Study on the breakup lengths of free round liquid jets

An experi ment was conducted to measure the breakup lengths of water jets with a high-speed video camera for Weber numbers from0 to about 1.1×103.The initial jet diameters are changed from0.3 mmto 1. 0 mm.The results indicate that at lowjet velocity the breakup lengths of the jets are increased linearly from 0 to a maxi mumvalue.At the Weber number about 20 the breakup length of the jet reaches its maxi mum value for different initial jet diameter.Acomputation based onthe dispersion equationis conducted to study the relationship between the growth rate of the jet surface wave and the maxi mumbreakup length.The computations showthat the maxi mumgrowth rate for the axisymmetric surface wave has a turning point at Weber number about 20,and that agrees well with the experi ments.

Extremum response surface method of reliability analysis on two-link flexible robot manipulator

In order to present a new method for analyzing the reliability of a two-link flexible robot manipulator,Lagrange dynamics differential equations of the two-link flexible robot manipulator were established by using the integrated modal method and the multi-body system dynamics method.By using the Monte Carlo method,the random sample values of the dynamic parameters were obtained and Lagrange dynamics differential equations were solved for each random sample value which revealed their displacement,speed and acceleration.On this basis,dynamic stresses and deformations were obtained.By taking the maximum values of the stresses and the deformations as output responses and the random sample values of dynamic parameters as input quantities,extremum response surface functions were established.A number of random samples were then obtained by using the Monte Carlo method and then the reliability was analyzed by using the extremum response surface method.The results show that the extremum response surface method is an efficient and fast reliability analysis method with high-accuracy for the two-link flexible robot manipulator.

Numerical Investigation of Electrohydrodynamic (EHD) Flow Control in an S-Shaped Duct

An electrohydrodynamic （EHD） method, which is based on glow discharge plasma, is presented for flow control in an S-shaped duct. The research subject is an expanding channel with a constant width and a rectangular cross section. An equivalent divergence angle and basic function are introduced to build the three-dimensional model. Subsequently, the plasma physical models are simplified as the effects of electrical body force and work （done by the force） on the fluid near the wall. With the aid of FLUENT software, the source terms of momentum and energy are added to the Navier-Stokes equation. Finally, the original performance of three models （A, B and C） is studied, in which model A demonstrates better performance. Then EHD control based on model A is discussed. The results show that the EHD method is an effective way of reducing flow loss and improving uniformity at the duct exit. The innovation in this study is the assessment of the EHD control effect on the flow in an S-shaped duct. Both the parametric modeling of the S-shaped duct and the simplified models of plasma provide valuable information for future research on aircraft inlet ducts.

Study of modeling unsteady blade row interaction in a transonic compressor stage part 1:code development and deterministic correlation analysis

The average-passage equation system （APES） provides a rigorous mathematical framework for account- ing for the unsteady blade row interaction through multi- stage compressors in steady state environment by introduc- ing deterministic correlations （DC） that need to be modeled to close the equation system. The primary purpose of this study is to provide insight into the DC characteristics and the influence of DC on the time-averaged flow field of the APES. In Part 1 of this two-part paper, firstly a 3D viscous unsteady and time-averaging flow CFD solver is developed to investi- gate the APES technique. Then steady and unsteady simu- lations are conducted in a transonic compressor stage. The results from both simulations are compared to highlight the significance of the unsteady interactions. Furthermore, the distribution characteristics of DC are studied and the DC at the rotor/stator interface are compared with their spatial cor- relations （SC）. Lastly, steady and time-averaging （employing APES with DC） simulations for the downstream stator alone are conducted employing DC derived from the unsteady re- suits. The results from steady and time-averaging simula- tions are compared with the time-averaged unsteady results. The comparisons demonstrate that the simulation employing APES with DC can reproduce the time-averaged field and the 3D viscous time-averaging flow solver is validated.

Numerical design optimization of compressor blade based on ADOP

An aerodynamic design optimization platform(ADOP) has been developed.The numerical optimization method is based on genetic algorithm(GA),Pareto ranking and fitness sharing technique.The platform was used for design optimization of the stator of an advanced transonic stage to seek high adiabatic efficiency.The compressor stage efficiency is increased by 0.502% at optimal point and the stall margin is enlarged by nearly 1.0% at design rotating speed.The flow fields of the transonic stage were simulated with FINE/Turbo software package.The optimization result indicates that the optimization platform is effective in 3D numerical design optimization problems.

