Visualization of Three-Dimensional Flow Structures Caused by Rotating Instability

2019 ◽  
Author(s):  
Julija Peter ◽  
Paul Uwe Thamsen
Keyword(s):  
High Speed ◽  
Spectral Characteristics ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Flow Structures ◽  
Experimental Investigations ◽  
Flow Topology ◽  
Time Resolved ◽  
Characteristic Flow ◽  
Rotating Instability

Abstract The present study deals with the flow phenomenon Rotating Instability (RI), which is predominantly observed in axial compressors at off-design conditions e.g. near stall. It potentially induces noise and triggers blade vibrations. Despite numerous studies, the characteristics and the source of RI are not completely understood. The objective of this work is to identify and to visualize characteristic flow topology corresponding to RI by means of Stereo High Speed Particle Image Velocimetry (PIV). The experimental investigations were carried out in an annular compressor stator cascade with and without hub clearance at an inflow Mach number of Ma = 0.4 and the Reynolds number of Re = 300 000. The time-resolved 3C flow field is measured in a single blade passage in planes tangential to the hub. Additionally, the time-resolved pressure fluctuations are captured synchronously to the PIV system. By using combined correlation techniques the spectral characteristics, the spatial extension of the RI and the characteristic flow structures were identified and visualized in configurations with and without hub clearance. The investigations point out that the general flow mechanism of RI is similar in compressor cascades with and without hub clearance. Overall, this work gives important insights into the complex phenomenon Rotating Instability, which can be taken into account when developing compressors in the future.

Exploratory Studies on the Control of High-Speed Flows With Magnetogasdynamics

2002 ◽  
Author(s):  
Datta V. Gaitonde
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Control Mechanisms ◽  
Ground Testing ◽  
Simulation Efficiency ◽  
The Status ◽  
Physical Phenomena ◽  
Insight Into

Magnetogasdynamics (MGD) has the potential to lift many of the constraints presently inhibiting sustained hypersonic flight and affordable access to space. Given the difficulty of ground-testing under the expected harsh conditions, numerical methods can provide insight into the physical phenomena, and thus complement experimental investigations in the development of future concepts. This paper describes the status of an effort to develop a high-fidelity, fully three-dimensional method to explore MGD flow control in complex configurations. The theoretical model includes several non-ideal effects and takes recourse to a blend of first principles and phenomenological approaches to enhance simulation efficiency. Boundary conditions are summarized and sample verification exercises are presented. Exploratory calculations on a reentry vehicle and flow-through scramjet flowpath with MGD-bypass demonstrate the versatility of the approach and yield insight into dominant flow control mechanisms.

Investigations on Energy Shares and Flow Structures of the Mixing Flow Using 3D-POD Analyses

2019 ◽  
Author(s):  
Daekyeong Kong ◽  
Gyeongrae Cho ◽  
Myoung-Jin Kim ◽  
Deog Hee Doh ◽  
Sangmo Kang ◽  
...  
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Flow Structures ◽  
Optical Encoder ◽  
Energy Distributions ◽  
Three Dimensional Flow ◽  
Mixing Properties ◽  
Vortical Structures ◽  
Flow Features ◽  
Proper Orthogonal

Abstract The objective of this report is investigate the influences of the mixing state to the productions of the vaterite crystal of CaCO3. In order to quantify the three-dimensional flow structures and their physical contribution to the mixing properties, a stereoscopic PIV (SPIV) has been adopted. The SPIV systems consists of two high speed cameras and an optical encoder which is used for trigging the SPIV system to capture the instantaneous flow images. A continuous laser (550nm) has been used. For mixing, an agitator having four blades has been used. The mixing tank has been filled with water up to 85% level of the tank height. The agitator has been rotated with 200rpm, 250rpm and 300rpm, and the 3D flow structures have been captured by the constructed SPIV system. Using measured instantaneous 3D vectors, POD (proper orthogonal decomposition) analyses has been adopted to investigate the energy distributions of the major vortical structures, and to evaluate the flow features regarding on the production of the vaterite crystal of CaCO3.

