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1.
Flow in a turbulent nonisothermal heterogeneous jet is characterized by considerable velocity [1, 2] and temperature disequilibrium [3] (us u and Ts T, where us, Ts and u, T are velocity and temperature of dispersed and gas components). As was shown in [4], an impurity is not passive, and it leads to suppression of jet turbulence (a result of interphase exchange by pulse and heat). Nonetheless, during reaction of a heterogeneous jet with a barrier orientated along the normal to the running flow, a significant increase is observed in heat emission characteristics in the vicinity of the point of deceleration [5] (for a single-phase jet an increase in heat exchange is typical with an increase in the intensity of turbulence [6]). The intensity of the change in heat emission in this case is a result of velocity and temperature disequilibrium for flow in jets, and it depends on a number of factors (temperature, concentration, phase condition of the dispersed impurity, etc.) and on the nature of the reaction of the dispersed component with the barrier surface [7]. There are numerous experimental data devoted to this. Apart from work in [5, 7], attention is drawn to [8] where an increase is also noted in the heat flow (by a factor of 1.4) at the deceleration point for a plane cylindrical end and a hemisphere. The aim of the present work is a study of the effect of a dispersed component on heat exchange with jet flow around a barrier.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 63–68, November–December, 1986.  相似文献   

2.
A systematic procedure has been laid out for assessment of fluid flow and heat transfer parameters for a slot jet impinging on a concave semicylindrical surface. Based on Walz's modifications of the Karman-Pohlhausen integral method, expressions have been derived for evaluation of the momentum thickness, boundary layer thickness and the displacement thickness at the stagnation point. The work then has been extended for the estimation of thermal boundary layer thickness and local heat transfer coefficients. A correlation has been presented for the Nusselt number at the stagnation point as a function of the Reynolds number for different non-dimensional distances from the exit plane of the jet to the impingement surface.
Berechnung des Wärmeübergangs im Staupunkt eines Strahles, der aus einer rechteckigen öffnung auf eine konkave halbzylindrische Fläche auftrifft
Zusammenfassung Es wurde eine systematische Prozedur für die Abschätzung von Strömungs- und Wärmeübergangsparametern für einen Strahl, der auf eine konkave halbzylindrische Fläche auftrifft, aufgestellt. Basierend auf Walz's Modifikationen der Karman-Pohlhausen Integral-Methode, wurden Ausdrücke für die Berechnung der Impulsdicke, der Grenzschichtdicke und die Versetzungsdicke am Staupunkt abgeleitet. Die Arbeit wurde dann auf die Abschätzung der thermischen Grenzschichtdicke und der lokalen Wärmeübertragungskoeffizienten ausgedehnt. Es wird eine Beziehung für die Nusselt-Zahl am Staupunkt als eine Funktion der Reynolds-Zahl für verschiedene dimensionslose Abstände von der Austrittsfläche des Schlitzes bis zur Aufprallfläche aufgestellt.

Nomenclature c p specific heat at constant pressure - h 0 heat transfer coefficient at the stagnation point - H distance from the exit plane of the jet to the impingement surface - k thermal conductivity - Nu .5 Nusselt number based on impinging jet quantities =h 0.50/k - Nu .5,0 stagnation point Nusselt number =h 0 0.50/k - p pressure - p a ambient pressure - p 0 maximum pressure or stagnation pressure - p(x) static pressure at a distancex from the stagnation point - p(x*) static pressure at nondimensional distancex* from the stagnation point - Re J jet Reynolds number =U J W/ - Re 0.5 Reynolds number based on impinging jet quantities =u m0 0.50/ - T temperature - T* nondimensional temperature =(T–T W)/(T JT W) - T a room temperature - T J jet temperature - T W wall temperature - u velocity component inx andx directions - u m jet centerline (or maximum) free jet velocity: external (or maximum) boundary layer velocity aty = m - u m0 arrival velocity defined as the maximum velocity the free jet would have at the plane of impingement if the plane were not there - U J jet exit velocity - W jet nozzle width - x* nondimensional coordinate starting at the stagnation point =x/2 0.50 - x, y rectangular cartesian coordinates - y coordinate normal to the wall and starting at the wall - ratio of thermal to velocity boundary layer thickness = T/ m - 0 ratio of thermal to velocity boundary layer thickness at the stagnation point - * inner layer displacement thickness - .50 jet half width at the plane of impingement if the plate were not there - d.5 free jet (half width) thickness whereu=u m/2 - m inner boundary layer thickness atu =u m - T thermal boundary layer thickness - nondimensional coordinate normal to wall =y/ m - T nondimensional coordinate normal to wall =y/ T - Pohlhausen's form parameter - dynamic viscosity - kinematic viscosity = / - fluid density - momentum thickness - 0 momentum thickness at the stagnation point  相似文献   

