Showing papers in "Transactions of The Korean Society of Mechanical Engineers B in 1996"
TL;DR: In this article, the shape of free-jets is estimated based on the nozzle pressure ratio and the exit Mach number and Reynolds number of axisymmetric nozzles.
Abstract: Supersonic axisymmetric jets issuing from various kinds of nozzles with a throat diameter of a few millimeters were experimentally investigated The exit Mach number and Reynolds number based on the throat diameter of nozzle were in the range of 10 ~ 59 and 84 ~ 29, respectively The nozzle pressure ratio was varied from 5 to 85 Present paper aims to offer fundamental information of the supersonic free-jets, with an emphasis to give data with which the shape of the free-jets can be depicted under a specified condition Experimental data are summarized to enable an estimation of the shape of the supersonic free-jets The result shows that the shape of free-jets is dependent on only the nozzle pressure ratio
11 citations
TL;DR: In this article, a finite-volume method for radiation in a three-dimensional non-orthogonal gas turbine combustion chamber with absorbing, emitting and anisotropic scattering medium is presented.
Abstract: The finite-volume method for radiation in a three-dimensional non-orthogonal gas turbine combustion chamber with absorbing, emitting and anisotropically scattering medium is presented. The governing radiative transfer equation and its discretization equation using the step scheme are examined, while geometric relations which transform the Cartesian coordinate to a general body-fitted coordinate are provided to close the finite-volume formulation. The scattering phase function is modeled by a Legendre polynomial series. After a benchmark solution for three-dimensional rectangular combustor is obtained to validate the present formulation, a problem in three-dimensional non-orthogonal gas turbine combustor is investigated by changing such parameters as scattering albedo, scattering phase function and optical thickness. Heat flux in case of isotropic scattering is the same as that of non-scattering with specified heat generation in the medium. Forward scattering is found to produce higher radiative heat flux at hot and cold wall than backward scattering and optical thickness is also shown to play an important role in the problem. Results show that finite-volume method for radiation works well in orthogonal and non-orthogonal systems.
10 citations
TL;DR: In this article, the authors extended the range of Rayleigh numbers to systematically investigate the transition during melting processes, especially focusing on the complex multi-cellular flow pattern and thermal instability.
Abstract: The constrained melting inside an isothermally heated horizontal cylinder has been repeatedly investigated in many studies only for the moderate Rayleigh numbers. This study extends the range of Rayleigh numbers to systematically investigate the transition during melting processes, especially focusing on the complex multi-cellular flow pattern and thermal instability. The enthalpy-porosity formulation, with appropriate source terms to account for the phase change, is employed. For low Rayleigh numbers, initially developed single-cell base flow keeps the flow stable. For moderate Rayleigh numbers, even small disturbances in balance between thermal buoyance force and viscous force result in branched flow structure. For high Rayleight numbers, Benard type convection is found to develop within a narrow gap between thee wall and the unmelted solid. The marginal Rayleigh number and the corresponding wave number are in excellent agreement with those from linear stability theory.
5 citations
TL;DR: In this paper, the effects of angle of divergence and design Mach number of nozzle on the structure of underexpanded jets were explored and compared with the results of a linear theory and other experiments.
Abstract: Numerical calculation was applied to supersonic under-expanded jets, and compared with the results of a linear theory and other experiments. TVD difference scheme was employed to solve 2-dimensional and axisymmetric inviscid Euler equation. This paper aims to explore the effects of angle of divergence and design Mach number of nozzle on the structure of under-expanded jets. The angle of divergence was varied from 0 to 20 deg. The results show that the length of the first cell of the under-expanded jets decreases and Mach disk generates at lower nozzle pressure ratio, if the angle of divergence or design Mach number of nozzle increases. The distance from the nozzle exit to Mach disk in 2-dimensional jets becomes much larger than that of axisymmetric jets, and the widths of the jet boundary and the barrel shock wave are also larger than that of axisymmetric jets. Calculation results indicate that the configuration of the under-expanded jets is strongly dependent on the nozzle pressure ratio.
