Comparisons of Flow and Mixing Characteristics between Unforced and Excited Elevated Transverse Jets

2013 ◽  
Vol 30 (1) ◽  
pp. 87-96 ◽  
Author(s):  
C. M. Hsu ◽  
R. F. Huang
Keyword(s):  
Velocity Field ◽  
Momentum Flux ◽  
High Speed ◽  
Symmetry Plane ◽  
Image Processing Technique ◽  
Large Momentum ◽  
Acoustic Excitation ◽  
Recirculation Bubble ◽  
Transverse Jet ◽  
Mixing Characteristics

ABSTRACTThe influences of acoustic excitation on the velocity field and mixing characteristic of a jet in cross-flow were investigated in a wind tunnel. The acoustic excitation waves at resonance Strouhal number were generated by a loudspeaker. The time-averaged velocity field and streamlines of the excited elevated transverse jet in the symmetry plane were measured by a high-speed particle image velocimetry. The visual penetration height and spread width were obtained by using an image processing technique. The dispersion characteristics were obtained from the tracer-gas concentration measurement. The results showed that the streamline pattern of the non-excited transverse jet was significantly modified by the acoustic excitation—the bent streamlines evolved from the jet exit escalated and the vortex rings in the jet and tube wakes and the recirculation bubble in the jet wake disappeared. The time-averaged velocity distributions revealed that the excited transverse jet produces large momentum in the up-shooting direction so that the velocity trajectories were located at levels higher than those of the non-excited one. The mixing characteristics, which include the visual penetration height, spread width, and dispersion, were drastically improved by the acoustic excitation due to the changes in the flow structures. The excited transverse jet characterized at larger jet-to-crossflow momentum flux ratios presented larger improvement in the mixing characteristics than at lower jet-to-crossflow momentum flux ratios.

The Application of PIV in the Study of Impeller-Diffuser Interaction in Centrifugal Fan: Part I — Impeller-Vaneless Diffuser Interaction

2001 ◽  
Author(s):  
Tarek Mekhail ◽  
Zhang Li ◽  
Du Zhaohui ◽  
Willem Jansen ◽  
Chen Hanping
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
High Speed ◽  
Maximum Flow ◽  
Image Processing Technique ◽  
High Speed Photography ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Vaneless Diffuser ◽  
Unstable Flow

Abstract The PIV (Particle Image Velocimetry) technology is a brand-new technique of measuring velocity. It started in the 1980’s with the development of high-speed photography and the image processing technique of computers. This article deals with PIV applied to the study of unsteady impeller-vaneless diffuser interaction in centrifugal fen. Experiments were carried out at The Turbomachinery Laboratory of Shanghai Jiaotong University. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A series of performance measurements were carried out at different speeds and different vaneless diffuser widths. PIV measurements were applied to measure the unsteady flow at the exit part of the impeller and the inlet part of the diffuser for the case of the same width vaneless diffuser. The absolute flow field is measured at medium flow rate and at maximum flow rate. It is informative to capture the whole flow field at the same instant of time, and it might be more revealing to observe the unstable flow in real time.

A Theory on the Onset of Acoustic Resonance in a Multistage Compressor

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Xiaohua Liu ◽  
Tobias Willeke ◽  
Florian Herbst ◽  
Jun Yang ◽  
Joerg Seume
Keyword(s):  
Rotor Blade ◽  
High Speed ◽  
Flow Instability ◽  
Computational Simulation ◽  
Computational Cost ◽  
Acoustic Resonance ◽  
Excitation Source ◽  
Acoustic Excitation ◽  
Tip Leakage Flow ◽  
Suction Surface

A novel theoretical model of the internal flow field in multistage axial compressors based on an eigenvalue approach is developed, in order to predict the onset of acoustic resonance in aircraft engines. Using an example high-speed four-stage compressor, it is shown that one of the resultant frequencies is in excellent agreement with the experimental data in terms of acoustic resonance. On the basis of the computed natural frequency of the whole compression system and the measured spanwise distribution of static pressure, the location of the acoustic excitation source can be found in the third stage. Unsteady flow simulations of the full annulus of this stage reveal two criteria for acoustic excitation at the rotor-blade tip, reversed flow near the suction surface and flow impingement on the pressure surface. Additionally, a fast Fourier transform of the unsteady pressure field at the upper rotor-blade span verifies the existence of the computed unstable frequency of the oscillating tip leakage flow. Using this novel theory, which combines a theoretical calculation of flow-instability frequency of the global system with the computational simulation of a single stage, the onset mechanism and location of the excitation source of acoustic resonance in multistage turbomachinery can be explained at acceptable computational cost.