Classification of the Hydraulic Behavior Along the No-Load Curve of Francis Turbines

2021 ◽  
Author(s):  
Melissa Fortin ◽  
Bernd Nennemann ◽  
Claire Deschênes ◽  
Sébastien Houde
Keyword(s):  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Flow Structures ◽  
Load Curve ◽  
Flow Topology ◽  
Flow Features ◽  
Hydraulic Turbines ◽  
Operating Points ◽  
Load Conditions

Abstract For hydraulic turbines, no-load is considered a homogeneous family of operating conditions although the literature exposes a wide variety of flow structures depending on many factors. A better understanding of the flow structures developed during NL operation is necessary since they generate pressure fluctuations in the turbine causing significant fatigue damage and reducing the life expectancy of the machines. Hydraulic turbines at model scale show that behavioral trends can be identified for no-load conditions. This paper presents a classification of no-load operating conditions following the swirl level at the runner outlet. The main tendencies linking the cavitation level to the runner speed and the discharge for operating points along no-load curves of different turbines are also detailed. To study the no-load conditions, data from 26 Francis turbines, measured between 2007 and 2020 at the laboratory of Andritz Hydro Canada Inc., are analyzed. This study demonstrates that no-load operating conditions exhibit flow features very similar to those at regular operation with similar runner outlet swirl. The runner acceleration or deceleration with cavitation is related to the flow topology at the runner outlet.

Measurement of Viscoelastic Fluid Flow in the Curved Microchannel Using Digital Holographic Microscope and Polarized Camera

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Xiao-Bin Li ◽  
Masamichi Oishi ◽  
Tsukasa Matsuo ◽  
Marie Oshima ◽  
Feng-Chen Li
Keyword(s):  
Real Time ◽  
Viscoelastic Fluid ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Three Dimensional ◽  
Flow Structures ◽  
Tracer Particles ◽  
Microfluidic Flow ◽  
First Time ◽  
Measurement Approach

This paper aims to develop a three-dimensional (3D) measurement approach to investigate the flow structures of viscoelastic fluid in the curved microchannel by using digital holographic microscope (DHM). The measurement system uses off-axis holographic/interferometric optical setup for the moving target, and the real-time three-dimensional-three-components (3D3C) particle tracking velocimetry (PTV) can be achieved based on the analysis of phase information of holograms. To diagnose the irregular flow inside the microchannel, the 3D temporal positions of tracer particles in the volume of 282 μm × 282 μm × 60 μm have been detected and velocity field was calculated based on the PTV algorithm. Moreover, to explain the flow field inside the curved microchannel, for the first time the polarized high-speed camera was utilized to identify the strong elongation in the viscoelastic fluid. The DHM is proven to be successful for the measurements of microfluidic flow, especially for the truly real-time 3D motions.

LES Study of the Influence of a Train-Nose Shape on the Flow Structures Under Cross-Wind Conditions

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Hassan Hemida ◽  
Siniša Krajnović
Keyword(s):  
High Speed ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Surface Flow ◽  
Flow Structures ◽  
Local Pressure ◽  
Freestream Velocity ◽  
Train Simulation ◽  
Long Nose

Cross-wind flows around two simplified high-speed trains with different nose shapes are studied using large-eddy simulation (LES) with the standard Smagorinsky model. The Reynolds number is 3×105 based on the height of the train and the freestream velocity. The cross section and the length of the two train models are identical while one model has a nose length twice that of the other. The three-dimensional effects of the nose on the flow structures in the wake and on the aerodynamic quantities such as lift and side force coefficients, flow patterns, local pressure coefficient, and wake frequencies are investigated. The short-nose train simulation shows highly unsteady and three-dimensional flow around the nose yielding more vortex structures in the wake. These structures result in a surface flow that differs from that in the long-nose train flow. They also influence the dominating frequencies that arise due to the shear-layer instabilities. Prediction of vortex shedding, flow patterns in the train surface, and time-averaged pressure distribution obtained from the long-nose train simulation are in good agreement with the available experimental data.

scholarly journals Separated Flow Topology in Compressors

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
James V. Taylor
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Separated Flow ◽  
Cell Behavior ◽  
Blade Design ◽  
Flow Topology ◽  
Design Point ◽  
Topological Reasoning ◽  
Blade Row ◽  
Different Response

Abstract When a multistage high-speed compressor is operated away from its design point, extreme incidence is caused in some blade rows. This results in large, localized separations that are three dimensional in nature. In this paper, topological reasoning is used to describe the behavior of these three-dimensional separations. It is shown that two classes of separation exist: one in which the flow progresses from attached to separate in a smooth way and another where there is a discontinuity in the response of the flow topology. It is shown that the global structure of the flow depends on the type of topological response that occurs. When the response is discontinuous, nonaxisymmetric cells of separated blades are formed. When the response is smooth, the resultant separated flow is axisymmetric. The paper is split into two broad sections: The first section presents examples of the two different classes of topological response that can occur in a single blade row, and it also shows how an engineer can achieve a different response by altering the blade design. The second section covers the analysis of a multistage high-speed compressor. The compressor initially presents the discontinuous behavior with rotating cells of separations. It is then redesigned to reduce the severity of the cell behavior or remove it entirely.

