Turbulent jet interaction with a long rise-time pressure signature

A sonic boom signature with a long rise time has the ability to reduce the sonic boom, but it does not necessarily minimize the sonic boom at the ground level because of the real atmospheric turbulence. In this study, an effect of the turbulence on a long rise-time pressure signature was experimentally investigated in a ballistic range facility. To compare the effects of the turbulence on the long and short rise-time pressure signatures, a cone-cylinder projectile that simultaneously produces these pressure signatures was designed. The pressure waves interacted with a turbulent field generated by a circular nozzle. The turbulence effects were evaluated using flow diagnostic techniques: high-speed schlieren photography, a point-diffraction interferometer, and a pressure measurement. In spite of the fact that the long and short rise-time pressure signatures simultaneously travel through the turbulent field, the turbulence effects do not give the same contribution to these overpressures. Regarding the long rise-time pressure signature, the overpressure fluctuation due to the turbulence interaction is almost uniform, and a standard deviation 1.5 times greater than that of the no-turbulence case is observed. By contrast, a short rise-time pressure signature which passed through the same turbulent field is strongly affected by the turbulence. A standard deviation increases by a factor of 14 because of the turbulence interaction. Additionally, there is a non-correlation between the overpressure fluctuations of the long and short rise-time pressure signatures. These results deduce that the length of the rise time is important to the turbulence effects such as the shock focusing/diffracting

Thermal fluctuation characteristics around a nanosecond pulsed dielectric barrier discharge plasma actuator using a frequency analysis based on Schlieren images

A thermal fluctuation driven by a burst plasma discharge is experimentally investigated using a frequency analysis based on the Schlieren images. The burst plasma discharge is controlled by an interval frequency fint = 200 Hz and a pulse frequency fB = 3.6 kHz as well as the duration time of the burst event: Ton. A burst feature is defined as a burst ratio BR = Ton/(1/fint). The burst plasma discharge generates a burst-induced hot plume growing above a ground electrode. In a high burst ratio, which is BR = 0.45 and 0.57, the burst-induced hot plume is formed as a wave thermal pattern that is mainly fluctuated at the interval frequency of 200 Hz. Additionally, a maximum fluctuation spot of 200 Hz appears near the edge of an exposed electrode in a low burst ratio, whereas it moves towards the ground electrode in the high burst ratio. The possible scenario is that a relatively strong ionic wind and/or an induced jet generated in the high burst ratio might cause the movement of the maximum fluctuation spot

Active Flow Control by Jet Injection on Shock-Boundary Layer Interaction Phenomena

No abstract available

Experimental investigation of surface flow pattern on truncated cones in Mach 5 flow: influence of truncation ratio

The flow characteristics on a truncated cone with a cylinder were experimentally investigated in a Mach 5 flow with a Reynolds number 3.8 × 105, based on the cylindrical diameter. Two different truncation ratios of 0.5 and 0.7 were used. The incidence angle varied from −12 to 0° with 3° intervals to investigate the influence of the truncation ratio on the surface flow pattern. The measurement techniques: unsteady pressure-sensitive paint (anodized aluminium method), color Schlieren photography, and surface oil flow were used. It was found that the distance of the external shock wave from the conical surface depends on the truncation ratio, and the surface pressure on the conical portion increases when the external shock wave moves closer to the model surface. The “external” shock wave denotes a detached shock wave and the “internal” one is the shock wave formed between the detached bow shock wave and the model surface. In the higher truncation ratio at the higher incidence angle, the internal shock wave induced by the flow separation on the conical surface impinges on the external shock wave, which results in its reflection. This reflection leads to the pressure increase on the model surface. On the other hand, this reflection does not appear in the lower truncation ratio. In spite of the different truncation ratios, the angle of the internal shock wave is identical at the same incidence angle. From the oil flow results, the wall shear stress on the leeward conical surface is lager in the higher truncation ratio model

Flow structure generated by laser-induced blast wave propagation through the boundary layer of a flat plate

Laser energy deposition generates localized flow structures that can be used as flow control devices in high-speed flows. In the present study, the interaction between a laser-induced blast wave and an incoming laminar boundary layer on a flat plate was experimentally investigated at a Mach 5 flow with three different unit Reynolds numbers. A hemispherical laser-induced blast wave (LIBW) is induced by focusing a 532 nm pulsed Nd:YAG laser beam on the surface of the plate. The hemispherical shaped fore wave front of the LIBW is locally transformed to an oblique shape, which results in a laser-induced oblique shock wave (LIOSW). As LIOSW propagates through the laminar boundary layer increases its thickness. With laser energy deposition near the leading edge of the flat plate, the LIOSW interacts and influences the leading edge shock wave (LSW). This interaction could contribute to the modulation of the LSW in scramjet intakes. A weak shock limb generated at the shape transition point of the LIBW or thermal spot due to laser-induced gas breakdown causes the boundary layer perturbation. The geometrical pattern produced due to the interaction between the LIOSW and the disturbed boundary layer remains similar to itself as it grows with time as well as at different local Reynolds numbers, to 2.2 x 105 to 5.7 x 105

