An experimental investigation of flow control for supersonic inlets

This thesis focuses on the control of shock wave / boundary layer interactions (SWBLIs) in supersonic inlets. The overall aim of this study is to determine to what extent vortex generators (VGs) can mitigate flow separations within supersonic inlets. To achieve this, an experimental investigation was undertaken in a small-scale wind tunnel, because small-scale wind tunnels are much more amenable to numerous measurement techniques than real inlets. A new geometry was designed and developed as part of this study to make the configuration more representative of typical inlet conditions than previous studies. The flow-field that was determined to be relevant, yet still simple, comprised of a Mach 1.4 normal shock followed by a region of subsonic diffusion created by a 6° straight-angled diffuser. A shock holder was used to improve shock stability and the Reynolds number was set to 25 million per metre throughout. This flow was examined in three different shock positions. The flow was found to be highly sensitive to the relative position of the shock and diffuser: when the shock was positioned somewhat upstream of the diffuser the flow was relatively benign and, apart from small corner separations, the majority of the boundary layers remained attached; but as the shock was moved close to the diffuser, separation was introduced on the channel floor; and once inside the diffuser the entire diffuser boundary layer was separated. In the first instance, VGs were employed on the channel floor. While the VGs were able to produce a thin attached region on the channel floor and therefore improve the centre-span region somewhat, they were detrimental to the corner separations. As a result, corner suction was employed to reduce the prominence of the corner flows. Corner suction dramatically reduced the corner separations, however, flow separation still dominated the diffuser because separation was now introduced at centre-span. These results demonstrate that a strong coupling between the centre-span and corner flow regions exists in this configuration. When flow control was applied to one region, although the flow is improved locally, increased losses in other regions tended to offset this gain. This is because an overall improvement in the pressure within the diffuser can only be maintained if all areas can sustain the pressure-rise. As a result, only when all the problem regions were appropriately controlled—the corners using suction and the centre-span using VGs—could a notable improvement in the flow be obtained. In this combined configuration, more than 50% of the diffuser-span remained attached throughout the diffuser and there was a 15% drop in stagnation pressure losses and 6% increase in the wall-pressure recovery. Although further VG studies are required, this investigation does suggest that VGs do have the potential to alleviate the current dependency on boundary-layer bleed for flow control in supersonic inlets

A review of the use of vortex generators for mitigating shock-induced separation

This article reviews research into the potential of vortex generators to mitigate shock-induced separation. Studies ranging from those conducted in the early post-war era to those performed recently are discussed. On the basis of the investigations described in this report, it is clear that vortex generators can alleviate shock-induced boundary layer separation. Yet, it will be shown that their potential and efficiency varies considerably in practical applications. Much more success is reported in transonic test cases compared to separation induced in purely supersonic interactions. Under a variety of flow conditions, the best performance is achieved with vortex generators with a height of roughly half the boundary layer thickness and a shape similar to a swept vane. Notwithstanding this, vortex generator performance is not as consistent as it is in low-speed applications. Further work is required before vortex generators can be implemented into the design process for eliminating shock-induced separation on transonic wings and in supersonic inlets

On the calculation of boundary-layer parameters from discrete data

An investigation of the errors inherent in the calculation of integral boundary-layer parameters from discrete datasets has been carried out. The primary errors examined were those due to discretization of the velocity profile, distance of the first data location from the wall, and uncertainty in the floor location. A range of turbulent velocity profiles with different shape factors from analytical models and published DNS investigations has been examined. This analysis demonstrates that the spacing of the first measurement point from the floor is by far the most critical error source. Furthermore, the error is shown to be a function of boundary-layer shape factor, and therefore, a correction factor chart has been derived. Two alternative methods of estimating integral boundary-layer parameters have been examined: wall modeling and a gradient-based formulation. These have both been shown to generate smaller errors than the basic integration approach, although both are susceptible to external influences.Engineering and Physical Sciences Research Counci

A multi-laboratory evaluation of a clinically-validated incurred quality control material for analysis of allergens in food

A dessert matrix previously used for diagnosis of food allergies was incurred with pasteurised egg white or skimmed milk powder at 3, 6, 15 and 30 mg allergen protein per kg of dessert matrix and evaluated as a quality control material for allergen analysis in a multi-laboratory trial. Analysis was performed by immunoassay using five kits each for egg and milk (based on casein) and six ‘other’ milk kits (five based on β-lactoglobulin and one total milk). All kits detected allergen protein at the 3 mg kg−1 level. Based on ISO criteria only one egg kit accurately determined egg protein at 3 mg kg−1 (p = 0.62) and one milk (casein) kit accurately determined milk at 6 (p = 0.54) and 15 mg kg−1 (p = 0.83), against the target value. The milk “other” kits performed least well of all the kits assessed, giving the least precise analyses. The incurred dessert material had the characteristics required for a quality control material for allergen analysis