Design Rules for the Velocity Field of Vortex Breakdown Swirl Burners

2006 ◽  
Author(s):  
Stephan Burmberger ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Velocity Field ◽  
Combustion Chamber ◽  
Pressure Distribution ◽  
Vortex Core ◽  
Total Pressure ◽  
Vortex Breakdown ◽  
Azimuthal Velocity ◽  
Velocity Profiles ◽  
Flame Stabilization ◽  
Stable Vortex

Most gas turbine premix burners without centrebody employ the breakdown of a swirling flow at the transition between the mixing section and the combustor for aerodynamic flame stabilization. As the formation of the desired vortex breakdown pattern depends very sensibly on the shape of the axial and azimuthal velocity profiles in the mixing section, the design of suitable swirlers is typically a cumbersome process and requires an iterative approach consisting of numerical as well as experimental development steps to be iteratively applied until a geometry is found, that provides a spatially as well as temporarily stable vortex breakdown in the primary zone of the combustion chamber without backflow on the centerline of the vortex into the swirler. These difficulties stem from the lack of generally applicable aerodynamic design criteria. The paper attempts to contribute to the development of such design guidelines, which lead quickly to successful swirler designs without need for an excessive number of iterations. For this purpose a family of swirl profiles was generated and the corresponding axial velocity profiles were calculated assuming several radial total pressure distributions. In the next step, the flows were calculated using CFD in order to find out, which velocity profiles produce stable vortex breakdown bubbles at the burner exit. This study reveals that the stable breakdown of the vortex can be achieved for a wide range of velocity distributions, if the radial total pressure distribution is properly selected. However, the radial total pressure distribution in the vortex core is essential for the robustness of the design. Interestingly, velocity profiles with constant total pressure do not show a stable transition of the velocity field at the cross-sectional area change at the entrance of the combustion chamber. In addition, theoretical considerations reveal that an increase of the azimuthal velocity in the vortex core in streamwise direction avoids backflow on the centreline as well as flame flashback. This increase can be achieved using a slightly conical nozzle and introducing a swirl free jet on the centreline upstream of the mixing zone. All effects are explained using the vorticity transport equation.

A Numerical Investigation of the Influence of Casing Treatments on the Tip Leakage Flow in a HPC Front Stage

2002 ◽  
Author(s):  
I. Wilke ◽  
H.-P. Kau
Keyword(s):  
High Pressure ◽  
Vortex Core ◽  
Total Pressure ◽  
Vortex Breakdown ◽  
Leakage Flow ◽  
Compressor Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Surge Line ◽  
Casing Treatments

This paper describes the influence of casing treatments on the tip leakage flow and its resulting vortex. The presented results and conclusions are based on steady state numerical simulations of a high pressure compressor stage. Without casing treatments a significant change of behavior of the tip leakage flow can be observed near surge. This change is termed as vortex breakdown and occurs after passing the shock in the blade passage. The simulations indicate the losses in total pressure inside the vortex core as the main reason for the vortex breakdown. These losses mainly depend on the blade loading. Running the compressor stage at high pressure ratios these losses can reach such a high level that the total pressure inside the vortex measured in the rotating system of the rotor falls below the static pressure after the shock. This pressure difference works as a physical barrier for the low energy vortex core and prevents it from reaching the high pressure rotor outlet. Consequently, this blockage must lead to the onset of recirculation zones — the so called vortex breakdown. Different casing treatments have been tested on their ability to delay vortex breakdown and to move the surge line to lower mass flows. Numerical simulations show that configurations with axial slots as well as circumferential grooves weaken or even destroy the characteristic tip leakage vortex and reduce its resulting losses in total pressure. This reduction in losses delays or prevents the onset of vortex breakdown compared to the untreated case explaining the effectiveness of casing treatments. Observations indicate that casing treatments do not interfere with the vortex directly. The key mechanism seems to lay mainly in the interaction with the tip leakage alone. Taking advantage of existing pressure differences in the rotor blade row casing treatments remove tip leakage flow in zones of high pressure and interrupt temporarily the feeding of the vortex. The separated tip leakage reenters the main flow in zones of low pressure again. The way how this tip leakage bypass is realized defines the influence of casing treatments on efficiency and surge line.

