Processing of high-speed videos of shock wave boundary layer interactions

This paper presents a framework for processing high-speed videos recorded during gas experiments in a shock tube. The main objective is to study boundary layer interactions of reflected shock waves in an automated way, based on image processing. The shock wave propagation was recorded at a frame rate of 500,000 frames per second with a Kirana high-speed camera. Each high-speed video consists of 180 frames, with image size [$$768 \times 924$$ 768 × 924 ] pixels. An image processing framework was designed to track the wave front in each image and thereby estimate: (a) the shock position; (b) position of triple point; and (c) shock angle. The estimated shock position and shock angle were then used as input for calculating the pressure exerted by the shock. To validate our results, the calculated pressure was compared with recordings from pressure transducers. With the proposed framework, we were able to identify and study shock wave properties that occurred within less than $$300\, \upmu \hbox {sec}$$ 300 μ sec and to track evolveness over a distance of 100 mm. Our findings show that processing of high-speed videos can enrich, and give detailed insight, to the observations in the shock experiments.

Study on integrated control for supersonic inlet and turbofan engine model

Considering the supersonic inlet model with normal shock position feedback, the integrated control method of inlet and turbofan engine is studied. The integrated model includes the supersonic inlet model and the component level model of engine. Combining the relationship between the normal shock position and the total pressure recovery coefficient, the supersonic inlet and engine model is constructed. On the basis of this model, the normal shock position closed-loop control simulation is carried out, which shows that the normal shock position matching point could be stabilized near the optimal value while restraining the inlet stream disturbance. Furthermore, based on the H∞ control algorithm, an inlet and engine integrated control is designed to control the installation thrust and turbine pressure ratio with fuel, nozzle throat area, and normal shock position as control variables. The simulation results show that the response time of the integrated control is faster than the independent control. The integrated control has stronger ability to restrain the atmospheric disturbance, which could ensure the stable and reliable operation of the propulsion system.

Non-locality of Earth's quasi-parallel bow shock: injection of thermal protons in a hybrid-Vlasov simulation

We study the interaction of solar wind protons with Earth's quasi-parallel bow shock using a hybrid-Vlasov simulation. We employ the global hybrid model Vlasiator to include effects due to bow shock curvature, tenuous upstream populations, and foreshock waves. We investigate the uncertainty of the position of the quasi-parallel bow shock as a function of several plasma properties and find that regions of non-locality or uncertainty of the shock position form and propagate away from the shock nose. Our results support the notion of upstream structures causing the patchwork reconstruction of the quasi-parallel shock front in a non-uniform manner. We propose a novel method for spacecraft data to be used to analyse this quasi-parallel reformation. We combine our hybrid-Vlasov results with test-particle studies and show that proton energization, which is required for injection, takes place throughout a larger shock transition zone. The energization of particles is found regardless of the instantaneous non-locality of the shock front, in agreement with it taking place over a larger region. Distortion of magnetic fields in front of and at the shock is shown to have a significant effect on proton injection. We additionally show that the density of suprathermal reflected particles upstream of the shock may not be a useful metric for the probability of injection at the shock, as foreshock dynamics and particle trapping appear to have a significant effect on energetic-particle accumulation at a given position in space. Our results have implications for statistical and spacecraft studies of the shock injection problem.

Converging shock waves in a Van der Waals gas of variable density

Summary The converging problem of cylindrically or spherically symmetric strong shock wave collapsing at the axis/centre of symmetry, is studied in a non-ideal inhomogeneous gaseous medium. Here, we assume that the undisturbed medium is spatially variable and the density of a gas is decreasing towards the axis/centre according to a power law. In the present work, we have used the perturbation technique to the implosion problem and obtained a global solution that also admits Guderley’s asymptotic solution in a very good agreement which holds only in the vicinity of the axis/centre of implosion. The similarity exponents together with their corresponding amplitudes are determined by expanding the flow parameters in powers of time. We also refined the leading similarity exponents near the axis/centre of convergence. We compared our calculated results with the already existing results and found them in good agreements up to two decimal places. Shock position and flow parameters are analysed graphically with respect to the variation of values of different parameters. It is observed that an increase in the density variation index, adiabatic exponent and Van der Waals excluded volume, causes the time of shock collapse to decrease due to which the shock acceleration gets increased and shock reaches the axis/centre much faster.

