For practical purposes, it is beneficial to be able to predict the useful operating range of an aerofoil in oscillatory motion before the onset of the strong non-linear effects associated with dynamic stall. In the current work, a range of criteria which have been used to indicate the onset of dynamic stall are presented. It is observed that, since all of these are based on physical manifestations of the dynamic stall process, they may only provide an indication that the process has started rather than identifying the initiation itself. A more suitable criterion for this is the concept of critical angle, first proposed by Wilby. It is shown that the critical angle, which is normally determined through an extensive programme of oscillatory tests on a given aerofoil, is achieved in advance of all the other criteria. The present work presents a correlation which has the potential to determine the critical angle, and hence the useful oscillatory range of an aerofoil, on the basis of simple ramp function tests.

Experiments have been conducted to investigate the flowfield associated with two co-rotating vortices which represent the idealised vortex system associated with a novel rotor blade tip planform. These vortices were generated by two rectangular NACA 0015 half wings positioned upstream of the working section of a low speed windtunnel. Hot-wire measurements were conducted downstream of the generators using X-wire probes to document the strength, position and size of the vortices. A numerical model was utilised to provide an accurate means of determining vortex strength, position and size. Finally, the model was successfully extended to consider the rotation of the vortex system.

Presented in this paper are the preliminary results from a blade-vortex interaction (BVI) test series conducted in the University of Glasgow's 1·61m x 2·13m closed-return, low-speed windtunnel, in which a single vortex interaction with a rigid, loaded rotor blade was studied. This work is an extension of that by Horner and Galbraith, which describes the flow phenomena present during single vortex interaction with an unloaded blade. The paper presents blade surface pressure data recorded by 72 pressure transducers located in the outer regions of the blade during these interactions. Integrated Cn and Cm1/4 data are also presented to provide a detailed history of a BVI event. In addition, a method of isolating the bound circulation and vortex induced effects is presented, from which it is concluded that for a BVI event the vortex-induced effects are (to a first approximation) independent of rotor pitch setting.

This paper examines the dynamic stalling of three wing planforms and characterises the main features of the stalling process in each case. The particular data were obtained during a three year research programme in the Department of Aerospace Engineering, University of Glasgow to collect high-resolution unsteady pressure data on the dynamic stalling characteristics of finite wing planforms. In this study, which was motivated by the pressing need for a greater understanding of the strongly three-dimensional effects in the tip region of helicopter rotors, the three wing planforms considered were a straight rectangular wing, a rectangular wing with swept tips and a delta wing. The initial test programme was followed by a further three years of detailed analysis and interpretation of the test data. Results from this analysis are presented in the present paper for cases in which the wings were subject to ramp motions.

This paper describes a facility for the acquisition of simultaneous high quality particle image velocimetry (PIV) and unsteady surface pressures with high spatial and temporal resolution. The facility, developed through a long-standing collaboration between the Department of Aerospace Engineering at Glasgow University and the Fluid Loading and Instrumentation Centre at Heriot-Watt University, is currently being used in collaborative projects and has the potential to provide a level of detail previously unattainable for CFD validation.

Results from both measurement techniques will be presented to demonstrate the range and potential of the two systems. In addition, the value of combining the two techniques will be demonstrated by results from a blade-vortex interaction experiment in which both methods were applied. Finally, future applications of the combined system will be discussed.

Surface pressure measurements were obtained during a three-dimensional vortex interaction with a NACA 0015 aerofoil. The upper and lower surfaces of the blade experienced different aerodynamic loads which appear to be controlled by the impact of the vortex axial core flow on the blade surface. On the upper surface of the blade, where the vortex core flow was away from the aerofoil, the interaction was characterised by the generation of a suction peak. On the lower surface, where the axial component was towards the blade, a pressure pulse developed and seemed to be influenced by the vortex approach angle. These features resulted in rapid changes in normal force and quarter chord pitching moment during the interaction. This impulsive loading of the blade may provide some explanation for sound generation and control degradation problems associated with the tail rotor of helicopters.

This paper proposes a correlation which attempts to relate an aerofoil's low speed dynamic stall onset incidence to particular parameters describing its stall behaviour in steady conditions. These parameters, which can be derived from experiment or predictive algorithm, are the incidence of steady stall and a term related to trailing-edge separation characteristics. The correlation is based on a large amount of data obtained from a number of aerofoils broadly classified into two families: the NACA four digit series of symmetrical sections and a family of four profiles with the NACA 23012 as the generic shape.

The correlation has been extended to low pitch rates outside the “deep” dynamic stall range and, whilst it pertains to stalling under ramp motions, a link has been established with oscillatory motions. The potential of the correlation is demonstrated by its application to the design of a symmetric aerofoil for use on wind turbines.

