Amplitude-Dependent Flow Field and Flame Response to Axial and Tangential Velocity Fluctuations

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Sebastian Schimek ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Steffen Terhaar ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Tangential Velocity ◽  
Azimuthal Velocity ◽  
Forced Flow ◽  
Laser Doppler Velocimeter ◽  
Amplitude Dependence ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
Flame Response ◽  
The Mean

The current paper investigates the nonlinear interaction of the flow field and the unsteady heat release rate and the role of swirl fluctuations. The test rig consists of a generic swirl-stabilized combustor fed with natural gas and equipped with a high-amplitude forcing device. The influence of the phase between axial and azimuthal velocity oscillations is assessed on the basis of the amplitude and phase relations between the velocity fluctuations at the inlet and the outlet of the burner. These relations are determined in the experiment with the multimicrophone-method and a two component laser Doppler velocimeter (LDV). Particle image velocimetry (PIV) and OH*-chemiluminescence measurements are conducted to study the interaction between the flow field and the flame. For several frequency regimes, characteristic properties of the forced flow field and flame are identified, and a strong amplitude dependence is observed. It is found that the convective time delay between the swirl generator and the flame has an important influence on swirl-number oscillations and the flame dynamics in the low-frequency regime. For mid and high frequencies, significant changes in the mean flow field and the mean flame position are identified for high forcing amplitudes. These affect the interaction between coherent structures and the flame and are suggested to be responsible for the saturation in the flame response at high forcing amplitudes.

Amplitude-Dependent Flow Field and Flame Response to Axial and Tangential Velocity Fluctuations

2012 ◽  
Author(s):  
Sebastian Schimek ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Steffen Terhaar ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Amplitude Dependence ◽  
Mean Flow ◽  
Modeling Tools ◽  
Velocity Fluctuations ◽  
Flame Response ◽  
The Mean

Lean premixed combustion is prone to thermoacoustic instabilities. These mostly self-excited instabilities are caused by a feedback mechanism between the acoustic field, hydrodynamic structures, and the heat release rate in the flame. While various modeling tools are available for the linear analysis of thermoacoustic systems, a detailed knowledge of the governing nonlinearities, responsible for the saturation in the flame response, is still missing. The fundamental understanding of the flow field–heat release interaction is of crucial importance for the prediction of the pressure oscillation amplitude. To improve the understanding of these interaction processes, the current paper investigates the nonlinear interaction of the flow field and the unsteady heat release rate and the role of swirl fluctuations. The test rig that is used in the present work consists of a generic swirl-stabilized combustor fed with natural gas and equipped with a high-amplitude forcing device. The influence of the phase between axial and azimuthal velocity oscillations is assessed on the basis of the amplitude and phase relations between the velocity fluctuations at the inlet and the outlet of the burner. These relations are determined in the experiment with the Multi-Microphone-Method and a two component laser-Doppler velocimeter. Particle image velocimetry and OH*-chemiluminescence measurements are conducted to study the interaction between the flow field and the flame. For several frequency regimes, characteristic properties of the forced flow field and flame are identified, and a strong amplitude dependence is observed. It is found that the convective time delay between the swirl generator and the flame has an important influence on swirl-number oscillations and the flame dynamics in the low-frequency regime. For mid and high frequencies, significant changes in the mean flow field and the mean flame position are identified for high forcing amplitudes. These affect the interaction between coherent structures and the flame and are suggested to be responsible for the saturation in the flame response at high forcing amplitudes.

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

Heat Release Response to Forced Flow Oscillations of a Low-Order Modelled Laboratory Scale Dump Combustor

2015 ◽  
Author(s):  
Alessandro Orchini ◽  
Matthew P. Juniper
Keyword(s):  
Flow Field ◽  
Heat Release ◽  
Bluff Body ◽  
Forced Flow ◽  
Mean Flow ◽  
Order Model ◽  
Qualitative Comparison ◽  
Velocity Fluctuations ◽  
Dump Combustor ◽  
Low Order

