PIV Measurement of Secondary Flow in a Rotating Two-Pass Cooling System With an Improved Sequencer Technique

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
Martin Elfert ◽  
Michael Schroll ◽  
Wolfgang Förster
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Cooling System ◽  
Flow Direction ◽  
Rotational Flow ◽  
Complex Flow ◽  
Reference Length ◽  
Rotation Numbers ◽  
Piv Measurement ◽  
Image Position

The flow field characteristics of a two-pass cooling system with an engine-similar layout have been investigated experimentally using the nonintrusive particle image velocimetry (PIV). It consists of a trapezoidal inlet duct, a nearly rectangular outlet duct, and a sharp 180 deg turn. The system has been investigated with smooth and ribbed walls. Ribs are applied on two opposite walls in a symmetric orientation inclined with an angle of 45 deg to the main flow direction. The applied rib layout is well proven and optimized with respect to heat transfer improvement versus pressure drop penalty. The system rotates about an axis orthogonal to its centerline. The configuration was analyzed with the planar two-component PIV technique, which is capable of obtaining complete maps of the instantaneous as well as the averaged flow field even at high levels of turbulence, which are typically found in sharp turns, in ribbed ducts, and, especially, in rotating ducts. In the past, a slip between motor and channel rotation causes additional non-negligible uncertainties during PIV measurements due to an unstable image position. These were caused by the working principle of the standard programmable sequencer unit used in combination with unsteady variations in the rotation speed. Therefore, a new sequencer was developed using FPGA-based hardware and software components from National Instruments (NI), which revealed a significant increase in the stability of the image position. Furthermore, general enhancements of the operability of the PIV system were achieved. The presented investigations of the secondary flow were conducted in stationary and, with the new sequencer technique applied, in rotating mode. Especially in the bend region, vortices with high local turbulence were found. The ribs also change the fluid motion as desired by generating additional vortices impinging the leading edge of the first pass. The flow is turbulent and isothermal; no buoyancy forces are active. The flow was investigated at a Reynolds number of Re=50,000, based on the reference length d (see Fig. 3). The rotation numbers are Ro=0.0 (nonrotating) and 0.1. Engine relevant rotation numbers are in order of 0.1 and higher. A reconstruction of some test rig components, especially the model mounting, has become necessary to reach higher values of the rotational speed compared with previous investigations such as the work of Elfert et al. (2008, “Detailed Flow Investigation Using PIV in a Rotating Square-Sectioned Two-Pass Cooling System With Ribbed Walls,” ASME Turbo Expo, Berlin, Germany, Jun. 9–13, Paper No. GT-2008-51183). This investigation is aimed to analyze the complex flow phenomena caused by the interaction of several vortices, generated by rotation, flow turning, or inclined wall ribs. The flow maps obtained with PIV are of good quality and high spatial resolution and therefore provide a test case for the development and validation of numerical flow simulation tools with special regard to the prediction of flow turbulence under the rotational flow regime, which is typical of turbomachinery. Future work will include the investigation of buoyancy effects to the rotational flow. This implicates wall heating, which results from the heater glass in order to provide transparent models.

PIV-Measurement of Secondary Flow in a Rotating Two-Pass Cooling System With an Improved Sequencer Technique

2010 ◽  
Author(s):  
M. Elfert ◽  
M. Schroll ◽  
W. Fo¨rster
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Cooling System ◽  
Flow Direction ◽  
Flow Simulation ◽  
Rotational Flow ◽  
Complex Flow ◽  
Reference Length ◽  
Piv Measurement ◽  
Image Position

