The Interaction of the Precessing Vortex Core and Reverse Flow Zone in the Exhaust of a Swirl Burner

1994 ◽  
Vol 208 (1) ◽  
pp. 27-36 ◽  
Author(s):  
N Syred ◽  
T O'Doherty ◽  
D Froud
Keyword(s):  
Vortex Core ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Basic Structure ◽  
Flow Zone ◽  
Three Dimensional Flow ◽  
Laser Anemometry ◽  
Precessing Vortex Core ◽  
First Time

This paper describes recent work at Cardiff to gain further understanding of the fundamental processes occurring in swirl burners. The phenomenon of the precessing vortex core has been characterized via the use of a two-component laser anemometry system and the signal from a hot-wire anemometry probe for triggering purposes. This has allowed the rotating three-dimensional flow associated with the precessing vortex core to be characterized for the first time at different downstream sections. Regions of reversed mean tangential velocity have been identified while new insights into the basic structure of the reverse flow zone have been provided.

Alternate Eddy Shedding Set Up by the Nonaxisymmetric Recirculation Zone at the Exhaust of a Cyclone Dust Separator

1998 ◽  
Vol 120 (1) ◽  
pp. 193-199 ◽  
Author(s):  
A. J. Griffiths ◽  
P. A. Yazdabadi ◽  
N. Syred
Keyword(s):  
Recirculation Zone ◽  
Laser Doppler Anemometry ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Time Dependent ◽  
Velocity Measurements ◽  
Flow Zone ◽  
Precessing Vortex Core ◽  
Dust Separator ◽  
Set Up

Two cyclone dust separators with geometric swirl numbers of 3.324 and 3.043 were used to analyze the motion of the complex three-dimensional time dependent motion set up in the free exhaust. A quantitative analysis of the flow was carried out, obtaining time dependent velocity measurements with the use of laser Doppler anemometry (L.D.A.) techniques. The investigations highlighted a eddy or vortex shedding mechanism in two distinct areas of the flow. This was in part caused by a reverse flow zone and a precessing vortex core within the exhaust region of the separator. Changes in the Reynolds number by a factor of 2 were observed to have no effect on the main characteristics of the flow. Some changes were seen in the flow structure with change in swirl number, particularly the size of the reverse flow zone and the position of the large engulfment vortices.

Vortex formation on surging aerofoils with application to reverse flow modelling

2018 ◽  
Vol 859 ◽  
pp. 59-88 ◽  
Author(s):  
Philip B. Kirk ◽  
Anya R. Jones
Keyword(s):  
Surface Pressure ◽  
Reverse Flow ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Field Measurements ◽  
Reduced Frequency ◽  
Advance Ratio ◽  
Convection Speed

The leading-edge vortex (LEV) is a powerful unsteady flow structure that can result in significant unsteady loads on lifting blades and wings. Using force, surface pressure and flow field measurements, this work represents an experimental campaign to characterize LEV behaviour in sinusoidally surging flows with widely varying amplitudes and frequencies. Additional tests were conducted in reverse flow surge, with kinematics similar to the tangential velocity profile seen by a blade element in recent high-advance-ratio rotor experiments. General results demonstrate the variability of LEV convection properties with reduced frequency, which greatly affected the average lift-to-drag ratio in a cycle. Analysis of surface pressure measurements suggests that LEV convection speed is a function only of the local instantaneous flow velocity. In the rotor-comparison tests, LEVs formed in reverse flow surge were found to convect more quickly than the corresponding reverse flow LEVs that form on a high-advance-ratio rotor, demonstrating that rotary motion has a stabilizing effect on LEVs. The reverse flow surging LEVs were also found to be of comparable strength to those observed on the high-advance-ratio rotor, leading to the conclusion that a surging-wing simplification might provide a suitable basis for low-order models of much more complex three-dimensional flows.

