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![Schematic showing the time-averaged hypersonic leading-edge separated flow over a generic flat-face forebody with an axial protrusion undergoing flapping type of unsteadiness. Prominent flow attributes include a leading-edge shock, a reattachment shock, a separated shear layer, a boundary layer, and an expansion fan. A streamline passing through the system of shocks and expansion fans is added. The governing parameters of the problem include the freestream Reynolds number (ReD\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Re}_D$$\end{document}) and the geometrical parameters of the protrusion (length-L and diameter-D)](profile/Sengunthapuram-Kandasamy-Karthick/publication/366851000/figure/fig1/AS:11431281115490757@1674961223406/Schematic-showing-the-time-averaged-hypersonic-leading-edge-separated-flow-over-a-generic.png)
Schematic showing the time-averaged hypersonic leading-edge separated flow over a generic flat-face forebody with an axial protrusion undergoing flapping type of unsteadiness. Prominent flow attributes include a leading-edge shock, a reattachment shock, a separated shear layer, a boundary layer, and an expansion fan. A streamline passing through the system of shocks and expansion fans is added. The governing parameters of the problem include the freestream Reynolds number (ReD\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{Re}_D$$\end{document}) and the geometrical parameters of the protrusion (length-L and diameter-D)
Source publication
Hypersonic leading-edge separation is studied toward understanding the varying shock-related unsteadiness with freestream Reynolds number (\(1.66 \times 10^5 \le \text{Re}_D \le 5.85 \times 10^5\)) in the newly constructed hypersonic Ludwieg tunnel (HLT) at a freestream design Mach number of \(M_\infty =6.0\). An axisymmetric flat-face cylinder of...
Citations
... At θ = [π/2] ( Figure 4 I-d), the leading-edge separation is highly unstable to an extent, the stationary shock system as seen in the previous case starts to oscillate violently. Such an oscillation is called 'pulsation' as seen in the spiked-body flows at supersonic and hypersonic speeds 29,58 . A typical pulsation cycle contains three phases of shock motion: inflate, with-hold, and collapse. ...
... When one is negative, then the other is positive. The separation and reattachment shock hangs about the point and oscillates, indicating that there must be an out-of-phase shock motion as described in the work of 51,58 . Downstream the control surface, only weak correlations are seen. ...
... For example, the downstream motion of the separation shock ejects the fluid mass by pushing the reattachment shock upstream and eventually shrinks the separation bubble volume and vice versa. A similar event is seen in the leading-edge separation of the spiked body flows in supersonic 28 and hypersonic flow field 58 . It is also seen in the classic forward-facing step in a supersonic flow 43,66 . ...
Control surface deployment in a supersonic flow has many applications, including flow control, mixing, and body-force regulation. The extent of control surface deflections introduces varying flow unsteadiness. The resulting fluid dynamics influence the downstream flow characteristics and fluid-structure interactions severely. In order to understand the gas dynamics, an axisymmetric cylindrical body with a sharp-tip cone at zero angles of attack (α=0∘) is examined in a free stream Mach number of M∞=2.0 and Reynolds number of ReD=2.16×106 (D=50 mm). Four static control surface deflection angles (θ=π/36,π/6,π/3,π/2, rad) are considered around the base body. The cases are computationally investigated through a commercial flow solver adopting a two-dimensional detached eddy simulation (DES) strategy. Recirculation bubble length, drag coefficient's variation, wall-static pressure statistics, acoustic loading on the model and the surroundings, x−t trajectory and x−f spectral analysis, pressure fluctuation's correlation coefficient on the model, and modal analysis are obtained to understand the flow unsteadiness. At θ=[π/36], the wall-static pressure fluctuations behind the control surface are minimal and periodic, with a mere acoustic load of about 50 dB. At θ=[π/2], a violent periodic fluctuation erupted everywhere around the control surface, leading to a higher acoustic load of about 150 dB (3 times higher than the previous). For θ=[π/6] and [π/3], high-frequency fluctuations with small and large-scale structures continuously shed along the reattaching shear layer, thereby causing broadened spectra in the control surface wake.