The flow field characteristics of a two-pass cooling system with an engine-similar lay-out have been investigated experimentally using the non-intrusive Particle Image Velocimetry (PIV). It consists of a trapezoidal inlet duct, a nearly rectangular outlet duct, and a sharp 180 degree turn. The system has been investigated with smooth and ribbed walls. Ribs are applied on two opposite walls in a symmetric orientation inclined with an angle of 45 degrees to the main flow direction. The applied rib lay-out is well-proved and optimized with respect to heat transfer improvement versus pressure drop penalty. The system rotates about an axis orthogonal to its centreline. The configuration was analyzed with the planar two-component PIV technique (2C PIV), which is capable of obtaining complete maps of the instantaneous as well as the averaged flow field even at high levels of turbulence, which are typically found in sharp turns, in ribbed ducts and, especially, in rotating ducts. In the past, slip between motor and channel rotation causes additional not negligible uncertainties during PIV measurements due to unstable image position. These were caused by the working principle of the standard programmable sequencer unit used in combination with unsteady variations of the rotation speed. Therefore, a new sequencer was developed using FPGA-based hardware and software components from National Instruments which revealed a significant increase of the stability of the image position. Furthermore, general enhancements of the operability of the PIV system were achieved. The presented investigations of the secondary flow were conducted in stationary and, with the new sequencer technique applied, in rotating mode. Especially in the bend region vortices with high local turbulence were found. The ribs also change the fluid motion as desired by generating additional vortices impinging the leading edge of the first pass. The flow is turbulent and isothermal, no buoyancy forces are active. The flow was investigated at Reynolds number of Re = 50,000, based on the reference length d (see Fig. 3). The rotation number is Ro = 0 (non-rotating) and 0.1. Engine relevant rotation numbers are in order of 0.1 and higher. A reconstruction of some test rig components, especially the model mounting, has become necessary to reach higher values of the rotational speed compared to previous investigations like in Elfert [2008]. This investigation is aimed to analyze the complex flow phenomena caused by the interaction of several vortices, generated by rotation, flow turning or inclined wall ribs. The flow maps obtained with PIV are of good quality and high spatial resolution and therefore provide a test case for the development and validation of numerical flow simulation tools with special regard to prediction of flow turbulence under rotational flow regime as typical for turbomachinery. Future work will include the investigation of buoyancy effects to the rotational flow. This implicates wall heating which result from the heater glass in order to provide transparent models.

Investigation of the Effect of Rotation on the Flow in a Two-Pass Cooling System With Smooth and Ribbed Walls Using PIV

2011 ◽  
Author(s):  
Michael Schroll ◽  
Lena Lange ◽  
Martin Elfert
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Cooling System ◽  
Angular Position ◽  
Axial Flow ◽  
Strong Impact ◽  
Pass System ◽  
Flow Maps ◽  
Rotation Numbers ◽  
Two Component

A rotating cooling system with a 180 deg turn is investigated experimentally using the 2C PIV technique to measure the flow inside. This cooling configuration consists of two ducts of arbitrary cross-sections representing a two-pass front part of an idealized but nevertheless engine relevant turbine blade cooling design. The system has been investigated with ribbed walls in both passages for cooling enhancement as well as with smooth walls as a reference version in order to identify the effects induced by ribs. The rib orientation on the walls is 45 deg. With a rib height of 0.1 of hydraulic duct diameter and a pitch of 10 times rib height, a representative well-established rib lay-out was selected. This paper presents measurements of the axial flow during rotation of this two-pass system for rotation numbers up to 0.1. Together with previously obtained stationary results [1], this data completes the investigation of the secondary flow field with rotational results acquired with a two-component PIV measuring technique with improved sequencer technique [2]. The Two-Pass Cooling System was analyzed on the rotating test rig using two-component Particle Image Velocimetry (2C PIV) a non-intrusive optical planar measurement technique. PIV is capable of obtaining complete flow maps of the instantaneous as well as averaged flow field even at high turbulence levels, which are typical for the narrow serpentine-shaped ribbed cooling systems. An in-house developed synchronization device enables very accurate control of the laser flashes and image acquisition with regard to the angular position of the measurement plane (light sheet) and thereby very accurately stabilizes the position of the channel within the image during PIV recording which then leads to very accurate mean velocities. The presented investigations were conducted in stationary and rotating mode. The results demonstrate the combined interaction of different vortices induced by several effects such as the inclination of ribs, Coriolis forces due to rotation and inertial forces within the bend. Additionally, a flow separation was observed at the divider wall downstream of the bend (in the second pass) that has a strong impact on the flow field depending on the rotational speed. The axial flow maps presented in this paper in combination with the secondary flow maps published previously are of sufficient high quality and spatial resolution to serve as a benchmark test case for the validation of flow solvers. The turbulent channel flow was investigated at a Reynolds number of 50,000 and at rotation numbers of 0.0 and 0.1.

