Browsing by Author "Shaw, Scott T."

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    Development of a boundary layer transition model for helicopter rotor CFD
    (Cranfield University, 2005) Hill, J. L.; Shaw, Scott T.
    A novel transition model has been developed for use in CFD simulations of helicopter rotor aerodynamics. The model includes significantly improved physical modelling of the transition processes occurring in the steady and unsteady flows found on helicopter rotors. The model has been coupled with the k-co and k-co SST two equation turbulence models using a novel adaptation of the technique developed by Wilcox for the low Reynolds number k-oa model. The method has been employed to calculate transitional flows occurring in three key ow regimes found in helicopter aerodynamics; that around steady and unsteady aerofoils and that around a hovering helicopter rotor. The performance of the k-co and the k-w SST turbulence models have been investigated for transitional flow simulations and the k-w SST shown to provide substantial improvements for transitional flows containing separations. Dramatic improvements in the computed pressure and skin friction distributions for several aerofoil flows have been observed over those computed using a conventional fully turbulent simulation. Corresponding improvements are observed in the computed lift and drag polars and transition on set is well predicted for both low and high Reynolds number flows. A novel structured/unstructured a priori adapted grid generation strategy has been developed for hovering rotor flows that provides improved rotor solutions for transitional flow analysis. The method offers vast improvements in the preservation of vorticity in the solution at greatly reduced computational expense. Tip vortices have been maintained to a Wake age of 1170 degrees with just 2 million cells per blade. The transition model has then been applied to the high quality rotor solutions and good agreement obtained between computed and experimental results, highlighting that three-dimensional effects have a relatively small effect on hovering rotor transition in-board of the blade tip. I addition, the first known verification of a Navier-Stokes rotor code against the Fogarty semi-analytical rotating at plate case was presented and excellent agreement obtained.
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    Hypersonic flow control using magneto-hydrodynamics
    (Cranfield University, 2008-01) Bennett, J. S.; Shaw, Scott T.
    The focus of the present work is on the use of magneto hydrodynamics as a flow control device for supersonic and hypersonic vehicles. A three dimensional parabolized Navier Stokes solver was developed to take into account the effects of magnetic fields , by incorporating two magneto-hydrodynamic models. The modified solver was then used to study the effects of magneto-hydrodynamics on a variety of configurations, one study of which involved surrogate model based optimisation procedures. The first component of research involved validation of the low magnetic Reynolds number model model against well documented test cases. Good agreement with the nu- merical test cases for flows past a blunt body and a flat plate boundary layer flow, both in the presence of a magnetic field, was found. A novel application of the method of man- ufactured solutions to the simplified mapeto-hydrodynamic model was made to ensure its Accuracy. Assessment of the procedures used for numerical optimisation, were made against known closed-form solutions, and a theoretical axisymmetric body of revolution. An investigation for an optimal magnetic field configuration, for an over-sped Ram- jet intake was made. It was found that for a suitable choice of magnetic field strength, shock on lip could be achieved. Furthermore, for a suitable choice for the position of the magnetic field source, the design condition can also be satisfied using a weaker mag- netic field. Finally a study examining the use of magnetic fields for flows past a slender body were was performed. Given a suitably orientated dipole source, it was shown that the magnetic field can introduce asymmetries, for an otherwise symmetric flowfield, and thereby introduce side form on the missile.
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    Numerical methods for vortical flows
    (Cranfield University, 2007-01) Knight, Katherine; Shaw, Scott T.; Garry, Kevin P.
    An investigation into the current methods employed to conserve vorticity in numerical calculations is undertaken. Osher’s flux for the artificial compressibility equations is derived, implemented and validated in Cranfield University’s second order finite volume compressible flow solver MERLIN. Characteristic Decomposition is applied as a method of vorticity conservation in both the compressible and artificial compressibility MERLIN solvers. The performance of this method for vorticity conservation in both these solvers is assessed. Following a discussion of the issues associated with application of limiter functions on unstructured grids three modified versions of the method of Characteristic Decomposition are proposed and tested in both the compressible and incompressible solvers. It is concluded that the method of Characteristic Decomposition is an effective method for improving vorticity conservation and compares favourably in terms of increased computational cost to vorticity conservation through grid refinement.
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    Reduced-order modelling for high-speed aerial weapon aerodynamics
    (Cranfield University, 2008-10) Mifsud, Michael; Shaw, Scott T.; MacManus, David G.
    In this work a high-fidelity low-cost surrogate of a computational fluid dynamics analysis tool was developed. This computational tool is composed of general and physics- based approximation methods by which three dimensional high-speed aerodynamic flow- field predictions are made with high efficiency and an accuracy which is comparable with that of CFD. The tool makes use of reduced-basis methods that are suitable for both linear and non-linear problems, whereby the basis vectors are computed via the proper orthogonal decomposition (POD) of a training dataset or a set of observations. The surrogate model was applied to two flow problems related to high-speed weapon aerodynamics. Comparisons of surrogate model predictions with high-fidelity CFD simulations suggest that POD-based reduced-order modelling together with response surface methods provide a reliable and robust approach for efficient and accurate predictions. In contrast to the many modelling efforts reported in the literature, this surrogate model provides access to information about the whole flow-field. In an attempt to reduce the up-front cost necessary to generate the training dataset from which the surrogate model is subsequently developed, a variable-fidelity POD- based reduced-order modelling method is proposed in this work for the first time. In this model, the scalar coefficients which are obtained by projecting the solution vectors onto the basis vectors, are mapped between spaces of low and high fidelities, to achieve high- fidelity predictions with complete flow-field information. In general, this technique offers an automatic way of fusing variable-fidelity data through interpolation and extrapolation schemes together with reduced-order modelling (ROM). Furthermore, a study was undertaken to investigate the possibility of modelling the transonic flow over an aerofoil using a kernel POD–based reduced-order modelling method. By using this type of ROM it was noticed that the weak non-linear features of the transonic flow are accurately modelled using a small number of basis vectors. The strong non-linear features are only modelled accurately by using a large number of basis vectors.