scholarly journals Experimental Investigations of Three-Dimensional Effects on Cavitating Hydrofoils

1961 ◽  
Vol 5 (03) ◽  
pp. 22-43
Author(s):  
R. W. Kermeen
Keyword(s):  
Aspect Ratio ◽  
High Speed ◽  
Three Dimensional ◽  
Cavitating Flow ◽  
Experimental Investigations ◽  
Water Tunnel ◽  
Pitching Moment ◽  
Two Dimensional ◽  
Dimensional Effects ◽  
Aspect Ratios

An investigation in the high-speed water tunnel of the hydsrodynamic characteristics of a family of three-dimensional sharp-edged hydrofoils is described. Four rectangular plan-form, 6-deg wedge profiles with aspect ratios of 4.0, 2.0, 1.0 and 0.5 were tested over a range of cavitation numbers from noncavitating to fully cavitating flow. The effects of aspect ratio on the flow and cavity configurations and on the lift, drag and pitching moment are discussed. Where data were available the results have been compared with the two-dimensional case.

Tomographic PIV in the Near Field of a Swirl-Stabilised Fuel Injector

2018 ◽  
Author(s):  
Adrian Spencer ◽  
Mark Brend ◽  
Daniel Butcher ◽  
David Dunham ◽  
Liangta Cheng ◽  
...  
Keyword(s):  
Near Field ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Isothermal Flow ◽  
Structure Identification ◽  
Experimental Investigations ◽  
Fuel Injector ◽  
Flow Topology ◽  
Tomographic Piv ◽  
Velocity Statistics

The isothermal flow fields of injectors have undergone several computational and experimental investigations using point and planar measurement techniques,. Within the swirl induced vortex breakdown region it is only LES that has been able to predict fully the presence of a three dimensional helical vortex structure for a particular injector, and in certain conditions (no central fuel jet), a precessing vortex core. These structures can be elucidated from point and planar measurements and favorable comparisons of velocity statistics between experiment and LES predictions strengthen these findings. However, volumetric, 3-component measurement of velocity data has not been widely available to provide conclusive evidence of the exact three dimensional nature of the vortex structures that exist. An experimental setup utilizing time resolved tomographic PIV on a water flow rig is described in this paper. This is used to provide as high-quality aerodynamic study as possible of a single stream radially-fed air swirl gaseous fuel injector. The level of accuracy of the tomographic PIV technique is demonstrated by calculating the divergence of the velocity field as well as validating the results against a comprehensive 2 and 3 component standard PIV velocity database and other measurement techniques and predictions. Structure identification methods have been employed to visualise and understand the complex flow topology within the near field of the injector. The change in topology with and without the stabilising central jet is further investigated and agrees with findings of planar PIV results. While the velocity error associated with the tomo-PIV results is higher than the planar results the data agree well within the identified uncertainty bounds and are complimentary in understanding the flow field structure. Thus a full volumetric aerodynamic survey is available for the first time on this isothermal flow case.

scholarly journals Time-resolved scanning ion conductance microscopy for three-dimensional tracking of nanoscale cell surface dynamics

2021 ◽  
Author(s):  
Samuel M. Leitao ◽  
Barney Drake ◽  
Katarina Pinjusic ◽  
Xavier Pierrat ◽  
Vytautas Navikas ◽  
...  
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Cellular Structures ◽  
Surface Dynamics ◽  
Dynamic Changes ◽  
Ion Conductance ◽  
Time Resolved ◽  
Scanning Ion Conductance Microscopy ◽  
3D Information

Understanding cellular function requires high-resolution information about cellular structures as well as their evolution over time. The major challenge is to obtain three-dimensional (3D) information at nanometer resolution without affecting the viability of the cells and avoiding interference with the process. Here, we develop a scanning ion conductance microscope (SICM) for high-speed and long term imaging that can resolve spatiotemporally diverse processes on the cell membrane. We tracked dynamic changes in live cell morphology with nanometer details and temporal ranges of sub-second to days, imagining diverse processes ranging from endocytosis, micropinocytosis, and mitosis, to bacterial infection and cell differentiation in cancer cells. This technique enables a detailed look at membrane events and may offer insights into cell-cell interactions for infection, immunology, and cancer research.

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