The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Osami Kitoh - One of the best experts on this subject based on the ideXlab platform.
-
A general formulation for the decay of swirling motion along a straight pipe
International Communications in Heat and Mass Transfer, 1994Co-Authors: Osami KitohAbstract:Abstract This paper describes an analytical approach, based on the conservation of angular momentum flux, to predict the decay of swirling motion due to frictional effects along a straight duct. A combined Forced Vortex and shear-type velocity profiles were used and the analysis could be applicable to any types of swirling flow. Good agreement with measurements in a straight pipe with different level of inlet swirl intensities (Kitoh O.; J. Fluid Mechanics, 1991) can be obtained with the approximate solution. The present formulation can also demonstrate that the swirling motion along a straight pipe does not always decay exponentially but depending on inlet conditions and the variation of friction coefficient with downstream distance.
-
experimental study of turbulent swirling flow in a straight pipe
Journal of Fluid Mechanics, 1991Co-Authors: Osami KitohAbstract:Swirling flow through a pipe is a highly complex turbulent flow and is still challenging to predict. An experimental investigation is performed to obtain systematic data about the flow and to understand its physics. A free-Vortex-type swirling flow is introduced in a long straight circular pipe. The swirling component decays downstream as a result of wall friction. The velocity distributions are continuously changing as they approach fully developed parallel flow. The swirl intensity Ω, defined as a non-dimensional angular momentum flux, decays exponentially. The decay coefficients, however, are not constant as conventionally assumed, but depend on the swirl intensity. The wall shear stresses are measured by a direct method and, except in a short inlet region, are a function only of the swirl intensity and the Reynolds number. The velocity distributions and all Reynolds stress components are measured at various axial positions in the pipe. The structure of the tangential velocity profile is classified into three regions: core, annular and wall regions. The core region is characterized by a Forced Vortex motion and the flow is dependent upon the upstream conditions. In the annular region, the skewness of the velocity vector is noticeable and highly anisotropic so that the turbulent viscosity model does not work well here. The tangential velocity is expressed as a sum of free and Forced Vortex motion. In the wall region the skewness of the flow becomes weak, and the wall law modified by the Monin–Oboukhov formula is applicable. Data on the microscale and the spectrum are also presented and show quite different turbulence structures in the core and the outer regions.
Janice Enagonio - One of the best experts on this subject based on the ideXlab platform.
-
Tropical Cyclogenesis via Convectively Forced Vortex Rossby Waves in a Shallow Water Primitive Equation Model
Journal of the Atmospheric Sciences, 2001Co-Authors: Janice Enagonio, Michael T. MontgomeryAbstract:Abstract This work examines further the problem of tropical cyclogenesis by convective generation of vertical vorticity within a preexisting cyclonic circulation whose initial maximum tangential wind is approximately 5 m s−1. This paper validates and extends recent work examining the suggested upscale cascade mechanism in a three-dimensional quasigeostrophic framework using a simple shallow water primitive equation (SWPE) numerical model and helps clarify certain aspects of the Rossby adjustment problem on a nonresting basic state for finite-amplitude nonaxisymmetric disturbances. The SWPE approach serves as a meaningful intermediate step between the quasigeostrophic and full-physics frameworks and allows a simple investigation of the effects of unbalanced dynamics (contributions of gravity waves) and Rossby numbers of order unity. The authors compare quantitative results of the two models on the storm spinup time and magnitude. For asymmetric initial conditions whose mass and wind field are out of balanc...