3.
Some results are presented of experimental studies of the equilibrium temperature and heat transfer of a sphere in a supersonic rarefied air flow.The notations D sphere diameter - u, , T,,l, freestream parameters (u is velocity, density, T the thermodynamic temperature,l the molecular mean free path, the viscosity coefficient, the thermal conductivity) - T0 temperature of the adiabatically stagnated stream - Te mean equilibrium temperature of the sphere - Tw surface temperature of the cold sphere (Twe) - mean heat transfer coefficient - e air thermal conductivity at the temperature Te - P Prandtl number - M Mach number  相似文献   

4.
In this study, the flow and heat transfer characteristics of a round air jet have been experimentally investigated in details using two techniques: Particle Image Velocimetry (PIV) and the Laser Doppler Velocimetry (LDV). The measurement of the mean velocity components are compared, and agree well with the experimental data obtained by Baydar (1999). The distributions of the velocity, turbulence quantities and temperature profiles are analyzed in the main characteristic regions of the jet where the heat transfer occurs. Parametric variations were conducted to produce information about the influences of the Reynolds number (Re = 1000, 2000, 3000), the distance between the pipe exit and the flat impingement plate (h/d = 1 and h/d = 2) and the temperature of the plane (Tp = 22 °C, 54 °C, 96 °C) on the impinging jet flow field.  相似文献   

5.
A converging nozzle-constant area parallel passage with an outer duct encasing the constant-area passage has been built for investigating the effect of heat transfer on subsonic flow of an air stream. It is concluded experimentally as can be predicted analytically that large quantities of heat are needed in order to accelerate very slow air stream (incompressible) to sonic conditions. It is observed experimentally as confirmed analytically, that the increase in Mach number with heat addition is associated with a decrease in the local static pressure along the axis of the duct. It could be concluded that any more heat added beyond thermal choking will be accompanied by a decrease in the mass flow rate of the compressible flowing air.Nomenclature A cross-sectional area of the duct - C P air specific heat of air joules/kg. °K - C d discharge coefficient - D duct diameter - d orifice diameter m - dA d elemental lateral area of the duct - h overall heat transfer coefficient - h head across orifice, mm. - M Mach number - m air mass flow rate of air - P local static pressure - P b back pressure at duct outlet - P 01 stagnation pressure at duct inlet - gas density - u air density upstream of orifice - q incremental heat flow - T local static temperature - T 01 stagnation temperature at duct inlet - T h hot water temperature - q heat added per kg of flowing air - V flow speed  相似文献   

6.
The heat transfer taking place between the gas and the surface of the plate in the zone of three-dimensional separation of the turbulent boundary layer in front of a set of supersonic jets injected perpendicularly to a subsonic carrier flow is considered. The aim of this investigation is to establish the main physical characteristics of heat transfer in the separation zones in front of jet obstacles and to obtain the distributions of the local heat-transfer coefficients and the temperature of the thermally insulating wall as functions of the parameters of the carrier flow and the injected jets. Analysis of the experimental results yields certain approximating relationships for the distribution of the local heat-transfer coefficients as functions of the Mach number of the carrier flow M, the Mach number of the jet Mj, the relative boundary-layer displacement thickness s= s * /d, and the degree of jet superheating TojTo relative to the separation zones in front of supersonic jet obstacles.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 68–72, July–August, 1975.  相似文献   