Decaying, Swirling Flow in a Pipe: Axial Velocity Field Development With Reversed Axial Flow

2003 ◽  
Author(s):  
Heather L. McClusky ◽  
Donald E. Beasley
Keyword(s):  
Velocity Field ◽  
Axial Velocity ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Axial Flow ◽  
Axial Direction ◽  
Velocity Profiles ◽  
Field Development ◽  
Constant Diameter ◽  
Spatial Oscillations

Streamwise development of the axial velocity field in a confined, decaying swirling flow is explored in the present study. A tangential injection mechanism produces swirling flow at the inlet of a constant diameter pipe. Particle image velocimetry is employed for axial velocity measurements. Representative axial velocity profiles are presented for axial locations of 3 to 67 pipe diameters. The axial velocity profiles are asymmetric relative to the pipe centerline and the asymmetries persist as the flow develops in the axial direction. The eccentricity of the swirling flow spatially oscillates as the flow develops in the axial direction. The spatial oscillations of the axial velocity suggest that a vortex breakdown may be located near the inlet of the pipe and the entire pipe is the wake region of the vortex breakdown. The centerline axial velocity is also used to document the axial development of the flow. A comprehensive view of the flow field is provided by considering theoretical explanations presented in the literature for decaying, swirling pipe flows and for vortex breakdown.

Designing a Radial Swirler Vortex Breakdown Burner

2006 ◽  
Author(s):  
Stephan Burmberger ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Flow Field ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Azimuthal Velocity ◽  
Design Guidelines ◽  
Flame Stabilization ◽  
Fuel Flexibility ◽  
Primary Zone ◽  
Large Eddy ◽  
Flame Flashback

Most gas turbine premix burners without centrebody employ the breakdown of a swirling flow at the transition between the mixing section and the combustor for aerodynamic flame stabilization [1]. As the formation of the desired vortex breakdown pattern depends very sensibly on the distribution of axial and azimuthal velocity in the mixing section, the design of suitable swirlers is usually a cumbersome iterative process. The presented burner design was found through the implementation of design guidelines derived from CFD-calculations and on the basis of analytical considerations [5]. The swirling flow is generated by a radial swirler with tangential inlets. In order to stabilize the flow pattern, the swirling flow confines a slow non-swirling flow on the centreline. The centre flow being set into azimuthal motion creates increasing azimuthal velocity in streamwise direction in the vortex core. This process is reinforced by a conical nozzle and leads to the production of positive azimuthal vorticity inside the nozzle which stabilizes the flow field. First atmospheric test runs and Large Eddy Simulations of the isothermal as well as reactive flow field prove that the design goals have been reached: The burner creates stable vortex breakdown in the primary zone of the combustion chamber without flame flashback or backflow on the centreline over the entire operating range and even for difficult fuels like hydrogen containing gases. This finding indicates that reliable vortex breakdown burners with remarkable fuel flexibility can be designed using the guidelines presented in [5].

The Effect of Longitudinal Core Flow on Trailing Vortex Stability

2014 ◽  
Author(s):  
Amir Allaf-Akbari ◽  
A. Gordon L. Holloway ◽  
Joseph Hall
Keyword(s):  
Experimental Study ◽  
Velocity Field ◽  
Kinetic Energy ◽  
Vortex Core ◽  
Vortex Generator ◽  
Core Flow ◽  
Vortex Stability ◽  
Vorticity Distribution ◽  
Air Jet ◽  
Jet Velocities

The current experimental study investigates the effect of longitudinal core flow on the formation and structure of a trailing vortex. The vortex is generated using four airfoils connected to a central hub through which a jet flow is added to the vortex core. Time averaged vorticity, circumferential velocity, and turbulent kinetic energy are studied. The statistics of vortex wandering are identified and corrections applied to the vorticity distribution. The vortex generator used in this study was built on the basis of the design described by Beninati et al. [1]. It uses four NACA0012 airfoils connected to a central hub. The wings orientation can be adjusted such that each contributes to a strong trailing vortex on the center of the test section. The vortex generator also had the capability to deliver an air jet directed longitudinally through a hole in the hub at the joint of the airfoils. Tests were done without the jet and with the air jet at jet velocities of 10 and 20 m/s. Planar PIV was used to measure the velocity field in the vicinity of the vortex core. The measurements were taken at 3 chords behind the vortex generator.

