Flow equation and similarity criterion during centrifugal casting in micro-channel

Liquid metal filling flow process in the microscale during the centrifugal casting process was studied by means of similar physical simulation. The research was focused on derived similarity criterion. Based on the traditional flow equations, the flow equation and the Bernoulli＇s equation for liquid metal flows in micro-scale space were derived, which provides a mathematical model for numerical simulation of micro-scale flow. In the meanwhile, according to the micro-flow equation and the similarity theory, the similarity criterion for the physical simulation of the mold filling behaviors was presented under centrifugal force field, so as to achieve the visual observation and quantitative analysis of micro-flow process.

Improved similarity criterion for seepage erosion using mesoscopic coupled PFC–CFD model

Conventional model tests and centrifuge tests are frequently used to investigate seepage erosion. However, the centrifugal test method may not be efficient according to the results of hydraulic conductivity tests and piping erosion tests. The reason why seepage deformation in model tests may deviate from similarity was first discussed in this work. Then, the similarity criterion for seepage deformation in porous media was improved based on the extended Darcy-Brinkman-Forchheimer equation. Finally, the coupled particle flow code–computational fluid dynamics(PFC-CFD) model at the mesoscopic level was proposed to verify the derived similarity criterion. The proposed model maximizes its potential to simulate seepage erosion via the discrete element method and satisfy the similarity criterion by adjusting particle size. The numerical simulations achieved identical results with the prototype, thus indicating that the PFC-CFD model that satisfies the improved similarity criterion can accurately reproduce the processes of seepage erosion at the mesoscopic level.

A basic model of unconventional gas microscale flow based on the lattice Boltzmann method

A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time was modified by considering the influence of the boundary Knudsen layer.On this basis,the second-order slip boundary condition of the wall was considered,and the key parameters in the corresponding combined bounce-back/specular-reflection boundary condition were deduced to build a new model of unconventional gas microscale flow simulation based on the lattice Boltzmann method suitable for high temperatures and high pressures.The simulation results of methane gas flow driven by body force in infinite micro-channels and flow driven by inlet-outlet pressure differential in long straight channels were compared with the numerical and analytical solutions in the literature to verify the accuracy of the model,and the dimensionless relaxation time modification was formally optimized.The results show that the new model can effectively characterize the slippage effect,compression effect,gas density and the effect of boundary Knudsen layer in the micro-scale flow of unconventional natural gas.The new model can achieve a more comprehensive characterization of the real gas flow conditions and can be used as a basic model for the simulation of unconventional gas flow on the micro-nano scale.

HYDRAULIC SIMILARITY CALCULATION IN MODEL OF SEPARATION OF LIQUID AND SOLID PARTICLES BY WATER INTAKE HEAD WITH INCLINED BOARDINGS

The water intake head installed with inclined boardings is called laminate sediment precipitation, which separates liquid and solid particles in two-phase flow by gravity. The paper presents the equations for calculating the distance H between two incllined boardings, indicating that H has a key effect on the particle precipitation velocity V_2. The paper focuses also on the cal- culation of hydraulic similarity of model with the theoretic model.

Hydraulic experiment on mushroom head in bottom-blown smelting furnace

There are many bottom-blown smelting furnaces in metallurgical industry. When oxygen or air sprays from the jet nozzle into the bottom of the furnace, the melting phase will be frozen and a hemispherical porous zone with a mushroom head shape will be formed around the nozzle. The mushroom head can pro- tect the jet nozzle and mitigate the liquid spray on the surface of melt. In order to analyze the formation process of a mushroom head in the bottom-blown smelting furnaces, a hydraulic experiment system was designed and the formation of the mushroom head was investigated by hydraulic experiment. The hydrau- lic experiment results show that the formation process is mainly divided into generating crushing genera- ting process and stable mushroom head generation process. The formation of stable mushroom head re- quires certain thermodynamic condition and water splash is more intense without a mushroom head than with a mushroom head. The size, porosity and diameter of the mushroom head are affected by the flow rate, temperature and heat capacity of the bottom-blowing gas and the temperature of the superheat and the physical parameters of the melt.

