Mixing and Entrainment Characteristics of Circular and Noncircular Confined Jets

2003 ◽  
Vol 125 (5) ◽  
pp. 835-842 ◽  
Author(s):  
Ghanshyam Singh ◽  
T. Sundararajan ◽  
K. A. Bhaskaran
Keyword(s):  
Cross Section ◽  
Similarity Solution ◽  
Isosceles Triangle ◽  
Exit Plane ◽  
Ambient Fluid ◽  
Entrainment Ratio ◽  
Confined Jets ◽  
Maximum Value ◽  
Circular And Noncircular Jets ◽  
Jet Axis

The present work deals with the experimental investigation of entrainment characteristics of confined/semiconfined circular and noncircular jets. The jet fluid, after issuing out of a nozzle of circular or noncircular cross section, enters a circular mixing tube of larger area, and during this process it entrains some ambient fluid into the mixing tube. The flow is incompressible and isothermal at a jet Reynolds number of 7200. The experimental results obtained in the study are first validated with the approximate theoretical analysis of Pritchard et al. (1997) and also with the similarity solution proposed by Becker et al. (1963) for circular nozzles. It is observed that the similarity solution is applicable for circular as well as noncircular jets in the region close to the jet axis and away from the nozzle exit plane. The entrainment ratio increases to a maximum value as the jet location is shifted away from the tube inlet; for the configurations studied, enhancement up to 30% has been observed in the entrainment ratio with shift in jet location. For a smaller mixing tube diameter and jet located at the inlet of the mixing tube, the circular jet entrains more than noncircular jets. For a larger mixing tube or shifted jet locations, the noncircular jets entrain more of ambient fluid, in general. Among the different noncircular geometries considered, the jet having the cross section of an isosceles triangle causes maximum entrainment.

Evaporation and Viscous Flow in Triangular Grooves in Micro Heat Pipes

2005 ◽  
Author(s):  
Mulugeta Markos ◽  
Vladimir S. Ajaev ◽  
G. M. Homsy
Keyword(s):  
Cross Section ◽  
Flow Rate ◽  
Cross Sections ◽  
Wedge Angle ◽  
Heat Pipes ◽  
Type Model ◽  
Pressure Gradients ◽  
Maximum Value ◽  
Dry Out ◽  
Micro Heat Pipes

We develop a lubrication type model of a liquid flow in a wedge in the limit of small capillary numbers and negligible gravity. The model incorporates the effects of capillary pressure gradients and evaporation. Steady vapor-liquid interface shapes are found for a range of parameters. In the limit of weak evaporation the flow is the same in all cross-sections and can be controlled by changing the wedge angle. We find the wedge angle that results in the maximum value of the flow rate for a given contact angle. For high evaporation rates, both the flow rate and the amount of liquid in each cross-section along the wedge decrease until the point of dry-out is reached. The location of the dry-out point is studied as a function of evaporation. Practical suggestions about optimization of micro heat pipes are given.

A measurement of the ionization cross-section of Ne + to Ne 2+ by electron impact

1963 ◽  
Vol 274 (1359) ◽  
pp. 546-551 ◽  
Keyword(s):  
Electron Energy ◽  
Cross Section ◽  
Ionization Cross Section ◽  
Incident Electron Energy ◽  
Ionization Cross ◽  
Maximum Value ◽  
Beam Method ◽  
The Cross ◽  
Semi Empirical ◽  
Limits Of Error

The crossed-beam method described by the authors in 1961 was used to measure the cross-section of Ne + in the reaction Ne + + e → Ne 2+ + 2 e . The cross-section increases linearly with electron energy near the threshold and attains a maximum value of 3·13 x 10 -17 cm 2 at 200 eV. The errors in the measurements were estimated to be less than ± 10% and the highest incident electron energy used was 1000 eV. A semi-empirical formula proposed by Drawin in 1961 describes the measured cross-section within the above limits of error when the two adjustable parameters take the values ξf 1 = 5·25 and f 2 = 0·70.

scholarly journals Optimization of the cross-sectional shape of the belts of trihedral lattice supports

2019 ◽  
Vol 7 (4) ◽  
pp. 5-8
Author(s):  
Linar Sabitov ◽  
Ilnar Baderddinov ◽  
Anton Chepurnenko
Keyword(s):  
Objective Function ◽  
Nonlinear Optimization ◽  
Cross Section ◽  
Optimization Methods ◽  
Cross Sectional ◽  
Maximum Value ◽  
Axial Moment ◽  
The Cross ◽  
Nonlinear Optimization Methods ◽  
Sectional Shape

The article considers the problem of optimizing the geometric parameters of the cross section of the belts of a trihedral lattice support in the shape of a pentagon. The axial moment of inertia is taken as the objective function. Relations are found between the dimensions of the pentagonal cross section at which the objective function takes the maximum value. We introduce restrictions on the constancy of the consumption of material, as well as the condition of equal stability. The solution is performed using nonlinear optimization methods in the Matlab environment.

