矢量控制技术在风洞动力系统中的应用

介绍了无速度传感器矢量控制技术的基本原理,通过对HY 750开口回流低速风洞的实验数据分析,从具体精度指标上对风洞动力系统应用矢量控制的效果进行了评估。结果表明:矢量控制技术在HY 750风洞动力系统中的应用是成功的,能够有效提高动压稳定性,改善流场品质。

EFFECT OF AXIAL SPACING ON COMPRESSOR STABILITY

Experimental studies are carried out at a low speed axial compressor with five different rotor/stator gaps. Analysis of the effect of axial spacing of two successive blade rows on the measured mean flow coefficient at stall inception and on the flow range of compressor under multi-cell rotating stall operating conditions proves that the stator can suppress the flow disturbance in the compressor and strengthen the stability of the compressor. Experimental data show that the stall flow coefficient decreases by reducing the axial spacing of successive blade rows. Moreover, by reducing the axial spacing, the stall pattern transition pace from multi-cell stall to single-cell stall can be shifted. And the compressor directly slips into single-cell stall at 21.0% CR axial spacing. By analyzing the pressure fluctuation closed to the surge line, it can be known that there exists an eigenfrequency where the amplitude of the oscillating pressure suddenly and dramatically increases as the compressor runs close to the surge line and this pressure disturbance is relevant to the compressor instability.

Active Vibration Control and Stability Analysis of Cantilever Plate

Active vibration control and stability analysis of cantilever plate are discussed. Based on the analysis of characteristic equation of the closed loop control system, it is shown that such an active control may increase damping properties of the system, meanwhile it may result in instability of the system. It is stable when the feedback only occurs between the collocated sensors and actuators, but it may be unstable when there exists the feedback between sensors and actuators, which mainly depends on the property of the gain matrix of feedback. If the gain matrix is symmetric and definitely positive, the system is stable.

Three-Dimensional Lattice Boltzmann Model for High-Speed Compressible Flows

A highly efficient three-dimensional （31）） Lattice Boltzmann （LB） model for high-speed compressible flows is proposed. This model is developed from the original one by Kataoka and Tsutahara [Phys. Rev. E 69 （2004） 056702]. The convection term is discretized by the Non-oscillatory, containing No free parameters and Dissipative （NND） scheme, which effectively damps oscillations at discontinuities. To be more consistent with the kinetic theory of viscosity and to further improve the numerical stability, an additional dissipation term is introduced. Model parameters are chosen in such a way that the von Neumann stability criterion is satisfied. The new model is validated by well-known benchmarks, （i） Riemann problems, including the problem with Lax shock tube and a newly designed shock tube problem with high Mach number; （ii） reaction of shock wave on droplet or bubble. Good agreements are obtained between LB results and exact ones or previously reported solutions. The model is capable of simulating flows from subsonic to supersonic and capturing jumps resulted from shock waves.

Analytical solution for slope instability assessment considering impact of confined aquifer

An analytical approach was presented for estimating the factor of safety(FS) for slope failure, with consideration of the impact of a confined aquifer. An upward-moving wetting front from the confined water was assumed and the pore water pressure distribution was then estimated and used to obtain the analytical expression of FS. Then, the validation of the theoretical analysis was applied based on an actual case in Hong Kong. It is shown that the presence of a confined aquifer leads to a lower FS value, and the impact rate of hydrostatic pressure on FS increases as the confined water pressure increases, approaching to a maximum value determined by the ratio of water density to saturated soil density. It is also presented that the contribution of hydrostatic pressure and hydrodynamic pressure to the slope stability vary with the confined aquifer pressure.

SELECTION OF HORIZONTAL DISTANCE X BETWEEN ROADWAY AND THE EDGE OF ITS UPPER PILLAR

The horizontal distance X between roadway and the edge of its upper pillar is considered as an important parameter for layout of roadway in floor strata or in the adjacent coal seam. Based on the research achievements of rockstrata pressure, this paper illustrates the quantitative relationship among the mining situation of upper searn, the rockstrata properties around roadway, the vertital distanee Z (between roadway and its upper pillar), and the horizontai distance X (between roadway and the edge of its upper pillar), and provides a main basiS for the selection of value X and the relative location between roadway and its upper seam.

Slide stability of hydraulic structures on subbed soil

The study on slide stability of hydraulic structures on subbed soil was made. Using the slide test results of dragged concreting base plates on subbed soil pits, the decreased value of bearing capacity on slide after re- bound and repression influence of subbed soil was determined, and the envelope of ultimate slide shear resistance was also quantitatively determined. Due to the lack of similar mechanisms of slide stability on subbed soil and base plate of hydraulic structures, different safety coefficients for the slide stability were adopted. It was suggested to use the maximum compressive stress O＇m~ of eccentric load to predict structure displacement, slide and creepy slippage of subbed soil, to determine the sliding creepy contour and limit the maximum load on subbed soil. Two hydraulic structures that had been put into operation were reviewed by this method, and the results accorded with the real conditions.