Laser-Doppler Measurements of the Velocity Along a Heated Vertical Wall of a Rectangular Enclosure

1983 ◽  
Vol 105 (4) ◽  
pp. 782-788 ◽  
Author(s):  
H. Ozoe ◽  
M. Ohmuro ◽  
A. Mouri ◽  
S. Mishima ◽  
H. Sayama ◽  
...  
Keyword(s):  
Numerical Solutions ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Laser Doppler ◽  
Central Core ◽  
Heated Wall ◽  
Critical Test ◽  
Three Dimensional Flow ◽  
Rectangular Enclosure ◽  
First Time

The horizontal and vertical velocity profiles near a heated vertical wall of rectangular enclosure were measured for the laminar regime of natural convection with a laser-Doppler anemometer. The horizontal temperature profiles near the heated wall were measured with a thermocouple. An almost perfect two-dimensional mode of flow was confirmed for the central regime of the box. A minimum in the temperature profile between the hot wall and the thermally stratified central core resulted in a downward flow just outside the boundary layer of upward flow, but the central core was stagnant. Visualization of the flow with a phenolphtalein tracer confirmed the two-dimensionality of the flow along the vertical heated wall and revealed a zone of three-dimensional flow in the form of spiral streaklines along the insulated top plate toward the opposing cooled vertical wall. Measurements such as these provide for the first time the basis for a critical test of the accuracy of numerical solutions.

Transient Growth of Three-Dimensional Vortex Perturbations During Near-Parallel Collision With a Circular Cylinder

2006 ◽  
Author(s):  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Circular Cylinder ◽  
Vortex Core ◽  
Computational Study ◽  
Three Dimensional ◽  
The Body ◽  
Transient Growth ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Features

A computational study is reported that examines the transient growth of three-dimensional flow features for nominally parallel vortex-cylinder interaction problems. We consider a helical vortex with small-amplitude perturbations that is advected onto a circular cylinder whose axis is parallel to the nominal vortex axis. The study assesses the applicability of the two-dimensional flow assumption for parallel vortex-body interaction problems in which the body impinges on the vortex core. The computations are performed using an unstructured finite-volume method for an incompressible flow, with periodic boundary conditions along the cylinder axis. Growth of three-dimensional flow features is quantified by use of a proper-orthogonal decomposition of the Fourier-transformed velocity and vorticity fields in the cylinder azimuthal and axial directions. The interaction is examined for different axial wavelengths and amplitudes of the initial helical waves on the vortex core, and the results for cylinder force are compared to the two-dimensional results. The degree of perturbation amplification as the vortex approaches the cylinder is quantified and shown to be mostly dependent on the dominant axial wavenumber of the perturbation. The perturbation amplification is observed to be greatest for perturbations with axial wavelength of about 1.5 times the cylinder diameter.

scholarly journals A Design Study of Radial Inflow Turbines With Splitter Blades in Three-Dimensional Flow

1996 ◽  
Vol 118 (2) ◽  
pp. 353-361 ◽  
Author(s):  
W. D. Tjokroaminata ◽  
C. S. Tan ◽  
W. R. Hawthorne
Keyword(s):  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Inverse Design ◽  
Design Technique ◽  
Design Study ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Rotational Part ◽  
Blade Geometry

An inverse design technique to design turbomachinery blading with splitter blades in three-dimensional flow is developed. It is based on the use of Clebsch transformation, which allows the velocity field to be written as a potential part and a rotational part. It is shown that the rotational part can be expressed in terms of the mean swirl schedule (the circumferential average of the product of radius and tangential velocity) and the blade geometry that includes the main blade as well as the splitter blade. This results in an inverse design approach, in which both the main and the splitter blade geometry are determined from a specification of the swirl schedule. Previous design study of a heavily loaded radial inflow turbine, without splitter blades, for a rather wide variety of specified mean swirl schedules results in a blade shape with unacceptable nonradial blade filament; the resulting reduced static pressure distribution yields an “inviscid reverse flow region” covering almost the first half of the blade pressure surface. When the inverse design technique is applied to the design study of the turbine wheel with splitter blades, the results indicate that the use of splitter blades is an effective means for making the blade filament at an axial location more radial as well as a potential means for eliminating any “inviscid reverse flow” region that may exist on the pressure side of the blades.

scholarly journals Computational Fluid Dynamic Studies of Vortex Amplifier Design for the Nuclear Industry—II. Transient Conditions