7.
This paper deals with a systematic procedure for assessment of fluid flow and heat transfer parameters for a single round jet impinging on a concave hemispherical surface. Based on Scholkemeier's modifications of the Karman-Pohlhausen integral method, expressions are derived for evaluation of the momentum thickness, boundary layer thickness and the displacement thickness at the stagnation point. This is followed by the estimation of thermal boundary layer thickness and local heat transfer coefficients. A correlation is presented for the Nusselt number at the stagnation point as a function of the Reynolds number for different non-dimensional distances from the exit plane of the jet to the impingement surface.
Bestimmung des Staupunktes bei der Wärmeübertragung für einen einzelnen Strahl, der auf eine konkave halbkugelige Oberfläche trifft
Zusammenfassung Diese Arbeit beschäftigt sich mit dem systematischen Verfahren der Bewertung von Fluidströmungen und Wärmeübertragungsparametern für einen einzelnen runden Strahl, der auf eine konkave halbkugelförmige Oberfläche trifft. Das Verfahren beruht auf Scholkemeiers Modifikation des Karman-Pohlhausen Integrationsverfahrens. Ausdrücke sind für die Berechnung der Impuls-Dicke, der Grenzschichtdicke und der Verschiebungsdicke am Staupunkt hergeleitet worden. Dies ist aus der Berechnung der thermischen Grenzschichtdicke und des lokalen Wärmeübertragungskoeffizienten abgeleitet worden. Es wird eine Gleichung für die Nusselt-Zahl am Staupunkt als Funktion der Reynolds-Zahl für verschiedene dimensionslose Abstände vom Strahlaustrittspunkt bis zum Auftreffpunkt auf die Oberfläche vorgestellt.

Nomenclature c p specific heat at constant pressure - d diameter of single round nozzle - h 0 heat transfer coefficient at the stagnation point - H distance from the exit plane of the jet to the impingement surface - k thermal conductivity - Nu 0.5 Nusselt number based on impinging jet quantities=h 0.50/k - Nu 0.5, 0 stagnation point Nusselt number=h 0 0,50/k - p pressure - p a ambient pressure - p 0 maximum pressure or stagnation pressure - p(x) static pressure at a distancex from the stagnation point - R radius of curvature of the hemisphere - Re J jet Reynolds number=U Jd/ - Re 0.5 Reynolds number based on impinging jet quantities=u m0 0.50/ - T temperature - T a room temperature - T J jet temperature - T W wall temperature - u velocity component inx andx directions (Fig. 1) - u m jet centerline (or maximum) free jet velocity: external (or maximum) boundary layer velocity aty= m - u m0 arrival velocity defined as the maximum velocity the free jet would have at the plane of impingement if the plane were not there - U J jet exit velocity - x* non-dimensional coordinate starting at the stagnation point=x/2 0.50 - x, y rectangular Cartesian coordinates - y coordinate normal to the wall starting at the wall - ratio of thermal to velocity boundary layer thickness= T/m - 0 ratio of thermal to velocity boundary layer thickness at the stagnation point - * inner layer displacement thickness - 0.50 jet half width at the plane of impingement if the plate were not there - m inner boundary layer thickness atu=u m - Pohlhausen's form parameter - dynamic viscosity - kinematic viscosity=/ - fluid density - momentum thickness - 0 momentum thickness at the stagnation point  相似文献   

8.
The results are given of an experimental investigation of the flow in the initial section of a turbulent underexpanded jet exhausting from a profiled nozzle with Mach number M a = 2.56 at the exit into a parallel stream with Mach number M = 3.1. Analysis of the results of measurement of the fields of the total head p0 and the stagnation temperature T0 in conjunction with results of calculation of a jet of an ideal gas make it possible to construct the velocity profile in the mixing layer of the underexpanded jet in the parallel supersonic flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 161–163, January–February, 1981.  相似文献   