... At θ = [π/2] ( Figure 4 I-d), the leading-edge separation is highly unstable to an extent, the stationary shock system as seen in the previous case starts to oscillate violently. Such an oscillation is called 'pulsation' as seen in the spiked-body flows at supersonic and hypersonic speeds 29,53 . A typical pulsation cycle contains three phases of shock motion: inflate, with-hold, and collapse. ...
... When one is negative, then the other is positive. The separation and reattachment shock hangs about the point and oscillates, indicating that there must be an out-of-phase shock motion as described in the work of 51,53 . Downstream the control surface, only weak correlations are seen. ...
... For example, the downstream motion of the separation shock ejects the fluid mass by pushing the reattachment shock upstream and eventually shrinks the separation bubble volume and vice versa. A similar event is seen in the leading-edge separation of the spiked body flows in supersonic 28 and hypersonic flow field 53 . It is also seen in the classic forward-facing step in a supersonic flow 49,61 . ...
Control surface deployment in a supersonic flow has many applications, including flow control, mixing, and body-force regulation. The extent of control surface deflections introduces varying flow unsteadiness. The resulting fluid dynamics influence the downstream flow characteristics and fluid-structure interactions severely. In order to understand the gas dynamics, an axisymmetric cylindrical body with a sharp-tip cone at zero angles of attack ($\alpha=0^\circ$) is examined in a free stream Mach number of $M_\infty=2.0$ and Reynolds number of $Re_{D}=2.16 \times 10^6$ ($D=50$ mm). Four static control surface deflection angles ($\theta = \pi/36,\pi/6,\pi/3,\pi/2$, rad) are considered around the base body. The cases are computationally investigated through a commercial flow solver adopting a two-dimensional detached eddy simulation (DES) strategy. Recirculation bubble length, drag coefficient's variation, wall-static pressure statistics, acoustic loading on the model and the surroundings, $x-t$ trajectory and $x-f$ spectral analysis, pressure fluctuation's correlation coefficient on the model, and modal analysis are obtained to understand the flow unsteadiness. At $\theta = [\pi/36]$, the wall-static pressure fluctuations behind the control surface are minimal and periodic, with a mere acoustic load of about 50 dB. At $\theta = [\pi/2]$, a violent periodic fluctuation erupted everywhere around the control surface, leading to a higher acoustic load of about 150 dB (3 times higher than the previous). For $\theta = [\pi/6]$ and $[\pi/3]$, high-frequency fluctuations with small and large-scale structures continuously shed along the reattaching shear layer, thereby causing a broadened spectra in the control surface wake.
Experiments and computations were performed at Mach number 2.0 for various nose cone fairing bodies with a sharp spike and conical spike of [Formula: see text] and with a sharp spike having a fixed tip location of different [Formula: see text] ratios. Attempts were made to alter the flowfield of various nose cone fairing bodies with the adoption of the spike. Qualitative and quantitative measurement studies indicate the changes that support the reduction of drag forces, not only on hemispherical blunt bodies but also on various nose cone fairings. This drag reduction with the configurations tested in this study indicates the importance of the region between the spike and the blunt-body face. The results presented here justify the quality and quantity of recirculating flow and its implication for drag reduction.
Shock tubes have emerged as an effective tool for applications in various fields of research and technology. The conventional mode of shock tube operation employs a frangible diaphragm to generate shock waves. The last half-century has witnessed significant efforts to replace this diaphragm-bursting method with fast-acting valves. These diaphragmless methods have good repeatability, quick turnaround time between experiments, and produce a clean flow, free of diaphragm fragments, in contrast to the conventional diaphragm-type operation. The constantly evolving valve designs target shorter opening times for improved performance and efficiency. The present review is a compilation of the different diaphragmless shock tubes that have been conceptualized, developed, and implemented for various research endeavors. The discussions focus on essential factors, including the actuation mechanism, driver-driven configurations, valve opening time, shock formation distance, and operating pressure range, that ultimately influence the shock wave parameters obtained in the shock tube. A generalized mathematical model to study the behavior of these valves is developed. The advantages, limitations, and challenges in improving the performance of the valves are described. Finally, the present-day applications of diaphragmless shock tubes have been discussed, and their potential scope in expanding the frontiers of shock wave research and technology is presented. CONTENTS
