Numerical simulation of confined laminar jet flows
15 Jul 2000-International Journal for Numerical Methods in Fluids (Wiley)-Vol. 33, Iss: 5, pp 609-626
TL;DR: In this paper, the authors studied two-dimensional incompressible jet development inside a laminar duct with and without entrainment of ambient fluid and found that the stability of the jet flow is higher with entrainments.
Abstract: Two-dimensional incompressible jet development inside a duct has been studied in the laminar flow regime, for cases with and without entrainment of ambient fluid Results have been obtained for the flow structure and critical Reynolds number values for steady asymmetric jet development and for the onset of temporal oscillations, at various values of the duct-to-jet width ratio (aspect ratio) It is found that at low aspect ratios and Reynolds numbers, jet development inside the duct is symmetric For larger aspect ratios and Reynolds numbers, the jet flow at steady state becomes asymmetric with respect to the midplane, and for still higher values, it becomes oscillatory with respect to time When entrainment is present, the instabilities of asymmetric development and temporal oscillations occur at a much higher critical Reynolds number for a given aspect ratio, indicating that the stability of the jet flow is higher with entrainment Copyright © 2000 John Wiley & Sons, Ltd
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TL;DR: In this article, a two-dimensional laminar premixed flame is stabilized over a burner in a confined duct and is subjected to external acoustic forcing from the downstream end, and time-averaged chemiluminescence images of the perturbed flame front display time-mean changes as compared to the unperturbed flame shape.
28 citations
TL;DR: In this paper, a steady-state conjugate heat transfer study of a slab and fluid is carried out for a two-dimensional laminar incompressible offset jet.
Abstract: Steady-state conjugate heat transfer study of a slab and fluid is carried out for a twodimensional laminar incompressible offset jet. The unsteady stream function–vorticity formulation is used to solve the governing equations. The energy equation in the fluid and the conduction equation in the solid are solved simultaneously. The conjugate heat transfer characteristics are studied with four parameters, Re, Pr, S=h, and k. The fluid properties affect the heat transfer in the solid slab. The conjugate interface temperature is decreased up to the recirculation region and further increased to a developed condition. As the k is increased, its effect on Nu is reduced. Variation of local Nusselt number and average Nu are reported in detail.
27 citations
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TL;DR: In this paper, a two-dimensional transient laminar incompressible offset jet is simulated numerically to gain insight into convective recirculation and flow processes induced by an offset jet.
Abstract: Two-dimensional transient laminar incompressible offset jet is simulated numerically to gain insight into convective recirculation and flow processes induced by an offset jet. The behaviour of the jet with respect to offset ratio (OR) and Reynolds number (Re) are described in detail. The transient development of the velocity is simulated for various regions: recirculation, impingement and wall jet development. It is found that the reattachment length is dependent on both Re and OR for the range considered. Simulations are made to show the effect of entrainment on recirculation eddy. A detailed study of u velocity decay is reported. The decay rate of horizontal velocity component (u) is linear in impingement region. It is found that at high OR, velocity decay depends on Re only. Velocity profile in the wall jet region shows good agreement with experimental as well as similarity solutions. It is found that the effect of Re and OR are significant to bottom wall vorticity up to impingement region. Far downstream bottom wall vorticity is independent of OR. Copyright © 2005 John Wiley & Sons, Ltd.
23 citations
TL;DR: In this paper, a two-dimensional incompressible flow in a confined sinusoidal converging jet in the turbulence flow regime is numerically investigated and results have been obtained for the flow structure at different Reynolds numbers for steady asymmetric jet development at various values of the duct-to-jet width ratio (aspect ratio) and different amplitudes.
21 citations
TL;DR: In this paper, a finite volume technique on a collocated grid is employed for discretizing the governing equations by applying the SIMPLE algorithm to link the pressure and velocity fields.
Abstract: In this paper two-dimensional incompressible water–Al2O3 nanofluid flow in a confined jet in the laminar flow regime is numerically investigated. A finite volume technique on a collocated grid is employed for discretizing the governing equations by applying the SIMPLE algorithm to link the pressure and velocity fields. The present computations are in a very good agreement with experimental results in open literature.
17 citations
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TL;DR: In this article, the authors studied the stability of steady axisymmetric parallel flows of uniform fluid in the absence of rigid boundaries, and they focused on the stability characteristics in the limit of large Reynolds number and determined the (integral) value of n at which the growth rate is a maximum in these simpler circumstances.
