ON SUBSONIC AND SUBSONIC-SONIC FLOWS IN THE INFINITY LONG NOZZLE WITH GENERAL CONSERVATIVES FORCE

In this article, we study irrotational subsonic and subsonic-sonic flows with gen- eral conservative forces in the infinity long nozzle. For the subsonic case, the varified Bernoulli law leads a modified cut-off system. Because of the local average estimate, conservative forces do not need any decay condition. Afterwards, the subsonic-sonic limit solutions are constructed by taking the extract subsonic solutions as the approximate sequences.

基于SubSonic和Nhibernate框架的在线购书系统设计与实现

为营造客户与销售商之间互动和谐的购物环境,设计了一个基于SubSonic+Nhibernate的ASP.NET架构的在线购书系统。论述了基于.NET技术的开源框架SubSonic和Nhibernate的技术特点,提出了系统的总体架构图,分析了系统的主要实现方法,最后介绍了系统的关键技术。

TWO DIMENSIONAL SUBSONIC AND SUBSONIC-SONIC SPIRAL FLOWS OUTSIDE A POROUS BODY

In this paper,we investigate two dimensional subsonic and subsonic-sonic spiral flows outside a porous body.The existence and uniqueness of the subsonic spiral flow are obtained via variational formulation,which tends to a given radially symmetric subsonic spiral flow at far field.The optimal decay rate at far field is also derived by Kelvin ’s transformation and some elliptic estimates.By extracting spiral subsonic solutions as the approximate sequences,we obtain the spiral subsonic-sonic limit solution by utilizing the compensated compactness.The main ingredients of our analysis are methods of calculus of variations,the theory of second-order quasilinear equations and the compensated compactness framework.

Numerical simulation and analysis of aerodynamic drag on a subsonic train in evacuated tube transportation

The aerodynamic drag on a train running in an evacuated tube varies with tube air pressure, train speed and shape, as well as blockage ratio. This paper uses numerical simulations to study the effects of different factors on the aerodynamic drag of a train running at subsonic speed in an evacuated tube. Firstly, we present the assumption of a steady state, two dimensional, incompressible viscous flow with lubricity wall conditions. Subsequently, based on the Navier-Stokes equation and the k-c turbulent models, we calculate the aerodynamic drag imposed on the column train with a 3-meter diameter running under different pressure and blockage ratio conditions in an evacuated tube transporta- tion （ETT） system. The simulation is performed with FLUENT 6.3 software package. An analyses of the simulation re- sults suggest that the blockage ratio for ETT should be in the range of 0.25-0.7, and the tube internal diameter in the range of 2-4 m, with the feasible vacuum pressure in the range of 1-10 000 Pa for the future subsonic ETT trains.

Bifurcation and dynamic behavior analysis of a rotating cantilever plate in subsonic airflow

Turbo-machineries,as key components,have wide applications in civil,aerospace,and mechanical engineering.By calculating natural frequencies and dynamical deformations,we have explained the rationality of the series form for the aerodynamic force of the blade under the subsonic flow in our earlier studies.In this paper,the subsonic aerodynamic force obtained numerically is applied to the low pressure compressor blade with a low constant rotating speed.The blade is established as a pre-twist and presetting cantilever plate with a rectangular section under combined excitations,including the centrifugal force and the aerodynamic force.In view of the first-order shear deformation theory and von-K′arm′an nonlinear geometric relationship,the nonlinear partial differential dynamical equations for the warping cantilever blade are derived by Hamilton’s principle.The second-order ordinary differential equations are acquired by the Galerkin approach.With consideration of 1:3 internal resonance and 1/2 sub-harmonic resonance,the averaged equation is derived by the asymptotic perturbation methodology.Bifurcation diagrams,phase portraits,waveforms,and power spectrums are numerically obtained to analyze the effects of the first harmonic of the aerodynamic force on nonlinear dynamical responses of the structure.

