A method is given for the calculation of incompressible inviscid flow through non-axisymmetric contracting ducts with rectangular cross-sections. The method is based on a finite difference approximation to Laplace's equation and solved by the method of successive over relaxation. In an attempt to provide practical criteria for the design of such contractions, the flows through a series of contraction shapes were calculated, each shape being based on a pair of matched elliptic arcs. This permitted choice of such parameters as length, local (ie two-dimensional) contraction ratio, position and magnitude of the maximum slope. It was found that reducing the length of the contraction also reduced its effective length, although increasing the effects of overshoot and undershoot. This could be compensated for by designing a contraction with a steep maximum slope which with associated low curvatures at entrance and exit reduced the values of overshoot and undershoot. The axial positions of maximum slope on wall and roof should be the same.

The predictions of the numerical method were tested against experiment and, in general, satisfactory comparisons were obtained.

It has long been pointed out by Gray that large aquatic animals, notably the dolphin, have been observed to achieve speeds which appear to be far beyond their muscular capabilities, unless they somehow experience laminar flow. Many workers have puzzled over this problem, and various possibilities have been propounded. In particular Wu has carried out a long theoretical analysis of the swimming of a slender fish in two dimensions, and he mentions the prospect of the zero momentum wake.

The principle of the zero momentum wake (or boundary layer propulsion, as it is sometimes called) has often attracted the attention of aircraft propulsion engineers. A small wind tunnel experiment by Göbel and Oehler is of interest. They took a circular sieve, representing profile drag, and set this in relation to a propeller of the same diameter as the sieve. The sieve and the propeller were set side-by-side on a bar, and the power required to propel the model was measured. Then the sieve and the propeller were set in tandem, with the sieve in front of the propeller, and the power required measured again. The power required for the tandem arrangement was found to be significantly less than that required for the side-by-side arrangement.

Classic theory of helicopter ground resonance studies the phenomenon on a planar model obtained by reducing the dynamic parameters of the full helicopter into the plane of rotation. In this paper the phenomenon is studied on a spatial helicopter model of six degrees of body freedom. It is found that in general there exist six regions of instability, whereas the planar theory of Coleman determines only one region. The theoretical results obtained here are verified by experiments conducted on a dynamic model of helicopter. In addition, this paper reviews all the existing analyses which have studied the problem.

Boundary layer equations are derived for viscous high-Reynolds number flow along streamwise concave corners using a simple non-orthogonal Cartesian co-ordinate system. The equations are solved numerically for corner angles of 30°, 60°, 90°, 120° and 150°, with emphasis given to the cross-flow velocity and streamwise vorticity fields. The results are discussed in the context of the inherent instability of this boundary layer at high Reynolds numbers.

A technique for the prediction of buffeting response in flight from wind-tunnel tests on models of conventional construction is described and assessed. Results are presented from tests on models of a Gnat T Mk 2 trainer aircraft, and predictions are compared with flight measurements of buffeting made during high incidence manoeuvres. Flight/tunnel comparisons of buffeting response measurements on the TACT F-111 and SAAB 105 aircraft are also discussed. In general, good agreement is demonstrated between measured and predicted responses. Some remarks are also made on the determination of damping ratios from accelerometer or strain gauge readings recorded under buffeting conditions.