Unsteady Flow Effects Research Articles

Paper 29: Unsteady Flow Effects Downstream of an Annular Cascade of Self-Excited Blades

This paper presents a two-dimensional theory for calculating streamwise perturbations in the flow downstream of a cascade of self-excited blades and gives details of hot-wire measurements of unsteadiness downstream of an annular cascade. The theoretical values show little variation from blade to blade, whereas the experiments exhibit a large concentration of perturbations near the hub and a comparatively smaller one near the tip. It is thought that periodic circulation is shed largely from the blade tip and root within the annulus wall boundary layers, in a manner similar to the shedding of steady circulation from the aeroplane wings.

Currentmeter Errors under Pulsating flow Conditions

The paper deals with the effect of unsteady flow on the velocity registration of current-meters. In the first section of the paper, experiments are described which show that axial flow pulsations cause currentmeters to over-estimate and that flow fluctuations transverse to the mean velocity generally cause under-registration by amounts depending on the flow and meter parameters. From these tests general comments are made concerning the choice of metering station and to a lesser extent meter design. The second section is theoretical and deals with the effects of axially pulsating flows. It has been possible, using simple aerodynamic principles, to show how the meter design can be improved to minimize registration errors. The agreement between this theoretical approach and the registration errors obtained from experiment is fair.

Trends in aeronautical science and engineering: Tercentenary lecture delivered by Sir Arnold Hall, F. R. S., at 10.15 a.m. on Monday 25 July ig6o at the Royal Institution

The Lecture reviewed some of the advances in scientific understanding which had influenced aeronautical engineering in the past ten years, and are likely to influence it in the coming decade. The shape of aircraft had changed from the traditional straight wing and tail configuration to the swept-back wing, and delta-wing form. These changes were guided by understanding of the influence of compressibility in the air, and of the effects due to the presence of shock waves at speeds near and above that of sound. Particularly significant among these effects is the interaction between shock waves and the boundary layer, which has strong influence on the lift and drag forces in steady flow, and introduces unsteady flow effects which in some circumstances can be self-exciting. Several of these effects were illustrated, and discussed and the design procedures to bring them under control outlined.

Effects of Flow Unsteadiness in Turbomachines

Effects of Flow Unsteadiness in Turbomachines

Two Methods for Predicting Air Loads on a Wing in Accelerated Motion

Aircraft taking off over a distance of 25 chord lengths or less are shown to experience an appreciable loss of lift due to unsteady flow effects. Two methods, the first based on Laplace-transformation solution of the integral equation and the second a simplified approximate iterative approach, are presented for evaluating the two-dimensional lift build-up during a maneuver involving changing forward speed and angle of attack. These schemes are applied to a number of examples, including Wagner's problem, which permit numerical comparisons. The effect of head wind on the unsteady lift deficiency is discussed.