5 citations
TL;DR: In this article, the CSCM type upwind flux difference splitting Navier-Stokes method has been applied to study the ARL-SL19 transoni ersonic compressor cascade flow.
Abstract: In this paper the CSCM type upwind flux difference splitting Navier-Stokes method has been applied to study the ARL-SL19 transoni ersonic compressor cascade flow. First, the general characteristics of baseline cascade flow were analyzed. At freestream Mach n.1.612 and exit/inlet pressure ratio 2.15, the results from current laminar flow were compared well in suction surface with the experiment; however, not well in pressure surface. Second, numerical study of the transoni ersonic compressor cascade flow demonstrated the effectiveness of a passive control by the various size cavities. A cavity under the shock foot point at the suction surface of the blades was used as a passive control. The passive control of shock-boundary layer interaction by a cavity reduced total pressure losses. The effect of cavity length and depth was studied. The total pressure loss was reduced by about 10% and the isentropic efficiency was improved slightly. The effect of cavity depth in current study(d/l = 0.05, 0.02) was not found strong. Further adequate turbulence modeling and TVD schemes would help to capture the shock more accurately and increase the effectiveness of the current shock-boundary layer interaction study using upwind flux difference splitting computational methods.thods.
3 citations
TL;DR: In this paper, the authors used a four-step fractional method combined with an equal order bilinear finite element method to solve the problem of simultaneously developing and simultaneously developing laminar flows of Bingham plastic in a circular pipe.
Abstract: Hydro dynamically developing and simultaneously (hydro dynamically and thermally) developing laminar flows of a Bingham plastic in a circular pipe have been investigated numerically. Solutions have been obtained by using a four-step fractional method combined with an equal order bilinear finite element method. For the hydro dynamically developing flow, shorter entrance length is required to reach fully developed velocity field for larger yield stress and non-monotonic pressure drop along the pipe centerline is observed when the yield stress exceeds a certain critical value. For the simultaneously developing flow, the heat transfer characteristics show the same trends as those predicted for the thermally developing flow (Graetz problem).
3 citations
TL;DR: In this paper, experimental study on vortex tube efficiency was performed with various cold end orifices and nozzles type, and the experimental results indicated that there is an optimum diameter of cold-end orifice and nozzle type for the best cooling performance.
Abstract: Vortex tube is a simple device which splits a compressed gas stream into a cold stream and a hot stream without any chemical reactions. The phenomena of energy separation taking place in a vortex tube has been investigated experimentally. Recently, vortex tube is widely used to local cooler of industrial equipments and air conditioner of special purpose. In this study, experimental study on vortex tube efficiency was performed with various cold end orifices and nozzles type. The experimental results indicate that there is an optimum diameter of cold end orifice and nozzle type for the best cooling performance. The variation of the maximum wall temperature along the vortex tube surface provides useful information about the location of the stagnation point of the flow field at the axis of the vortex tube. The similarity relation for the prediction of the temperature of the cold exit air was obtained.
3 citations
TL;DR: In this paper, a generalized Scheil equation for the solute redistribution in the absence of the back diffusion during the dendritic solidification of binary alloys is derived, in which coarsening of the secondary dendrite arms is taken into account.
Abstract: A generalized Scheil equation for the solute redistribution in the absence of the back diffusion during the dendritic solidification of binary alloys is derived, in which coarsening of the secondary dendrite arms is taken into account. The obtained equation essentially includes the original Scheil equation as a subset. Calculated results for typical cases show that the coarsening affects the microsegregation significantly. The eutectic fraction predicted for coarsening is considerably smaller than that for fixed arm spacing. The most important feature of the present equation in comparison with the Scheil equation lies in the fact that there exists a lower limit of the initial composition below which the eutectic is not formed. Based on the generalized Scheil equation and the lever rule, a new regime map of the eutectic formation on the initial composition-equilibrium partition coefficient plane is proposed. The map consists of three regimes: the eutectic not formed, conditionally formed and unconditionally formed, bounded by the solubility and diffusion controlled limit lines.