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
J. Francis ◽  
M. J. Birch ◽  
D. Parker
Keyword(s):  
Vortex Core ◽  
Transient Flow ◽  
Reverse Flow ◽  
Fluid Dynamic ◽  
Good Evidence ◽  
Nuclear Industry ◽  
Time Step ◽  
Back Flow ◽  
Precessing Vortex Core ◽  
Flow Through

In this paper computational fluid dynamics (CFD) techniques have been used to investigate the effect of changes to the geometry of a vortex amplifier (VXA) in the context of glovebox operations in the nuclear industry. These investigations were required because of anomalous behavior identified when, for operational reasons, a long-established VXA design was reduced in scale. The study simulates the transient aspects of two effects: back-flow into the glovebox through the VXA supply ports, and the precessing vortex core in the amplifier outlet. A temporal convergence error study indicates that there is little to be gained from reducing the time step duration below 0.1 ms. Based upon this criterion, the results of the simulation show that the percentage imbalance in the domain was well below the required figure of 1%, and imbalances for momentum in all three axes were all below measurable values. Furthermore, there was no conclusive evidence of periodicity in the flow perturbations at the glovebox boundary, although good evidence of periodicity in the device itself and in the outlet pipe was seen. Under all conditions the modified geometry performed better than the control geometry with regard to aggregate reversed supply flow. The control geometry exhibited aggregate nonaxisymmetric supply port back-flow for almost all of the simulated period, unlike the alternative geometry for which the flow through the supply ports was positive, although still nonaxisymmetric, for most of the period. The simulations show how transient flow structures in the supply ports can cause flow to be reversed in individual ports, whereas aggregate flow through the device remains positive. Similar to the supply ports, flow through the outlet of the VXA under high swirl conditions is also nonaxisymmetric. A time-dependent reverse flow region was observed in both the outlet and the diffuser. It is possible that small vortices in the outlet, coupled with the larger vortex in the chamber, are responsible for the oscillations, which cause the shift in the axis of the precessing vortex core (and ultimately in the variations of mass flow in the individual supply ports). Field trials show that the modified geometry reduces the back-flow of oxygen into the glovebox by as much as 78%. At purge rates of 0.65 m3/h the modified geometry was found to be less effective, the rate of leakage from the VXA increasing by 16–20%. Despite this reduced performance, leakage from the modified geometry was still 63% less than the control geometry.

scholarly journals A Design Study of Radial Inflow Turbines With Splitter Blades in Three-Dimensional Flow

1994 ◽  
Author(s):  
W. D. Tjokroamlnata ◽  
C. S. Tan ◽  
W. R. Hawthorne
Keyword(s):  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Inverse Design ◽  
Design Technique ◽  
Design Study ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Rotational Part ◽  
Blade Geometry

An inverse design technique to design turbomachinery blading with splitter blades in three-dimensional flow is developed. It is based on the use of Clebsch transformation which allows the velocity field to be written as a potential part and a rotational part. It is shown that the rotational part can be expressed in terms of the mean swirl schedule (the circumferential average of the product of radius and tangential velocity) and the blade geometry that includes the main blade as well as the splitter blade. This results in an inverse design approach in which both the main and the splitter blade geometry are determined from a specification of the swirl schedule. Previous design study of a heavily-loaded radial inflow turbine, without splitter blades, for a rather wide variety of specified mean swirl schedules result in a blade shape with unacceptable non-radial blade filament; the resulting reduced static pressure distribution yields an “inviscid reverse flow region”1 covering almost the first half of the blade pressure surface. When the inverse design technique is applied to the design study of the turbine wheel with splitter blades, the results indicate that the use of splitter blades is an effective means for making the blade filament at an axial location more radial as well as a potential means for eliminating any “inviscid reverse flow” region that may exist on the pressure side of the blades.

scholarly journals Effect of Nozzle Confinement in the Axial Swirler

2019 ◽  
Vol 196 ◽  
pp. 00032
Author(s):  
Roman Yusupov ◽  
Ivan Litvinov ◽  
Sergey Shtork
Keyword(s):  
Unsteady Flow ◽  
Strouhal Number ◽  
Vortex Core ◽  
Recirculation Zone ◽  
Averaging Method ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Secondary Vortex ◽  
Precessing Vortex Core ◽  
Swirl Parameter

