Experimental investigation of rarefied gas flow through rectangular slits and nozzles

The flow of a rarefied gas through rectangular configuratons of different geometries has been experimentally studied to determine their discharge coefficient characteristics. The configurations used are a set of sharp-edged slit orifices, a smooth converging nozzle and a tube. The range of the Reynolds number based on the throat conditions varied from 0.01 to 100. The equivalent Knudsen number range based on the upstream conditions and inlet diameter varied from 0.0521 to 2.521. The results for the smooth nozzle are compared with calculations using a numerical method with one-dimensional stream tube approximation based on integrated boundary layer equations. The slit and the tube results are compared with the experimental results of Sreekanth and Davis [1988].     

Experimental investigation of laval nozzles with gas blown asymmetrically

An experimental determination was made of the transverse forces resulting from asymmetric blowing of a transverse gas jet into the supersonic part of a Laval nozzle. The experimental data are generalized on the basis of the analogy between blowing and flow over an equivalent body and using the generalized theory of one-dimensional flows. An approximating dependence is obtained for determining the gain as a result of blowing.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 188–193, March–April, 1981.     

Experimental investigation of flow in a trench

An experimental investigation was made of the flow of a viscous incompressible liquid in a trench of square transverse cross section, using a laser Doppler velocimeter. The investigation was made with two values of the Reynolds number Re, corresponding to laminar and turbulent flow conditions in the channel. The experimental data show that a core with a constant vorticity is formed in the trench, that a jet propagates near the walls of the trench, and that there are secondary eddies in the corners of the trench. The motion of a viscous liquid in a trench of rectangular cross section is part of a broad class of breakaway flows. Experimental data on the investigation of flow in trenches are extremely few. A majority of the existing information is limited to visual observations [1–4]. In [2, 5, 6] the question of the unstable character of flow in trenches was discussed. Quantitative measurements of stable eddy flows in trenches were made in [7–9] using a thermoanemometer, and in [7] measurements were made of the pressure at the bottom and walls of trenches; there are data on the distribution of the velocity in the middle sections of trenches. In [8] the mean velocity, the intensity of the turbulence, and the stress of the turbulent flow were obtained in several sections parallel to the side walls of the trench, In [9] a measurement was made of the velocities also in two cross sections of a trench in which one component of the velocity prevails. A brief analysis of the existing experimental results shows that these data are insufficient to form a detailed representation of the character of flow in a trench.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 76–86, March–April, 1976.     

Numerical investigation of two-phase flow with coagulation and fragmentation of particles in axisymmetric laval nozzles

The method and results of a calculation of the parameters of a polydis-perse two-phase flow with coagulation and fragmentation of particles in collisions are described. The problem is considered in a two-dimensional formulation. The secondary particles (fragments) formed by fragmentation are assumed to have arbitrary mass and velocity distributions.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 145–153, May–June, 1982.We thank F. G. Gaponich for assistance in the computer calculations.     

Experimental investigation of nonstationary flow in cavities in a supersonic flow

An experimental investigation was made into the flow and pressure pulsations in cylindrical cavities open toward a supersonic flow and set up at zero angle of attack (i.e., the cavity axis and the direction of the flow coincide).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 180–183, September–October, 1979.     

Radiating hydrogen flow in axisymmetric nozzles

A considerable number of studies published in recent years have been devoted to the study of gas in channels and pipes. In view of the complexity of the question and the lack of analytic techniques, individual aspects of the problem are generally considered. The determination of the radiant field characteristics in regions of simple geometric form filled with a stationary radiating-absorbing medium has been carried out in several studies. The articles [1–3] are devoted to the calculation of the radiant field and the temperature field for a given flow of a perfect inviscid nonheat-conducting radiating gas with constant absorption coefficient. The flow is assumed to be irrotational [1, 2] or nearly potential [3]. The authors investigated the accuracy of the solution obtained with the aid of various approximate methods and found that the diffusion approximation yields a small error in calculating the radiation density field and the values of the radiant thermal fluxes for a quite broad class of wall reflecting properties. We may note also [4, 5], in which a calculation is made of one-dimensional steady flow of a viscous heat-conducting radiating perfect gas with constant transport coefficients.In [1–5] the absorption coefficient is considered constant. This assumption simplifies the solution process considerably, since as the independent variables we can take the corresponding optical thicknesses. The study [3] contains a remark that the calculation method proposed there may be used with a variable absorption coefficient. However, this possibility was not used in the calculations presented.For a constant absorption coefficient these studies yield a rather complete analysis of the methods for solving two-dimensional problems in geometrically simple regions in the absence of mechanical motion and one-dimensional problems with motion. They contain results obtained for the exact integral or integrodlfferential equations and present an analysis of the approximate methods. The study [3] considers broader possibilities of solving two-dimensional problems (using the Monte-Carlo method), but the flow is assumed known ahead of time.In the following we present a method for calculating the two-dimensional equilibrium flow of an inviscid non-heat-conducting radiating gas with variable absorption coefficient. As an example, we consider the flow of radiating-absorbing hydrogen in axisymmetric nozzles. It is assumed that the radiation is gray and is in local thermodynamic equilibrium. The transport equation is considered in the diffusion approximation. The nozzles examined have a semi-infinite cylindrical inlet section. The initial gas flow in the cylindrical section is supersonic. In the solution process we determine the radiation density field and all the flow parameters within the nozzle.The author wishes to thank Yu. D. Shmyglevskii for his continued interest in this study.     