Virtual flight test techniques to predict a blended-wing-body aircraft in-flight departure characteristics

As one of the promising configurations of the next generation of commercial aircraft,research on departure characteristics of the Blended-Wing-Body(BWB)is of great signification to safe flight limits.A three-degree-of-freedom(3-DOF)virtual flight test in a wind tunnel has been implemented for a candidate configuration to predict the departure characteristics.The support mechanism,the test model and the control law of the virtual flight test are introduced.In order to show the relationship between virtual flight test and actual flight test,the similarity criterion is also given.In open loop,the model has mild oscillations in the longitudinal and lateral directions,which are stable in closed-loop.The effect of flight control has been verified in virtual flight and actual subscale flight test.The analysis of system identification results indicate that the model has a good response to the excitation signal,and the response is in reasonable agreement with the flight test.Finally,the virtual flight departure test results are compared with the flight test.It shows that there is a good correspondence between the angle of attack and the elevator deflection at departure.This gives promising evidence of the practicability of virtual flight testing to predict departure of a BWB.

Formation of defects in selective laser melted Inconel 718 and its correlation with mechanical properties through dimensionless numbers

This paper presents a profound study on the formation of three typical types of defects(i.e.,lack of fusion,keyholes,and gas pores)observed in selective laser melting(SLM)printed Inconel 718 samples,along with their correlations with mechanical properties of the samples.Computed tomography,scanning electron microscopy,and mechanical property tests revealed that the three types of defects fall into three stages of porosity evolution classified by recently-proposed dimensionless numbersηm(melting efficiency)andηv(vaporization efficiency).Meanwhile,experimental tests verified that the mechanical properties of products,such as strength and elongation,are remarkably sensitive to lack of fusion.However,these properties are slightly affected by the keyholes and gas pores.An optimal process window characterized by dimensionless numbers is realized by adjusting the processing parameters and employing different powders.This process window allows products to have relatively low defects and high mechanical performances.A quantitative relation between processing parameters,dimensionless numbers,defects,and mechanical properties is established based on these observations.This relation,along with the optimal process window,is believed to enhance the quality of SLM products of Inconel 718 alloy and can be further extended to SLM with other metal materials.

Numerical studies on issues of Re-independence for indoor airflow and pollutant dispersion within an isolated building

This study conducted the numerical models validated by wind-tunnel experiments to investigate the issues of Re-independence of indoor airflow and pollutant dispersion within an isolated building.The window Reynolds number(Re_(w))was specified to characterize the indoor flow and dispersion.The indicators of RRC(ratio of relative change)or DR(K_DR)(difference ratio of dimensionless concentration)<5%were applied to quantitatively determine the critical Rew for indoor flow and turbulent diffusion.The results show that the critical Re(Re_(crit)) value is position-dependent,and Re_(crit) at the most unfavorable position should be suggested as the optimal value within the whole areas of interest.Thus Re(H,orit)=27,000 is recommended for the outdoor flows;while Re_(w,crit)=15,000 is determined for the indoor flows due to the lower part below the window showing the most unfavorable.The suggested Re_(w,crit)(=15,000)for indoor airflow and cross ventilation is independence of the window size.Moreover,taking K_DR≤5% as the indicator,the suggested Re_(w,crit) for ensuring indoor pollutant diffusion enter the independence regime should also be 15,000,indicating that indoor passive diffusion is completely determined by the flow structures.The contours of dimensionless velocity(U/U_(0))and concentration(K)against the increasing Re(w) further confirmed this critical value.This study further reveals the Re-independence issues for indoor flow and dispersion to ensure the reliability of the data obtained by reduced-scale numerical or wind-tunnel models.