Abstract: This paper is a contribution to the mathematical analysis of the stability of steady axisymmetric parallel flows of uniform fluid in the absence of rigid boundaries. A jet at sufficiently high Reynolds number for the angle of viscous spreding to be small is the typical example of the primary flows considered, and the theoretical velocity profile far downstream in such a jet is kept in mind continually. It is obvious from experience that such jets are unstable, presumably to infinitesimal disturbances, but there is little observational data about the critical Reynolds number or the mode of disturbance that grows most rapidly at a given Reynolds number.The typical small disturbance considered is a Fourier component with sinusoidal dependence on both ax and nϕ (x, r, ϕ are cylindrical polar co-ordinates). There is no analogue of Squire's theorem for two-dimensional primary flows, and both α and n are essential parameters of the disturbance. We have concentrated on the stability characteristics in the limit of large Reynolds number, and have aimed in particular at determining the (integral) value of n at which the growth rate is a maximum in these simpler circumstances.A number of general results for inviscid fluid are established, many of them analogues of corresponding results for two-dimensional primary flow. A necessary condition for the existence of amplified disturbances is that should have a numerical maximum a t some point in the fluid; this condition is satisfied for all n in the case of a cylindrical shear layer or ‘top-hat’ jet profile (for which a complete solution of the disturbance equation can be obtained), and for n > 1 in the case of a ‘far-downstream’ jet profile. The wave speed cr of a neutral disturbance is equal to the value of U either a t the point where dQ/dr = 0 or at r = 0. In the latter case the eigen-function (if one exists) is singular at the axis in general; the former case is presumably relevant to the ‘upper branch’ of the curve of neutral stability (for given n). The Reynolds stress due to the disturbance acting across a cylindrical surface is examined. Here, as in some other contexts, it is useful to consider components of velocity parallel and perpendicular to a circular helix on which the phase of the disturbance wave is constant. For a neutral disturbance the component of disturbance velocity parallel to the local wave helix is infinite a t the critical point where U = cr, (corresponding to the known singularity for a three-dimensional disturbance to two-dimensional flow), and there is a peak in the Reynolds stress there.It is shown from the form of the disturbance equation that there is an upper limit to the value of n (≠ 0) for a neutral (inviscid) disturbance with cr equal to the value of U at the point where Q′ = 0. In the case of a jet with a ‘far-downstream’ profile, only the value n = 1 satisfies this restriction; thus only the sinuous mode n = 1 can yield amplified disturbances in an inviscid fluid. A numerical investigation shows that for this profile the wave-number of the neutral disturbance with n = 1 is α = 1·46.
562 citations
TL;DR: In this article, the origin of steady asymmetric flows in a symmetric sudden expansion is studied using experimental and numerical techniques, and it is shown that the asymmetry arises at a symmetry-breaking bifurcation and good agreement between the experiments and numerical calculations is obtained.
Abstract: The origin of steady asymmetric flows in a symmetric sudden expansion is studied using experimental and numerical techniques. We show that the asymmetry arises at a symmetry-breaking bifurcation and good agreement between the experiments and numerical calculations is obtained. At higher Reynolds numbers the flow becomes time-dependent and there is experimental evidence that this is associated with three-dimensional effects.
352 citations
TL;DR: In this paper, a 3: 1 symmetric expansion in a duct with an aspect ratio of 9·2: 1 downstream of the expansion is reported. But the velocity profiles were in good agreement with those obtained by solving the two-dimensional momentum equation, although there were substantial threedimensional effects in the vicinity of the separation regions.
Abstract: Flow visualization and laser-anemometry measurements are reported in the flow downstream of a plane 3: 1 symmetric expansion in a duct with an aspect ratio of 9·2: 1 downstream of the expansion. The flow was found to be markedly dependent on Reynolds number, and strongly three-dimensional even well away from the channel corners except at the lowest measurable velocities. The measurements at a Reynolds number of 56 indicated that the separation regions behind each step were of equal length. Symmetric velocity profiles existed from the expansion to a fully developed, parabolic profile far downstream, although there were substantial three-dimensional effects in the vicinity of the separation regions. The velocity profiles were in good agreement with those obtained by solving the two-dimensional momentum equation. At a Reynolds number of 114, the two separation regions were of different lengths, leading to asymmetric velocity profiles; three dimensional effects were much more pronounced. At a Reynolds number of 252, a third separation zone was found on one wall, downstream of the smaller of the two separation zones adjacent to the steps. As at the lower Reynolds numbers, the flow was very stable. At higher Reynolds numbers the flow became less stable and periodicity became increasingly important in the main stream; this was accompanied by a highly disturbed fluid motion in the separation zones, as the flow tended towards turbulence.
312 citations
TL;DR: In this article, the modal distribution of coherent structures evolving near the nozzle of a circular jet was studied experimentally and theoretically, with particular attention given to the effects produced on the instability modes by transverse curvature, flow divergence, inhomogeneous inflow conditions, and the detailed shape of the mean velocity profile.
Abstract: The modal distribution of coherent structures evolving near the nozzle of a circular jet was studied experimentally and theoretically, with particular attention given to the effects produced on the instability modes by transverse curvature, flow divergence, inhomogeneous inflow conditions, and the detailed shape of the mean velocity profile. Experiments were performed using a specially constructed air-jet facility; hot-wire anemometers were used in conjunction with Disa Model 55P11 sensors for flow measurements. The linear model used as a transfer function is capable of predicting the spectral distribution of the velocity perturbations in a jet. Consideration was also given to studies of leading nonlinear interactions generated by waves externally superimposed on an axisymmetric jet; theoretical predictions were verified experimentally.
304 citations
TL;DR: In this article, the response characteristics of laminar jets to artificial external excitation were investigated in detail by using sound as an exciting agent, where the frequency of excitation coincides with that of self-excited sinusoidal fluctuations.
Abstract: A study was made of the transition of a two-dimensional jet. In the region where laminar flow becomes unstable, two kinds of sinusoidal velocity fluctuation have been found; one is symmetrical and the other is anti-symmetrical with respect to the centre line of the jet. The fluctuations grow exponentially at first and develop into turbulence without being accompanied by abrupt bursts or turbulent spots.The response characteristics of laminar jets to artificial external excitation were investigated in detail by using sound as an exciting agent. The effect of excitation was seen to be most remarkable when the frequency of excitation coincides with that of self-excited sinusoidal fluctuations.Numerical solutions of equation of small disturbances superposed on laminar flow were obtained assuming the Reynolds number as infinity. Theoretical eigenvalues and eigenfunctions are in good agreement with experimental results, thus verifying the existence of a region of linear disturbance in the two-dimensional jet.
268 citations