Experimental and theoretical study of shock wave propagation through double-bend ducts (original) (raw)
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Shock wave propagation in a branched duct
Shock Waves, 1998
The propagation of a planar shock wave in a 90 • branched duct is studied experimentally and numerically. It is shown that the interaction of the transmitted shock wave with the branching segment results in a complex, two-dimensional unsteady flow. Multiple shock wave reflections from the duct's walls cause weakening of transmitted waves and, at late times, an approach to an equilibrium, one-dimensional flow. While at most places along the branched duct walls calculated pressures are lower than that existing behind the original incident shock wave, at the branching segment's right corner, where a head on-collision between the transmitted wave and the corner is experienced, pressures that are significantly higher than those existing behind the original incident shock wave are encountered. The numerically evaluated pressures can be accepted with confidence, due to the very good agreement found between experimental and numerical results with respect to the geometry of the complex wave pattern observed inside the branched duct.
Interaction of travelling shock waves with orifices inside ducts
International Journal of Mechanical Sciences, 1971
When a shock wave moves down in a duct and reaches an orifice plate located inside it, reflected and transmitted shocks appear. A theoretical model to estimate such effects has been outlined, and experiments have been carried out measuring pressures upstream and downstream of the orifice. The experimental results obtained agree fairly well with the theoretical ones. Some anomalous phenomena have been observed, probably due to unsteady boundary layer growth or time lag in the establishment of steady-flow conditions through the orifice. NOTATION a acoustic velocity d orifice hole diameter f contact surface i incident shock wave m = d~/D 2 constriction factor p pressure r reflected shock wave s axial thickness of the orifice t transmitted shock wave u gas velocity A cross-section D pipe diameter K discharge coefficient M Mach number T temperature ae = AdA~ fl = pip, ratio of specific heats St~fixes i, r, t refer to the incident, reflected and trar~mitted shock waves Suffix e denotes the conditions in the minimum area A e Numbers 0, 1, 2, 3 and 4 refer to the regions drawn in Fig. 1
Three-Dimensional Passive and Active Control Methods of Shock Wave Train Physics in a Duct
In the present work, the physics of a three-dimensional shock train in a convergent-divergent nozzle is numerically investigated. In this regards, the Ansys-Fluent Software with Algebraic Wall-Modeled Large-Eddy Simulation (WMLES) is used. To estimate precision and errors accumulation we used the Smirinov's method; fine flow structures are obtained via Laplacian of density called shadowgraph and the shock parameter is defined as multiplication of flow Mach number by the normalized pressure gradient, in which shock wave structures are visible distinctly. The results are compared with the experimental data of Weiss et al. [Experiments in Fluids 49(2) (2010) 355–365], in the same conditions including geometry, boundary conditions, etc. The results show that there is good agreement with experimental trends concerning wall pressure and center-line Mach number profiles. Therefore, the focus of the present study is an assessment of various flow control methods to change the shock structures. Consequently, we investigated the effects of passive (bump and cavity) and active (suction and blowing) control methods on the starting point of shock, shock strength, minimum pressure, maximum flow Mach number, etc. All CFD investigations are carried out by High Performance Computing Center (HPCC).
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Journal of Fluid Mechanics, 1996
The interaction of a planar shock wave with a square cavity is studied experimentally and numerically. It is shown that such a complex, time-dependent, process can be modelled in a relatively simple manner. The proposed physical model is the Euler equations which are solved numerically, using the second-order-accurate highresolution GRP scheme, resulting in very good agreement with experimentally obtained findings. Specifically, the wave pattern is numerically simulated throughout the entire interaction process. Excellent agreement is found between the experimentally obtained shadowgraphs and numerical simulations of the various flow discontinuities inside and around the cavity at all times. As could be expected, it is confirmed that the highest pressure acts on the cavity wall which experiences a head-on collision with the incident shock wave while the lowest pressures are encountered on the wall along which the incident shock wave diffracts. The proposed physical model and the numerical simulation used in the present work can be employed in solving shock wave interactions with other complex boundaries.
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Journal of Applied Fluid Mechanics, 2015
The complex flow features behind a diffracted shock wave on a convex curved wall is investigated using large scale experimentation complemented by numerical computation. The study aimed at explaining the global flow behavior within the perturbed region behind the diffracted shock wave. Experiments were conducted in a purpose built shock tube that is capable of generating a range of incident shock Mach numbers Mn ≤ 1.6. Analysis of higher Mach number shocks on different wall geometries were carried out using numerical code that has been validated by earlier authors. Many flow features that were only distinct at high Mach numbers are clearly identified at low Mach numbers in the present investigation. The separation point moves upstream at incident shock Mach number Mn = 1.5 but moves downstream at higher Mach numbers and is nearly stationary at Mn = 1.6. At incident shock Mach number 3.0 the movement of the separation point tends to be independent of the wall curvature as the wall radius approaches infinity. The present investigation is important in the design of high speed flow devices and in the estimation of flow resistance on supersonic devices and space vehicles.
Numerical and Experimental Investigations on Mach 2 and 4 Pseudo-Shock Waves in a Square Duct
Transactions of The Japan Society for Aeronautical and Space Sciences, 2005
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Numerical simulations of high-pressure air, helium, and hydrogen discharging into a low-pressure air section through an orifice, representing a partially opened diaphragm in a shock tube, are performed using OpenFOAM. Synthetic schlieren images are used to visualize the development of shock waves, expansion waves, and mixing layers as the initial pressure ratio, area ratio, jet Reynolds number, and gas driver type are varied. Insight from the simulations are used to develop and assess theoretical shock strength models, based on discharge coefficients for orifice plates in compressible pipe flow and sonic nozzles. Model predictions are compared to an empirical model from the literature to assess performance. Limitations of the models are examined, and simple corrections are proposed to increase the range of applicability. The proposed shock strength models can be used to predict jet-ignition associated with an accidental hydrogen explosion.
TsAGI Science Journal, 2012
The phenomenon of recirculation zones during the interaction of free or fixed pseudo-shock with perturbations from a thin needle, vortex filament and low-pressure jet is considered. The effect of this interaction on the integral characteristics of flows in ducts and the methods of their control are evaluated. Based on studies of the interaction of vortex filament generated ahead of the entry of the duct with pseudo-shock, a method to improve the characteristics of the flow in the duct in the case of a vortex filament passing into the inlet is offered. Improvement can be accomplished by the creation of a local recirculation zone at the duct entry by the sharp needle placed in front of the entry plane.