Thesis (MSportwet)--University of Stellenbosch, 2005. / Includes bibliographical references. Also available via the Internet.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xiii, 85 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 82-84).

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xiv, 129 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 92-98).

Thesis PlanB (M.S.)--University of Wisconsin--Stout, 2006. / Includes bibliographical references.

Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 75-78.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xii, 105 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 96-100).

This thesis presents evidence on the ability of grid-based, Computational Fluid Dynamics methods based on the Unsteady Reynolds Averaged Navier-Stokes equations to accurately predict axial flight performance of rotors with modest computer resources. Three well-studied blades, the B0-105, S-76, and PSP main rotor blades, are used and results are compared with experimental data. Likewise, performance analyses of the JORP propeller and XV-15 tiltrotor blades are carried out, respectively, aiming to validate the employed CFD method for such relevant flows. Validation of the HMB3 CFD solver for complete tiltrotors is also presented. The aim is to assess the capability of the present CFD method in predicting tiltrotor airloads at different flight configurations. In this regard, three representative cases of the ERICA tiltrotor were selected, corresponding to aeroplane, transition corridor, and helicopter modes, covering most modes of tiltrotor flight. Aerodynamic optimisation of tiltrotor blades with high-fidelity computational fluid dynamics coupled with a discrete adjoint method is also carried out. This work shows how the main blade shape parameters influence the optimal performance of the tiltrotor in helicopter and aeroplane modes, and how a compromise blade shape can increase the overall tiltrotor performance. Finally, the implementation and validation of an efficient, high-order, finite-volume scheme (up to 4th-order of spatial accuracy) in the HMB3 CFD solver is presented. The scheme shows a higher level of accuracy if compared with the standard-MUSCL, and 4th-order accuracy was achieved on Cartesian grids. Furthermore, a significantly high spectral resolution (dispersion and dissipation) of the new scheme is observed. Two-and three-dimensional test cases were considered to demonstrate the new formulation. Results of the steady flow around the 7AD, S-76, JORP propeller, and XV-15 blades showed a better preservation of the vorticity and higher resolution of the vortical structures compared with the standard MUSCL solution. The method was also demonstrated for three-dimensional unsteady flows using overset and moving grid computations for the UH-60A rotor in forward flight and the ERICA tiltrotor in aeroplane mode. For medium grids, the new high-order scheme adds CPU and memory overheads of 22% and 23%, respectively. The parallel performance of the scheme is fair but can be further improved.

This thesis addresses the problem of controlling the unsteady flow separation over an aerofoil using plasma actuators, with the aim of improving the performance of fluid systems through the use of robust feedback controllers. Despite the complexity of the dynamics of interest, it is shown how the problem of controlling flow separation can be successfully formulated and solved as a simple output regulation problem. First, a novel control-oriented reduced-order model for nonlinear systems evolving on attractors is obtained. Its application to the incompressible Navier-Stokes equations is proposed, in order to obtain a linear reduced-order model (whose state variables have a clear and consistent physical meaning) of the complex flow/actuator dynamics. On the basis of the proposed model, a new robust multivariable feedback control algorithm for flow separation suppression is designed, using real-time velocity measurements, which are available in realistic applications. The presented control scheme is tested in both Single-Input-Single-Output (SISO) and Multi-Input-Multi-Output (MIMO) configurations, thus allowing for optimising the closed-loop system, with the aim of selecting suitable numbers and positions of the actuator/sensor pairs along the aerofoil, as well as desired references for the real-time measurements, according to the specific application (e.g., flow separation suppression, mixing enhancement etc.). Accurate numerical simulations of incompressible flows around both 2D aerofoils and 3D wings are performed in order to optimise the closed-loop system and illustrate the effectiveness of the proposed approach in the presence of complex dynamics that are neglected at the design stage. Robust performances, with respect to both parameter variations (e.g. geometry of the domain and Reynolds number) and model uncertainties, are demonstrated. The designed controller is able to effectively suppress the flow separation along the aerofoil, as well as the shedding vortices, thus yielding both a reduction of the drag and an increase of the lift. This allows for stall avoidance and increased efficiency.