Propeller Loading-Induced Velocity Field by Means of Unsteady Lifting Surface Theory

1973 ◽  
Vol 17 (03) ◽  
pp. 129-139
Author(s):  
W. R. Jacobs ◽  
S. Tsakonas
Keyword(s):  
Velocity Field ◽  
High Speed ◽  
Pressure Field ◽  
Numerical Procedure ◽  
Nonuniform Flow ◽  
Surface Theory ◽  
Loading Function ◽  
Lifting Surface ◽  
Space Function ◽  
Induced Velocity

An analysis based on the lifting surface theory has been developed for evaluation of the vibratory velocity field induced by the loading of an operating propeller in both uniform and nonuniform inflow fields. The analysis demonstrates that in the case of nonuniform flow the velocity at any field point is made up of a large number of combinations of the frequency constituents of the loading function with those of the space function (propagation or influence function). A numerical procedure has been developed adaptable to a high-speed digital computer (CDC 6600), and the existing program, which evaluates the steady and unsteady propeller loadings, the resulting hydrodynamic forces and moments, and the pressure field, has been extended to include evaluation of the velocity field as well. This program should thus become a highly versatile and useful tool for the ship researcher or designer.

The local extinction and the nonlinear behaviors of a premixed methane/air flame under low-frequency acoustic excitation

2020 ◽  
Vol 34 (13) ◽  
pp. 2050138 ◽  
Author(s):  
Yongchao Sun ◽  
Mingbo Sun ◽  
Jiajian Zhu ◽  
Yang Xie ◽  
Hongbo Wang ◽  
...  
Keyword(s):  
High Speed ◽  
Excitation Frequency ◽  
Dominant Frequency ◽  
Local Extinction ◽  
Acoustic Excitation ◽  
Flame Extinction ◽  
Buoyant Force ◽  
Hot Gas ◽  
Nature Frequency ◽  
Production Zone

The local extinction and the nonlinear behavior of a premixed methane/air flame under acoustic excitation are investigated experimentally. High-speed photography and high-speed schlieren imaging are used to investigate the oscillation characteristics of the premixed methane/air flame. The flame structure shows a periodic fluctuation when the acoustic excitation is performed to the flame. The local flame extinction can be observed during the flame evolution process. During the local flame extinction process, the flame is found to be cut into two components, then the downstream one extinguishes shortly. The Particle Image Velocimetry (PIV) results suggest that the lower velocity at the separation point is one of the reasons for the flame local extinction. The flame without the acoustic excitation oscillates with a dominant frequency of 18 Hz, which is shown by the schlieren images to be related to the evolution of the hot gas around the flame driven by the buoyant force. When the acoustic excitation frequency is 100 Hz, the structure of the hot gas is destroyed, meanwhile the amplitude of the nature frequency decreases significantly. The hot gas structure appears regularly with the increasing excitation frequency. As a result, the amplitude of the nature frequency also increases gradually. Proper Orthogonal Decomposition (POD) analysis shows that the dominant frequency of the flame without the acoustic excitation is mainly caused by the evolution of the production zone of the flame and the fluctuation of the flame tip. The evolution of the production zone is driven by the buoyant force, which indicates that the result from POD method is consistent with the conclusion obtained from the high-speed schlieren images. Two dominant modes are obtained when the excitation frequencies are 100 and 200 Hz. The two modes are mainly caused by the process of the local flame extinction and the increasing flame length.

Development of Numerical Simulation for Jet Break Up Behavior in Complicated Structure of BWR Lower Plenum (7) Measurement of Fragment Diameter by Image Processing Technique

2016 ◽  
Author(s):  
Yuki Narushima ◽  
Yutaka Abe ◽  
Akiko Kaneko ◽  
Tetsuya Kanagawa ◽  
Hiroyuki Yoshida
Keyword(s):  
Numerical Simulation ◽  
Image Processing ◽  
Liquid Flow ◽  
High Speed ◽  
Nuclear Power ◽  
Processing Method ◽  
Image Processing Technique ◽  
Diameter Distribution ◽  
Injection Velocity ◽  
Image Processing Method