9.
Rayleigh scattering temperature measurements were made in a slightly heated plane jet at various Reynolds numbers and the effect of this parameter on the temperature field was determined. The axial and lateral distributions of the mean and rms temperature as well as the temperature spectra along the jet axis were determined. Results indicated that increasing Reynolds numbers led to lower levels of rms temperature and jet dilution in the moderate Reynolds number regime (between 700 and 2500). It was also found that slower spread rates of the thermal jet occured with larger Reynolds numbers in this regime.List of symbols b T temperature half-width of the jet - C calibration constant for Rayleigh scattering optics - C T, C T,0 constants defining the temperature decay rate - D nozzle width - E T power spectrum of temperature fluctuations - f frequency - I L laser light intensity - I R Rayleigh signal intensity - K T, K T,0 constants defining the jet spread rate - k wavenumber (2f/ U) - N total molecular number density - Re Reynolds number (U 0D/) - T mean excess temperature - T m mean excess temperature on the jet axis - T 0 mean excess temperature at jet exit - T fluctuating temperature - U local mean velocity - U 0 mean velocity at the jet exit - x axial distance from the nozzle exit - y lateral distance from the jet axis - z spanwise distance from the jet axis - Rayleigh scattering cross section - density - kinematic viscosity A version of this paper was presented as paper no 86-WA/ HT-98 at the 1986 ASME Winter Annual Meeting.  相似文献   

10.
A computational investigation is carried out to study the flow and heat transfer from a row of circular jets impinging on a concave surface. The computational domain simulates the impingement cooling zone of a gas turbine nozzle guide vane. The parameters, which are varied in the study include jet Reynolds number (Re d = 5000–67800), inter-jet distance to jet diameter ratio (c/d = 3.33 and 4.67) and target plate distance to jet diameter ratio (H/d = 1, 3 and 4). The flow field, predicted with K-ω turbulence model and using Fluent 6.2.16, is characterized with the presence of a pair of counter rotating vortices, an upwash fountain flow and entrainment. The local pressure coefficient and Nusselt number variations along the concave plate are presented and these values are found to under predict the available experimental data by about 12%.  相似文献   

11.
The article describes a method for calculating the flow of heat through a wavy boundary separating a layer of liquid from a layer of gas, under the assumption that the viscosity and heat-transfer coefficients are constant, and that a constant temperature of the fixed wall and a constant temperature of the gas flow are given. A study is made of the equations of motion and thermal conductivity (without taking the dissipation energy into account) in the approximations of the theory of the boundary layer; the left-hand sides of these equations are replaced by their averaged values over the layer. These equations, after linearization, are used to determine the velocity and temperature distributions. The qualitative aspect of heat transfer in a thin layer of viscous liquid, under regular-wavy flow conditions, is examined. Particular attention is paid to the effect of the surface tension coefficient on the flow of heat through the interface.Notation x, y coordinates of a liquid particle - t time - v and u coordinates of the velocity vector of the liquid - p pressure in the liquid - cv, , T,, andv heat capacity, thermal conductivity coefficient, temperature, density, and viscosity of the liquid, respectively - g acceleration due to gravity - surface-tension coefficient - c phase velocity of the waves at the interface - Tw wall temperature - h0 thickness of the liquid layer - u0 velocity of the liquid over the layer Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 147–151, July–August, 1970.  相似文献   

