Rayleigh–Taylor and Richtmyer-Meshkov instability induced flow, turbulence, and mixing. II

Origins of the deflagration-to-detonation transition in gas-phase combustion

We consider the effect of preexisting, large-scale, broadband turbulent density fluctuations on propagating hydromagnetic shock waves. We present results from several numerical simulations that solve the two-dimensional magnetohydrodynamic equations. In our simulations, a plasma containing large-scale, low-amplitude density and magnetic field turbulence is forced to flow into a rigid wall, forming a shock wave. We find that the density fluctuations not only distort the shape of the shock front and lead to a turbulent postshock fluid, but they also produce a number of important changes in the postshock magnetic field. The average downstream magnetic field is increased significantly, and large fluctuations in the magnetic vector occur, with the maximum field strength reaching levels such that magnetic stresses are important in the postshock region. The downstream field enhancement can be understood in terms of the stretching and forcing together of the magnetic field entrained within the turbulent fluid of the postshock flow. We suggest that these effects of the density fluctuations on the magnetic field are observed in astrophysical shock waves such as supernova blast waves and the heliospheric termination shock.

https://iopscience.iop.org/article/10.1086/519994/pdf

Magnetic field amplification by shocks in turbulent fluids

Golf clubs according to at least some example aspects of this disclosure may include a golf club head and a shaft configured to engage with the golf club head which includes a grip engaged with the shaft. Further, the golf club may include a monitoring device, which includes a sensor and a transmitter. Additionally, the monitoring device may be configured to determine data related to the characteristics of a golf swing. Further, the monitoring device may be configured to transmit the data related to the characteristics of a golf swing to a remote computer.

Golf clubs and golf club heads

When a shock wave propagates through a medium of nonuniform thermodynamic properties, several processes occur simultaneously that alter the geometry of the shock wave and the thermodynamic state of the medium. These include shock compression and acceleration of the medium, refraction of the shock, and vorticity generation within the medium. The interaction of a shock wave with a cylinder or a sphere (both referred to as a bubble in this review) is the simplest configuration in which all these processes take place and can be studied in detail. Shock acceleration leads to an initial compression and distortion of the bubble, followed by the formation of a vortex pair in the two-dimensional (2D) case and a vortex ring in the 3D case. At later times, for appropriate combinations of the incident shock strength and density contrast between the bubble and ambient materials, secondary vortices are formed, mass is stripped away from the original bubble, and mixing of the bubble and ambient fluids occurs.

Shock-Bubble Interactions

▪ Abstract The Richtmyer-Meshkov instability arises when a shock wave interacts with an interface separating two different fluids. It combines compressible phenomena, such as shock interaction and refraction, with hydrodynamic instability, including nonlinear growth and subsequent transition to turbulence, across a wide range of Mach numbers. This review focuses on the basic physical processes underlying the onset and development of the Richtmyer-Meshkov instability in simple geometries. It examines the principal theoretical results along with their experimental and numerical validation. It also discusses the different experimental approaches and techniques and how they can be used to resolve outstanding issues in this field.

/pdf/the-richtmyer-meshkov-instability-1nx8lydk69.pdf

The richtmyer-meshkov instability

We present a model for the effects of scale, via molecular diffusion phenomena, on the generation and propagation of shock waves. A simple parametrization of the shear stresses and heat flux at the wall leads to the determination of new jump conditions, which show that, for a given wave Mach number at small scales, the resulting particle velocities are lower but the pressures are higher. Also, the model predicts that the flow at small scale is isothermal and that the minimum wave velocity can be subsonic. Experiments with a miniature shock tube using low pressures to simulate the effects of small scale have shown qualitative agreement with the proposed model. In fact, the effects of scale appear even more important than what has been incorporated in the model.

Shock waves at microscales

A ball striking device, such as a golf club head, includes a face having a ball striking surface configured for striking a ball and a body connected to the face and extending rearwardly from the face. The body has an impact-influencing structure in the form of a channel positioned on at least one surface of the body. A majority of a force generated by impact with a ball is absorbed by the impact-influencing structure, and a majority of a response force generated by the head upon impact with the ball is generated by the impact-influencing structure. The face may have increased stiffness as compared to existing faces, and may include a stiffening structure to create the increased stiffness, such as a porous or cellular stiffening structure.

Golf club heads or other ball striking devices having distributed impact response

An engine for providing rotary power about an output shaft with a high power-to-weight ratio includes a plurality of flow guiding blades mounted on the inner surface of an annular thruster base. The flow guiding blades cooperate with the peripheral surface of a rotor for forming a plurality of ramjet-like thrusters. The configuration of the flow guiding blades allows for optimization of the number of thrusters. The centrifugal forces generated by the rotating components is compensated by an annular reinforcement wall made with high strength materials allowing for downsizing of the rotor and associated components.

Rotary ramjet engine

A one-dimensional model for the numerical simulation of transport effects in small-scale, i.e., low Reynolds number, shock tubes is presented. The conservation equations have been integrated in the lateral directions and three-dimensional effects have been introduced as carefully controlled sources of mass, momentum and energy, into the axial conservation equations. The unsteady flow of gas behind the shock wave is reduced to a quasi-steady flow by choosing a coordinate system attached to the shock. The boundary layer problem is thereby reduced to a laminar solution, similar to the Blasius solution, with the exception that the wall velocity can be nonzero. The resulting one-dimensional equations are then solved numerically using a two-step Lax-Wendroff/ MacCormack scheme with flux correction transport. For validation purposes, comparisons are performed against previously published shock structure and low Reynolds number shock tube experiments; good agreement is observed. The model has been used to predict the performance of a 10µm shock tube and the result of this simulation shows the possibility of shock wave disappearance at lower pressure ratios for a micro-scale shock tube.

Martin Brouillette

Papers

The richtmyer-meshkov instability

Shock waves at microscales

Golf club heads or other ball striking devices having distributed impact response

Rotary ramjet engine

One-dimensional model for microscale shock tube flow