Transonic swirling flow in axisymmetric nozzles

Summary The transonic flow in axisymmetric choked nozzles is computed in the case of a radial distribution of tangential velocity. The flow configuration is obtained by means of a time-dependent technique. The swirling flow is achieved through a particular surface located at the inlet of the nozzle. The pressure distribution and the sonic line are presented for choked flows without or with swirling.

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Sommario Viene calcolato il flusso transonico in ugelli assialsimmetrici in condizione critica, nel caso di distribuzione radiale di velocità tangenziale.La soluzione è ottenuta numericamente tramite una tecnica instazionaria. Il flusso vorticoso viene creato attraverso una opportuna superficie all'ingresso dell'ugello. Vengono presentati i campi di pressione e la posizione della linea sonica per flussi critici, con e senza vortice.

     

Supersonic flow separation in planar nozzles

We present experimental results on separation of supersonic flow inside a convergent–divergent (CD) nozzle. The study is motivated by the occurrence of mixing enhancement outside CD nozzles operated at low pressure ratio. A novel apparatus allows investigation of many nozzle geometries with large optical access and measurement of wall and centerline pressures. The nozzle area ratio ranged from 1.0 to 1.6 and the pressure ratio ranged from 1.2 to 1.8. At the low end of these ranges, the shock is nearly straight. As the area ratio and pressure ratio increase, the shock acquires two lambda feet. Towards the high end of the ranges, one lambda foot is consistently larger than the other and flow separation occurs asymmetrically. Downstream of the shock, flow accelerates to supersonic speed and then recompresses. The shock is unsteady, however, there is no evidence of resonant tones. The separation shear layer on the side of the large lambda foot exhibits intense instability that grows into large eddies near the nozzle exit. Time-resolved wall pressure measurements indicate that the shock oscillates in a piston-like manner and most of the energy of the oscillations is at low frequency.      

Experimental investigation of turbulence in a supersonic flow

The structure of disturbances carried by the flow into the working section of a supersonic wind tunnel has been investigated by means of a constant-current hot-wire anemometer. In order to generate the disturbances grids consisting of round rods were introduced upstream from the nozzle throat. It was found that in the working section the disturbances consist of non-correlating vortex, entropy and acoustic modes. The latter is generated by the boundary layer on the nozzle walls and the first two by the grids. The spectral compositions of the various modes are compared. Because of the presence of grid turbulence the point of laminar-turbulent transition in the boundary layer on a flat plate varied widely.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 119–124, May–June, 1990.     

Turbulent flow through bifurcated nozzles

A finite-element model has been used to study steady-state turbulent flow through bifurcated submerged-entry nozzles with oversized ports typical of those used in the continuous casting of steel. Both 2D and 3D simulations have been performed with the commercial code FIDAP, using the standard K–? turbulence model. Predicted velocities from 3D simulations compare reasonably with experimental measurements using a hot-wire anemometer conducted in a physical water model, where severe turbulent fluctuations are present. Results show that a 2D simulation can also capture the main flow characteristics of the jet existing the nozzle and requires two orders of magnitude less computer time than the 3D simulation. A model combining the nozzle and mould was set up to study the effect of the outlet boundary conditions of the nozzle on the jet characteristics. This modelling technique will assist in the design of submerged-entry nozzles, especially as applied to enhance steel quality in the continuous casting process. Further, the model will provide appropriate inlet boundary conditions for a separate numerical model of the mould.     

Calculation of the flow in ejector nozzles

A method is proposed for calculating the two-dimensional nonviscous flows in ejector nozzles of arbitrary shape, for two operating cycles: the subsonic flow cycle of a secondary stream and a cycle when the secondary stream attains critical velocity, i.e., it is cut off. In the second case, the possibility is allowed for the appearance of a direct compression shock in the supersonic part of the secondary stream.Translated from Mekhanika Zhidkosti i Gaza, No. 1, pp. 111–118, January–February, 1974.The authors thank A. N. Kraiko and M. Ya. Ivanov for useful discussions and assistance, V. V. Polyakov for interest in the project and L. P. Frolova for assistance in drawing up the task.     

Some peculiarities of two-phase flow in nozzles

Calculations are conducted for unidimensional two-phase flow in nozzles for a wide range of particle concentrations and dimensions. It is established that there exists a maximum in loss of specific momentum due to a lag in particle velocity and temperature relative to the gas. The results obtained are compared with calculations using linearized theory as well as with experimental data. The agreement between calculation and experiment is noted. Equilibrium flow of a two-phase mixture with solidification of liquid particles is considered. The presence of an anomalous flow region is established, where in the model of an ideal unidimensional equilibrium flow in a nozzle with discharge into a vacuum the presence of two successively located minimum sections is necessary.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 50–57, May–June, 1973.     

Experimental investigation on flow modes of electrospinning

Electrospinning experiments are performed byusing a set of experimental apparatus,a stroboscopic systemis adopted for capturing instantaneous images of the conejet configuration.The cone and the jet of aqueous solutionsof polyethylene oxide(PEO) are formed from an orifice of acapillary tube under the electric field.The viscoelastic constitutive relationship of the PEO solution is measured anddiscussed.The phenomena owing to the jet instability aredescribed,five flow modes and corresponding structures areobtained with variations of the fluid flow rate Q,the electricpotential U and the distance h from the orifice of the capillary tube to the collector.The flow modes of the cone-jetconfiguration involves the steady bending mode,the rotating bending mode,the swinging rotating mode,the blurringbending mode and the branching mode.Regimes in the Q-Uplane of the flow modes are also obtained.These results mayprovide the fundamentals to predict the operating conditionsexpected in practical applications.