Specificity of Flow Structure in a Dual Elbow and Its Visualization by PIV Measurement

2008 ◽  
Author(s):  
Kazuhiro Yoshida ◽  
Yuki Kazuhisa ◽  
Hidetoshi Hashizume ◽  
Saburo Toda
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Flow Structure ◽  
Nuclear Power ◽  
Power Plants ◽  
Curvature Radius ◽  
Complex Flow ◽  
Unstable Flow ◽  
Straight Pipe ◽  
Piv Measurement

A large number of pipe failures caused by wall thinning have been reported in nuclear power plants, some of which occur in a dual elbow or the vicinity of it. These pipe failures could be influenced by complex flow induced in the elbow. This study, therefore, aims at predicting the whole flow structure in the dual elbow as the first step by taking a secondary flow after the elbow by PIV measurement. A test section consists of two elbows that are 2-dimentionally connected with/without a straight pipe. They are made of acrylic resin. The diameter of the elbow is 56mm and the curvature radius ratio is 1.5. Reynolds number in this experiment is 4×104. It is confirmed that the flow structure in the dual elbow has specificity depending on the inlet flow condition to the elbow and that the secondary flow itself has swirling motion in a streamwise direction. The dual elbow seems to generate more complex and unstable flow field even when the flow field at the inlet of the elbow slightly changes from a fully developed flow. However, there is a strong possibility that putting a straight pipe between the two elbows makes it ease the occurrence of the complex flow field.

Experimental and Numerical Investigation of Stator Exit Flow Field of an Automotive Torque Converter

1996 ◽  
Vol 118 (4) ◽  
pp. 835-843 ◽  
Author(s):  
B. V. Marathe ◽  
B. Lakshminarayana ◽  
Y. Dong
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Numerical Investigation ◽  
Three Dimensional ◽  
Axial Flow ◽  
Torque Converter ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Complex Flow ◽  
Rate Of Decay

The objective of this investigation is to understand the nature of the complex flow field inside each element of the torque converter through a systematic experimental and numerical investigation of the flow field. A miniature five-hole probe was used to acquire the data at the exit of the stator at several operating conditions. The flow field is found to be highly three dimensional with substantial flow deviations, and secondary flow at the exit of the stator. The secondary flow structure, caused by the upstream radial variation of the through flow, induces flow overturning near the core. Flow separation near the shell causes flow underturning in this region. The rate of decay of stator wake is found to be slower than that observed in the wakes of axial flow turbine nozzles. The flow predictions by a Navier–Stokes code are in good agreement with the pressure and the flow field measured at the exit of the stator at the design and the off-design conditions.

On the definition of the secondary flow in three-dimensional cascades

2009 ◽  
Vol 223 (6) ◽  
pp. 667-676 ◽  
Author(s):  
G Persico ◽  
P Gaetani ◽  
V Dossena ◽  
G D'Ippolito ◽  
C Osnaghi
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Secondary Flow ◽  
Boundary Layers ◽  
Complex Geometry ◽  
Flow Direction ◽  
Flow Analysis ◽  
Secondary Flows ◽  
Streamwise Vorticity ◽  
Reference Flow

The present article proposes a novel methodology to evaluate secondary flows generated by the annulus boundary layers in complex cascades. Unlike two-dimensional (2D) linear cascades, where the reference flow is commonly defined as that measured at midspan, the problem of the reference flow definition for annular or complex 3D linear cascades does not have a general solution up to the present time. The proposed approach supports secondary flow analysis whenever exit streamwise vorticity produced by inlet endwall boundary layers is of interest. The idea is to compute the reference flow by applying slip boundary conditions at the endwalls in a viscous 3D numerical simulation, in which uniform total pressure is prescribed at the inlet. Thus the reference flow keeps the 3D nature of the actual flow except for the contribution of the endwall boundary layer vorticity. The resulting secondary field is then derived by projecting the 3D flow field (obtained from both an experiment and a fully viscous simulation) along the local reference flow direction; this approach can be proficiently applied to any complex geometry. This method allows the representation of secondary velocity vectors with a better estimation of the vortex extension, since it offers the opportunity to visualize also the region of the vortices, which can be approximated as a potential type. Furthermore, a proficient evaluation of the secondary vorticity and deviation angle effectively induced by the annulus boundary layer is possible. The approach was preliminarily verified against experimental data in linear cascades characterized by cylindrical blades, not reported for the sake of brevity, showing a very good agreement with the standard methodology based only on the experimental midspan flow field. This article presents secondary flows obtained by the application of the proposed methodology on two annular cascades with cylindrical and 3D-designed blades, stressing the differences with other definitions. Both numerical and experimental results are considered.