scholarly journals Asymptotically based self-similarity solution of the Navier–Stokes equations for a porous tube with a non-circular cross-section

2017 ◽  
Vol 826 ◽  
pp. 396-420 ◽  
Author(s):  
M. Bouyges ◽  
F. Chedevergne ◽  
G. Casalis ◽  
J. Majdalani
Keyword(s):  
Cross Section ◽  
Similarity Solution ◽  
Stokes Equations ◽  
Circular Cross Section ◽  
Internal Flow ◽  
Navier Stokes ◽  
Solid Rocket Motor ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Radial Deviation

This work introduces a similarity solution to the problem of a viscous, incompressible and rotational fluid in a right-cylindrical chamber with uniformly porous walls and a non-circular cross-section. The attendant idealization may be used to model the non-reactive internal flow field of a solid rocket motor with a star-shaped grain configuration. By mapping the radial domain to a circular pipe flow, the Navier–Stokes equations are converted to a fourth-order differential equation that is reminiscent of Berman’s classic expression. Then assuming a small radial deviation from a fixed chamber radius, asymptotic expansions of the three-component velocity and pressure fields are systematically pursued to the second order in the radial deviation amplitude. This enables us to derive a set of ordinary differential relations that can be readily solved for the mean flow variables. In the process of characterizing the ensuing flow motion, the axial, radial and tangential velocities are compared and shown to agree favourably with the simulation results of a finite-volume Navier–Stokes solver at different cross-flow Reynolds numbers, deviation amplitudes and circular wavenumbers.

The generation of internal waves by vibrating elliptic cylinders. Part 2. Approximate viscous solution

1997 ◽  
Vol 351 ◽  
pp. 119-138 ◽  
Author(s):  
D. G. HURLEY ◽  
G. KEADY
Keyword(s):  
Approximate Solution ◽  
Circular Cylinder ◽  
Flow Field ◽  
Cross Section ◽  
Similarity Solution ◽  
Internal Gravity Waves ◽  
Approximate Theory ◽  
Viscous Effects ◽  
Typical Dimension ◽  
Viscous Solution

An approximate theory is given for the generation of internal gravity waves in a viscous Boussinesq fluid by the rectilinear vibrations of an elliptic cylinder. A parameter λ which is proportional to the square of the ratio of the thickness of the oscillatory boundary layer that surrounds the cylinder to a typical dimension of its cross-section is introduced. When λ[Lt ]1 (or equivalently when the Reynolds number R[Gt ]1), the viscous boundary condition at the surface of the cylinder may to first order in λ be replaced by the inviscid one. A viscous solution is proposed for the case λ[Lt ]1 in which the Fourier representation of the stream function found in Part 1 (Hurley 1997) is modified by including in the integrands a factor to account for viscous dissipation. In the limit λ→0 the proposed solution becomes the inviscid one at each point in the flow field.For ease of presentation the case of a circular cylinder of radius a is considered first and we take a to be the typical dimension of its cross-section in the definition of λ above. The accuracy of the proposed approximate solution is investigated both analytically and numerically and it is concluded that it is accurate throughout the flow field if λ is sufficiently small, except in a small region near where the characteristics touch the cylinder where viscous effects dominate.Computations indicate that the velocity on the centreline on a typical beam of waves, at a distance s along the beam from the centre of the cylinder, agrees, within about 1%, with the (constant) inviscid values provided λs/a is less than about 10−3. This result is interpreted as indicating that those viscous effects which originate from the characteristics that touch the cylinder (places where the inviscid velocity is singular) reach the centreline of the beam when λs/a is about 10−3. For larger values of s, viscous effects are significant throughout the beam and the velocity profile of the beam changes until it attains, within about 1% when λs/a is about 2, the value given by the similarity solution obtained by Thomas & Stevenson (1972). For larger values of λs/a, their similarity solution applies.In an important paper Makarov et al. (1990) give an approximate solution for the circular cylinder that is very similar to ours. However, it does not reduce to the inviscid one when the viscosity is taken to be zero.Finally it is shown that our results for a circular cylinder apply, after small modifications, to all elliptical cylinders.

scholarly journals Increasing the range of ultra wideband radars based on antenna arrays

2019 ◽  
Vol 30 ◽  
pp. 05017
Author(s):  
Boris Lagovsky ◽  
Alexander Samokhin ◽  
Malay Tripathy
Keyword(s):  
Cross Section ◽  
Antenna Arrays ◽  
Numerical Solutions ◽  
Narrow Band ◽  
Variational Problems ◽  
Optimal Shape ◽  
Ultra Wideband ◽  
Maximum Value ◽  
Efficient Processing ◽  
Processing Algorithms

Analytical and numerical solutions are presented for increasing the range of ultra wideband radars based on antenna arrays by optimizing their characteristics. It is shown that the shape of UWB pulses significantly affects the maximum value of the reflected signal. Solutions of variational problems of searching for the optimal shape of probing UWB pulses are investigated. Optimization of the form allows to obtain good results when using even approximate data on the dispersion dependences of the radar cross-section. The use of new efficient processing algorithms for UWB signals that do not have direct narrow-band analogs is substantiated.

