Shock Boundary Layer Interaction and Aero-Optical Effects in a Transonic Flow over Hemisphere-on-Cylinder Turrets
Xiang Ren, Huahua Yu, Xianghong Yao, Hua Su, Peng Hu
Abstract
Hemisphere-on-cylinder turrets are the main airborne optical platform structure. However, an unsteady shock boundary layer interaction (SBLI) would act on flow separation and turbulent wake, which causes serious aero-optical effects with high spatial and temporal frequency characteristics. In this paper, the SBLI phenomenon of a hemisphere-on-cylinder turret is recorded in a wind tunnel at <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:mtext>Ma</a:mtext> <a:mo>=</a:mo> <a:mn>0.7</a:mn> </a:math> using shadowing and Mach-Zehnder interferometer measurements. Its wavefront distortion is measured using the Shack-Hartmann measurement. The detached eddy simulation (DES) based on SST <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" id="M2"> <c:mi>k</c:mi> </c:math> - <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" id="M3"> <e:mi>ω</e:mi> </e:math> turbulence model and ray-tracing methods are used to reproduce the transonic flow and optical aberration. Experiments and simulations suggest that the SBLI causes the flow to separate earlier relative to a subsonic flow over the turret. The time-averaged root-mean-square of optical path difference (OPD) over the beam aperture is 0.56 λ∼0.59 λ with <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" id="M4"> <g:mi>λ</g:mi> </g:math> as the wavelength, while the root-mean-square of the time-averaged OPD is about 0.45 λ. The local shock and wavefront distortion have dual peak frequencies at <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" id="M5"> <i:mtext>S</i:mtext> <i:msub> <i:mrow> <i:mtext>t</i:mtext> </i:mrow> <i:mrow> <i:mi>D</i:mi> </i:mrow> </i:msub> <i:mo>=</i:mo> <i:mi>f</i:mi> <i:mi>D</i:mi> <i:mo>/</i:mo> <i:msub> <i:mrow> <i:mi>U</i:mi> </i:mrow> <i:mrow> <i:mo>∞</i:mo> </i:mrow> </i:msub> <i:mo>=</i:mo> <i:mn>0.24</i:mn> </i:math> and 0.34, different from the single-peak-frequency phenomenon of a subsonic flow over turrets. Fast model decomposition of wavefront can be performed by proper orthogonal decomposition (POD) of its Zernike coefficients. The first two modes contain the shock’s reciprocating motion.