Visualization experiment of complex flow field in a sphere-packed pipe by detailed PIV measurement

2014 ◽  
Vol 89 (7-8) ◽  
pp. 1251-1256 ◽  
Author(s):  
Shinji Ebara ◽  
Mohammad Reza Nematollahi ◽  
Hidetoshi Hashizume
Keyword(s):  
Flow Field ◽  
Complex Flow ◽  
Piv Measurement ◽  
Visualization Experiment

Microfluidic Flow Control and Particle Transport Using Acoustically Actuated Bubbles in Teardrop Shaped Cavities

2012 ◽  
Author(s):  
Ali Hashmi ◽  
Garrett Heiman ◽  
Gan Yu ◽  
Hyuck-Jin Kwon ◽  
Jie Xu
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Flow Direction ◽  
Complex Flow ◽  
Actuation Frequency ◽  
Microfluidic Flow ◽  
Flow Speeds ◽  
Acoustic Actuation ◽  
Induced Flow ◽  
A Chain

It is well known that a symmetric microstreaming flow field will present in the vicinity of an acoustically actuated bubble. In this study, we demonstrate that oscillating microbubbles confined in teardrop-shaped cavities can result in a break in the symmetry of a microstreaming flow field. The teardrop cavity controls the size and shape of the bubble, regulating the volume and therefore its resonance frequency. If actuated in an acoustic field, the induced flow field can then be turned on and off by changing the acoustic actuation frequency. By harnessing the flow field directing capabilities of symmetry breaks and the switching properties of selective excitation of microbubbles, we generate and characterize a microfluidic switch for directing flow direction. We also show that a chain of multiple teardrop-shaped cavities can be used as a transport mechanism for directing particles spatially at high flow speeds. Our results demonstrate that teardrop cavities have great potential in future lab-on-a-chip devices by providing simple solutions to complex flow circuits for temporal and spatial flow control.

Volumetric Velocimetry Measurements of Purge-Mainstream Interaction in a 1-Stage Turbine

2020 ◽  
Author(s):  
A. J. Carvalho Figueiredo ◽  
B. D. J. Schreiner ◽  
A. W. Mesny ◽  
O. J. Pountney ◽  
J. A. Scobie ◽  
...  
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Suction Side ◽  
Secondary Flows ◽  
Complex Flow ◽  
Blade Passage ◽  
Passage Vortex ◽  
Purge Flow ◽  
Secondary Flow Field

Abstract Air-cooled gas turbines employ bleed air from the compressor to cool vulnerable components in the turbine. The cooling flow, commonly known as purge air, is introduced at low radius, before exiting through the rim-seal at the periphery of the turbine discs. The purge flow interacts with the mainstream gas path, creating an unsteady and complex flow-field. Of particular interest to the designer is the effect of purge on the secondary flow structures within the blade passage, the extent of which directly affects the aerodynamic loss in the stage. This paper presents a combined experimental and Computational Fluid Dynamics (CFD) investigation into the effect of purge flow on the secondary flows in the blade passage of an optically-accessible 1-stage turbine rig. The experimental campaign was conducted using Volumetric Velocimetry (VV) measurements to assess the three-dimensional inter-blade velocity field; the complementary CFD campaign was carried out using URANS computations. The implementation of VV within a rotating environment is a world first and offers an unparalleled level of experimental detail. The baseline flow-field, in the absence of purge flow, demonstrated a classical secondary flow-field: the roll-up of a horseshoe-vortex, with subsequent downstream convection of a pressure-side and suction-side leg, the former transitioning in to the passage vortex. The introduction of purge, at 1.7% of the mainstream flow-rate, was shown to modify the secondary flow field by enhancing the passage vortex, both in strength and span-wise migration. The computational predictions were in agreement with the enhancement revealed by the experiments.