Experimental investigation on continuous N_(2) injection to improve light oil recovery in multi-wells fractured-cavity unit

The purpose of this experimental study is to evaluate the feasibility and oil recovery efficiency of continuous N_(2) injection in a multi-well fractured-cavity reservoir.In this study,the similar criterion of physical simulation was firstly discussed.In order to reveal the mechanism of remaining oil startup and production performance characteristic by continuous N_(2) injection,a visualized twodimensional fractured-cavity model and a three-dimensional pressure resistant model were designed and fabricated respectively based on the similar theory.And the 2D visualized physical experiments and 3D physical experiments were performed with the simulated oil and brine reservoir samples in Tahe oilfield.Four groups of experiments in 2D and 3D model were performed,each of which included bottom water depletion driving,water injection and N_(2) injection.The 2D visualized experiments indicated the main mechanism of N_(2) developing remaining oil was to occupy the high position and replace the attic oil due to gravitational differentiation.Furthermore,both the 2D and 3D experiments demonstrated that higher oil recovery factor could be achieved if N_(2) was injected through high positional wells.The 3D physical model is closer to the real reservoir condition,so the production performance can reflect the real field production process.This paper confirmed the efficiency of continuous N2 flooding in the light oil saturated fractured-cavity reservoir.

Laboratory experiments of well testing for fracture-cave carbonate gas reservoirs

It is well known that the flowing of oil and gas in fracture and cave does not obey Darcy law,which makes it unable to interpret parameters correctly when doing well testing for those kinds of formation for having no flowing test used to correct corresponding flowing equations.Based on similarity criterion,a physical experimental method for gas flowing from cave to wellbore through fracture has been built up.The characteristics of fluid flowing in fracture and cave can be seen clearly according to logelog curves with the measured data,which was obtained from the experimental model test and dealt with Savitzky-Golay filtering method.In addition,a new mathematical model reflecting those transient-flow behaviors as well as its solution has been presented in this paper.Logelog curves obtained from our new model could reflect the characteristics of flowing in fracture and cave.The results showed that test experiments can reflect the influence of large-scaled cave and fracture on the flowing characteristics and the new model can be applied to explain parameters of fracture and cave for similar cases.

SITMILARITY LAW FOR HYDRAULIC DISTORTED MODEL

Newton's general similarity criterion was applied to the distorted model. Theresults for the similarities of gravity force, drag force and pressure force are identical withthose derived from relevant differential equations of fluid flow. And the selected limits of thedistorted ratio were studied and the simulation of roughness coefficient of distorted model wasconducted by means of hydraulic test.

A theoretical study on the unsteady aerothermodynamics for attached flow models

The principle of the unsteady aerothermodynamics was theoretically investigated for the attached flow. Firstly, two simplified models with analytic solutions to the N-S equations were selected for the research, namely the compressible unsteady flows on the infinite flat plate with both time-varying wall velocity and time-varying wall temperature boundary conditions. The unsteady temperature field and the unsteady wall heat flux (heat flow) were analytically solved for the second model. Then, the interaction characteristic of the unsteady temperature field and the unsteady velocity field in the simplified models and the effects of the interaction on the transient wall heat transfer were studied by these two analytic solutions. The unsteady heat flux, which is governed by the energy equation, is directly related to the unsteady compression work and viscous dissipation which originates from the velocity field governed by the momentum equation. The main parameters and their roles in how the unsteady velocity field affects the unsteady heat flux were discussed for the simplified models. Lastly, the similarity criteria of the unsteady aerothermodynamics were derived based on the compressible boundary layer equations. Along with the Strouhal number Stu, the unsteadiness criterion of the velocity field, StT number, the unsteadiness criterion of the temperature field was proposed for the first time. Different from the traditional method used in unsteady aerodynamics which measures the flow unsteadiness only by the Stu number, present results show that the flow unsteadiness in unsteady aerothermodynamics should be comprehensively estimated by comparing the relative magnitudes of the temperature field unsteadiness criterion StT number with the coefficients of other terms in the dimensionless energy equation.