Cylindrical Wall Jet Research Articles

Evaluation of Turbulence Models for External Flows

An industry-motivated investigation of the application of turbulence models to external fluid flows has been carried out. The motivating application is the melt-blowing fiber production process used by 3M in which friction forces exerted by high-speed air jets stretch pliable polymeric fibers. The complex fluid flow is turbulent and unique. The closest traditional fluid flow is the wall jet. In order to achieve results of sufficient accuracy to be used in the design of the production equipment, a necessary prerequisite is the identification of an appropriate turbulence model. To this end, five turbulence models, commonly offered in commercially available CFD software (FLUENT® Software, ANSYS® CFX® Software, and Star-CD™ Software) were carefully implemented in appropriate numerical simulations of the available experimental data. The investigated turbulence representations included several two-equation models and a direct solution of the RANS equation. The experimental data consisted of measured velocity profiles for the plane wall jet and the cylindrical wall jet. A comparison of the velocity profiles extracted from the simulations with those of experiment enabled a clear conclusion to be drawn about the most suitable turbulence model, which was found to be the standard k − ϵ model with enhanced near-wall treatment. For all the simulations, the accuracy of the numerical simulations was carefully investigated with respect to three critical issues: number of control volumes, deployment of the control volumes, and the geometry and the extent of the solution domain. The deployment issue is of great significance in the neighborhood of a bounding wall and directly influences the near-wall treatment. The choice of the solution domain controls the boundary conditions and the surfaces at which they are applied. A general conclusion that follows from this study is that it is essential to verify the suitability of a turbulence model before applying it to real-world applications.

A Turbulent Cylindrical Wall Jet Equipped with a Front-Facing Step Impinging Normally on a Flat Plate.

This is an experimental study of a turbulent cylindrical wall jet that issues from an annular nozzle, flows along a cylindrical wall and finally impinges normally on a flat plate. In order to disturb the flow near the wall and to control the thickness of the wall shear layer, a front-facing step is equipped at an arbitrary location on the cylindrical wall. This type of jet flow has properties characterized by a pressure increase and boundary layer growth in the downstream direction, so that the flow separates from the cylindrical wall and reattaches to the impingement plate. This report mainly concerns the effects on the separation and reattachment properties of the flow with various nozzle-step distances and step-impingement distances. Mean velocity and static pressure on the cylindrical wall were measured. The flow patterns in the x-y plane normal to the cylindrical wall in the region near the step and before the impingement plate were obtained by the mean flow vectors and the flow visualization by an oil film method. The results show that the flow patterns can be classified into three main types.

211 表面に粗面形状を持つ円柱壁面噴流と平板の衝突に関する研究

211 表面に粗面形状を持つ円柱壁面噴流と平板の衝突に関する研究

An Experimental Investigation of a Turbulent Cylindrical Wall Jet Equipped with Front-Facing Step. Separation and Reattachment Properties of Wall Jet Flow.

This paper deals with an experimental study of a turbulent cylindrical wall jet with a front-facing step equipped at an arbitrary location on the cylindrical wall, in order to disturb the flow near the wall and to cantrol the thickness of the wall shear layer. This report is mainly concerned with our search for the effects on the separation and reattachment properties of the jet flow in the region before and after a step with various heights and locations. The variations in the static pressures on the cylindrical wall surface, jet half-widths and boundary layer thicknesses in the downstream direction were examined. The relationships among the separation point from the cylindrical wall, the reattachment point and the nozzle-step distance were obtained. The results were compared with those already obtained for an ordinary cylindrical wall jet without the step. Furthermore, the flow patterns in the x-y plane normal to the wall in the region before and after the step were visualized by an oil film method.

NONSIMILAR SOLUTIONS FOR HEAT TRANSFER IN WALL JET FLOWS

An analysis is presented to investigate the flow and heat transfer characteristics of a laminar plane wall jet with non-isothermal wall as well as uniform suction and blowing at the surface and a laminar cylindrical wall jet. The approach used is local nonsimilarity method, wherein, the nonsimilanty terms appearing in the momentum and energy equations are retained and simplifications are introduced only in the auxiliary system of equations. To insure the accuracy of the results, solutions are obtained for three levels of truncation of the governing equations. For the case of plane wall jet problem, both a series solution as well as local nonsimilarity solution have been given and the agreement between the two is found to be very good. For the cylindrical wall jet problem, the results obtained by the local nonsimilarity approach in the present paper have been compared with the series solution results. Numerical results for the wall shear stress, velocity distribution, wall heat transfer rate and temperatur...

HEAT TRANSFER IN A LAMINAR CYLINDRICAL WALL JET WITH UNIFORM SURFACE HEAT FLUX

Abstract The steady state flow and heat transfer characteristics of a laminar cylindrical wall jet are obtained for uniform surface heat flux conditions. Local nonsimilarity solutions as well as series solutions are presented for the velocity and thermal fields. Numerical results are given for the wall shear stress, surface temperature variation and temperature field for a Prandtl number of 0.73.

Investigation of a turbulent cylindrical wall jet impinging normally on a flat plate

Investigation of a turbulent cylindrical wall jet impinging normally on a flat plate

Investigation of a Turbulent Cylindrical Wall Jet Impinging Normally on a Flat Plate. (2nd Report. Impinging Jet Properties by Mean Flow).

This paper presents an experimental study of a turbulent cylindrical wall jet impinging normally on a flat plate. This type of jet flow may have properties including boundary layer separation on the cylindrical wall and reattachment on the impingement plate. The effect of the nozzle impingement distance on the mean flow properties of the jet before and after the impingement was investigated. The changes in the static pressure on the cylindrical wall surface, the maximum jet velocity and the boundary layer thickness were examined. Both the separation point from the cylindrical wall and the reattachment point on the impingement plate were divided into three trends depending on the nozzle impingement distance.