2 citations
TL;DR: In this paper, the authors evaluated three finite differencing schemes for the convection term of the k-epsilon turbulence model and found that the simulation with the QUICK or SOU scheme predicts fairly well the flow field and gives more accurate drag coefficient.
Abstract: The Reynolds-averaged Navier-Stokes equations with the equations of the k-.epsilon. turbulence model are solved numerically in a general curvilinear system for a three-dimensional turbulent flow around an Ahmed body. The simulation is especially aimed at the evaluation of three finite differencing schemes for the convection term, which include the upwind differencing scheme(UDS), the second order upwind differencing scheme(SOU scheme) and the QUICK scheme. The drag coefficient, the velocity and pressure fields are found to be changed considerably with the adopted finite differencing schemes. It is clearly demonstrated that the large difference between computation and experiment in the drag coefficient is due to relatively high predicted values of pressure drag from both front part and vertical rear end base. The results also show that the simulation with the QUICK or SOU scheme predicts fairly well the flow field and gives more accurate drag coefficient than other finite differencing scheme.
2 citations
TL;DR: A numerical study for vapor absorption into LiBr-HO solution film flowing over horizontal circular tubes has been carried out in this article, where the momentum, energy and diffusion equations, which are parabolized by the boundary layer approximation, are solved simultaneously for various mass-flow rates and inlet conditions.
Abstract: A numerical study for vapor absorption into LiBr-HO solution film flowing over horizontal circular tubes has been carried out. The momentum, energy and diffusion equations, which are parabolized by the boundary- layer approximation, are solved simultaneously for various mass-flow rates and inlet conditions. The results for the velocity, temperature and concentration fields, as well as the heat and mass flux at the free surface are presented. The effects of inlet conditions, i.e., flow rate, temperature and concentration, on the absorption process are also examined and discussed.
2 citations
Abstract: Small-amplitude harmonic oscillations of multi-cylinders are considered both experimentally and theoretically. For the theoretical model, the flow regime is separated into inner and outer regions. In the inner region, the flow is governed by the generalized Stokes boundary layer equation. In the outer region, the full Navier-Stokes equation for the steady streaming flow is solved numerically by using ADI scheme and FVM coupled with the boundary integral method. Flow visualization experiments are conducted by using the Laser Sheet Image Technique. The case of two circular cylinders and square cylinders with variable distances are chosen as a typical example. Although experimental results are based on the flow in the finite domain, both experimental and numerical results agree well qualitatively. As the separation of cylinders is increased, a numerical result shows the asymptotic convergence to a single cylinder case.
TL;DR: In this article, an unsteady two dimensional model for the thermal stratification in the pressurizer surge line of PWR plant has been proposed to numerically investigate the heat transfer and flow characteristics.
Abstract: In this paper, the unsteady two dimensional model for the thermal stratification in the pressurizer surge line of PWR plant has been proposed to numerically investigate the heat transfer and flow characteristics. The dimensionless governing equations are solved by using the Control Volume Formulation and SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The temperature profile of fluids and pipe wall with time are shown when the thermal stratification occurs in the horizontal pipe. The numerical result shows that the maximum dimensionless temperature difference is about O.514 between hot and cold section of pipe wall at dimensionless time 1,632.
TL;DR: In this article, the effects of methanol blending fuel on combustion in cylinder were investigated under various conditions of engine cycle and blending ratio, and the results showed that the engine performance was influenced by the mixed fuel and the variations of operating conditions of test engine.
Abstract: The engine performance and combustion characteristics of methanol blended fuel in spark ignition engine were discussed on the basis of experimental investigation. The effects of methanol blending fuel on combustion in cylinder were investigated under various conditions of engine cycle and blending ratio. The results showed that the engine performance was influenced by the methanol blending ratio and the variations of operating conditions of test engine. The increase of fuel temperature brought on the improvement of combustion characteristics such as cylinder pressure, the rate of pressure rise and heat release in an engine. The burning rate of fuel-air mixture, the exhaust emissions and the other characteristics of performance were discussed also.
