| Summary: | When two slender bodies are closely spaced within a supersonic freestream, substantial aerodynamic
interference precipitates between the bodies. The bow-shock wave and forebody expansion field
produced by an adjacent body (the disturbance generator) impinge onto the body of interest (the
disturbance receiver), which modifies its surface pressure distribution, effectively altering its nominal
centre of pressure and overall aerodynamic behaviour. The three-dimensional, curved bow-shock
interactions have increased complexity due to the multiple shock reflections, shock wave diffraction
and viscous-shock interactions manifesting with the receiver at incidence in the interference domain.
This research aims to uncover and characterise the underlying flow physics that are generated in the
disturbance flowfield for several multi-slender body configurations.
Parametric wind tunnel investigations were conducted on pairs of slender bodies with ogival,
conical and hemispherical forebody profiles over a wide incidence range. Primary experimental data
was collected using the surface oil flow visualisation technique, where a quantitative data extraction
method was employed to measure the shock impingement location and diffraction path over the
receiving body. Supporting schlieren images of the flowfield were captured through a standard ztype
schlieren system. In addition, time-averaged numerical solutions of the Reynolds-averaged
Navier-Stokes governing equations were conducted using a commercial flow solver. A custom,
gradient-based adaptive mesh refinement algorithm was tailored into the package, providing fine
resolution of the pressure waves in the flowfield. The high-fidelity computational predictions showed
excellent agreement with the experimental data and was used to examine the vortex and shock wave
dynamics produced by the interactions.
A high geometric dependence was observed across all interactions, where the magnitude and
extent of impinging disturbances were bespoke to each configuration, making it challenging to
extract overall trends. However, the interactions could be categorised under three general genres:
The first were the primary windward interactions, where the receivers were negatively pitched
relative to the generator bodies and the impinging disturbances made first contact with the
receivers’ windward surface. The second category had the receiver bodies at positive incidence in
relation to the generators, where impinging disturbances impacted the bodies’ leeward surface
directly, and were designated as primary leeward interactions. The last category assessed the
receiver bodies at angles of sideslip relative to the disturbance generators, where the disturbance
bow-shocks impinged asymmetrically on the receivers. Under each of these categories, the mechanics
of the interactions were observed to be predominantly similar.
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Primary windward interactions: Characteristic to these interactions was the locally elevated
windward surface pressure, which created favourable pressure gradients in the natural crossflow
direction over the bodies. Disturbance shock wave diffraction over the bodies induced significant
effects of compressibility onto the separated flow in the leeward region, producing body-vortices that
were elongated, more elliptic and intensified in comparison to that produced by equivalent
undisturbed bodies. Moreover, the receivers’ body-vortices had a significant influence on the
disturbance shock waves’ transit into the leeward flow region, where the wave was tempered during
passage through the vortices.
Primary leeward interactions: These configurations generated direct shock wave-leeward flow
structure interactions where the inherent low pressure in the receivers’ leeward region attracted the
approaching waves, causing the bow-shocks to bulge out locally towards the bodies. The opposing
natural crossflow over the receivers tempered the disturbance shock waves’ transit into the
windward region, generating complex three-dimensional shock wave geometries around the bodies.
Moreover, the viscous-shock interactions caused severe distortions to the vortical structures disposed
by the receiver bodies.
Interactions with the receiver bodies at angle of sideslip: Additional complexities were generated
by these interactions due to the inherent three-dimensional flow asymmetry, where waves of unequal
strengths diffracted over the windward and leeward surfaces of the receiving bodies. The windward
portion of the diffracted wave caused substantial elevations in surface pressure and an enhanced
crossflow condition over the bodies. The wave that diffracted over the leeward surface interacted
progressively with the receivers’ body-vortices, which caused an imbalance in the strength of the
vortices disposed on either side of the bodies. The strong rotational velocity field of the vortices
influenced the disturbance waves’ transit over the leeward surface substantially, producing complex
compression wave topologies in the receivers’ leeward region.
In general, significant reorganisation of the receivers’ near-surface flow topologies was observed
across all three categories of interactions, the extent of which varied with incidence and the strength
of impinging disturbances. It was also found that the inhomogeneous pressure field introduced by
the disturbance shock waves caused significant modification to the receivers’ incidence-induced
body-vortices. In addition, the inhomogeneous velocity field of the receivers’ body-vortex pair were
observed to affect the disturbance waves’ transit into the bodies’ leeward region. Overall, studying
the slender bodies orientated to produce 3D, curved bow-shock interactions revealed several
fundamental mechanisms and flow physics in the flowfield, with rich phenomena manifesting in the interference domain.
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