Study of modeling unsteady blade row interaction in a transonic compressor stage part 2:influence of deterministic correlations on time-averaged flow prediction

The average-passage equation system （APES） provides a rigorous mathematical framework for account- ing for the unsteady blade row interaction through multistage compressors in steady state environment by introducing de- terministic correlations （DC） that need to be modeled to close the equation system. The primary purpose of this study was to provide insight into the DC characteristics and the in- fluence of DC on the time-averaged flow field of the APES. In Part 2 of this two-part paper, the influence of DC on the time-averaged flow field was systematically studied; Several time-averaging computations boundary conditions and DC were conducted with various for the downstream stator in a transonic compressor stage, by employing the CFD solver developed in Part 1 of this two-part paper. These results were compared with the time-averaged unsteady flow field and the steady one. The study indicat;d that the circumferential- averaged DC can take into account major part of the unsteady effects on spanwise redistribution of flow fields in compres- sors. Furthermore, it demonstrated that both deterministic stresses and deterministic enthalpy fluxes are necessary to reproduce the time-averaged flow field.

Heat transport mechanisms of low Mach number turbulent channel flow with spanwise wall oscillation

Large eddy simulation （LES） of low Mach num- ber compressible turbulent channel flow with spanwise wall oscillation （SWO） is carried out. The flow field is analyzed with emphases laid on the heat transport as well as its rela- tion with momentum transport. When turbulent coherent structures are suppressed by SWO, the turbulent transports are significantly changed, however the momentum and heat transports change in the same manner, which gives the evi- dence of inherently consistent transport mechanisms between momentum and heat in turbulent boundary layers. The Reynolds analogies of all the flow cases are quite good, which confirms again the fact that the transport mechanisms of momentum and heat are consistent, which gives theoreti- cal support for controlling the wall heat flux control by using the drag reducing techniques.

Numerical Investigation of Plasma Active Flow Control

Based on the theory of EHD （electronhydrodynamic）, a simplified volume force model is applied to simulation to analyze the traits of plasma flow control in flow field, in which the cold plasma is generated by a DBD （dielectric-barrier-discharge） actuator. With the para- electric action of volume force in electric field, acceleration characteristics of the plasma flow are investigated for different excitation intensities of RF （radio frequency） power for the actuator. Furthermore, the plasma acceleration leads to an asymmetric distribution of flow field, and hence induces the deflection of jet plume, then results in a significant deflection angle of 6.26° thrustvectoring effect. It appears that the plasma flow control technology is a new tentative method for the thrust-vectoring control of a space vehicle.

DEVELOPMENT OF HYBRID RANS / LES CODE AND ITS VALIDATION

A computational code based on the hybrid RANS-LES approach is developed.The hybrid approach combines the delayed detached-eddy simulation ( DDES ) with an improved RANS-LES hybrid model aiming at wall modeling in LES ( WMLES ) .In the code , the convective flux is solved using the fourth-order skew-symmetric scheme so as to diminish the negative effect of numerical dissipation.The Spalart-Allmaras ( S-A ) model is applied as a subgrid scale ( SGS ) model.To validate the developed code , homogeneous isotropic turbulence and turbulent channel flow are simulated and the results are compared with experimental data and DNS results.The results of the isotropic turbulence show that the fourth-order skew-symmetric scheme is adequate enough and the model works well coupling with the convective scheme.The results of the turbulent channel flow agree well with the DNS data , the predicted velocity profiles at Reynolds number from 178to 2 700match well with the Reichardt′s law , and the organized vortical structures are well captured.

Effect of an adverse pressure gradient on the streamwise Reynolds stress profile maxima in a turbulent boundary layer

It is widely accepted that in a turbulent boundary layer （TBL） with adverse pressure gradient （APG） an outer peak usually appears in the profile of streamwise Reynolds stress. However, the effect of APG on this outer peak is not clearly understood. In this paper, the effect of APG is analysed using the numerical and experimental results in the literature. Because the effect of upstream flow is inherent in the TBL, we first analyse this effect in TBLs with zero pressure gradient on flat plates. Under the individual effect of upstream flow, an outer peak already appears in the profile of streamwise Reynolds stress when the TBL continues developing in the streamwise direction. The APG accelerates the appearance of the outer peak, instead of being a trigger.