This work is devoted to the study of unsteady flow with the precessing vortex core (PVC) formed at the exit of a compact vane swirler with varying vanes angle and nozzles diameters. Amplitude-frequency characteristics of the PVC were obtained using two microphones. The modified Strouhal number dependence have showed a good generalization of the data for all nozzle diameters. The averaged and phase-averaged distributions of three components of velocity have been measured via the LDA system. The increasing the recirculation zone at increasing nozzle diameter for the swirl parameter Sg=0.53 and Re=1.5·104 was detected. The degeneration of PVC was detected for all studied nozzle diameters D = 30, 40, 50 mm. In case of smallest diameter D = 30 mm the PVC ceases to be periodic due to the absence of a recirculation zone. The three-dimensional structure of the PVC is reconstructed by the phase averaging method and visualized using the Q-criterion. Formation of the shifted recirculation zone, outer secondary vortex (OSV) and inner secondary vortex (ISV) is observed.

The Third Two-Dimensional Problem of Three-Dimensional Blade Systems of Hydraulic Machines—Part 1: Theoretical Analysis

1981 ◽  
Vol 103 (1) ◽  
pp. 33-41
Author(s):  
P. K. Agarwal ◽  
G. V. Viktorov
Keyword(s):  
Three Dimensional ◽  
Tangential Velocity ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Analysis Method ◽  
Flow Conditions ◽  
Three Dimensional Flow ◽  
Hydraulic Machines ◽  
The Mean ◽  
Axisymmetric Stream

This is the first part of a study of “third” two-dimensional problem of three-dimensional blade systems of hydraulic machines. Proposed herein is a method of obtaining and evaluating the three-dimensional effect on a system of hydraulic machine blades with arbitrary geometry. An analysis method indicating the velocity distributions on surfaces perpendicular to the mean axisymmetric stream surfaces has been formulated to help create a general understanding and awareness of the flow conditions in the runner passage. An application of generalized analytic functions for inviscid, incompressible flow has been made to find out the general solution on an auxiliary plane, transformed conformally from the physical plane. Integral equation systems for the tangential velocity and the velocity potential function have been deduced. Thus, the solution of the three-dimensional flow problem is supplied by two-dimensional computation methods.

scholarly journals Three-Dimensional Flow of a Vortex Drop Shaft Spillway with an Elliptical Tangential Inlet

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 504
Author(s):  
Zhou Yang ◽  
Jinbu Yin ◽  
Yangliang Lu ◽  
Zhiming Liu ◽  
Haoyu Yang ◽  
...  
Keyword(s):  
Froude Number ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Three Dimensional Flow ◽  
Cross Sectional ◽  
Dimensional Flow ◽  
Drop Shaft ◽  
Resultant Velocity ◽  
Tangential Inlet

Vortex drop shaft (VDS) spillways are eco-friendly hydraulic structures used for safely releasing flood. However, due to the complexity of the three-dimensional rotational flow and the lack of suitable measuring devices, current experimental work cannot interpret the flow behavior reliably inside the VDS spillway, consequently experimental and CFD study on a VDS spillway with an elliptical tangential inlet was conducted to further discern the interior three-dimensional flow behavior. Hydraulic characteristics such as wall pressure, swirl angle, annular hydraulic height and Froude number of the tapering section are experimentally obtained and acceptably agreed with the numerical prediction. Results indicated that the relative dimensionless maximum height of the standing wave falls off nearly linearly with the increasing Froude number. Nonlinear regression was established to give an estimation of the minimum air-core rate. The normalized height of the hydraulic jump depends on the flow phenomena of pressure slope. Simulated results sufficiently reveal the three-dimensional velocity field (resultant velocity, axial velocity, tangential velocity and radial velocity) with obvious regional and cross-sectional variations inside the vortex drop shaft. It is found that cross-sectional tangential velocity varies, resembling the near-cavity forced vortex and near-wall free vortex behavior. Analytic calculations for the cross-sectional pressure were developed and correlated well with simulated results.

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