Experimental and Numerical Investigation of Stator Exit Flow Field of an Automotive Torque Converter

1994 ◽  
Author(s):  
B. V. Marathe ◽  
B. Lakshminarayana ◽  
Y. Dong
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Numerical Investigation ◽  
Three Dimensional ◽  
Axial Flow ◽  
Torque Converter ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Complex Flow ◽  
Rate Of Decay

The objective of this investigation is to understand the nature of the complex flow field inside each element of the torque converter through a systematic experimental and numerical investigation of the flow field. A miniature five-hole probe was used to acquire the data at the exit of the stat or at several operating conditions. The flow field is found to be highly three-dimensional with substantial flow deviations, and secondary flow at the exit of the stator. The secondary flow structure, caused by the upstream radial variation of the through flow, induces flow overturning near the core. Flow separation near the shell causes flow underturning in this region. The rate of decay of stator wake is found to be slower than that observed in the wakes of axial flow turbine nozzles. The flow predictions by a Navier-Stokes code are in good agreement with the pressure and the flow field measured at the exit of the stator at the design and the off-design conditions.

Detailed Flow Investigation Using PIV in a Rotating Square-Sectioned Two-Pass Cooling System With Ribbed Walls

2008 ◽  
Author(s):  
M. Elfert ◽  
M. Voges ◽  
J. Klinner
Keyword(s):  
Cooling System ◽  
Flow Direction ◽  
Fluid Motion ◽  
Flow Distribution ◽  
Turbulent Channel Flow ◽  
Light Sheet ◽  
Generic Model ◽  
Test Case ◽  
Complex Flow ◽  
Flow Maps

In a 2-pass cooling system the pressure driven air flow distribution is investigated experimentally using the non-intrusive PIV Technique. The generic model as part of a complex and sophisticated cooling system consists of two square-sectioned ducts with a length of 20 diameters and an inherent 180 degree bend. The system has been investigated basically with smooth walls (case 0) and, later on, with two different kinds of ribbed walls in both legs. Ribs are applied to enhance the cooling performance; they are placed on two opposite walls of both legs in a symmetric (case A) and an asymmetric manner (case B), respectively. The ribs are inclined with an angle of 45 degrees versus the duct axis (i.e. main flow direction). The applied rib lay-out is well-proved and optimized with respect to heat transfer improvement and the inherent pressure drop increase. The system rotates about an axis orthogonal to the centreline of the straight passes. The configuration was analyzed with the planar the two-component Particle Image Velocimetry (2C PIV), which is capable of obtaining complete maps of the instantaneous as well as the averaged flow field even at high turbulence levels, which are typically present within duct turns, near ribs and, above all, during rotation. The presented investigations were conducted in stationary and rotating mode. Especially in the bend region separation phenomena and vortices with high local turbulence are apparent. The presence of ribs changes the fluid motion by generating additional vortices impinging the side walls. Flow visualization with injected oil smoke using the laser light sheet visualization technique was helpful to detect vortex structures and separations. Especially in the bend area separation regions and vortices with high local turbulence are apparent. The results shown in this paper demonstrate the effect of the 180 degree bend in combination with the two rib turbulator geometries for isothermal flow conditions excluding any buoyancy with and without rotation. Turbulent channel flow was investigated at a Reynolds number of 50,000, derived with the hydraulic diameter of the pass, non-rotating and at a rotation number of 0.02 which was chosen still moderate. Engine relevant rotation numbers are in order of .1 or higher. A reconstruction of model mountings will allow higher values for the next tests. Future work will expand to higher rotational speed and, also, will include buoyancy effects. This investigation shall help to clarify the complex flow phenomena due to the interaction of several vortices, present in two-pass cooling systems. The flow maps obtained with PIV are of good quality and high spatial resolution and therefore provide a test case for the development and validation of numerical simulation tools like the DLR flow solver TRACE which is not a topic of this paper.

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