Evaluation of properties and thermal stress field for thermal barrier coatings

In order to get thermal stress field of the hot section with thermal barrier coating (TBCs), the thermal conductivity and elastic modulus of top-coat are the physical key properties. The porosity of top-coat was tested and evaluated under different high temperatures. The relationship between the microstructure (porosity of top-coat) and properties of TBCs were analyzed to predict the thermal properties of ceramic top-coat, such as thermal conductivity and elastic modulus. The temperature and stress field of the vane with TBCs were simulated using two sets of thermal conductivity data and elastic modulus, which are from literatures and this work, respectively. The results show that the temperature and stress distributions change with thermal conductivity and elastic modulus. The differences of maximum temperatures and stress are 6.5% and 8.0%, respectively.

In-situ measurement of elastic modulus for ceramic top-coat at high temperature

The ceramic thermal barrier coatings (TBCs) play an increasingly important in advanced gas turbine engines because of their ability to further increase the engine operating temperature and reduce the cooling, thus help achieve future engine low emission, high efficiency and improve the reliability goals. Currently, there are two different processes such as the plasma spraying (PS) and the electron beam-physical vapor deposition (EB-PVD) techniques. The PS coating was selected to test the elastic modulus. Using the nanoindentation and resonant frequency method, the mechanical properties of ceramic top-coat were measured in-situ. According to the theory of the resonant frequency and composite beam, the testing system was set up including the hardware and software. The results show that the accurate characterization of the elastic properties of TBCs is important for stress-strain analysis and failure prediction. The TBCs systems are multi-layer material system. It is difficult to measure the elastic modulus of top-coat by tensile method. The testing data is scatter by nanoindentation method because of the microstructure of the ceramic top-coat. The elastic modulus of the top-coat between 20?1 150 ℃ is obtained. The elastic modulus is from 2 to 70 GPa at room temperature. The elastic modulus changes from 62.5 GPa to 18.6 GPa when the temperature increases from 20 ℃ to 1 150 ℃.

Numerical analysis and optimization of the inlet stage of a multi-stage high pressure compressor

An opti mization process is used to redesign blades of a high-pressure compressor.An artificial neural network (ANN) method is coupled to Navier-Stokes solvers and is applied to three different redesigns.A newrotor blade of a transonic compressor is designed by modifying thick,stacking line andinlet angle using a 3Dapproach,with a significant efficiencyi mprovement at the design point.The off-design behavior of this new compressor is also checked afterwards,which shows that the whole performance of the inlet stage is improved over a wide range of mass flow.The losses are reduced,proving the good performance of the opti mum.The whole results indicate that the opti mization method can find i mproved design and can be integrated in a design procedure.

Development of a micro gas turbine combustor with T-type vaporizers

The study includes the experimental investigation of the evaporation performance of T-type vaporizer,mainly studied the relationship of the inlet air temperature and vaporizer wall temperature with the evaporation ratio.Then,it studied the LBO(lean blow out) and combustion efficiency of the micro aero-engine combustor with T-type vaporizer on the normal pressure test rig.The inlet air condition is environmental pressure and temperature.The gas analysis method is used to study the combustion efficiency,and the inlet air temperature is 300 K,400 K and 500 K.It could be concluded that the evaporation performance is improved with the increasing of the inlet air temperature and vaporizer wall temperature;the average LBO is 0.003;the combustion efficiency rises with the inlet air temperature,and it remain constant when the fuel/air ratio changed in the range from 0.008 to 0.02.The vaporization ratio is the key factor to determine the combustion performance.

Numerical simulation of quasi-streamwise hairpin-like vortex generation in turbulent boundary layer

A mechanism for generation of near wall quasi-streamwise hairpin-like vortex （QHV） and secondary quasi-streamwise vortices （SQV） is presented. The conceptual model of resonant triad in the theory of hydrodynamic instability and direct numerical simulation of a turbulent boundary layer were applied to reveal the formation of QHV and SQV. The generation procedures and the characteristics of the vortex structures are obtained, which share some similarities with previous numerical simulations. The research using resonant triad conceptual model and numerical simulation provides a possibility for investigating and controling the vortex structures, which play a dominant role in the evolution of coherent structures in the near-wall region.

