Browsing by Author "Peacock, R. E."

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    The aerodynamic behaviour of a compressor rotor with steady and unsteady inlet flow
    (Cranfield University, 1974-11) Overli, J. M.; Peacock, R. E.
    Recent developments in have made possible the mic behaviour of rotor stage compressor using I pressure sensing and transfer techniques detailed investigation of the aerodyna- blades. Tests on a low speed single this instrumentation have given new evidence on rotor behaviour. The rotor blade performance with steady inlet flow condition was assessed from surveys of total pressure, static pressure and flow direction made upstream and downstreäm of the rotor hub, mid-height and tip section. In addition, measurements of the static pressure distributions of the same blade sections were completed. It is concluded that the combined effect of centrifugal force and annulus wall boundary layer skewing aid the performance of the rotor. This suggests that the efficiency of compressors would be improved if they were designed for reactions of rather more than 50%. The presence of a tip shroud has the effect of enhancing the overall compressor performance. A comparison of compressor rotor and two-dimensional cascade blade results is given, and predictions of the boundary layer development and the pressure distribution around the blades under various flow conditions are also presented. A series of experiments were also conducted at the mid-height section in which the compressor was subjected to 'sine-wave' and 'square-wave' circumferential stagnation pressure distortions including tests with the compressor operating in the surge regime. The deteriorating effect of total pressure distortion on overall compressor performance is clearly demonstrated, and a critical sector of spoiling is found. The effect of the level of reduced frequency on the unsteady normal force response of rotor blades is shown. II In all cases of distorted inlet flow, stallwinception is dela ed until values of normal force coefficient are reached well in excess of those encountered at steady state maximum. For 'square-wave' type distortion this is ensued by a complex stall situation with separation bubbles apparently traversing the rotor blade section and promoting dynamic lift patterns which pass through secondary and tertiary peaks. One may conclude that the aerodynamic rotor behaviour in the presence of such an unsteady flow environment is not predictable by current mathematical models. A theoretical analysis of the transient flow applicable at low values of reduced frequency is given. The transient response of the pressure-transmitting system was examined thoroughly theoretically, and experimental frequency response tests were conducted on the rotor blades as well as on a subsidiary rig. Careful examination of the fluctuating pressure signal was performed including time and frequency analyses.
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    Aerodynamic interactions between compressor blades and circumferential temperature distortions
    (Cranfield University, 1976-09) Hashem, A. A. F.; Peacock, R. E.
    A unifying principle was discovered to treat square-wave, steady state, circumferential temperature distortions at arbitrary levels of distorted stagnation pressure, applicable to the low speed range., ' ' A velocity transformation was found to relate the physical 4 properties of a two-dimensional, non-viscous flow field collectively, to the\introduced modified velocity. Furthermore, the flow in the modified plane retains the characteristics of classical incompressible flow and, in general, is rotational. The flow was divided into regions of either constant or linearly â º varying modified velocities. Each two regions were separated by a free streamline initíally of unknown position. A non-linear,large disturbance,mathematical model was set-up to find out the correct free streamlines location in the presence of a single aerofoil. Considering first order derivatives of the induced modified velocities of the flow modified vortices and the aerofoil,.when applying a modified continuity equation,_the model converges rapidly. - .Results showed the aerofoil lift coefficient to fluctuate above and below its undistorted value, near the regions of shear flow,~º - depending on the relative directions of the flow modified vortices, and the circulation around the aerofoil - « . . Experimental investigations included tests on«a single blade' 'mounted near the intake of an axial compressor of constant annulus - height. Results showed that at this level of temperature distortions _ the stagnation pressure of the distorted flow had a dominant effect on the behaviour of the lift coefficient.
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    A general solution for distorted flows in aerofoil cascades and contributions to distortion sensitivity reductions
    (Cranfield University, 1975) El-Attar, M. A. R. A. A.; Peacock, R. E.
    This thesis presents a number of new solutions to reduce the sensitivity of an existing compressor stage to a specified inlet flow distortion._ The interacting effects of flow vorticity, the change of rotor incidence and the time rate of change of íncidence are then studied, yielding a new design criterion to reduce the sensitivity of a compressor stage to any circumferential inlet flow maldistribution. Furthermore, the application of the unsteady thin a stator or inlet guide vane and a rotor, results unsteady fluctuating lift function which contains .functions as special cases. - Minimisation of the aerofoil theory to inia new generalised Sears and Hor1ock's resultant fluctuating ' lift leads to a design criterion for inlet guide vanes in agreement with the above conceptwhich is obtained by a different approach. The thesis also discusses a number of possible mathematical models for Cascade shear flow investígating their advantages and disadvantages and'the possibilities°of obtaining solutions. gA linearised theory for-_ nonuniform cascade flow is presented.i This fs'main1y an extension of Schlichting's method,`ref;(27) for uniform flow,i ' The main contribution of this work is the development of a nonlinear theory for nonuniform~cascade shear flow.â The.theory-accepts large amplitudes of distortion of any smooth shape, that is, cusps and 'g sharp corners in the Velocity distribution should be rounded. It is also capable of treating cascades of thick and highly cambered blades. The solution of Poisson's equation is obtained in the form of Fredholm'sV integral equation of the second kind which reduces to Martensen's equations, ref.(29), when the vorticity is zero everywhere in the flow field (clean flow). .The vorticity transport equation is satisfied in the flow field and its simultaneous solution with the solution of Poisson equation is carried out through an iteration process. Good agreement is obtained between the theoretical predictions and experimental test result