TL;DR: In this paper, the phase criterion of the feedback cycle of low-speed edgetones has been obtained using the jet-edge interaction model which is based on the substitution of an array of dipoles for the reaction of the wedge to the impinging jet.
Abstract: The phase criterion of the feedback cycle of low-speed edgetones has been obtained using the jet-edge interaction model which is based on the substitution of an array of dipoles for the reaction of the wedge to the impinging jet. The edgetone is produced by the feedback loop between the downstream-convected sinuous disturbance and upstream-propagating waves generated by the impingement of the disturbance on the wedge. By estimation of the phase difference between the downstream and the upstream disturbances, the relationship between the edge distance and the wavelength is obtained according to the phase-locking condition at the nozzle lip. With a little variation depending on the characteristics of jet-edge interaction, the criterion can be approximated as follows: h/.LAMBDA. + h/.lambda. = n - 1/4, where h is the stand-off distance between the nozzle lip and the edge tip, .LAMBDA. is the wavelength of downstream-convected wave, .lambda. is the wavelength of the upstream-propagating acoustic wave and n is the stage number for the ladder-like characteristics of frequency. The present criterion has been confirmed by estimating wavelengths from available experimental data and investigating their appropriateness. The above criterion has been found to be effective up to 90.deg. of wedge angle corresponding to the cavitytones.
TL;DR: In this paper, an experimental investigation has been carried out to examine the influence of injector design variables and operating conditions on the resultant drop size for triplet impinging streams injectors. But it is found that there is no noticeable droplet-size change which results from change in orifice length to diameter ratio or impinging point distance within the investigated range.
Abstract: An experimental investigation has been carried out to examine the influence of injector design variables and operating conditions on the resultant drop size for triplet impinging streams injectors. The variables studied in this investigation are pressure drop, impinging angle, orifice length to diameter ratio, and impinging point distance. Droplet-size data are obtained using water as the propellant simulant by Malvern Particle Analyzer System. Drop size decreases with increasing impinging angle and pressure drop while other injector parameters remain constant at the same point. But it is found that there is no noticeable droplet-size change which results from change in orifice length to diameter ratio or impinging point distance within the investigated range.
TL;DR: In this article, the relationship between the change of flame shape and emission has also been examined, where the flame shape on the ceramic matrix plate changes from a diffusion flame, R(radiant)-type flame, to B(Blue)-type flames around the equivalence of 0.7.
Abstract: Emission characteristics of nitric oxides and carbon monoxide from a porous media combustor has been experiment studied. The relationship between the change of flame shape and emission has also been examined. As the equivalence ratio decreases, the flame shape on the ceramic matrix plate changes from a diffusion flame, R(radiant)-type flame, to B(Blue)-type flame. With large fuel flow rate, R-type flame turns to be two dimensional R-II type flame around the equivalence of 0.7. Carbon monoxide emission increases very rapid with decreasing equivalence ratio. It changes a lot from some 10 ppm to 100-10,000 ppm with the change of flame type from R-I to R-II type. Nitric oxide emission from the premixed burner is less than 25 ppm over all range of fuel flow rate, which is less than 20% of NOx emission from conventional gas burners.
TL;DR: In this article, the instantaneous flame temperature and soot formation and oxidation in a D.I. diesel engine are measured using a two-color method based on the continuous spectral radiation from the soot particles in the flame.
Abstract: The instantaneous flame temperature and soot formation and oxidation in a D.I. diesel engine are measured using a two-color method. The proposed method based on the continuous spectral radiation from the soot particles in the flame is applicable to industrial diesel engines without major modifications of their main characteristics. Measurements are performed at one location inside the combustion chamber of a D.I. diesel engine. Effects of different engine speeds and loads on flame temperature and KL factor which is an index of soot concentration were examined. Little temperature change were observed with increasing rpm, while increased with loads. The higher the flame temperature is, the lower the KL factor is.