Local similarity solutions and their limitations

1980 ◽  
Vol 96 (2) ◽  
pp. 299-313 ◽  
Author(s):  
H. K. Moffatt ◽  
B. R. Duffy
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Similarity Solution ◽  
Similarity Solutions ◽  
Normal Velocity ◽  
Local Similarity ◽  
Reynolds Number Flow ◽  
Interesting Conclusion ◽  
Number Flow ◽  
Pressure Driven Flow

Two problems exhibiting breakdown in local similarity solutions are discussed, and the appropriate asymptotic form of the exact solution is determined in each case. The first problem is the very elementary problem of pressure driven flow along a duct whose cross-section has a sharp corner of angle 2α. When 2α < ½π, a local similarity solution is valid, whereas, when 2α > ½π, the solution near the corner depends on the global geometry of the cross-section. The transitional behaviour when 2α = ½π is determined.The second problem concerns low-Reynolds-number flow in the wedge-shaped region |θ| < α when either a normal velocity proportional to distance from the vertex is imposed on both boundaries, or a finite flux 2Q is introduced or extracted at the vertex (the Jeffery–Hamel problem). It is shown that the similarity solution in either case is valid only when 2α < 2αc ≈ 257·5°; a modified problem is solved exactly revealing the behaviour when α > αc, and the transitional behaviour when α = αc (when the similarity solutions become infinite everywhere). An interesting conclusion for the Jeffery–Hamel problem is that when α > αc, inertia forces are of dominant importance throughout the flow field no matter how small the source Reynolds number 2Q/ν may be.

scholarly journals Calculation of the interaction of a supersonic jet with a flat obstacle inclined off the jet axis

2020 ◽  
Vol 2020 (4) ◽  
pp. 72-81
Author(s):  
V.P. Halynskyi ◽  
Keyword(s):  
Flow Field ◽  
Pressure Distribution ◽  
Cross Section ◽  
Inclination Angle ◽  
Supersonic Jet ◽  
Jet Flow ◽  
Plate Surface ◽  
Front Edge ◽  
Flow Parameters ◽  
Jet Axis

This paper presents results of a numerical solution of the model problem of the interaction of a plane supersonic jet with a semiinfinite flat plate inclinable off the jet axis. The paper is devoted to the study of the flow parameters in the jet flow field and the pressure distribution over the plate surface as a function of the plate inclination. The aim of the paper is to obtain the flow parameters in the jet flow field and the pressure distribution over the plate surface as a function of the plate inclination angle and front edge position. To obtain numerical results, marching algorithms in the inviscid gas and viscous layer approximation were used. At specified values of the supersonic underexpanded/overexpanded jet parameters, calculations were conducted in the plate inclination angle range of 0 to 20?. The position of the plate front edge was specified by two coordinates: a longitudinal and a transversal one, and in the parametric calculations the transversal coordinate was varied at a fixed longitudinal one. The cross-section at which the nonuniform jet field starts to interact with the plate was determined as a function of both the plate front edge position and the plate inclination. The numerical study showed the following: with increasing plate inclination angle, the oscillation frequencies of the flow parameters in the jet flow field and on the plate surface decrease, while their oscillation amplitudes increase, and the position of the maximum pressure point on the plate surface depends on the initial position of the plate front edge and may not coincide with the cross-section at which the jet–plate interaction starts. The results obtained may be used in qualitative estimation of the effect of different parameters in the jet flow field.

scholarly journals Research on Thermal Neutron Shielding Performance of TiB2-Al Composite Materials

2021 ◽  
Author(s):  
Chao Wang ◽  
Zhefu Li ◽  
Mengge Dong ◽  
Lu Zhang ◽  
Jianxing Liu ◽  
...  
Keyword(s):  
Thermal Neutron ◽  
Cross Section ◽  
Neutron Fluence ◽  
Thermal Neutrons ◽  
Neutron Shielding ◽  
Preparation Methods ◽  
Neutron Fluence Rate ◽  
Maximum Value ◽  
Al Composite ◽  
Macroscopic Cross Section

<p>Although the various excellent properties and preparation methods of TiB<sub>2</sub>-based composites have been extensively studied, their neutron shielding properties have not received as much attention. In this article, the neutron shielding performance of the previously prepared TiB<sub>2</sub>-Al composite will be studied. The photo neutron source device was used to carry out neutron irradiation tests on test samples with a thickness of 10 mm. The average thermal neutron shielding rate of TiB<sub>2</sub>-based boron-containing composites is 17.55%, and the shielding rate increases with the increase of BN content. The macroscopic cross-section of thermal neutrons of the composites generally shows a stable trend, and when the BN content is 10%, the thermal neutrons macroscopic cross section reaches the maximum value of 7.58cm<sup>-1</sup>. With the increase of the BN content, the thermal neutron fluence rate shows a gradually decreasing trend.</p>

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