Reaction zone characterization of counter-flow diffusion flame with diluted and preheated reactants

Reaction zone characteristics were studied using hydroxy radical planar laser-induced fluorescence （OH-PLIF） technique for a counter-flow preheated （CH4＋N2）/（Air＋N2） diluted diffusion flames. The effects of preheat temperature and dilute ratio on the reaction zone characteristics were investigated by demonstrating the OH intensity distribution and reaction zone thickness from OH-PLIF images. Under the experimental conditions of constant cold flow velocity, the results show that the OH intensity and reaction zone thickness decrease with the increase of dilute ratio at constant preheat temperature and increase with preheat temperature at fixed dilute ratio. The OH maximum intensity shifts towards the ＂lean＂ side of counter flow at constant preheat temperature, and it shifts towards the fuel side with the increase of dilute ratio of fuel stream and towards the oxidizer side with the increase of dilute ratio of oxidizer stream respectively. The feasibility of OH as a reaction zone marker in this diluted combustion is verified further. The variation of diffusion and chemical reaction rate of reactants due to preheat and dilution contributes to the reaction zone characteristics simultaneously. The effect of strain on the flame reaction zone should be included in the future work.

Model of magnetostrictive actuator

The hysteresis of the magnetostrictive actuator was studied. A mathematical model of the hysteresis loop was obtained on the basis of experiment. This model depends on the frequency and the amplitude of the alternating current inputted to the magnetostrictive actuator. Based on the model, the effect of hysteresis on dynamic output of the magnetostrictive actuator was investigated. Then how to consider hysteresis and establish a dynamic model of a magnetostrictive actuator system is discussed when a practical system was designed and applied.

Analysis of Film Cooling Effectiveness on Shaped Hole and Antivortex Hole

Film cooling is introduction of a secondary fluid （coolant or injected fluid） at one or more discrete locations along a surface exposed to a high temperature environment to protect that surface not only in the immediate region of injection but also downstream region. This paper numerically investigated the film cooling effectiveness on two types of hole geometries which are cut-shaped hole and antivortex hole. The 3D computational geometries are modeled with a single 30 deg angled hole on a flat surface. The different blowing ratios of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5,5 and k-Epsilon turbulence model are used in this study. A two dimensional distribution of film cooling effectiveness in the downstream region of the cooling hole is performed. A comparison of spanwise averaged effectiveness is also performed in the field starts from center point of hole to X/D=-30.

Vibration Characteristics of Mistuned Bladed Disks

The finite element models of blade, disk and bladed disk are built up by finite element software ANSYS. The natural frequencies of the single blade, the whole bladed disk and the bladed disk with only one sector by cyclic symmetry boundary have been calculated. Then, based on the results above, a structure dynamic model of multiple degree-of-freedom （MDOF） systems is established to simulate the bladed-disk assembly. Solve the motion equation by using the Runge-Kutta Method （Gill Method）. The dynamic response of the MDOF system is achieved. As for the given mistuning patterns, the vibration responses of bladed disks are calculated. The results have been compared and analyzed, and the optimum pattern is selected.

Distributed collaborative extremum response surface method for mechanical dynamic assembly reliability analysis

To make the dynamic assembly reliability analysis more effective for complex machinery of multi-object multi-discipline(MOMD),distributed collaborative extremum response surface method(DCERSM)was proposed based on extremum response surface method(ERSM).Firstly,the basic theories of the ERSM and DCERSM were investigated,and the strengths of DCERSM were proved theoretically.Secondly,the mathematical model of the DCERSM was established based upon extremum response surface function(ERSF).Finally,this model was applied to the reliability analysis of blade-tip radial running clearance(BTRRC)of an aeroengine high pressure turbine(HPT)to verify its advantages.The results show that the DCERSM can not only reshape the possibility of the reliability analysis for the complex turbo machinery,but also greatly improve the computational speed,save the computational time and improve the computational efficiency while keeping the accuracy.Thus,the DCERSM is verified to be feasible and effective in the dynamic assembly reliability(DAR)analysis of complex machinery.Moreover,this method offers an useful insight for designing and optimizing the dynamic reliability of complex machinery.