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To investigate the in-depth mechanism of turbulence control and drag reduction in a channel flow by using a spatially oscillating Lorentz force, the pseudo-spectral method based on standard Fourier–Chebyshev spectral method is used to solve N-S equations. The characteristics of controlled flow fields and vortex structures are described as well as the mechanism of the flow field control. The result shows that the near-wall flow structure is altered substantially and the turbulence drag decreases sharply under the action of the distributed Lorentz force with proper control parameters, the boundary-layer fluid are reciprocating periodic moving, and the vortex generation is impacted, and that only periodically well-organized streamwise vortexes are observed in the near-wall region of the turbulent channel flow.

The control of vortex-induced vibration (VIV) in shear flow with different distributions of Lorentz force is numerically investigated based on the stream function–vorticity equations in the exponential-polar coordinates exerted on moving cylinder for Re = 150. The cylinder motion equation coupled with the fluid, including the mathematical expressions of the lift force coefficient C l , is derived. The initial and boundary conditions as well as the hydrodynamic forces on the surface of cylinder are also formulated. The Lorentz force applied to suppress the VIV has no relationship with the flow field, and involves two categories, i.e., the field Lorentz force and the wall Lorentz force. With the application of symmetrical Lorentz forces, the symmetric field Lorentz force can amplify the drag, suppress the flow separation, decrease the lift fluctuation, and then suppress the VIV while the wall Lorentz force decreases the drag only. With the application of asymmetrical Lorentz forces, besides the above-mentioned effects, the field Lorentz force can increase additional lift induced by shear flow, whereas the wall Lorentz force can counteract the additional lift, which is dominated on the total effect.

Based on the Fourier–Chebyshev spectral method, the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with direct numerical simulation (DNS) methods for different Reynolds numbers. A formula is derived to express the relation between fluctuating velocities and the friction drag coefficient. With the application of electromagnetic force, the in-depth relations among the fluctuating velocities near the wall, Reynolds stress, and the effect of drag reduction for different Reynolds numbers are discussed. The results indicate that the maximum drag reductions can be obtained with an optimal combination of parameters for each case of different Reynolds numbers. The fluctuating velocities along the streamwise and normal directions are suppressed significantly, while the fluctuating velocity along the spanwise direction is enhanced dramatically due to the spanwise electromagnetic force. However, the values of Reynolds stress depend on the fluctuating velocities along the streamwise and normal directions rather than that along the spanwise direction. Therefore, the significant effect of drag reduction is obtained. Moreover, the maximum drag reduction is weakened due to the decay of control effect for fluctuating velocities as the Reynolds number increases.

The interactions of a spherical flame with an incident shock wave and its reflected shock wave in a confined space were investigated using the three-dimensional reactive Navier-Stokes equations, with emphasis placed on the effect of chemical reactivity of mixture on the flame distortion and detonation initiation after the passage of the reflected shock wave. It is shown that the spatio-temporal characteristics of detonation initiation depend highly on the chemical reactivity of the mixture. When the chemical reactivity enhances, the flame can be severely distorted to form a reactive shock bifurcation structure with detonations initiating at different three-dimensional spatial locations. Moreover, the detonation initiation would occur earlier in a mixture of more enhanced reactivity. The results reveal that the detonations arise from hot spots in the unburned region which are initiated by the shock-detonation-transition mechanism.

Experiments study the Hydrofoil Lift Characteristic under the Action of Lorentz Force. With the streamwise wall-parallel Lorentz force applied on the whole suction side of the hydrofoil, The results show that the flow separation can be suppressed completely and the lift of hydrofoil is increased. The higher the Lorentz force, the larger the lift. It is also demonstrated that the Lorentz force actuator equipped on the front of the hydrofoil is more effective on the lift increase than that equipped on the tail.

A model of multiphase reactive boundary layer flow induced by a shock is presented. Because of the particle reaction in the boundary layer, the source terms are involved in the governing equations. The mass split technique is developed to deal with the problem. Based on the view of mass conservation, the concepts of extrinsic gas density and intrinsic gas density are defined and the mass equation can be split into the extrinsic mass equation and intrinsic mass equation. According to the intrinsic mass equation, a stream function can be introduced so that the similarity transformation can be implemented. By the above split technique, an extrinsic equation is added to the sets of equations, and solving the equations becomes possible. The BOX method is employed to solve the gas phase equations. The particle phase equations are solved by the fourth-order Runge–Kutta method. In order to give a coupling of the gas phase and the solid phase equations, the particle-source-in-cell (PSIC) method is modified to matc...

Self-sustaining detonations along a combustible dust deposit on a bottom wall have been investigated experimentally and theoretically. Experiments were conducted in a square cross-section tube. Three kinds of particles with a mean diameter of 15 μm were used: AL, RDX, and HMX. Sharp-shadow photographs were taken by means of a special optical system and shock-wave velocities were measured by pressure transducers. It has been shown that the steady-state detonation velocity is independent with initial shock wave strengths. An analytical model has been developed to describe the two-dimensional structure of dust-film detonations. A set of equations for the two-phase turbulent-reacting boundary layer considering the particle ingestion and the interphase transfers and a general Chapman-Jouguet condition were derived. The Lees-Dorodnytzin transformation usually applied to the compressible boundary layer has been extended to fit the two-phase reacting case, and the numerical simulations have been performed by applying a Box method and an improved particle source in cell (PSIC) method, which shows that the structure of the boundary layer behind the shock front consists of an induction zone, a reaction zone, and a diffusion zone. Computed and measured results are in reasonable agreement.

The underlying mechanisms of the electromagnetic control of cylinder wake are investigated and discussed. The effects of Lorentz force are found to be composed of two parts, one is its direct action on the cylinder (the wall Lorentz force) and the other is applied to the fluid (called the field Lorentz force) near the cylinder surface. Our results show that the wall Lorentz force can generate thrust and reduce the drag; the field Lorentz force increases the drag. However, the cylinder drag is dominated by the wall Lorentz force. In addition, the field Lorentz force above the upper surface decreases the lift, while the upper wall Lorentz force increases it. The total lift is dominated by the upper wall Lorentz force.

A comprehensive analytical model has been developed to describe the structure of dust detomations which simultaneously computes both the induction and reaction zones. Heterogeneous reactions which occur on the external particle surface and on the surface of potes within the particle are used to model the chemistry. The overall reaction rate in the induction zone is controlled by the heterogenous surface reaction rate while in the reaction zone diffusion of the gas into the pores is found to be the rate limiting step. Conduction heat transfer within the particles, convective heat transfer between the particles and the gas and chemical heat release within the particles are considered in this model to describe the temperature distribution within the particles in both the induction and reaction zones. Thermal runaway is used as the criterion of ignition at the end of the induction zone and the singularity at the C-J plane is used to terminate the reaction zone. Because of a lack of sufficient data, some constants used in this model were chosen to provide the best fit between the theory and experiment. The model made it possible to compute the structure of dust detonations without separate treatment of the induction and reaction zones and was used to determine the effects of particle size on detonation structure and propagation velocity. In those cases in which experimental data was available computed and measured results were in good agreement.