Inherited disturbances of phenylalanine metabolic kinetics in essential hypert ension

Objective To clarify whether the disturbances in metabolic kinetics of the essential aminoacid, phenylalanine (phe), are implicated in the genetic pathogenesis of essential hypertension (EH).Methods 1. L-(2, 3D3)-leucine, L-(2, 3D3)-isoleucine, L-15N-lysine, L-(2, 3D3)-valine and L-(2, 3D3)-phe were used for simultaneously studying comparative metabolic kinetics using stable isotope tracer methods with a GC-MS system. Study groups were the offspring with both parents suffering EH (n=10, FH+), 2 or more than 2 parents and grand-parents with EH and stroke (n=12, FS+) and those without genetic predisposition of EH and stroke (n=12, F) groups. 2. By comparing the radioactive counts of ［3H］-phe, and their weight transformation in blood after 1.5?Ci/kg i.v. administration at defined intervals and in tissues obtained after being sacrified among spontaneously hypertensive rats (SHR), 2 kidney-1 clip hypertensive rats (2K1C) and their normotensive controls (WKY). 3. The time transport and concentration transport of ［3H］-L-phe in cpm between the cultured vascular smooth muscle cell of 5th generation in SHR and WKY were compared.Results A single and unique disturbance of metabolic kinetics in phe were found in FH+, FS+ and SHR. The plasma pool or apparent volume of distribution was enlarged, and the turnover rate constants between plasma and cell tended to show a decrease. The pharmacokinetics of phe in 2K1C was not changed. Only phe content in heart and aorta, the vital organs for predicting BP, were higher in SHR than in WKY tissues studied. Both the time and concentration transport were higher in SHR, e.g., an increment in the net-uptake of L-phe by vascular tissue.Conclusion A unique aberrant of metabolic kinetics of phe might be implicated in the inherited pathogenesis of EH and stroke both from clinical and animal studies.

Experimental investigation on flame stabilization of a kerosene-fueled scramjet combustor with pilot hydrogen

Flame stabilization in a kerosene-fueled scramjet combustor was investigated experimentally through Schlieren,flame luminosity,and wall pressure measurement,aiming to obtain better insight into combustion characteristics.Experiments were conducted in a direct-connected supersonic combustion facility with inflow conditions of Mach number 2.0,stagnation pressure 0.82 MPa,and temperature 950 K,simulating the flight condition of Mach number 4.0.Results revealed that kerosene was able to be ignited when the equivalence ratio of pilot hydrogen reached 0.080,but was unsuccessful when the equivalence ratio was 0.040.Once ignited,the intense combustion induced high back pressure forcing the flame to spread into the isolator.The pilot flame invariably appeared in the cavity shear layer and attached to the cavity ramp under different equivalence ratios of pilot hydrogen.With the mass flux of pilot hydrogen increased,the kerosene flame located near the cavity ramp was asymmetrical and unstable since it propagated upstream repeatedly.Therefore,the kerosene could be ignited by a suitable equivalence ratio of continuous pilot hydrogen,potentially accompanied with unstable combustion.

Global existence and stability of a stationary Mach reflection

We prove the global existence and stability of a wave structure containing a stationary Mach con- figuration, which occurs when an incident shock front hits a wall with a large incident angle. Our result shows that tile data of the upstream flow and the pressure at downstream part jointly determine the whole flow, as well a the wave structure. Particularly, we show that the height of the Mach stem depends not only on the data of upstream flow, but also on the pressure at downstream flow. The flow with the assigned wave structure is governed by a free boundary value problem for the Euler system. In the problem the location of the triple point, the shock fronts and the contact discontinuity are all unknown, they are finally determined together with the solution.

Analysis of the secondary instability of the incompressible flows over a swept wing

The crossflow instability of a three-dimensional (3-D) boundary layer is an important factor which affects the transition over a swept-wing.In this report,the primary instability of the incompressible flow over a swept wing is investigated by solving nonlinear parabolized stability equations (NPSE).The Floquet theory is applied to study the dependence of the secondary and high-frequency instabilities on curvature,Reynolds number and angle of swept (AOS).The computational results show that the curvature in the present case has no significant effect on the secondary instabilities.It is generally believed that the secondary instability growth rate increases with the magnitude of the nonlinear mode of crossflow vortex.But,at a certain state,when the Reynolds number is 3.2 million,we find that the secondary instability growth rate becomes smaller even when the magnitude of the nonlinear mode of the crossflow vortex is larger.The effect of the angle of swept at 35,45 and 55 degrees,respectively,is also studied in the framework of the secondary linear stability theory.Larger angles of swept tend to decrease the spanwise spacing of the crossflow vortices,which correspondingly helps the stimulation of 'z' mode.