This paper presents an examination of dynamic stall onset on both a rectangular wing and a nominally two-dimensional aerofoil with the same cross-section. The intention is to determine the extent to which the onset of dynamic stall is changed in the three-dimensional case. To do this, three different criteria are applied to measured pressure data to identify both the onset of the stalling process and the formation of the dynamic stall vortex. It is shown that examination of the vorticity flux in the vicinity of the leading edge provides a means of determining vortex formation in the absence of strong three-dimensional effects. It is also shown that this technique is not applicable on outboard sections of the rectangular wing where the phasing of dynamic stall onset with respect to the leading edge response is altered by the three-dimensionality of the flow. It is concluded that the application of two-dimensional stall onset criteria is inappropriate under such conditions.

The results of a blade-vortex interaction (BVI) study incorporating particle image velocimetry (PIV) are presented. Test cases encompass a variety of intersection geometries, including head-on parallel interactions. Results provide quantified flow visualisation images of the flows generated near the blade tip and inboard during interactions. PIV results are examined in the light of understanding gained from previous pressure measurements made from the same BVI facility. Both the difficulties and the advantages of utilising the PIV technique in this application are discussed.

This paper presents a method for assessing two-dimensional aerofoil lift and pitching moment characteristics including trailing edge and gross laminar separation. The model used is a direct viscid-inviscid interaction scheme based on a vortex panel method with boundary-layer corrections and an inviscidly modelled wake. The integral boundary-layer methods adopted behave well in the region of separation and thus, good comparisons with measured separation characteristics are obtained. Generally the predictions of lift and pitching moment may be considered to be within the experimental error, but where this is not the case, the applicability of the modelling technique is discussed.

This paper examines the dynamic stalling of a finite wing of aspect ratio 3·0 when subject to constant pitch motions up to and beyond stall. In particular, unsteady surface pressure data were obtained at 192 locations on the wing surface and these were then analysed to provide information on the nature and phasing of dynamic stall events in both the chordwise and spanwise directions. It was also possible to obtain sectional force and moment coefficients by integration of the pressures measured on specific chordal arrays. This provided valuable insight into the load distribution on the wing throughout the range of motion. On this basis, it was established that the wing loading distribution was consistent with conventional understanding of steady wing loading up to the incidence at which the dynamic stall vortex was initiated. Beyond this point, the formation and subsequent convection of the vortex structure was found to be strongly three-dimensional but, nevertheless, exhibited many of the features of two-dimensional dynamic stall.

The interaction of a helicopter tail rotor blade with the tip vortex system from the main rotor is a significant source of noise and, in some flight states, can produce marked reductions in control effectiveness. This paper describes a series of wind-tunnel tests to simulate tail rotor blade vortex interaction with a view to providing data for the development and validation of numerical simulations of the phenomenon. In the experiments, which were carried out in the Argyll wind-tunnel of Glasgow University, a single-bladed rotor located in the tunnel’s contraction was used to generate the tip vortex which travelled downstream into the working section where it interacted with a model tail rotor. The tail rotor was instrumented with miniature pressure transducers that measured the aerodynamic response during the interaction. The results suggest that the rotor blade vortex interaction is similar in form to that measured at much higher spatial resolution on a fixed, non-rotating blade. The combination of the two datasets, therefore, provides a valuable resource for the development and validation of predictive schemes.

Hormonal anabolic compounds are used in certain countries to improve the efficiency of meat production from ruminant animals. The combination of trenbolone acetate (TBA) and oestradiol-17β (OE2) has been shown to be particularly effective in stimulating growth in cattle (e.g. Galbraith & Topps, 1981). These improvements in growth have been associated with increases in nitrogen retention and changes in protein metabolism within the animal. The present study therefore investigated the effect of implantation with TBA + OE2 on the growth and metabolic response of growing steers to alterations in protein nutrition.

Results and methods discussed in two previous papers are extended to other cases. Comparison is made with recent work by Pickard (1980) and an earlier conjecture is disproved.

Sufficient conditions are derived for ergodicity of the two-dimensional process of binary variables discussed by Galbraith and Walley (1976).

We consider a two-dimensional stochastic process of binary variables xij defined so that the conditional distribution of xij given its predecessors depends only on xi–1j and xij–1 Properties of the equilibrium distribution, when this exists, are investigated using three different representations of the process and explicit results are given in some special cases.

Expressions are obtained for the determinant and inverse of the covariance matrix of a set of n consecutive observations on a mixed autoregressive moving average process. Explicit formulae for the inverse of this matrix are given for the general autoregressive process of order p (n ≧ p), and for the first order mixed autoregressive moving average process.