In the transonic flow over a hemisphere-on-cylinder turret, strong aero-optical effects can be caused by local shock-boundary layer interactions and separation shear layers at the turret's zenith. The effects of an annular rough wall on the passive control of fluid and aero-optics are investigated by experimental measurements and numerical simulations. The local shock-boundary layer interaction and separated shear layer at the zenith of the turret are recorded using shadowing and Mach-Zehnder interferometer measurements. The aero-optics are measured using a Shack-Hartmann wavefront sensor. The experimental results show that the annular rough wall on the turret weakens the local shock wave, moves the flow separation point forward, and reduces the wavefront distortion at the zenith. The rough wall functions for the shear stress transport (SST) k- ω turbulence model proposed by Aupoix [ J. Fluid Eng., v137, 2014] and Lee [ Eng. Appl. Comp. Fluid, v137, 2014] are used to further study the control effect of different roughnesses. Numerical simulations based on both rough wall functions show good agreement with the experimental measurements. For various transonic flows, the steady wavefront distortions at the zenith with the rough wall at roughness k s = 1 mm are 21 % -- 50% smaller than those with smooth walls. The smaller the supersonic region, the more effective the rough wall is in reducing wavefront distortion.
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 Ma = 0.7 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 k - ω 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 λ 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 S t D = f D / U ∞ = 0.24 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.
Abstract. The step pressure generated by shock tube was used for calibration of dynamic pressure transducers. First, the performance of the shock tube based calibration installation was theoretically predicted. The influence of Mach number to the step pressure and the duration of the step pressure plateau was analyzed by numerical calculation. Second, the performance of the calibration installation was tested, whose result showed that the minimum and maximum value of the step pressure generated by the calibration installation was 9.60kPa and 1.101MPa, respectively, the maximum value of the rise time of the step pressure was 0.7μs, the minimum value of the duration of the step pressure plateau was 4.14ms, the fluctuation of the step pressure plateau was better than ±2%, and the maximum value of the 2 nd order expand uncertainty of the step pressure was 3.52%. The test result verified that the calibration installation met the requirements of the previous design and correlative verification regulations. Last, the sensitivity and syntonic frequency of standard pressure transducers were tested by the calibration installation. The result was in accord with the factory technical parameters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.