TL;DR: In this paper, the effect of pre-mixed combustion quantity and smoke emission in diesel engine was investigated. And the primary cause of the increase in the premixed combustible mixture during long ignition delay period with advancing injection timing was considered.
Abstract: The objective of this research is to apply effect of the pre-mixed combustion quantity and smoke emission in diesel engine. According as air fuel ratio is increased, emission of smoke concentration is linearly reduced. As Injection timing is advanced, smoke concentration is remarkably reduced. It is considered to be the primary cause of the increase in the premixed combustible mixture during long ignition delay period with advancing injection timing. Smoke is increased with increasing engine speed, so it is considered to be the primary cause of the increase of the mass of fuel injected. Smoke is decreased according to the increase of methanol volume ratio. It is considered that the primary cause of the increase in the quantity of pre-mixed combustion.
TL;DR: In this article, the accuracy of gas flow measurements using sonic nozzle and factors which influence on the discharge coefficients of sonic nozzle are investigated with high pressure gas flow standard measurement system, which comprises two compressors, storage tank, temperature control loop, sonic nozzle test section, weighing tank, gyroscopic scale and data acquisition system.
Abstract: Accuracy of gas flow measurements using sonic nozzle and factors which influence on the discharge coefficients of sonic nozzle are investigated with high pressure gas flow standard measurement system. The gas flow measurement system comprises two compressors, storage tank, temperature control loop, sonic nozzle test section, weighing tank, gyroscopic scale and data acquisition system. The experiments are performed at various nozzle throat diameter and inlet pressure. Overall uncertainty of discharge coefficients is estimated to less than .+-.0.2% and most of experimental data fall into this range. Dependence of discharge coefficients on the Reynolds number is good agreement with those suggested in ISO document. The influence of swirl on the discharge coefficients becomes greater as the nozzle throat diameter is enlarged. The discharge coefficient of conical nozzle shows about 4.5% lower discharge coefficients than those of toroidal nozzle, but variation trend with Reynolds number is very similar each other and reproducibility of data is very good.
TL;DR: In this paper, a series of model experiments were conducted on the impulsive waves emitted from an open end of a shock tube, and various kinds of silencers such as the exit boxes with baffle plates, were applied to the duct exit to reduce the noise.
Abstract: As a compression wave is emitted from a duct, an impulsive wave generates and causes an impulsive noise that is at present a serious environmental noise pollution. In order to clarify the acoustic characteristics of the noise and to reduce their pressure levels, a series of model experiments were conducted on the impulsive waves emitted from an open end of a shock tube. The impulsive waves with various intensities were obtained by controlling the operation pressure ratio of the shock tube. Various kinds of silencers such as the exit boxes with baffle plates, were applied to the duct exit to reduce the impulsive noises. The effects of geometry of silencers and shock Mach number on the noise reduction were clarified. From the measurements of sound pressure level, it was found that installing the baffle plate into the exit box is effective in lowering the noise level at far fields, and that the recommendable geometries of silencer are L/D=1, H/D=1 and H/D=0.75.
TL;DR: In this article, the authors measured the heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a), and compared with Chen's correlation.
Abstract: Boiling heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a) and refrigerant mixtures (R32/Rl34a, R290/ R600a, and R32/R125) are measured experimentally and compared with Chen's correlation. The test section is a seamless stainless steel tube with inner diameter of 7.7mm and uniformly heated by applying electric current directly to the tube. Heat fluxes range from 10 to 30kW. Mass fluxes are set to 424 ~ 742kg/ms for R22, R32, R134a, R32/R134a, and R32/Rl25 ; 265 ~ 583kg/ms for R290, R600a, and R290/R600a. Heat transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases. Convective boiling term in the Chen's correlation predicts experimental data of the pure refrigerants fairly well (relative error of 12.1% for the data of quality over 0.2). The correlation for pure substances overpredicts the heat transfer coefficients for nonazeotropic refrigerant mixtures.