-
Tropical Cyclogenesis via Convectively Forced Vortex Rossby Waves in a Three-Dimensional Quasigeostrophic Model
Journal of the Atmospheric Sciences, 1998Co-Authors: Michael T. Montgomery, Janice EnagonioAbstract:Abstract This work investigates the problem of tropical cyclogenesis in three dimensions. In particular, the authors examine the interaction of small-scale convective disturbances with a larger-scale Vortex circulation in a nonlinear quasigeostrophic balance model. Convective forcing is parameterized by its estimated net effect on the potential vorticity (PV) field. Idealized numerical experiments show that Vortex intensification proceeds by ingestion of like-sign potential vorticity anomalies into the parent Vortex and expulsion of opposite-sign potential vorticity anomalies during the axisymmetrization process. For the finite-amplitude forcing considered here, the weakly nonlinear Vortex Rossby wave mean-flow predictions for the magnitude and location of the spinup are in good agreement with the model results. Vortex development is analyzed using Lagrangian trajectories, Eliassen–Palm flux vectors, and the Lorenz energy cycle. Using numerical estimates of the magnitude of PV injection based on previous ...
Michael T. Montgomery - One of the best experts on this subject based on the ideXlab platform.
-
Tropical Cyclogenesis via Convectively Forced Vortex Rossby Waves in a Shallow Water Primitive Equation Model
Journal of the Atmospheric Sciences, 2001Co-Authors: Janice Enagonio, Michael T. MontgomeryAbstract:Abstract This work examines further the problem of tropical cyclogenesis by convective generation of vertical vorticity within a preexisting cyclonic circulation whose initial maximum tangential wind is approximately 5 m s−1. This paper validates and extends recent work examining the suggested upscale cascade mechanism in a three-dimensional quasigeostrophic framework using a simple shallow water primitive equation (SWPE) numerical model and helps clarify certain aspects of the Rossby adjustment problem on a nonresting basic state for finite-amplitude nonaxisymmetric disturbances. The SWPE approach serves as a meaningful intermediate step between the quasigeostrophic and full-physics frameworks and allows a simple investigation of the effects of unbalanced dynamics (contributions of gravity waves) and Rossby numbers of order unity. The authors compare quantitative results of the two models on the storm spinup time and magnitude. For asymmetric initial conditions whose mass and wind field are out of balanc...
-
Tropical Cyclogenesis via Convectively Forced Vortex Rossby Waves in a Three-Dimensional Quasigeostrophic Model
Journal of the Atmospheric Sciences, 1998Co-Authors: Michael T. Montgomery, Janice EnagonioAbstract:Abstract This work investigates the problem of tropical cyclogenesis in three dimensions. In particular, the authors examine the interaction of small-scale convective disturbances with a larger-scale Vortex circulation in a nonlinear quasigeostrophic balance model. Convective forcing is parameterized by its estimated net effect on the potential vorticity (PV) field. Idealized numerical experiments show that Vortex intensification proceeds by ingestion of like-sign potential vorticity anomalies into the parent Vortex and expulsion of opposite-sign potential vorticity anomalies during the axisymmetrization process. For the finite-amplitude forcing considered here, the weakly nonlinear Vortex Rossby wave mean-flow predictions for the magnitude and location of the spinup are in good agreement with the model results. Vortex development is analyzed using Lagrangian trajectories, Eliassen–Palm flux vectors, and the Lorenz energy cycle. Using numerical estimates of the magnitude of PV injection based on previous ...
Maheswar Gowd - One of the best experts on this subject based on the ideXlab platform.
-
Effect of Cold Fraction and Orifice Diameter on the Performance of Modified Vortex Tube with Dual Forced Vortex Flow
2015Co-Authors: Maheswar GowdAbstract:Pressurized gas is tangentially expanded to create a high swirling motion in the Vortex tube, the flow of gas splits in two parts: a free Vortex as the peripheral warm stream and a Forced Vortex as the inner cold stream. Through certain design modification, the Forced Vortex flow is made to strike back through the core results in formation of one more Forced Vortex flow. Thus the modified Vortex tube with two Forced Vortex flows is known as dual Forced flow Vortex tube (DFFVT). In the present work an attempt is made to analyze the effect of cold fraction through ends-I & II and orifice diameter at cold end-II on the performance of modified Vortex tube. Series of cold orifice with different diameters at cold end-II are used for experimentation and investigated for higher temperature drops and effective performance (COP).