12.
The article gives the results of an experimental investigation of the geometric structure of an opposing unexpanded jet. It discusses flow conditions with interaction between the jet and sub- and supersonic flows. It is shown that, with the outflow of an unexpanded jet counter to a supersonic flow, there are unstable flow conditions. For stable flow conditions with one roll, dependences are proposed determining the form of a jet in a supersonic opposing flow. A generalized dependence is obtained for the distribution of the pressure at the surface of a body with a jet, flowing out counter to a subsonic flow. The range of change in the determining parameters are the following: Mach numbers at outlet cross section of nozzle, M a = 1 and 3; Mach numbers of opposing flow, M = 0.6–0.9 and 2.9; degree of effectiveness of jet, n = p a /p = 0.5–800 (p a and p are the static pressures at the outlet cross section of the nozzle and in the opposing flow); the ratios of the specific heat capacities, a = = 1.4; the drag temperatures of the jet and the flow, To = Toa = 290°K.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 89–96, January–February, 1977.  相似文献   

13.
14.
In the present paper approximate solutions for the fluid and thermal boundary layers in an incompressible laminar plane wall jet with isothermal and adiabatic walls have been studied respectively, and comparisons with the known exact solutions have been made wherever possible. It is found that the present method is simple and straightforward, and gives results being in good agreement with the exact solutions. For moderate values of the Prandtl number the method may be used for calculating the heat transfer from an isothermal wall and temperature recovery factor for an adiabatic wall respectively.Nomenclature a* dimensionless temperature gradient at the wall - c p specific heat at constant pressure - K momentum flux through a cross-section of the jet - Q volume flux through a cross-section of the jet - r* temperature recovery factor - T temperature of the fluid in the boundary layer - T r adiabatic wall temperature - T temperature of the fluid at rest - u, v velocity components along and normal to the plane wall respectively - x, y rectangular coordinates along and normal to the plane wall respectively - z Greek symbols fluid boundary layer thickness - t, T thermal boundary layer thickness for an isothermal and an adiabatic wall respectively - dimensionless y-coordinate - dimensionless temperature difference (T–T )/T - coefficient of thermal conductivity - coefficient of viscosity - coefficient of kinematic viscosity - Prandtl number - w shearing stress on the plane wall  相似文献   

15.
Unsteady natural convection flow in a two-dimensional square cavity filled with a porous material has been studied. The flow is initially steady where the left-hand vertical wall has temperature T h and the right-hand vertical wall is maintained at temperature T c (T h > T c) and the horizontal walls are insulated. At time t > 0, the left-hand vertical wall temperature is suddenly raised to which introduces unsteadiness in the flow field. The partial differential equations governing the unsteady natural convection flow have been solved numerically using a finite control volume method. The computation has been carried out until the final steady state is reached. It is found that the average Nusselt number attains a minimum during the transient period and that the time required to reach the final steady state is longer for low Rayleigh number and shorter for high Rayleigh number.  相似文献   

16.
Summary Heat flux, wall heat transfer coefficients, and wall pressures are determined for high velocity flow of gas-solid mixtures in a converging-diverging nozzle. Flow separation accompanied with oblique shock formation occurs in the diverging section of the nozzle. The shock strength is reduced upon the addition of solid particles. The wall pressure in the convergent section of the nozzle appears unaffected by the presence of solid particles. In the divergent section, however, the wall pressure is slightly lowered. At the maximum ratio of solid to air flow used in the experiments (3.7) increases in the heat transfer rate of up to 20 and 50 percent are obtained in the convergent and separated (divergent) regions of the nozzle, respectively. Slightly larger increases in the wall heat transfer coefficients are also obtained. It is concluded that the wall heat flux and heat transfer coefficients are influenced strongly by the presence of disturbances upstream of the nozzle inlet.Nomenclature W a air flow rate - W s solids flow rate - x axial distance from nozzle entrance - L axial length of nozzle - specific heat ratio of fluid - A e exit cross section of flow - A * throat cross section of flow - P 0 inlet pressure - P s wall separation pressure - P a ambient exhaust pressure - shock wave angle - shock wave deflection angle - M 1 Mach number upstream of shock wave - Mach number normal to shock wave - q heat flux - k f thermal conductivity of fluid - T wi inside wall temperature - T wo outside wall temperature - T ad adiabatic wall temperature - h wall heat transfer coefficient - C nozzle constant - A local cross section of flow - c p specific heat of fluid - Pr Prandtl number - viscosity of fluid - r c throat radius of curvature - factor accounting for variation of and Units absolute temperature °R(ankine) °F+459.7 - conductivity 1 BTU (hr ft °F)–1 4.137×10–3 cal (s cm °C)–1 - specific heat 1 BTU (1b °F)–1 1 cal (g °C)–1 - absolute pressure 1 psia 0.0680 atm Supported in part by aid provided by the UCLA Space Science Center (Grant NsG 236-62 Libby).Listed for readers not familiar with the units adopted in this paper (editor).  相似文献   

