Parametric experimental studies on the shock related unsteadiness in a hemispherical spiked body at supersonic flow

TL;DR

This study experimentally investigates how geometrical parameters of a drag-reducing spike on a hemispherical forebody affect shock unsteadiness and drag in supersonic flow, identifying optimal configurations for flow stability and reduced drag.

Contribution

It provides new insights into the influence of spike length, stem diameter, and tip shape on shock unsteadiness and drag reduction in supersonic flows with detailed experimental analysis.

Findings

Longer spikes (l/D=1.5) significantly reduce drag.

Increasing spike stem diameter decreases shock unsteadiness.

Hemispherical spike tip with vertical base performs best in reducing drag and unsteadiness.

Abstract

Experimental studies are carried out to investigate the effects of the geometrical parameters with a drag reducing spike on a hemispherical forebody in a supersonic freestream of $M_\infty=2.0$ at $0^{\circ}$ angle of attack. The spike length $(l/D=0.5,1.0,1.5,2.0)$, spike stem diameter $(d/D=0.06,0.12,0.18)$, and spike tip shapes are varied and their influence on the time-averaged, and time-resolved flow field are examined. When $l/D$ increases, a significant reduction in drag ($c_d$) is achieved at $l/D=1.5$, whereas the variation in $d/D$ has only a minor effect. The intensity of the shock-related unsteadiness is reduced with an increase in {$d/D$ from $0.06$ to $0.18$}, whereas changes in $l/D$ have a negligible effect. The effects of spike tip geometry are studied by replacing the sharp spike tip with a hemispherical one having three different base shapes (vertical base, circular base, and elliptical base). Hemispherical spike tip with a vertical base is performing better by reducing $c_d$ and flow unsteadiness. The dominant Spatio-temporal mode arising due to the shock-related unsteadiness is represented through modal analysis of time-resolved shadowgraph images and the findings are consistent with the other measurements.