Effect of Divergence Angle on Flow Through Inlet Section of Diffuser of a Gas Turbine Combustion Chamber: The CFD Approach

2006 ◽  
Author(s):  
Digvijay B. Kulshreshtha ◽  
S. A. Channiwala ◽  
Jitendra Chaudhary ◽  
Zoeb Lakdawala ◽  
Hitesh Solanki ◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Total Pressure ◽  
Divergence Angle ◽  
Velocity Head ◽  
Turbine Engine ◽  
Inlet Velocity ◽  
Pressure Losses ◽  
Flow Through ◽  
Mach Numbers

In the combustor inlet diffuser section of gas turbine engine, high-velocity air from compressor flows into the diffuser, where a considerable portion of the inlet velocity head PT3 − PS3 is converted to static pressure (PS) before the airflow enters the combustor. Modern high through-flow turbine engine compressors are highly loaded and usually have high inlet Mach numbers. With high compressor exit Mach numbers, the velocity head at the compressor exit station may be as high as 10% of the total pressure. The function of the diffuser is to recover a large proportion of this energy. Otherwise, the resulting higher total pressure loss would result in a significantly higher level of engine specific fuel consumption. The diffuser performance must also be sensitive to inlet velocity profiles and geometrical variations of the combustor relative to the location of the pre-diffuser exit flow path. Low diffuser pressure losses with high Mach numbers are more rapidly achieved with increasing length. However, diffuser length must be short to minimize engine length and weight. A good diffuser design should have a well considered balance between the confliction requirements for low pressure losses and short engine lengths. The present paper describes the effect of divergence angle on diffuser performance for gas turbine combustion chamber using Computational Fluid Dynamic Approach. The flow through the diffuser is numerically solved for divergence angles ranging from 5 to 25°. The flow separation and formation of wake regions are studied.

scholarly journals Phenomenological model for determining velocity field of LPG jet in combustion chamber of direct injection S.I. engine

2004 ◽  
Vol 26 (2) ◽  
pp. 83-92
Author(s):  
Bui Van Ga ◽  
Phung Xuan Tho ◽  
Nhan Hong Quang ◽  
Nguyen Huu Huong
Keyword(s):  
Combustion Chamber ◽  
Phenomenological Model ◽  
Direct Injection ◽  
Spark Ignition ◽  
Velocity Profiles ◽  
Gas Jet ◽  
Liquefied Petroleum Gas ◽  
Si Engine ◽  
Si Engines ◽  
Stratified Combustion

A phenomenological model has been established to predict the velocity distribution of LPG (Liquefied Petroleum Gas) jet in combustion chamber of spark ignition (SI) engine. A shaped coefficient \(\beta\) governing the similarity of velocity profiles of LPG jets has been defined based on the theoretical and experimental analyses of turbulent diffusion jets. The results show that \(\beta\) is constant for steady jet but it is not the case for unsteady one. The model will enable us to calculate the velocity profiles of LPG jet after ending injection. This is necessary for research of stratified combustion in direct injection LPG SI engines.

scholarly journals Numerical study of the vortex breakdown and vortex reconnection in the flow path of high-pressure water turbine

2021 ◽  
Vol 2088 (1) ◽  
pp. 012040
Author(s):  
A V Sentyabov ◽  
D V Platonov ◽  
A V Minakov ◽  
A S Lobasov
Keyword(s):  
Vortex Core ◽  
Vortex Breakdown ◽  
Numerical Study ◽  
Pressure Fluctuations ◽  
Hydraulic Turbine ◽  
Sliding Mesh ◽  
Precessing Vortex Core ◽  
Vortex Reconnection ◽  
Water Turbine ◽  
Pressure Water

Abstract The paper presents a study of the instability of the precessing vortex core in the model of the draft tube of a hydraulic turbine. The study was carried out using numerical modeling using various approaches: URANS, RSM, LES. The best agreement with the experimental data was shown by the RSM and LES methods with the modelling of the runner rotation by the sliding mesh method. In the regime under consideration, the precessing vortex rope is subject to instability, which leads to reconnection of its turns and the formation of an isolated vortex ring. Reconnection of the vortex core leads to aperiodic and intense pressure fluctuations recorded on the diffuser wall.

scholarly journals Azimuthal velocity profiles in Rayleigh-stable Taylor–Couette flow and implied axial angular momentum transport

2015 ◽  
Vol 774 ◽  
pp. 342-362 ◽  
Author(s):  
Freja Nordsiek ◽  
Sander G. Huisman ◽  
Roeland C. A. van der Veen ◽  
Chao Sun ◽  
Detlef Lohse ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Couette Flow ◽  
Outer Cylinder ◽  
Azimuthal Velocity ◽  
Velocity Profiles ◽  
Body Rotation ◽  
Solid Body Rotation ◽  
Angular Momentum Transport ◽  
Taylor Couette ◽  
Taylor Couette Flow