17.
The problem of heat conduction in a thin rotating disk with heat input at a fixed point is considered. The disk is cooled by forced convection from its lateral surfaces. By defining a complex temperature, the temperature throughout the disk is presented as a series of Bessel functions of complex argument. Results are given for a range of rotational speeds.Nomenclature R radial coordinate - angular coordinate - a radius of disk - b thickness of disk - T temperature - T ambient temperature - rotational speed of disk - q heat flux into disk - k thermal conductivity of disk - density of disk - c specific heat of disk - h coefficient of convective heat transfer - r dimensionless radial coordinate, R/a - T* characteristic temperature, q 0 a/ k - t dimensionless temperature, (T–T )/T* - C 1, C 2 dimensionless parameters defined in (3)  相似文献   

18.
A numerical investigation has been made of the hypersonic flow of a rarefied monatomic gas past the windward part of the side surface of an infinite circular cylinder. The calculation was made by direct statistical Monte Carlo modeling for freestream Mach number Mt8=20, ratio of the surface temperature of the body to the stagnation temperature equal to ttw =T tw/T t0 = 0.03, sweep angle 75°, and Reynolds number Ret0 30.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 146–154, January–February, 1992.  相似文献   

19.
This paper deals with the effects of reactive particles on the performance of a pyrotechnic igniter. These particles are placed on the inner surface of a flash tube, released into the main flow of the gas and ignited by the passage of one of the two discontinuities (the shock wave or the contact surface). Two particle sizes have been studied (3m and 10m). It is shown that the best performance is achieved with small particles released into the flow by the shock wave. Another focal point of this study is the combining of two fundamentally different methods to calculate the two phase flow.Nomenclature a0 sound speed in region 0 - a2 sound speed in region 2 - C D drag coefficient - d average particle diameter - d rate change of the particle diameter - e g total internal energy of the gas - e s particle internal energy=C 3 T s - F drag force - rn mass flow rate - Mo c shock wave Mach number - N particle number desity - N u Nusselt number - P pressure - P 0 pressure in region 0 - P 2 pressure in region 2 - P r Prandtl number - Q heat convection - R e Reynolds number - T g gas temperature - T s particle temperature - u 2 velocity in region 2 - u g gas velocity - u s barycentric velocity of the particles - ratio of specific heats - g thermal conductivity of the gas - g gas dynamic viscosity - g gas density - s apparent density of the particles - s true density of the particles - defined by (8) This article was processed using Springer-Verlag TEX Shock Waves macro package 1990.  相似文献   

20.
The geometrical characteristics of jets injected through an opening in a flat plate into an oncoming supersonic flow have been studied on a number of occasions [1, 3]. However, the results were analyzed under different suppositions about the important dimensionless parameters. In [1], the degree of underexpansion of the jet, characterized by n = p a /p, was regarded as decisive; in [3], the experimental points were plotted against the relative dynamic head a u2 a /(u2 ) of the jet. In the present paper, dimensional considerations are used to determine the dimensionless parameters which influence the flow field when an injected jet interacts with an oncoming supersonic gas flow. The influence of these determining dimensionless parameters on the depth of penetration of injected jets into a flow was investigated experimentally. It is shown that the relative depth of penetration is determined basically by the relative specific impulse of the jet, the injection angle, and the shape of the blowing nozzle section.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 151–154, July–August, 1980.  相似文献   

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