Oblique shock

About: Oblique shock is a research topic. Over the lifetime, 6551 publications have been published within this topic receiving 119823 citations.

Oblique Shock Impinging on a Turbulent Boundary Layer: Low-Frequency Mechanisms

Abstract: The need for better understanding of the low-frequency unsteadiness observed in shock- wave turbulent boundary layer interactions (SBLI) has been driving SBLI research for several decades. We present here a Large-Eddy Simulation (LES) investigation of the in- teraction between an impinging oblique shock and a turbulent boundary layer under the same flow conditions as in the experiments performed at the "Institut Universitaire des Systemes Thermiques Industriels" in Marseille (France). 1,2 Contrary to past LES inves- tigations on SBLI, we have used a new inflow technique which does not introduce any energetically-significant low frequencies into the domain, hence avoiding possible interfer- ence with the SBLI system. We have run the LES over much longer time series than previous computational studies making a Fourier analysis of the low-frequency possible. The broadband and energetic low-frequency component found in the interaction is in ex- cellent agreement with the experimental findings. Furthermore, a linear stability analysis of the mean flow was performed and a stationary unstable global mode was found. The long-run LES data were analyzed and found to coincide with the global mode structure, leading to a possible mechanism for the observed low-frequency motions.

Bow Shock and magnetosheath waves at Mercury

Abstract: Mariner 10 measurements at the Mercury bow shock provide examples where the magnetic field is approximately parallel or perpendicular to the bow shock normal. Upstream of a broad irregular parallel shock, left hand circularly polarized waves are observed which cut off very sharply at approximately 4 Hz. Upstream of a perpendicular shock, right hand circularly polarized waves are observed which persist up to the Nyquist frequency of 12 Ha. Determination of the wave propagation vector as a function of frequency helps conclusively identify the waves as whistler mode waves propagating from the shock. The magnetosheath downstream of the parallel shock is disturbed more than that downstream of the perpendicular shock particularly below 1 Hz. In the latter case regular left hand polarized waves observed slightly above the proton gyrofrequency are identified as ion cyclotron waves with wavelength approximately 300 km which are Doppler shifted up to their observed frequency.

Modeling for Control of a Generic Airbreathing Hypersonic Vehicle

Abstract: The unique airframe-engine configuration of airbreathing hypersonic flight vehicles (AHFV) pose a significant challenge for design of controllers for these vehicles. The Airframe-engine configuration, the wide range of speed and the extreme flight conditions result in significant coupling among various dynamics and modeling uncertainties. There is almost a complete absence of models that adequately include and quantify the unique attributes for this class of vehicles. This paper describes a high-fidelity CFD-based model of a full scale generic airbreathing hypersonic flight vehicle under development at the Multidisciplinary Flight Dynamics and Control Laboratory (MFDCLab, www.calstatela.edu/centers/mfdclab) at California State University, Los Angeles (CSULA). The vehicle (CSULA-GHV), which has an integrated airframe-propulsion system configuration, resembles an actual test vehicle. The vehicle is specifically designed to study the challenges associated with modeling and control of airbreathing hypersonic vehicles and to investigate and quantify the couplings between the aerodynamics, the propulsion system, the structural dynamics, and the control system. The configuration of the vehicle and its dimensions are developed based on 2-D compressible flow theory, and a set of mission requirements broadly accepted for a hypersonic cruise vehicle intended for both space access and military applications. Analytical aerodynamic calculations are conducted assuming a cruising condition of Mach 10 at an altitude of 30 km. The 2-D oblique shock theory is used to predict the shock wave angles, the pressure on the frontal surface, and the Mach number at the engine inlet. The scramjet engine is simply modeled by a 1-D compressible flow with heating. The exit flow is modeled using 2-D expansion wave theory to predict the pressure on the rear surface. The unique aspect of this study is the use of coupled simulations using multi-physic software in conjunction with theory enabling quantification of the couplings which are broadly ignored in models used for control system design. Simulation results developed to date are presented.

Shock acceleration of diffuse ions at the Earth's bow shock: Acceleration efficiency and A/Z enhancement

Abstract: Observations of particle spectra, intensity, and enhancement of alpha particles over protons at diffuse ion events at the quasi-parallel earth bow shock are compared to a Monte Carlo simulation of diffusive shock acceleration. The simulation includes the back reaction of accelerated particles on the shock structure, particle escape at an upstream free escape boundary, and a low energy per nucleon threshold for thermal leakage of downstream, shock-heated particles into the upstream region. The simulation assumes that the same scattering operator that gives rise to shock acceleration can also describe a viscous shock governed by hydrodynamic turbulence. This implies that accelerated ions can be drawn directly from the thermal solar wind with no separate superthermal seed population. Good agreement between the simulation and observations made during nearly radial magnetic field configurations lends support to thermal leakage of downstream, shock-heated ions as the mode of injection for diffusion ion events.

Pre-Stall Behavior of a Transonic Axial Compressor Stage Via Time-Accurate Numerical Simulation

Abstract: CFD calculations using high-performance parallel computing were conducted to simulate the pre-stall flow of a transonic compressor stage, NASA compressor Stage 35. The simulations were run with a full-annulus grid that models the 3D, viscous, unsteady blade row interaction without the need for an artificial inlet distortion to induce stall. The simulation demonstrates the development of the rotating stall from the growth of instabilities. Pressure-rise performance and pressure traces are compared with published experimental data before the study of flow evolution prior to the rotating stall. Spatial FFT analysis of the flow indicates a rotating long-length disturbance of one rotor circumference, which is followed by a spike-type breakdown. The analysis also links the long-length wave disturbance with the initiation of the spike inception. The spike instabilities occur when the trajectory of the tip clearance flow becomes perpendicular to the axial direction. When approaching stall, the passage shock changes from a single oblique shock to a dual-shock, which distorts the perpendicular trajectory of the tip clearance vortex but shows no evidence of flow separation that may contribute to stall.