Study on Inlet and Engine Integrated Model with Normal Shock Position Feedback

In order to consider the inlet and engine integrated model of supersonic airliner, the dynamic identification and control of inlet normal shock are studied. The research is based on the bleed air flow rate under supersonic conditions. With the two-dimensional CFD model of supersonic inlet, the dynamic and static effects of the bleeding flow rate on the normal shock position were investigated. The transfer function was identified, and simultaneously the paper carried out a comprehensive study of inlet and engine integrated model, which is established based on the inlet shock position model and engine component level model. The relationship between normal shock position and total pressure recovery coefficient has been taken into consideration in this model. Based on the inlet and engine integrated model, the closed-loop control simulation of normal shock position is carried out. The results show that the model could resist the disturbance of the inlet flow and keep the inlet and engine matching operation point stable near the optimal value.

Turbulent Triggers and the Model Quality Influence on Aerodynamic Characteristics of the Laminar Aerofoil in Transonic Flow Regime

The test with a roughness application on the laminar aerofoil has been conducted in the N-3 trisonic wind tunnel of the Institute of Aviation in Warsaw. The main goal of tests was to investigate the influence of the boundary layer transition triggers on a laminar profile aerodynamic characteristic. For baseline configuration, the natural transition was applied. As a local roughness on the upper model surface, the carborundum strips with different heights were applied. These were positioned on the upper model surface in the front of the shock position occurrence. The Mach number during test was equal Ma = 0.7 and Reynolds number was about 2.85·106. Tests have been conducted for different model incidence in range 0°-7°. Current article refers partially to the previous study, where aerofoil model with lower quality of surface had been tested. Investigation results from previous work indicated that some of transition positions improved an aerodynamic characteristic by reducing the drag coefficient value and decreasing shock wave unsteadiness in the transonic regime. However, current article indicates that beneficial effects in respect to the baseline configuration are also strictly dependent on the model quality and turbulent triggers size. Improved surface quality of the laminar aerofoil model affected on aerodynamic characteristics with and without turbulent triggers. Resultant aerodynamic coefficients of all tested cases i.e. drag, lift and lift to drag ratio were compared.

Non-locality of the Earth's quasi-parallel bow shock: injection of thermal protons in a hybrid-Vlasov simulation

We study the interaction of solar wind protons with the Earth's quasi-parallel bow shock using a hybrid-Vlasov simulation. We employ the high-fidelity global hybrid model Vlasiator to include effects due to bow shock curvature, tenuous upstream populations, and foreshock waves. We investigate the local uncertainty of the position of the quasi-parallel bow shock as a function of several plasma properties, and find that for a significant portion of time, the local bow shock position is challenging to define. Our results support the notion of upstream structures causing patchwork reconstruction of the quasi-parallel shock front in a non-uniform manner. We propose a novel method for spacecraft data to be used to analyze this quasi-parallel reformation. We combine our hybrid-Vlasov results with test-particle studies and show that shock non-locality appears to have little direct efficient on particle injection. We show that proton energization, which is required for injection, takes place throughout a larger shock transition zone. Non-local energization of particles is found regardless of the instantaneous non-locality of the shock front. Distortion of magnetic fields in front of and at the shock is shown to have a significant effect on proton injection. We additionally show that the density of suprathermal reflected particles upstream of the shock may not be a useful metric for the probability of injection at the shock, as foreshock dynamics and particle trapping appear to have a greater effect on energetic particle accumulation at a given position in space. Our results have significant implications for statistical and spacecraft studies of the shock injection problem.

COLLISIONLES INTERACTIONS: MAGNETOPAUSE COMMUNICATES WITH BOW SHOCK?

Our analysis of a sunward Poynting flux throughout magnetosheath and foreshock (directly measured byINTERBALL-1, CLUSTER-4 and DOUBLE STAR TC1), for the first time clearly demonstrates, how the resonances in the magnetospheric boundary layers are transmitted back wards the bow shock: the short pulses of the sunward Poynting flux initiate the strongest (>80%!) 3-wave interactions with the incident dynamic pressure. They start in the foreshock, regulate the bow shock position and oscillations, and then another near- magnetopause 3-wave strong interactions assist plasma flow extra deflections and acceleration downstream the magnetopause.