TL;DR: In this article, a numerical study on natural convection induced by free surface heat flux and cold left and hot right walls in glass melting furnaces has been performed, where a function of heat flux derived from the combustion environments of actual glass melting furnace is applied to thermal boundary condition at free surface.
Abstract: A numerical study on natural convection induced by free surface heat flux and cold left and hot right walls in glass melting furnaces has been performed. A function of heat flux derived from the combustion environments of actual glass melting furnace is applied to thermal boundary condition at free surface. Fundamentally there exist two flow cells in cavity (left counterclockwise one and right clockwise one). The effects of heat flux and Rayleigh number are investigated through two-dimensional steady-state assumption. The convection strength of two flow cell located in left region continuously increases. In the mean time the strength of flow cell in right region increases and then decreases. Critical Rayleigh number in which two flow cells take place above and below show linear dependence on the free surface heat flux. To maintain the traditional flow pattern (left and right flow cells) in glass melting furnace, Rayleigh number is recommended to be below 10 .
TL;DR: In this article, the transitional boundary layer with arbitrary pressure gradient under various upstream conditions is studied for engineering applications like the performance prediction of the turbomachineries under various and strong disturbances.
Abstract: A study on the transitional boundary layer with arbitrary pressure gradient under various upstream conditions is very important for engineering applications like the performance predictions of the turbomachineries under various and strong disturbances. Experimental data on the transitional boundary layer for real cascades of the turbomachinery are rare because of difficulties in boundary layer experiments. Flow on NACA0012 airfoil is more similar to the real case than that on the flat plate with which many researches are done. The data of the transitional flow on the airfoil could be used to verify or to develop a turbulence model for numerical simulations. The experiment was performed with two cases of Reynolds number at a=0 and one case of Reynolds number at a=5 . The measured data are the transition length and the wall shear stresses. These two characteristic values are measured within 25%~90% of the airfoil chord by Computation Preston tube Method(CPM) proposed by Nitsche et al.(1983). At a=0 , transition occured at 70% and 55% of chord length when R =6*10 and 8* 10 , respectively. It started when R {\theta}=500 regardless of R , and ended when R {\theta}=750, and 850 respectively. The transition length was 15~20% of the chord length. At a=5 (R =6*10 ), boundary layer on the pressure side does not undergo transition, but on the suction side transition occured at .chi./c=0.16 and ended at .chi./c=0.22.c//c=0.22./c=0.22.c//c=0.22.
TL;DR: In this paper, the authors designed a hot wind tunnel to reproduce the conditions of utility boiler and carried out its performance test, in order to investigate the particulate two-phase flow behaviour, the fouling and heat transfer characteristics to the heat exchanger.
Abstract: We designed the hot wind tunnel to reproduce the conditions of utility boiler and carried out its performance test, in order to investigate the particulate two-phase flow behaviour, the fouling and heat transfer characteristics to the heat exchanger. The hot wind tunnel introduces the control system to control the temperature in the test section. The particle is injected into the hot gas stream. The fouling probe (cylindrical tube) is positioned normal to the particulate gas-particle two-phase flow and cooled by the air. The temperature of gas and cooling air, and temperature in the fouling probe are measured as a function of time, giving the local and averaged heat transfer and fouling factor. The shape of particulate deposition adhered to the fouling probe is also observed.
Journal Article•
Journal Article•
TL;DR: In this paper, a new consistent definition of the regenerator effectiveness can be expressed by the ratio of the heat transfer in axial direction to that in transverse direction, and its approximate form is obtained as a function of Nusselt number for practical utility.
Abstract: The effectiveness of the regenerator pertaining to Stirling cycle machines is studied by analyzing the heat transfer characteristics of the oscillating flow in a tube, and a new consistent definition of the regenerator effectiveness can be expressed by the ratio of the heat transfer in axial direction (Qaxial/) to that in transverse direction (Q/su w/), and its approximate form is obtained as a function of Nusselt number for practical utility. Since an approximate value of the ratio Qaxial//Qsub w/ can be expressed in terms of the time-averaged rather than transient temperatures, this expression is useful to estimate the heat transfer coefficient in the Stirling machine regenerator experimentally.