In this study we investigate the heat release response to forced harmonic velocity fluctuations of a bluff body dump combustor. We use the kinematic G-equation as a low-order model for the flame and heat release dynamics. The geometry considered is based on an experimental setup developed by R. Balachandran and widely investigated in the literature, and we look for a qualitative comparison with experimental and numerical results. We model the flow field dynamics adapting the well-known travelling wave model, which was originally developed for conical flames, to the case of a bluff-body stabilized flame in a non-uniform mean flow field. We impose velocity fluctuations at the dump plane at various frequencies and amplitudes and we integrate the nonlinear flame and heat release dynamics. Results show that the model qualitatively reproduces the kinematic behaviour observed in the experiments, although some major quantitative differences are found. We conclude by discussing our results, and adjustments that could be introduced in future in the low-order model in order to improve it.

An Investigation of Flow Fields Over Multi-Element Aerofoils

2001 ◽  
Vol 124 (1) ◽  
pp. 154-165 ◽  
Author(s):  
S. R. Maddah ◽  
H. H. Bruun
Keyword(s):  
Flow Field ◽  
Computational Study ◽  
Separated Flow ◽  
Mean Flow ◽  
Model Configuration ◽  
Attached Flow ◽  
The Mean ◽  
Flap Deflection ◽  
Comparative Results ◽  
Lift And Drag

This paper presents results obtained from a combined experimental and computational study of the flow field over a multi-element aerofoil with and without an advanced slat. Detailed measurements of the mean flow and turbulent quantities over a multi-element aerofoil model in a wind tunnel have been carried out using stationary and flying hot-wire (FHW) probes. The model configuration which spans the test section 600mm×600mm, is made of three parts: 1) an advanced (heel-less) slat, 2) a NACA 4412 main aerofoil and 3) a NACA 4415 flap. The chord lengths of the elements were 38, 250 and 83 mm, respectively. The results were obtained at a chord Reynolds number of 3×105 and a free Mach number of less than 0.1. The variations in the flow field are explained with reference to three distinct flow field regimes: attached flow, intermittent separated flow, and separated flow. Initial comparative results are presented for the single main aerofoil and the main aerofoil with a nondeflected flap at angles of attacks of 5, 10, and 15 deg. This is followed by the results for the three-element aerofoil with emphasis on the slat performance at angles of attack α=10, 15, 20, and 25 deg. Results are discussed both for a nondeflected flap δf=0deg and a deflected flap δf=25deg. The measurements presented are combined with other related aerofoil measurements to explain the main interaction of the slat/main aerofoil and main aerofoil/flap both for nondeflected and deflected flap conditions. These results are linked to numerically calculated variations in lift and drag coefficients with angle of attack and flap deflection angle.

Measurement of the Mean Flow Field in a Smooth Rotating Channel With Coriolis and Buoyancy Effects

2017 ◽  
Author(s):  
Ruquan You ◽  
Haiwang Li ◽  
Zhi Tao ◽  
Kuan Wei
Keyword(s):  
Flow Field ◽  
Coriolis Force ◽  
Indium Tin Oxide ◽  
Buoyancy Force ◽  
Flow Direction ◽  
Density Ratio ◽  
Mean Flow ◽  
The Mean ◽  
Static Conditions ◽  
Rotating Channel

The mean flow field in a smooth rotating channel was measured by particle image velocimetry under the effect of buoyancy force. In the experiments, the Reynolds number, based on the channel hydraulic diameter (D) and the bulk mean velocity (Um), is 10000, and the rotation numbers are 0, 0.13, 0.26, 0.39, 0.52, respectively. The four channel walls are heated with Indium Tin Oxide (ITO) heater glass, making the density ratio (d.r.) about 0.1 and the maximum value of buoyancy number up to 0.27. The mean flow field was simulated on a 3D reconstruction at the position of 3.5<X/D<6.5, where X is along the mean flow direction. The effect of Coriolis force and buoyancy force on the mean flow was taken into consideration in the current work. The results show that the Coriolis force pushes the mean flow to the trailing side, making the asymmetry of the mean flow with that in the static conditions. On the leading surface, due to the effect of buoyancy force, the mean flow field changes considerably. Comparing with the case without buoyancy force, separated flow was captured by PIV on the leading side in the case with buoyancy force. More details of the flow field will be presented in this work.