REVIEW OF THE GREEN＇S FUNCTION METHOD FOR STEADY ＆UNSTEADY，SUBSONIC，TRANSONIC ＆SUPERSONIC AERODYNAMICS AROUND COMPLEX CONFIGURATIONS

A general review of the Green's function method for steady and unsteady,subsonic,transonic and supersonic aerodynamics is outlined.First,the basic theory ofthe present method is briefly introduced.Then the developments of the method and itsapplications to

Study on the subsonic speed flame spraying coating of hydroxyapatite

A new method of preparation of biomaterial composite coating by the techniqueof subsonic thermal spraying was discussed in this paper. Ti_6Al_4V and pure Ti were chosen assubstrate and sublayer material respectively and the working layer was sprayed with biomaterialhydroxyapatite (HAP), forming the composite coating. The experiments of heat shock and tensilestrength showed that the bonding strength between coating and substrate is almost as same as that ofspecimen in which Ni/Al powder was adopted as sublayer. The phases of TiN, TiO_2, and Ti_2O_3 wereformed in the sublayer, which are free of toxic and have no side effects. The powder of workinglayer HAP was decomposed partly during spraying, but it can be solved by later treatment.

AN IMPROVED MEAN SURFACE METHOD FOR SUBSONIC PROPELLER NOISE PREDICTION

An improved mean surtace method (IMSM) for propeller noise predictionis presented, based on solving the Ffowes Williams & Hawking (FW & H) equation intime domain. Numerical calculation results show that the IMSM needs only 50% ofCPU time and memory of subsonic full surface method (SFSM), 50%～ 60% of CPUtime and meinory of old nican surfacc method (OMSM) and 10%～ 13% of CPU timeof transonic collapse spliere method (TCSM) while the calculation accuracy can be as-sured. Thus, the IMSM given in this paper could be a good alternative method forsubsonic propeller noise prediction. especially in preliminary aeroacoustics design of anew propeller.

Stability of Subsonic Jet Flows

An overview of recent experimental results on instability and dynamics of jets at low Reynolds numbers is given. Round and plane, macro and micro jets are under the consideration. Basic features of their evolution affected by initial conditions at the nuzzle outlet and environmental perturbations are demonstrated.

UNIFORM ERROR BOUNDS OF A CONSERVATIVE COMPACT FINITE DIFFERENCE METHOD FOR THE QUANTUM ZAKHAROV SYSTEM IN THE SUBSONIC LIMIT REGIME

In this paper,we consider a uniformly accurate compact finite difference method to solve the quantum Zakharov system(QZS)with a dimensionless parameter 0<ε≤1,which is inversely proportional to the acoustic speed.In the subsonic limit regime,i.e.,when 0<ε?1,the solution of QZS propagates rapidly oscillatory initial layers in time,and this brings significant difficulties in devising numerical algorithm and establishing their error estimates,especially as 0<ε?1.The solvability,the mass and energy conservation laws of the scheme are also discussed.Based on the cut-off technique and energy method,we rigorously analyze two independent error estimates for the well-prepared and ill-prepared initial data,respectively,which are uniform in both time and space forε∈(0,1]and optimal at the fourth order in space.Numerical results are reported to verify the error behavior.

On Subsonic and Subsonic-Sonic Flows with General Conservatives Force in Exterior Domains

In this paper, we study the irrotational subsonic and subsonic-sonic fows with general conservative forces in the exterior domains. The conservative forces indicate the new Bernoulli law naturally. For the subsonic case, we introduce a modified cut-off system depending on the conservative forces which needs the varied Bers skill, and construct the solution by the new variational formula. Moreover, comparing with previous results, our result extends the pressure-density relation to the general case. Afterwards we obtain the subsonic-sonic limit solution by taking the extract subsonic solutions as the approximate sequences.

On the nonexistence of a global nontrivial subsonic solution in a 3D unbounded angular domain

In this paper, under some assumptions on the flow with a low Mach number, we study the nonexistence of a global nontrivial subsonic solution in an unbounded domain Ω which is one part of a 3D ramp. The flow is assumed to be steady, isentropic and irrotational, namely, the movement of the flow is described by the potential equation. By establishing a fundamental a priori estimate on the solution of a second order linear elliptic equation in Ω with Neumann boundary conditions on Ω and Dirichlet boundary value at some point of Ω, we show that there is no global nontrivial subsonic flow with a low Mach number in such a domain Ω.

