Showing papers on "Oblique shock published in 2021"

Experimental Study of Swept Impinging Oblique Shock/Boundary-Layer Interactions

Abstract: An experimental investigation has been conducted on swept impinging oblique shock/boundary-layer interactions at a nominal Mach number of 2.28 with a fully turbulent incoming boundary layer (Reθ=55...

Particle acceleration and non-thermal emission in colliding-wind binary systems

Abstract: We present a model for the creation of non-thermal particles via diffusive shock acceleration in a colliding-wind binary. Our model accounts for the oblique nature of the global shocks bounding the wind-wind collision region and the finite velocity of the scattering centres to the gas. It also includes magnetic field amplification by the cosmic ray induced streaming instability and the dynamical back reaction of the amplified field. We assume that the injection of the ions and electrons is independent of the shock obliquity and that the scattering centres move relative to the fluid at the Alfven velocity (resulting in steeper non-thermal particle distributions). We find that the Mach number, Alfvenic Mach number, and transverse field strength vary strongly along and between the shocks, resulting in significant and non-linear variations in the particle acceleration efficiency and shock nature (turbulent vs. non-turbulent). We find much reduced compression ratios at the oblique shocks in most of our models compared to our earlier work, though total gas compression ratios that exceed 20 can still be obtained in certain situations. We also investigate the dependence of the non-thermal emission on the stellar separation and determine when emission from secondary electrons becomes important. We finish by applying our model to WR 146, one of the brightest colliding wind binaries in the radio band. We are able to match the observed radio emission and find that roughly 30 per cent of the wind power at the shocks is channelled into non-thermal particles.

Phase space transport in the interaction between shocks and plasma turbulence

Abstract: The interaction of collisionless shocks with fully developed plasma turbulence is numerically investigated. Hybrid kinetic simulations, where a turbulent jet is slammed against an oblique shock, are employed to address the role of upstream turbulence on plasma transport. A technique, using coarse graining of the Vlasov equation, is proposed, showing that the particle transport strongly depends on upstream turbulence properties, such as strength and coherency. These results might be relevant for the understanding of acceleration and heating processes in space plasmas.

Rotating Detonation Wave Direction and the Influence of Nozzle Guide Vane Inclination

Abstract: This study describes a rotating detonation combustor (RDC) equipped with a set of nozzle guide vanes (NGVs) of variable number and inclination angle. Different instrumented guide vanes were manufac...

The dynamics of a non-premixed rotating detonation engine from time-resolved temperature measurements

Abstract: The structure and dynamics of a hydrogen-air rotating detonation engine (RDE) are described based on 100-kHz laser absorption spectroscopy measurements of water temperature at four simultaneous locations within the detonation channel. The analysis focuses on the evolution of the flowfield over a 200 ms period for three separate air mass flow rate cases. Two-dimensional unwrapped visualizations of the temperatures show a flowfield structure containing regions with the detonation front, combustion products, oblique shock, and refilling reactants, qualitatively agreeing with previous simulations and experiments. A major conclusion is that water from the combustion products is measured throughout all space and time in the RDE, including near the injector, implying the presence of performance loss processes such as burning upstream of the detonation wave or the back recirculation of combustion products with fresh fuel–air. By analyzing the elevated temperatures of the reactants during the refill process, one estimation for the mass fraction of combustion products in the reactants is as high as 20–30% on average. This product mass fraction is found to be inversely proportional to the bulk air mass flow rate and decreases as time progresses. This indicates these non-ideal processes are more significant closer to RDE ignition for poorer performing operating conditions. For the largest air mass flow case, water temperatures near the nominally cold plenum conditions likely corroborate the presence of a recirculation region on the RDE inner body. Analysis of inter- and intra-cycle temperature dynamics further support non-ideal processes occurring behind the detonation wave and during the refill process. As a whole, the data indicates that the RDE performance is better as time progresses away from ignition or for higher air mass flow rates. These data are also important for comparison with numerical models.

Micro-Ramp Control for Shock Train Structure and Oscillation

Abstract: Micro-ramps for shock train control were investigated experimentally in a Mach 1.85 supersonic isolator flow using three device heights. A mechanical flap was mounted downstream and linearly choked...

Strange wave formation and detonation onset in narrow channels

Abstract: Experiments are conducted in a smooth 10 × 10 mm square cross-section, 1-m long channel, closed at the ignition end and open at the other end. Simultaneous two-direction schlieren visualization is used to investigate the three-dimensional dynamics of transition to detonation for a stoichiometric H2–O2 mixture. Results show the existence of two distinct structures before detonation onset: (i) asymmetric, composed of an oblique shock trailed by a flame, that runs preferentially along the wall, and seems to get ignited inside the boundary layer developed by the precursor shock; (ii) symmetric, referred to as strange wave in literature, propagating roughly at the speed of sound in combustion products. The combined effect of shock induced preheating and viscous heating near walls seem to be responsible for the formation of the complex flame-shock interactions observed. A simple thermodynamic analysis applied to the strange wave using the experimentally measured wave speed yield a pressure ratio of ~ 15 during its steady propagation; furthermore, an estimate of the total energy losses required to thermodynamically realize such propagation regime revealed that approximately half of the energy released by combustion should be dissipated (i.e. momentum and heat losses). Finally, simultaneous two-direction optical access allows to map the exact location of detonation onset, showing that 78 % of cases exploded in corners, highlighting the role of corner flows and boundary layers in transition to detonation at this scale.

Evaluating Shock-Tube Informed Biases for Shock-Layer Radiative Heating Simulations

Abstract: A methodology for directly informing flight vehicle radiative heating simulations based on shock-tube measurements is developed. The differences between these shock-tube informed (STI) radiative he...

Velocity and temperature fluctuations in a high-speed shock–turbulence interaction

Abstract: Shock-wave–turbulence interactions are important problems with ubiquitous applications in high-speed flight and propulsion. The complex physical processes during the interaction are not fully understood, where contemporary high-fidelity numerical simulations have brought into question classical linear interaction analyses (LIA). The differences are most pronounced at high Mach number (2). The objective of this study was to experimentally examine the role of a normal shock wave on the modification of velocity and temperature fluctuations to provide an empirical basis to help close the emerging knowledge gap between classical and contemporary theories. The experiments were performed in a pulsed wind tunnel facility at Mach 4.4. The free-stream disturbances provided the test bed for the study. A Mach-stem normal shock was generated through the interaction of two mirrored oblique shock waves. Molecular tagging velocimetry and two-line planar laser induced fluorescence thermometry were conducted upstream and downstream of the normal shock wave and the fluctuating intensities were compared. The measured axial velocity fluctuation amplification factor was nominally 1.1–1.2 over the Reynolds number range tested. The measured values were more consistent with LIA than contemporary theory. The temperature fluctuation amplification factor was found to vary between 3.0 and 4.5, where the lowest Reynolds number condition saw the highest free-stream disturbances and largest amplification. The free-stream fluctuations were primarily in the entropic mode, which is believed to lead to the significantly higher amplification of the entropic mode reported in these measurements.