Internal Flow Simulation of High-Performance Solid Rockets using a k-ω Turbulence Model

For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ω turbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.

Dynamic analysis on pressure fluctuation in vaneless region of a pump turbine

As the pump turbine tends to be operated with high head and high rotational speed, the study of stability problems becomes more important. The pump turbine usually works at operating conditions where the guide vanes experience strong vibrations. However, most traditional studies were carried out based on constant GVO(guide vane opening) simulations. In this work, dynamic analysis on pressure fluctuation in the vaneless region of a pump turbine model was conducted using a dynamic mesh method in turbine mode. 3D unsteady simulations were conducted where GVO was closed and opened by 1° from the initial 18°. Detailed time domain and frequency domain characteristics on pressure fluctuation in the vaneless region under different guide vane rotational states compared with constant GVO simulations were investigated. Results show that, during the guide vanes oscillating process, the low and intermediate frequency components in the vaneless region are significantly different. The amplitudes of pressure fluctuation are higher than those with constant GVO simulations, which agree better with the experimental data. In addition, the pressure fluctuation increases when GVO is opened, and vice versa. It can be concluded that pressure fluctuation in the vaneless region is strongly influenced by the oscillating of the guide vanes.

Dynamical System Analysis of Unsteady Phenomena inCentrifugal Compressor

Surge and rotating stall occurring in a centrifugal compressor system are investigated by using a phaseportrait reconstruction method. From experimentally measured time series of data, the method clari-fied the cyclic behavior of surge. For rotating stall, there still remain problems in the phase portraitdue to the chaotic behavior. However, the results obtained by the present method are able to providenew insights to the modelings for surge and rotating stall. Surge and rotating stall occurring in acentrifugal compressor system are investigated by using a phase portrait reconstruction method. Fromexperimentally measured time series of data, the method clarified the cyclic behavior of surge. Forrotating stall, there still remain problems in the phase portrait due to the chaotic behavior. However,the results obtained by the present method are able to provide new insights to the modelings for surgeand rotating stall.

On the Rayleigh-Taylor Instability for Two Uniform Viscous Incompressible Flows

The authors study the Rayleigh-Taylor instability for two incompressible immiscible fluids with or without surface tension, evolving with a free interface in the presence of a uniform gravitational field in Eulerian coordinates. To deal with the free surface, instead of using the transformation to Lagrangian coordinates, the perturbed equations in Eulerian coordinates are transformed to an integral form and the two-fluid flow is formulated as a single-fluid flow in a fixed domain, thus offering an alternative approach to deal with the jump conditions at the free interface. First, the linearized problem around the steady state which describes a denser immiscible fluid lying above a light one with a free interface separating the two fluids, both fluids being in(unstable) equilibrium is analyzed. By a general method of studying a family of modes, the smooth(when restricted to each fluid domain) solutions to the linearized problem that grow exponentially fast in time in Sobolev spaces are constructed, thus leading to a global instability result for the linearized problem.Then, by using these pathological solutions, the global instability for the corresponding nonlinear problem in an appropriate sense is demonstrated.

Characteristic analysis of hydraulic hybrid vehicle based on limit cycle

The theory of limit cycles was applied to hydraulic hybrid vehicle (HHV) to analyze the dynamic characteristics of the system. The exact mathematical models based on configuration diagram of HHV were built to study on equilibrium points, nonexistence of limit cycle and stability of equilibrium points. The analysis showed that if the Young's modulus of fluid is neglected, the equilibrium points of the system will be distributed on both sides of the initial function. In addition, there is a unique equilibrium point according to the practical signification of the system parameters. The nonexistence analysis showed that there is no limit cycle for the system, no matter how the viscosity coefficient B changes. The stability analysis of equilibrium points showed that the system is asymptotically stable about the equilibrium point at B≥0 and the equilibrium point is the center point of the system at B=0. Finally, the phase diagrams of global topological structure of HHV system were entirely described according to qualitative analysis of the singular points at infinity.

An Iterative Stabilized Scheme for Unsteady Incompressible Viscous Flow

An efficient iterative algorithm is presented for the numerical solution of viscous incompressible Navier-Stokes equations based on Taylor-Galerkin like split and pressure correction method in this paper. Taylor-Hood element is introduced to overcome the numerical difficulties arising from the fluid incompressibility. In order to confirm the properties of the algorithm, the numerical simulation on plane Poisseuille flow problem and lid- driven cavity flow problem with different Reynolds numbers is presented. The numerical results indicate that the proposed iterative version can be effectively applied to the simulation of viscous incompressible flows. Moreover, the proposed iterative version has a better overall performance in maximum time step size allowed, under comparable convergence rate, stability and accuracy, than other tested versions in numerical solutions of the plane PoisseuiUe flow with different Reynolds numbers ranging from low to high viscosities.