TL;DR: In this paper, a finite volume radiation solution method was applied to a non-orthogonal coordinate system for the analysis of radiative-convective heat transfer about a circular cylinder in crossflow.
Abstract: A finite volume radiation solution method was applied to a non- orthogonal coordinate system for the analysis of radiative-convective heat transfer about a circular cylinder in crossflow. The crossflow Reynolds number based on the cylinder radius was 20, and the fluid Prandtl number was 0.7. The radiative heat transfer coupled with convection was reasonably predicted by the finite volume radiation solution method. The investigation includes the effects of conduction- to-radiation parameter, optical thickness, scattering albedo and cylinder wall-emissivity on heat transfer about the cylinder. As the conduction- to-radiation parameter decreases, the radiative heat transfer rate increases and conduction rate as well due to the increase in temperature gradient on the cylinder wall which is caused by radiation enhancement. With an increase in the optical thickness, the Nusselt number increases significantly and the temperature gradient shows similar behavior. Though the radiative heat transfer increases with the scattering albedo, the total heat transfer decreases. This is because the decrease in the conduction heat transfer exceeds the increase in the radiation heat transfer. As the wall- emissivity increases, the radiation absorbed in the vicinity of the cylinder wall increases and thereby the total heat transfer increases, even though the conduction heat transfer decreases.
TL;DR: In this paper, a simplified model for approximate analysis of the solute redistribution in coarsening dendrite arms during solidification of binary metal alloys is presented, which is suitable for the micro-macroscopic solidification model as a microscopic component.
Abstract: This paper presents a simplified model for approximate analysis of the solute redistribution in coarsening dendrite arms during solidification of binary metal alloys. By introducing a quadratic concentration profile with a time-dependent coefficient, the integral equation for diffusion in the solid phase is reduced to a simple differential relation between the coefficient and the solid-liquid interface position. The solid fraction corresponding to the system temperature is readily determined from the relation, phase equilibrium and the overall solute balance in which the liquid phase is assumed to be completely mixed. In order to validate the developed model, calculations are performed for the directional solidification of Al-4.9 mass Cu alloy. The predicted eutectic fractions for a wide range of the cooling rate reasonably agree with data from the well-known experiment as well as sophisticated numerical analyses. Also, the results for the back diffusion limits are consistent with available references. Additional calculations show that the characteristic parameters such as the coarsening, density variation and nonlinarity in the phase diagram significantly affect the microsegregation. Owing to the simplicity, efficiency and compatibility, the present model may be suitable for the micro-macroscopic solidification model as a microscopic component.
TL;DR: In this article, the authors measured the static pressure distribution around the cylinder wall and flow characteristics in the near wake of an acoustic excitation issued from a thin slit along the cylinder axis.
Abstract: The flow around a circular cylinder was controlled by an acoustic excitation issued from a thin slit along the cylinder axis. The static pressure distributions around the cylinder wall and flow characteristics in the near wake have been measured. Experiments were performed under three cases of Reynolds number, 7.8 * 104/, 2.3 * 105/ and 3.8 * 105/. The effects of excitation frequency, sound pressure level and the location of the slit were examined. Data indicate that the excitation frequency and the slit location are the key parameters for controlling the separated flow. At Red/, = 7.8 * 104/, the drag is reduced and the lift is generated to upward direction, however, at Red/, =2.3 * 105/ and 3.8 * 105/, the drag is increased and lift is generated to downward direction inversely. It is thought that the lift switching phenomenon is due to the different separation point of upper surface and lower surface on circular cylinder with respect to the flow regime which depends on the Reynolds number. Vortex shedding frequencies are different at upper side and lower side. Time-averaged velocity field shows that mean velocity vector and the points of maximum intensities are inclined to downward direction at Red/ = 7.8 * 104/, but are inclined to upward direction at Red/ = 2.3 * 105/.