We present azimuthal velocity profiles measured in a Taylor–Couette apparatus, which has been used as a model of stellar and planetary accretion disks. The apparatus has a cylinder radius ratio of ${\it\eta}=0.716$, an aspect ratio of ${\it\Gamma}=11.74$, and the plates closing the cylinders in the axial direction are attached to the outer cylinder. We investigate angular momentum transport and Ekman pumping in the Rayleigh-stable regime. This regime is linearly stable and is characterized by radially increasing specific angular momentum. We present several Rayleigh-stable profiles for shear Reynolds numbers $\mathit{Re}_{S}\sim O(10^{5})$, for both ${\it\Omega}_{i}>{\it\Omega}_{o}>0$ (quasi-Keplerian regime) and ${\it\Omega}_{o}>{\it\Omega}_{i}>0$ (sub-rotating regime), where ${\it\Omega}_{i,o}$ is the inner/outer cylinder rotation rate. None of the velocity profiles match the non-vortical laminar Taylor–Couette profile. The deviation from that profile increases as solid-body rotation is approached at fixed $\mathit{Re}_{S}$. Flow super-rotation, an angular velocity greater than those of both cylinders, is observed in the sub-rotating regime. The velocity profiles give lower bounds for the torques required to rotate the inner cylinder that are larger than the torques for the case of laminar Taylor–Couette flow. The quasi-Keplerian profiles are composed of a well-mixed inner region, having approximately constant angular momentum, connected to an outer region in solid-body rotation with the outer cylinder and attached axial boundaries. These regions suggest that the angular momentum is transported axially to the axial boundaries. Therefore, Taylor–Couette flow with closing plates attached to the outer cylinder is an imperfect model for accretion disk flows, especially with regard to their stability.

A Combined CFD/MRV Study of Flow Through a Pin Bank

2014 ◽  
Author(s):  
Mike Siekman ◽  
David Helmer ◽  
Wontae Hwang ◽  
Gregory Laskowski ◽  
Ek Tsoon Tan ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Velocity Field ◽  
Turbulence Model ◽  
Field Data ◽  
Peak Velocity ◽  
Velocity Profiles ◽  
Mean Velocity ◽  
Magnetic Resonance Velocimetry ◽  
Sst Turbulence Model ◽  
Flow Through

RANS and time averaged URANS simulations of a pin bank are compared quantitatively and qualitatively to full 3D mean velocity field data obtained using magnetic resonance velocimetry (MRV). The ability of the CFD to match MRV velocity profiles through the pin bank is evaluated using the SST turbulence model. Quantitative comparisons of the velocity profiles showed an overprediction of peak velocity by the CFD at the first pin rows, and a smaller oscillatory error that diminishes as it moves through the pins, resulting in better matching towards the exit.

scholarly journals Investigating the In-Flow Characteristics of Multi-Operation Conditions of Cross-Flow Fan in Air Conditioning Systems

Processes ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 959
Author(s):  
Weijie Zhang ◽  
Jianping Yuan ◽  
Qiaorui Si ◽  
Yanxia Fu
Keyword(s):  
Pressure Distribution ◽  
Flow Rate ◽  
Total Pressure ◽  
Air Conditioning ◽  
Pressure Pulsation ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Operating Conditions ◽  
Aerodynamic Noise ◽  
Cross Flow Fan

Cross-flow fans are widely used in numerous applications such as low-pressure ventilation, household appliances, laser instruments, and air-conditioning equipment. Cross-flow fans have superior characteristics, including simple structure, small size, stable airflow, high dynamic pressure coefficient, and low noise. In the present study, numerical simulation and experimental research were carried out to study the unique secondary flow and eccentric vortex flow characteristics of the internal flow field in multi-operating conditions. To this end the vorticity and the circumferential pressure distribution in the air duct are obtained based on the performed experiments and the correlation between spectral characteristics of multiple operating conditions and the inflow state is established. The obtained results show that when the area of the airflow passage decreases while the area of the eccentric vortex area gradually increases, then the airflow of the cross-flow fan decreases, the outlet expands, and the flow pattern uniformity reduces. It was found that wakes form in the vicinity of the blade and the tail of the volute tongue, which generate pressure pulsation, and aerodynamic noise. The pressure distribution along the inner circumference shows that the total minimum pressure appears in the eccentric vortex near the volute tongue and the volute returns near the zone. Moreover, it was found that the total pressure near the eccentric vortex is significantly smaller than that of the main flow zone. As the flow rate decreases, the pressure pulsation amplitude of the eccentric vortex region significantly increases, while the static and total pressure pulsation amplitudes are gradually increased. Close to the eccentric vortex on the inner side of the blade in the volute tongue area, total pressure is low, total pressure on the outside of the blade is not affected, and pressure difference between the inner and outer sides is large. When the flow rate of the cross-flow fan is 0.4 Qd, there is no obvious peak at the harmonic frequency of the blade passage frequency. This shows that the aerodynamic noise is caused by the main unstable flow.

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