such flows.

The results of measurements in the flow along a rectangular corner are presented in the form of velocity profiles. The profiles form two sets: one for flow in a slightly favourable streamwise pressure gradient and one for flow when the pressure gradient is ‘practically zero’. The appearance of the profiles is quite different from that of previously reported experimental work and it is suggested here that the primary cause of this is the different type of corner leading edges used in each case. The flow appears to be only marginally stable and even very slightly changed entry conditions caused by alterations in the leading edge geometry may have a marked effect on the profiles further downstream. The new results are consistent with the notion of corner layer similarity (an implication in every attempted theoretical solution) but there remains a significant difference between the experimental results and the more reliable theoretical solutions available.

A double Fourier series solution is presented for the buckling of simply supported orthotropic and isotropic skew plates, subjected to in-plane compressive and shear edge loads. All the boundary conditions, including the vanishing of the normal bending moment along the edges, are satisfied. Numerical results, suitable for design purposes, are presented graphically for a number of independent parameters such as skew angle, ratio of flexural rigidities and aspect ratio. The results show that the buckling strength is substantially effected by the skew angle, and to a lesser extent, by the ratio of the flexural rigidities and aspect ratio. In contrast with positive shear edge loads, which tend to decrease the skew angle, negative shear edge loads appear to reduce the buckling strength of orthotropic and isotropic skew plates.

The flows resulting from a number of different methods for producing swirl in an axi-symmetric jet have been investigated. These methods include upstream vanes, tangential injection, a twisted plastic sheet and rotation of part of the jet pipe. Tests were also made with the first two types of swirl device in association with a radial distribution of axial velocity in the jet which had a minimum on the axis produced by a suitably graded wire grid or web inserted in the jet pipe. The measurements covered the mean (axial and swirl) velocity distributions as well as the main turbulence quantities at various stations downstream of the jet exit. It was found that the swirl considerably enhanced the rate of growth of the mixing region as previous workers have shown, but there was a significant reduction of this enhancement when the axial velocity increased from the centre outwards. This is in accordance with current concepts on the stability of curved turbulent shear flows.

Recently attention has been given to the effects of the stream turbulence on the characteristics of the turbulent boundary layers and the turbulent shear flows. For the boundary layers considerable information on the effects of the stream turbulence is available but for the shear flows it is limited. This paper describes an experimental investigation for the effects of stream turbulence on the development of an asymmetric jet and a plane mixing layer. It is shown that the characteristics of these flows are considerably affected by the stream turbulence but for the measurements in the plane mixing layers at large downstream distances the influence of the stream turbulence is negligible provided the intensities are less than 0.6%. For the plane mixing layer the results show that the flow characteristics are not affected significantly by the initial boundary layers, the acoustic disturbances and the boundary conditions imposed by the end plates.

This paper shows how thin shock layer theory may be applied to wing-body combinations and also to yawed wings of caret and diamond section. The common feature of these cases is the interaction of the crossflow with the body slope discontinuity and the manner in which the resulting disturbances propagate through the shock layer. Practical computation of surface pressures is straightforward and comparison with experiment appears to be fairly good for the limited results available.

Flow measurement by optical devices of various types, particularly those involving laser light sources, have received considerable attention over the last few years. Different schemes employing a wide range of optical layouts have evolved and the resulting signals have been processed in a number of ingenious ways. We report new experimental work on an optical instrument that can be considered as the forerunner of the laser anemometer in the belief that in certain circumstances this particular optical layout offers some real advantages over the majority of laser anemometers. One important advantage of this system is the ease with which both the shape and size of the sampling zone can be independently controlled. Another is the ability to position the sampling region very close to a boundary without having to contend with the surface reflection difficulties that often prevent such measurements being made with laser optics. The instrument measures the velocities of small particles suspended in the fluid in much the same way as the laser anemometer. In unsteady flows this results in a series of velocity estimates generated at random time instants. These intermittent samples of the velocity are used to form power spectral density estimates by methods recently developed for the analysis of randomly sampled records (Gaster and Roberts, 1975 & 1976). This method of analysis could well be applied to the processing of the signals generated by laser anemometers operating in the burst counter mode.

Many aspects of parachute behaviour are dominated by the permeability of the canopy cloth. Techniques employing kinematic principles to predict parachute opening behaviour, for example, must first be able to predict the air flow through the canopy material. This paper is concerned with the development of such a predictive capability.

The flow of air through cloth of gauze has been studied by many workers; since the 1850’s, in connection with filters; and since the early twenties, in connection with parachutes. Workers in each of these disciplines seemed unaware of the work being done in the other.

In the case of parachute cloth permeability we find the foundations being laid down by such eminent workers as Glauert in 1932 and Taylor in 1944. Yet most subsequent writers seem not to be aware of this, and since World War II, there have been many papers “rediscovering” basic principles; often with errors which could have been corrected by reference to the earlier authorities.

In this paper we attempt to bring together all the work which has been done in this field, and to rationalize the data by simple mathematical modelling. Individual elements of the model have been proposed before, of course.

We then examine the effect of tension on the geometric porosity of fabric, and hence the pressure loss Ap. A theoretical analysis shows that tension is likely to be a major factor. For cloths which have low porosity when unloaded our simple mathematical model shows that, for a given Ap, a stress equal to 50% of ultimate can increase the air volume flow Q by an order of magnitude. In general, the increase in permeability is greatest at the lower values of Ap, indicating that the viscous term is more influenced by tension than the dynamic term. This theoretical result is confirmed by some rather limited experiments carried out by Lashbrook and Marby. But their data also shows that a cloth made from relatively stiff glass fibers can experience a reduction in permeability when loaded, due to a “closing up” of the weave. The reasons for this are discussed.

Although the Cebeci-Smith method of calculating turbulent boundary layers is widely used and generally gives acceptably accurate results, highly inaccurate skin-friction values are obtained for relaxing flows and equilibrium layers in strong adverse pressure gradient. In the present paper, these anomalies are removed by suitable modifications to the basic eddy-viscosity model.

The basic physical idea underlying the theories based on the flow model of CHAPMAN and KORST is that the base pressure can be predicted if the pressure at the reattachment point is known. In the new theory of TANNER the fundamental idea is the connection between the drag of the body and the entropy increase in the flow. This paper presents the essence of both theories together with theoretical and experimental results.

The incompressible planar flow past a wing with a jet issuing from the trailing edge is calculated by two separate methods, both adaptations of conformal mapping routines that are numerically exact in the jet-free case. These are the well-known circle mapping method and the halfplane method. The former is rendered inexact by the jump conditions across the jet and an approximation is necessary. The halfplane method, however, remains exact in principle, and a range of results is presented below. The most accurate of the previous calculations is verified, and comparisons between the halfplane and circle methods are also made. The halfplane scheme seems well suited for such wake-controlled flows and has been extended to transonic conditions in a related study.