Influences of Turbulence Boundary Conditions on RANS and URANS Simulations for an Inter-Turbine Duct

2020 ◽  
Author(s):  
Alessio Firrito ◽  
Yannick Bousquet ◽  
Nicolas Binder ◽  
Ludovic Pintat
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Mean Flow ◽  
Time Resolved ◽  
Flow Solution ◽  
Low Pressure Turbine ◽  
Outlet Flow ◽  
Architecture Evolution ◽  
The Mean ◽  
Turbulence Length

Abstract In recent years, lot of turbine research is focused on the study and optimization of inter-turbine ducts, an aero-engine component for which the design is becoming more challenging due to the turbofan architecture evolution. Starting from the early design phase, the knowledge of the component performance and outlet flow pattern is crucial in the design of the low pressure turbine. To improve prediction, multi-row unsteady simulations are deployed. Unfortunately, some questions arise in the use of these simulations, among others the knowledge of the turbulent boundary conditions and the contribution of the unsteady simulations to the flow solution. In this paper steady and time resolved RANS simulations of a turning inter-turbine duct are investigated. Particularly, two questions are addressed. The first one is the influence of the turbulent quantities boundary conditions in the case of a k–ω Wilcox turbulence model in the flow field solution. The second one is the contribution of the unsteadiness to the mean flow prediction. It will be shown that the mean flow depends on inlet turbulence only if the turbulence length scale is relatively high; otherwise the flow field is almost turbulence-invariant. For the unsteady simulations, unsteadiness modifies the mean flow solution only with low inlet turbulence.

scholarly journals Large-Scale Flow in Micro Electrokinetic Turbulent Mixer

Micromachines ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 813 ◽  
Author(s):  
Keyi Nan ◽  
Zhongyan Hu ◽  
Wei Zhao ◽  
Kaige Wang ◽  
Jintao Bai ◽  
...  
Keyword(s):  
Flow Field ◽  
Electric Conductivity ◽  
Large Scale ◽  
Three Dimensional ◽  
Mixing Process ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
Two Fluids ◽  
Large Scale Flow ◽  
Particle Imaging

In the present work, we studied the three-dimensional (3D) mean flow field in a micro electrokinetic (μEK) turbulence based micromixer by micro particle imaging velocimetry (μPIV) with stereoscopic method. A large-scale solenoid-type 3D mean flow field has been observed. The extraordinarily fast mixing process of the μEK turbulent mixer can be primarily attributed to two steps. First, under the strong velocity fluctuations generated by μEK mechanism, the two fluids with different conductivity are highly mixed near the entrance, primarily at the low electric conductivity sides and bias to the bottom wall. Then, the well-mixed fluid in the local region convects to the rest regions of the micromixer by the large-scale solenoid-type 3D mean flow. The mechanism of the large-scale 3D mean flow could be attributed to the unbalanced electroosmotic flows (EOFs) due to the high and low electric conductivity on both the bottom and top surface.

Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder

2011 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Unsteady Flow ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Mean Flow ◽  
The Mean ◽  
Velocity Spectra

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α = 60° to α = 90°. Multi-point fluctuating surface pressure and hotwire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, span-wise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused and was still present and correlated from front to back, at least for the larger yaw angles investigated. When the cylinder was yawed to α = 60°, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.

Subsonic Turbulent Flow Past a Planar Fence

1979 ◽  
Vol 101 (3) ◽  
pp. 373-375
Author(s):  
M. L. Agarwal ◽  
P. K. Pande ◽  
Rajendra Prakash
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Boundary Conditions ◽  
Mean Flow ◽  
Governing Equations ◽  
Flow Past ◽  
Entire Flow ◽  
The Mean ◽  
Shape And Size

The mean flow past a fence submerged in a turbulent boundary layer is numerically simulated. The governing equations have been simplified by neglecting the convective effects of turbulence and solved numerically using experimental boundary conditions. The information obtained includes the shape and size of the upstream and downstream separation bubbles and the streamline pattern in the entire flow field. General agreement between the simulated and the experimental flow field was found.

Sign in / Sign up

Export Citation Format

Share Document