Investigation of a turbulent cylindrical wall jet impinging normally on a flat plate. 1st Report. Fundamental properties of each jet flow.

This paper presents the results of an experimental investigation of a turbulent cylindrical wall jet impinging normally on a flat plate. This type of jet flow may have properties including boundary layer separation and reattachment on the wall. Before dealing with this jet flow, this report describes the fundamental properties of three types of jet flow : a circular free jet from a circular nozzle, a cylindrical wall jet from an annular nozzle, and the impinging jet of a circular free jet with the flat plate normally. The changes of the maximum jet velocity, the jet half-width, the turbulence at the velocity maxima, and the static pressure for each jet flow are examined, and the results are compared with those obtained for the jet flow by the other investigators.

Analysis of a two-dimensional, turbulent wall jet along a circular cylinder. 3rd Report, Effects of nozzle exit velocity profile and injection angle.

In the previous papers, the flow characteristics (velocity and pressure distributions, position of separation, decay of jet centerline velocity, change of jet width, etc.) of a two-dimensional jet along a circular cylinder were clarified by theoretical analysis using an integral momentum equation and experimental analysis, and the effects of nozzle width were also clarified. This paper presents the effects of nozzle exit velocity profile and the injection angle on the flow characteristics of a cylindrical wall jet. It was also confirmed that the flow characteristics can be controlled to some degree by the nozzle exit velocity and the injection angle.

Experimental investigation of conical wall jets

The investigations described here pertain to the determination of the flowfields of different conical wall jet systems. The flow configuration is obtained by pushing a cone-frustum with a flow guide attached to its leading edge into a diffuser having the same included angle as the cone, creating a uniform gap. Air is blown through this gap along the conical surface to form a conical wall jet. A radial or cylindrical wall jet would occur if the apex angle a of the cone becomes 90 or 0 deg. A plane wall jet would occur if the radius of the cylinder becomes infinity for the case of a = 0. The experimental results show that the dimensionless velocity profiles and the rate of jet spread follow patterns similar to those reported for a radial, plane, or cylindrical wall jet. Based upon available skin friction data for wall jets, the velocity profiles have been satisfactorily expressed in terms of variables in the law of the wall and the defect law. No effect of transverse curvature is observed. An analytical model based upon conservation of momentum in the axial direction has been developed to predict the longitudinal decay of the maximum velocity. The experimental data conform to the trends of the predictions.

Heat transfer measurements in cylindrical wall jets

In this article measurements of mean velocities and heat-transfer rates in a cylindrical wall jet formed by a jet emerging through a convergent nozzle are presented. The heat-transfer rate and the maximum velocity decay are influenced by the transverse curvature present. The experimental results are correlated successfully by using the diameter of the cylinder to slot height ratio as the curvature parameter. With a diameter to slot height ratio of 0.125, the Stanton number values for a cylindrical wall jet are as much as 1.7 times that of a plane wall jet, under similar conditions.

Turbulence measurements in a cylindrical wall jet

A cylindrical wall jet is obtained when the jet emerges from a converging nozzle and flows along a cylinder placed concentric with the nozzle. The results of hot wire measurements in the developed zone of such a cylindrical wall jet are presented. The results obtained are compared with similar measurements in a free circular jet and in a plane wall jet. The comparisons show the effect of the cylinder in the inner region, but do not reveal any effect of the cylinder in the outer mixing region. Further, it is shown that the currently available method of determining eddy diffusivity distribution in jet flows is misleading.

Experiments on a turbulent cylindrical wall jet

The investigation described here is an experimental study directed toward determining flow field and surface friction characteristics of a cylindrical wall jet. The flow configuration is obtained by placing a cylindrical rod along the axis of a converging nozzle. The flow field thus produced consists of a developing turbulent boundary layer co-existing with an outer fluid layer that mixes freely with quiescent surroundings. Direct measurements of fluid friction at the rod surface, performed with a hot-film element, revealed a significant effect of transverse surface curvature on the local friction factor. Velocity profiles at various axial stations exhibited similarity in the outer mixing layer, but not in the boundary layer adjacent to the surface. Representations of the velocity field in terms of law of the wall variables and defect-law variables revealed significant transverse curvature effects. The measured wall-jet velocity profiles could be satisfactorily represented in terms of a law of the wake, wherein the wake function depends on a transverse curvature parameter. In the outer mixing layer, the eddy viscosity data correspond closely to those of free jets.

The laminar cylindrical wall-jet in the early part of the flow

The boundary layer equations of motion for the case of the laminar, cylindrical wall-jet have been investigated for the early part of the flow or when the boundary layer is thin compared to the cylinder. The effect of curvature has been considered by expanding the Stokes' stream function in a power series of a parameter which is the ratio of the boundary layer thickness to the radius of the cylinder, with the first term being the similarity solution to the two-dimensional wall-jet, which has been given by G lauert. The results are then restricted so that the boundary layer thickness is small compared to the diameter of the cylinder. The resulting set of ordinary differential equations has been evaluated analytically in part, and numerically for the remainder up to the second approximation. It has been found that the shear stress at the wall is greater than that of the two-dimensional case without transverse curvature. The corresponding problem of heat transfer from the surface of a cylinder surrounded by a wall-jet has been treated. The temperature distribution was also assumed expandable in a power series, the zero-th term being the same as that obtained for the two-dimensional wall-jet. The set of ordinary differential equations subsequently obtained has been evaluaed by numerical methods with a computer, for the cases of constant wall temperature and constant heat flux.