-
Effect of Hot End Obstruction and Nozzle on the Performance of Vortex Tube
2013Co-Authors: G. Maruthi Prasad Yadav, P. Mallikarjuna Reddy, K. Naga Lakshmi, Maheswar GowdAbstract:The Vortex tube is a very simple device injected with pressurized air through tangential nozzle which splits in to two streams of low pressure air, one warmer leaves near the periphery at plug end known as free Vortex and one colder leaves via an orifice at the opposite end known as Forced Vortex. The entry and exit of tube are key parameters affecting the performance of Vortex tube. The nozzle at entry effects the formation of free Vortex flow inside the tube and end region of hot pipe effects the converging of air and controls the Forced Vortex flow pattern. Providing an obstruction at the end of hot pipe boosts up the desired flow and enhances the energy separation. In the present work an attempt is made to revise the effect of inlet pressure, cold fraction, end obstruction of hot pipe end and also the nozzle on the performance of Vortex tube. A series of tubes with different level of obstruction and different nozzle inlet diameters were tested. The results indicate that temperature drop increases with increase of nozzle diameter up to 5mm and no significant improvement is
Joseph Majdalani - One of the best experts on this subject based on the ideXlab platform.
-
On the Viscous Bidirectional Vortex. Part 1: Linear Beltramian Motion
46th AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2010Co-Authors: Joshua W. Batterson, Joseph MajdalaniAbstract:In this article, a viscous approximation is obtained for the linear, inviscid, Beltramian motion that may be engendered in a confined, bidirectional Vortex chamber. Using the theory of matched-asymptotic expansions, viscous corrections are developed near the core region, where a Forced Vortex prevails, and near the cylindrical wall, where the no-slip requirement holds. Through proper scaling and variable transformations, a uniformly valid composite solution is subsequently constructed from which Majdalani’s helical profile may be recovered in the inviscid limit. The latter was derived directly from first principles (see Majdalani, J., “Exact Eulerian Solutions of the Cylindrical Bidirectional Vortex,” AIAA Paper 2009-5307, Denver, Colorado, Aug. 2009). However, because of its exact Eulerian nature, the strictly inviscid profile could not account for the effects of viscous stresses near the axis of rotation. The present approximation overcomes this deficiency by ensuring both the velocity adherence condition at the wall and the solid-body rotation of the Forced Vortex region. Being driven in large part by the inviscid character, the viscous-rectified swirl velocity component is also seen to exhibit small variations in the axial direction while continuing to vanish, as it should, at the sidewall. The advent of a viscous approximation enables us to quantifythesize of the core and wall boundary layers, improve our prediction of the vorticity and pressure distributions, and relate most relevant flow features to the Vortex Reynolds number.
-
Advancements in Theoretical Models of Confined Vortex Flowfields
2007Co-Authors: Joshua W. Batterson, Brian A. Maicke, Joseph MajdalaniAbstract:14. ABSTRACT In this article, we review some of the theoretical solutions used to describe swirl dominated flows in both unidirectional and bidirectional flow orientations. This short survey starts with the Rankine Vortex and culminates in the presentation of a compressible solution of the bidirectional Vortex. After classifying representative swirl motions as external or internal depending on physical boundary conditions, their commonalities are identified along with their relevance to either geophysical or industrial applications. For example, all swirl dominated flows comprise a Forced Vortex core centered around their axis of rotation. The core is due to viscous forces and increases in size with successive increases in viscosity. It is delineated by the point where the swirl velocity reaches its maximum. Within the Forced Vortex core, the tangential velocity is linearly proportional to the radius, a characteristic of rigid body rotation. Outside the Forced Vortex core, the tangential velocity gradually becomes inversely proportional to the radius, thus exhibiting a free Vortex tail. In internal flows, this free, irrotational tail is clipped at the boundaries in fulfillment of the no slip requirement. In external flows, it extends out to infinity. Finally, all swirl dominated flows decay axially and their vorticity is confined to either the core Vortex or wall boundary layers. These will be described in the context of the bidirectional Vortex confined in a cylindrical chamber. What is most prevalent here, and perhaps, what sets the analysis of the bidirectional Vortex apart lies in its true prediction of essential flow attributes directly from first principles. Unlike other studies that require conjecture or post-diction, for example, in estimating or adjusting the maximum swirl velocity and thickness of the core Vortex to fit a given flow pattern (e.g., the Rankine Vortex), these are obtained directly from the asymptotic solution of the tangential boundary layer equation for the bidirectional Vortex. We also identify the key similarity parameters that control the problem, including the inflow parameter, κ, and the Vortex Reynolds number, V. The latter combines the mean flow Reynolds number and the product of the swirl number and chamber aspect ratio. In this study, the core and sidewall boundary layers are quantified as function of V. The compressible solution is also obtained assuming a Rayleigh-Janzen expansion in the inflow Mach number squared.