Temporal variation of the spatial density distribution above a nanosecond pulsed dielectric barrier discharge plasma actuator in quiescent air

The thermal perturbation caused by a nanosecond pulsed dielectric barrier discharge (ns-DBD) plasma actuator may lead to boundary layer transition. Hence, understanding of the thermal flow induced by the ns-DBD plasma actuator will contribute to the development of an efficient flow control device for various engineering applications. In this study, the spatial density distribution related to the thermal flow was experimentally investigated using both qualitative and quantitative schlieren techniques. The focus of this study is to understand the initial temporal variation of the spatial density distribution above the ns-DBD plasma actuator in quiescent air. The quantitative visualisation showed that a hot plume is generated from the edge of the exposed electrode and moves slightly towards the ground electrode. A possible explanation is that an ionic wind and/or an induced jet leads to the movement of the hot plume. However, the plasma-induced flow (the ionic wind and the induced jet) is generated after the primary plasma discharges; namely, the hot plume does not move immediately after the first plasma discharge. At almost the same time as the movement of the hot plume, consecutive plasma discharges enhance the density of the hot plume; thereafter, the density reaches almost a steady state

Characterization of a novel open-ended shock tube facility based on detonation transmission tubing

This paper proposes and demonstrates a novel shock tube driven by commercially available detonation transmission tubing in a safe, repeatable, and controllable manner for laboratory scale experiments. A circular cross-sectional open-ended shock tube (inner-diameter D = 22 mm) driven by detonation transmission tubing was used to investigate the working principle of this novel shock tube using a dynamic pressure transducer and time-resolved shadowgraph photography. Specifically, the shock Mach number, repeatability, and flow structure generated from the tube exit were characterized. The experimental result shows that the flow structure including an initial shock wave, a vortex ring, an embedded shock, and an oblique shock pattern is similar to that of the conventional compressed-gas driven shock tubes. Furthermore, the shock tube has good repeatability of less than 2% with a shock Mach number up to 1.58. The versatile and cost-effective nature of the shock tube driven by detonation transmission tubing opens a new horizon for shock wave-assisted interdisciplinary applications

Experimental investigation of impinging shock – cavity interactions with upstream transverse jet injection

Mixing between the injected fuel and high speed free stream air is challenging at supersonic speeds. Placing cavities downstream of injection holes or slots addresses the problem of flame holding and stabilisation, however there are still open questions related to mixing enhancement, uniformity and efficiency. The present study examines experimentally the flow field interactions due to a transverse jet - cavity combination with shock impingement at supersonic speeds using PIV, Schlieren photography, and oil flow surface visualisation. The oblique shock lifts the shear layer over the cavity and combined with the instabilities generated by the transverse jet injection creates a highly complicated flowfield with numerous vortical structures. The interaction between the oblique shock and the jet leads to a relatively uniform velocity distribution within the cavity. The lifting of the shear layer is also believed to reduce the drag created by the cavity

Suspended liquid particle disturbance on laser-induced blast wave and low density distribution

The impurity effect of suspended liquid particles on the laser-induced gas breakdown was experimentally investigated in quiescent gas. The focus of this study is the investigation of the influence of the impurities on the shock wave structure as well as the low density distribution. A 532 nm Nd:YAG laser beam with an 188 mJ/pulse was focused on the chamber filled with suspended liquid particles 0.9 ± 0.63 μm in diameter. Several shock waves are generated by multiple gas breakdowns along the beam path in the breakdown with particles. Four types of shock wave structures can be observed: (1) the dual blast waves with a similar shock radius, (2) the dual blast waves with a large shock radius at the lower breakdown, (3) the dual blast waves with a large shock radius at the upper breakdown, and (4) the triple blast waves. The independent blast waves interact with each other and enhance the shock strength behind the shock front in the lateral direction. The triple blast waves lead to the strongest shock wave in all cases. The shock wave front that propagates toward the opposite laser focal spot impinges on one another, and thereafter a transmitted shock wave (TSW) appears. The TSW interacts with the low density core called a kernel; the kernel then longitudinally expands quickly due to a Richtmyer-Meshkov-like instability. The laser-particle interaction causes an increase in the kernel volume which is approximately five times as large as that in the gas breakdown without particles. In addition, the laser-particle interaction can improve the laser energy efficiency