Variable Clearance Characteristics of High Subsonic Compressor Cascades with Blade Tip Winglets

The gas turbine is the main power equipment for naval ship and special civil ship,while the compressor is one of the core structures of the gas turbine.The existing tip clearance could prevent the compressor blade and casing collision.Therefore,the flow loss in the tip region caused by the tip clearance will degrade the performance of the compressor.To improve the variable clearance characteristics of the high subsonic compressor cascades,the cascades with tip clearances of 1%,2%and 3%chord length are studied through experimental measurements and numerical calculations.The research results prove that the pressure surface tip winglet can cause a significant improvement effect under most working conditions.If the blade tip clearance size is gradually increasing within a reasonable range,the improvement effect becomes more remarkable,and the optimal tip winglet case changes.When tip clearance is 1%chord length,the PTW1.0 case(the width of the pressure surface tip winglet is 1.0 time of the original tip)reduces the flow loss by 3.09%compared with the NTW case(No Tip Winglet).When tip clearance is 2%chord length,the flow loss of PTW1.5 case(the width of the pressure surface tip winglet is 1.5 times of the original tip)is reduced by 3.46%.When tip clearance is 3%chord length,all alternative tip winglets reduce the total pressure loss,and PTW2.0 case(the width of the pressure surface tip winglet is 2.0 times of the original tip)is the best choice,which has a 6.53%degree of improvement.

Subsonic impulsively starting flow at a high angle of attack with shock wave and vortex interaction

Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.

Numerical Investigation of a Centrifugal Compressor with a Pre-Compression Wedge Diffuser under High Subsonic Conditions

As the total pressure ratio of centrifugal compressors increases, the diffuser inlet flow becomes highly subsonic or even supersonic, which causes additional shock loss. The shock loss leads the stage performance to drop greatly. Pre-compression is an efficient method for reducing shock loss and improving the stage performance. To study the effect of wedge diffusers with pre-compression blades on centrifugal compressor performance, wedge diffusers with various pre-compression angles, divergence angles and numbers of blades were designed and investigated via a numerical method. As a result, it is found that the compressor stage achieves high peak efficiency when the pre-compression angle ranges from 2.5° to 5.5° and when the divergence angle ranges from 7° to 9°. As the number of blades increases, the total pressure ratio and adiabatic efficiency of the compressor stage increase slightly, whereas the surge margin of the stage decreases.

Subsonic Euler flows in a divergent nozzle

We characterize a class of physical boundary conditions that guarantee the existence and uniqueness of the subsonic Euler flow in a general finitely long nozzle.More precisely,by prescribing the incoming flow angle and the Bernoulli’s function at the inlet and the end pressure at the exit of the nozzle,we establish an existence and uniqueness theorem for subsonic Euler flows in a 2-D nozzle,which is also required to be adjacent to some special background solutions.Such a result can also be extended to the 3-D asymmetric case.

Compressible Subsonic Potential Flow Past a 2D Given Sharp Angular Unbounded Domain

In this paper, we focus on the two-dimensional subsonic flow problem around an infinite long ramp. The flow is assumed to be steady, isentropic and irrotational, namely, the movement of the flow is described by a second elliptic equation. By the use of a separation variable method, Strum- Liouville theorem and scaling technique, we show that a nontriviM subsonic flow around the infinite long ramp does not exist under some certain assumptions on the potential flow with a low Mach number.

ILES of an array of three subsonic counter-flow jets issuing from a wing leading edge exposed to hypersonic aerodynamic heating

The flow of an active thermal protection system exploiting subsonic counter-flow jets for wing leading edges of hypersonic vehicles is numerically studied on the basis of the three dimensional Navier-Stokes equations.The coolant air issuing from around the stagnation point as an array of three jets spreads over both the upper and the lower sides of the cylinder surface and about 40~60%cooling effectiveness is achieved in the range up to 5 degrees angle of attack despite the occurrence of various three-dimensional fluid-dynamic instabilities.The numerical scheme is second order accurate but simple inclusion of high order polynomial approximation in the reconstruction enables the capturing of finer structure of the flow field.

Feature identification in complex fluid flows by convolutional neural networks

Recent advancements have established machine learning's utility in predicting nonlinear fluid dynamics,with predictive accuracy being a central motivation for employing neural networks.However,the pattern recognition central to the networks function is equally valuable for enhancing our dynamical insight into the complex fluid dynamics.In this paper,a single-layer convolutional neural network(CNN)was trained to recognize three qualitatively different subsonic buffet flows(periodic,quasi-periodic and chaotic)over a high-incidence airfoil,and a near-perfect accuracy was obtained with only a small training dataset.The convolutional kernels and corresponding feature maps,developed by the model with no temporal information provided,identified large-scale coherent structures in agreement with those known to be associated with buffet flows.Sensitivity to hyperparameters including network architecture and convolutional kernel size was also explored.The coherent structures identified by these models enhance our dynamical understanding of subsonic buffet over high-incidence airfoils over a wide range of Reynolds numbers.