-
Characterization of the Tangential Boundary Layers in the Bidirectional Vortex Thrust Chamber
42nd AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2006Co-Authors: Anand B. Vyas, Joseph MajdalaniAbstract:We consider the tangential boundary layers of the bidirectional Vortex, specifically, those forming near the core and sidewall of a swirl-driven cyclonic chamber. The analysis is based on the regularized, tangential momentum equation. The latter is rescaled in a manner to capture the Forced Vortex near the chamber axis and the no slip requirement at the sidewall. After identifying the coordinate transformations needed to resolve the rapid changes in the regions of nonuniformity, two inner expansions are arrived at. These expansions are then matched with the outer, free Vortex solution. By combining inner and outer expansions, uniformly valid approximations are obtained for the swirl velocity, vorticity, and pressure. These are shown to be strongly influenced by the Vortex Reynolds number, V. This key parameter appears as a ratio of the mean flow Reynolds number and the product of the swirl number and chamber aspect ratio. Based on V, several fundamental features of the bidirectional Vortex are quantified. Among them are the thicknesses of the viscous core and sidewall boundary layers; these decrease with V 1/2 and V, respectively. The converse may be said of the maximum swirl velocity which increases with V 1/2 . In the same vein, the angular speed of the rigid-body rotation characteristic of the Forced Vortex is found to be linearly proportional to V. The form of the swirl velocity is reminiscent of Sullivan's Vortex; here, it is based on the aspect ratio of the chamber. The resulting theoretical predictions are found to be in good agreement with PIV measurements and Navier-Stokes simulations.
-
The Bidirectional Vortex. Part 2: Viscous Core Corrections
39th AIAA ASME SAE ASEE Joint Propulsion Conference and Exhibit, 2003Co-Authors: Anand B. Vyas, Joseph Majdalani, Martin J. ChiaveriniAbstract:This article focuses on the viscous core of the bidirectional flowfield arising in a swirldriven thrust chamber. By regularizing the momentum equation in the tangential direction, the boundary layer equation that controls the Forced Vortex near the chamber axis is obtained. After identifying the coordinate transformation needed to resolve the rapid changes near the core, an inner expansion is arrived at. This expansion is then matched with the outer solution associated with the free Vortex; the latter is known to prevail in the outer region. By combining inner and outer expansions, uniformly valid approximations are obtained for the swirl velocity, vorticity, and pressure. These are shown to be strongly influenced by a dynamic similarity parameter that combines the mean flow Reynolds number and the chamber aspect ratio. Referred to as the Vortex Reynolds number V, this dimensionless grouping enables us to quantify the characteristic features of the bidirectional Vortex. Among them is the thickness of the viscous core which is found to decrease with the square root of V. The converse can be said of the maximum swirl velocity. In the same vein, the angular frequency of the rigid-body rotation of the Forced Vortex near the core is found to be linearly proportional to V. The form of the swirl velocity is reminiscent of the Burgers Vortex; here, it is based on the aspect ratio of the thrust chamber. The resulting theoretical predictions compare favorably with experimental measurements and computational results over the length of the chamber.