In order to decommission nuclear reactors and to improve the safety of BWR, it is important to estimate the falling behavior of molten core jet in the reactor vessel of BWR when an accident occurred as can be seen from Fukushima Daiichi nuclear power plant accident. Since the BWR lower plenum is consisted with various complicated structures, it is suggested that the jet falling behavior is affected by these structures. Thus we are developing the numerical simulation method to estimate the molten core falling behavior in BWR. To verify the code for the case of the BWR core melt accident, it is necessary to obtain the experimental data and validate the code by comparing the numerical results with the experimental results. The purpose of this study is to investigate the influence of these structures on behavior of jet breakup and fragmentation, and to construct the benchmarks of the numerical simulation experimentally. We used molten core simulant material and simulate the molten core falling behavior, focusing on the hydrodynamic behavior. The 1/10 planar type test section simulated the arrangement of complicated structures in the BWR lower plenum is used. Jet injection experiments were conducted under some conditions that experimental parameters were flow rate and nozzle diameter. To clarify the influence of complicated structures on the jet behavior, experiments were performed in the conditions with and without structures. Jet falling behaviors were recorded by a high speed video camera. The fragment diameters were measured from image by means of image processing techniques. Visual measurement is usually used to measure fragment diameter, but it will contain the arbitrariness and the amount of fragments are small. Since the outline of fragment is easy to recognize by the difference of refractive index between gas and liquid, image processing for measuring the diameters is used in gas liquid flow. On the other hand, it is difficult to recognize the interface in liquid-liquid flow. We developed the new image processing filter for detecting the outline of fragments precisely and established the image processing method including this filter. We measured about ten thousand fragments precisely and automatically. The measurement of fragment diameter was implemented by the image processing method mentioned above. The histogram of fragment diameter distribution shows that it can be fitted by the lognormal distribution in condition with and without structures. We calculated the volume median diameters in all conditions. The diameters were smaller that depended on the increasing injection velocity. Comparing between condition with and without structures, the fragment diameters became small in condition with structures than without structures. Since the velocity of tip of the jet was larger in condition with structures (Saito et al., J. Nucl. Sci. Tech, 2015), the velocity gradient between the jet and ambient fluid also would be larger. The shear force strongly acting on the interface made the diameter small.

Emission Measurements and CH* Chemiluminescence of a Staged Combustion Rig for Stationary Gas Turbine Applications

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Warren G. Lamont ◽  
Mario Roa ◽  
Scott E. Meyer ◽  
Robert P. Lucht
Keyword(s):  
Combustion Zone ◽  
High Speed ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Exhaust Gas ◽  
Staged Combustion ◽  
High Pressure Turbine ◽  
Transverse Jet ◽  
Sampling Probe ◽  
Good Agreement

An optically accessible combustion rig was constructed to study the combustion characteristics of a reactive jet in a vitiated crossflow. The rig features two staged combustion zones. The main combustion zone is a swirl stabilized dump combustor. The second combustion zone, which is axially downstream from the main combustion zone, is formed by a transverse jet injecting either fuel or a premixed fuel/air mixture into the vitiated stream. The rig was designed to investigate the transverse jet conditions, equivalence ratio, and momentum ratios that produce low NOx and give an adequate temperature rise before the simulated high pressure turbine. A water-cooled sampling probe extracts exhaust gas downstream for emission measurements. As a baseline, the main combustion zone was fired without the transverse jet and the results compare closely to the work of previous researchers. The emission survey with the transverse jet found several conditions that show a benefit of staging compared to the baseline of firing only the main combustion zone. The flame structure from the transverse jet was captured using high speed CH* chemiluminescence, which shows the extent of the flame front and its penetration depth into the vitiated stream. The chemiluminescence images were averaged and compared to the Holdeman correlation, which showed good agreement for injection with fuel only but poorer agreement when premixed.

Estimation of Dynamic Forces in Very High-Speed Impact Forging

1966 ◽  
Vol 88 (4) ◽  
pp. 369-372 ◽  
Author(s):  
M. J. Hillier
Keyword(s):  
Approximate Solution ◽  
Velocity Field ◽  
Plane Strain ◽  
Energy Method ◽  
Coulomb Friction ◽  
High Speed ◽  
Admissible Velocity ◽  
High Speed Impact ◽  
Dynamic Forces ◽  
Very High

A study is made of three methods of estimating die loads in impact forging: By approximate solution of the equations of equilibrium; by an energy method, assuming plane sections remain plane; and using the energy method in association with a kinematically admissible velocity field. Results are given for die pressures and die loads for axisymmetric and plane-strain forging of disks and slabs with smooth dies, perfectly rough dies, and for the case of Coulomb friction.

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