Browsing by Author "Shaw, Scott"

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    The applications of computational fluid dynamics to problems in rotorcraft aerodynamics:
    (1995) Shaw, Scott
    The flowfield around a helicopter rotor in forward flight is intrinsically unsteady and contains many complex interacting flow phenomena. As a consequence experimental investigations are difficult to perform, difficult to interpret and costly. There is a clear need for reliable computational methods whose uncertainties are less than those of experiment. In this paper computational methods currently available for the solution of problems in rotor aerodynamics are examined and the current direction of research in this field identified.
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    Comparison if the convergence behaviour of three linear solvers for large, sparse unsymmetric matrices
    (1995) Shaw, Scott
    Implicit methods for the calculation of unsteady flows require the solution of large, sparse non-symmetric systems of linear equations. The size of such systems makes their solution by direct methods impractical and consequently iterative techniques are often used. A popular class of such methods are those based upon the conjugate gradient method. In this paper we examine three such methods, CGS, restarted GMRES and restarted GMRESR and compare their convergence properties.
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    Numerical study of the unsteady aerodynamics of helicopter rotor aerofoils
    (Cranfield University, 1999-03) Shaw, Scott; Qin, N.
    A two-dimensional model of the aerodynamics of rotor blades in forward flight is proposed in which the motion of the blade is represented by periodical variations of the freestrearn velocity and incidence. A novel implicit methodology for the solution of the compressible Reynolds averaged Navier-Stokes equations and a twoequation model of turbulence is developed. The spatial discretisation is based upon Osher's approximate Riernann solver, while time integration is performed using a Newton-Krylov method. The method is employed to calculate the steady transonic aerodynamics of two supercritical aerofoils and the unsteady aerodynamics of pitching aerofoils. Comparison with experiment and independent calculations for these test cases is satisfactory. Further calculations are performed for the self-excited periodic flow around a biconvex aerofoil. Comparison of quasi-steady and unsteady calculations suggests that the flow instability responsible for the self-excited flow is due to the presence of a shock induced separation bubble in the corresponding steady flow. Finally the method is used to predict the aerodynamics of aerofoils performing inplane and combined inplane-pitching motions. Results show that quasi-steady aerodynamic models are unsuitable at conditions representative of high-speed forward flight. For shock free flows, the unsteady effects of freestrearn oscillations can be represented by a simple phase lag. For transonic flows the influence of unsteadiness on shock wave dynamics is shown to be complex. Calculations for indicial motion show that the unsteady behaviour of the flow is related to the finite time taken by disturbance waves to travel to the shock wave from the leading and trailing edges of the aerofoil.
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    ItemOpen Access
    Solution of the Navier-Stokes equations for aerofoils undergoing in-plane oscillations
    (1995) Shaw, Scott
    Although a full simulation of the flow field generated around helicopter rotor blades in forward flight requires consideration of many complex interacting flow phenomena, such a fluctuations in the velocity and incidence of the oncoming flow, three dimensional effects, moving shock waves, shock induced separation and dynamic stall, considerable physical insight may be obtained by removing the influence of many of these phenomena and studying the simplified flows which result. In the present work the problems of moving shock waves and shock induced separation commonly encountered on the advancing side of helicopter rotor blades during forward flight are addressed by examining the behaviour of the flow field around aerofoils undergoing inplane oscillations, of the form M∞ = M(1)(1+µsin(ωt))at constant angles of incidence.