Design and Performance Analyses of Osculating Cone Waveriders

Abstract

Modern mission requirements for long-range maneuverable hypersonic vehicles for space, military, and transportation applications necessitate vehicle design innovations. The primary challenges that a hypersonic vehicle faces are aero-heating, stability and high wave drag. Hypersonic waveriders are special shapes with leading edges coincident with the body’s shock wave, yielding high lift-to-drag ratios. The waverider geometry results from streamline tracing using the solutions of a basic flow field such as the wedge or the cone for specified shock and base curves. Cone-based waveriders have the fundamental drawback that, given a Mach number and shock angle, we can only alter the base curve. Osculating cone based waverider have the flexibility of including the shock curve as a variable, which significantly increases the design space. The thesis tackles three specific challenges related to osculating cone waveriders. Firstly, it delves into the selection of the appropriate shock curve to ensure a valid waverider design. Secondly, it seeks to comprehend how various design parameters influence the performance of osculating cone waveriders under both on-design and off-design conditions. Lastly, the thesis assesses the impact of bluntness on the aero-thermal characteristics of these waveriders.

Generally, low values of the conical shock angle (9◦ − 15◦) are used. The lack of any method to limit the maximum cone angle for osculating cone waverider motivates this study. Mathematical expressions are derived for geometrical conditions that result in successful osculating cone waverider generation. A power law curve and a B´ezier curve are analysed. Closed-form expressions for the maximum cone shock angle are obtained for the power law curve. A numerical procedure to solve the same for the B´ezier curve is developed. The results, for a typical Mach number of 6.0, evidently show that the maximum cone shock angle for successful waverider generation is significantly lower than the maximum angle for attached shock solutions. The limiting conditions developed will be essential in constraining the waverider sample space for automated multi-objective optimization routines. CFD simulations were conducted on waveriders designed with traditional shock angle of 12◦ and near limiting shock angle of 18◦. The analysis revealed a substantial 50% increase in volumetric efficiency, albeit with a minor decrease in aerodynamic performance. This highlights the critical need for determining the maximum conical shock angle when aiming for specific high volumetric efficiency.

The established limit, as discussed in the preceding chapter, serves the purpose of determining the maximum attainable tip height for a viable waverider design. This design involves the development of three distinct waverider shapes: specifically, anhedral, flat, and dihedral configurations. To evaluate their performance, on/off design simulations were conducted using the commercial CFD software CFD++. Noticeable differences in flow characteristics were observed when the airflow experienced side slip. The simulations also revealed that dihedral waveriders exhibited an increase in static lateral stability, while anhedral waveriders were found to be unstable in this regard. In terms of directional and longitudinal stability, all the three waveriders were stable and unstable respectively.

From the standpoint of aero-thermal loads and manufacturing, an ideal hypersonic waverider with sharp leading edge is a difficult proposition. One of the primary methods for resolving this issue is to blunt the leading edge. However, bluntness is detrimental to the aerodynamic performance of the waverider. A generic blunt leading edge osculating cone waverider for M= 6 is derived by using the adding material method on an initial sharp leading edge osculating cone waverider geometry. Viscous laminar CFD computations were carried out using commercial solver CFD++ to understand the effect of bluntness. It is seen that the aerodynamic performance drops with the amount of bluntness owing to the presence of larger bow shock standoff distance leading to spillage. The heat transfer rates at the upper and lower surfaces are nearly same for all the bluntness which is significantly lower than the heat transfer rates at the blunt part of the waverider suggesting the need for appropriate thermal protection system for the blunt part of the waverider.