Cavity flow induces strong flow oscillations, which increase noise, drag, vibration, and structural fatigue. This type of flow impacts a wide range of low speed applications, such as aircraft wheel wells, ground transportations, and pipelines. The objective of the current study is to examine the reverse flow interaction inside the cavity, which has a significant impact on the cavity flow oscillations. The study also investigates the impact of steady jets with different-configurations on the time-average field and the oscillations of the cavity separated shear layer. The purpose of the steady jets is suppressing the oscillations of the cavity separated shear layer. The experiments were performed for an open cavity with L/D = 4 at Reθ between 1.28×103 to 4.37×103. The steady jets were applied with different: momentum fluxes (J = 0.11 kg/m.s2,0.44 kg/m.s2 and 0.96 kg/m.s2), slot configurations (sharp edge and coanda), and blowing locations (blowing from the cavity leading and trailing edges). The data were acquired using qualitative (surface oil flow visualisation) and quantitative (hot-wire anemometry, laser Doppler anemometry, particle image velocimetry, and pressure measurements) flow diagnostics techniques. The study found that a low-frequency instability dominates the velocity spectra of the cavity separated shear layer. This instability decreases with increasing Reθ and is related to the reverse flow interaction. This interaction takes place when the reverse flow influences the sensitive separation point of the cavity separated shear layer. As a result, a large amplitude flapping wave is generated and propagates downstream of the cavity separated shear. It was also revealed that increasing J for the leading and trailing edges blowing enhances the reverse flow interaction and increases the broadband level of the unsteady wall pressure spectra. Thus, these types of jet blowing are not suitable for controlling the oscillations of the cavity separated shear layer.

Automotive manufacturers are receiving pressure from customers and regulators to reduce emissions. Reducing the weight of the vehicle through the use of carbon fibre is seen as one of these mechanisms. The challenge is to develop suitable manufacturing processes that can offer appropriate cycle times to meet demand and deliver materials with adequate mechanical properties for structural applications. Compression moulding of discontinuous fibre moulding compounds with local continuous fibre inserts provide better production rates and part complexity compared to the autoclave components and higher performances than injection moulding. However, combining a unidirectional carbon fibre (UD) material with a random short fibre orientation sheet moulding compound (SMC) that flows heterogeneously will lead to degradation in the properties of the continuous reinforcement. This work aims to demonstrate a hybrid of continuous and discontinuous fibre compounds in a single moulding operation with increased stiffness and determine if the surface distortion of the reinforcement can be used to predict local stiffness. A benchmarking study was carried out with UD and the SMC followed by hybridisation. This was non-destructively tested for flexural moduli providing a localised map of stiffness which was compared with a theoretical value. This work demonstrated that simply placing unidirectional (UD) prepreg with the SMC caused significant distortion and migration of the reinforcement in a one-dimensional flow scenario. Resin tended to bleed out of the hybrid reinforcement, causing a resin rich area at the UD ply drop off point. This resin bleed was more prominent at the ends of the UD fibres. The resin system in the UD was staged by partially curing it to a controlled level through the measurement of the storage modulus, and showed that flow could be dramatically reduced. This was determined by rheology and inter-laminar shear tests to measure material degradation from staging to improve flow control. It was found that for flow control of the reinforcement staging beyond gelation was required. The inter-laminar shear strength of UD is significantly higher than the SMC, and found that even with 50% staging properties were still higher. Where there were high levels of flow resistance in compression moulding, staged hybrids resulted in to two moulding defects; a dry region on the SMC under the reinforcement and rippling outside the reinforcement, which reduced the stiffness by nearly 50% in the affected areas. Staging accompanied with charge layout design of the UD to 902/0 showed markedly reduced flow in one, two and three dimensional scenarios, almost completely resisting the flow of the SMC. In the 2D flow scenario where the SMC charge coverage was 60% compared to the manufacturers’ recommended 80%, flow was limited to 3% and the stiffness could be locally predicted to an accuracy of 16%. By controlling the level of staging and careful consideration of the charge design, hybrid components can be manufactured repeatedly with increased accuracy in stiffness prediction and demonstrated an improved flexural strength and modulus increase of >44%, increasing the potential use to a wider range of complex geometry structural applications.