The Maximum Skin Friction and Flow Field of a Planar Impinging Gas Jet

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Adam Ritcey ◽  
Joseph R. McDermid ◽  
Samir Ziada
Keyword(s):  
Flow Field ◽  
Skin Friction ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Gas Jet ◽  
Potential Core ◽  
Piv Measurements ◽  
Turbulence Transition ◽  
Image Velocimetry ◽  
Plane Jets

The maximum skin friction and flow field are experimentally measured on a planar impinging gas jet using oil film interferometry (OFI) and particle image velocimetry (PIV), respectively. A jet nozzle width of W = 15 mm, impingement ratios H/W = 4, 6, 8, 10, and a range of jet Reynolds numbers Rejet = 11,000–40,000 are tested to provide a parametric map of the maximum skin friction. The maximum skin friction predictions of Phares et al. (2000, “The Wall Shear Stress Produced by the Normal Impingement of a Jet on a Flat Surface,” J. Fluid Mech., 418, pp. 351–375) for plane jets agree within 5% of the current OFI results for H/W = 6, but deviates upward of 28% for other impingement ratios. The maximum skin friction is found to be less sensitive to changes in the impingement ratio when the jet standoff distance is roughly within the potential core length of the jet. PIV measurements show turbulence transition locations moving toward the nozzle exit with increasing Reynolds number, saturation in the downstream evolution of the maximum axial turbulence intensity before reaching a maximum peak upon impingement, followed by sudden damping at the plate surface. As the flow is redirected, there is an orthogonal redistribution of the fluctuating velocity components, and local peaks in both the axial and transverse turbulence intensity distributions at the plate locations of the maximum skin friction.

Effect of Jet Oscillation on the Maximum Impingement Plate Skin Friction

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Adam Ritcey ◽  
Joseph R. McDermid ◽  
Samir Ziada
Keyword(s):  
Flow Field ◽  
Skin Friction ◽  
Field Measurements ◽  
Friction Reduction ◽  
Gas Jet ◽  
Impingement Plate ◽  
Image Velocimetry ◽  
Skin Friction Reduction ◽  
Jet Oscillation ◽  
Quiescent Fluid

The maximum impingement plate skin friction and flow field is measured for an acoustically forced planar impinging gas jet using oil film interferometry (OFI) and particle image velocimetry (PIV), respectively. The study is performed at a jet Reynolds number of Rejet = 11,000 and an impingement distance H, which is set to eight times the nozzle width W. The planar impinging gas jet is forced at the jet nozzle exit using Strouhal numbers StH = 0.39, 0.76, and 1.1, which are similar to those associated with the jet-plate tones measured in air-knife wiping experiments. The flow-field measurements indicate that the jet column oscillates at the applied forcing frequency, and depending on the forcing frequency, organized vortex structures can be identified in the shear layers that impinge on the plate surface. Both of these jet oscillation features result in a reduction in the time-averaged maximum impingement plate skin friction. This skin friction reduction is attributed to momentum loss at the jet centerline caused by increased levels of fluid entrainment and mixing of the surrounding quiescent fluid.

scholarly journals On the challenge of five-hole-probe measurements at high subsonic Mach numbers in the wake of transonic turbine cascades

2018 ◽  
Vol 2 ◽  
pp. JPRQQM
Author(s):  
Marcel Boerner ◽  
Martin Bitter ◽  
Reinhard Niehuis
Keyword(s):  
Flow Field ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Sensitivity Study ◽  
Wake Flow ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Measurement Results ◽  
Transonic Turbine ◽  
Probe Measurements

Five-hole-probes are common use in turbomachinery flow investigations, even though, inserting a probe into a flow field inevitably induces perturbations to the flow which can falsify the measurement results, especially when exposed to transonic flows. The objective of the investigations presented here is to evaluate the Mach number measurements of a five-hole-probe (5HP) in the wake flow of a transonic turbine cascade at engine relevant Reynolds numbers by comparing them to the results of particle image velocimetry (PIV). Furthermore, PIV measurements were performed with inserted probe to investigate the influence of the probe on the wake flow field. Together with a sensitivity study of 5HP measurements in flow regimes close to Ma = 1, the results demonstrate how the measurement uncertainty can be improved in high subsonic flow regimes.

Two-Dimensional Experimental Investigation on the Effects of a Fowler Flap Gap and Overlap Size on the Wake Flow Field

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
David Demel ◽  
Mohsen Ferchichi ◽  
William D. E. Allan ◽  
Marouen Dghim
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Angle Of Attack ◽  
Wake Flow ◽  
Two Dimensional ◽  
Edge Region ◽  
Suction Surface ◽  
Trailing Edge ◽  
Piv Measurements ◽  
Image Velocimetry

This work details an experimental investigation on the effects of the variation of flap gap and overlap sizes on the flow field in the wake of a wing-section equipped with a trailing edge Fowler flap. The airfoil was based on the NACA 0014-1.10 40/1.051 profile, and the flap was deployed with 40 deg deflection angle. Two-dimensional (2D) particle image velocimetry (PIV) measurements of the flow field in the vicinity of the main wing trailing edge and the flap region were performed for the optimal flap gap and overlap, as well as for flap gap and overlap increases of 2% and 4% chord beyond optimal, at angles of attack of 0 deg, 10 deg, and 12 deg. For all the configurations investigated, the flow over the flap was found to be fully stalled. At zero angle of attack, increasing the flap gap size was found to have minor effects on the flow field but increased flap overlap resulted in misalignment between the main wing boundary layer (BL) flow and the slot flow that forced the flow in the trailing edge region of the main wing to separate. When the angle of attack was increased to near stall conditions (at angle of attack of 12 deg), increasing the flap gap was found to energize and improve the flow in the trailing edge region of the main wing, whereas increased flap overlap further promoted flow separation on the main wing suction surface possibly steering the wing into stall.

scholarly journals Secondary flows and heat transfer in shallow flow around a cylinder: LES, PIV

2019 ◽  
Vol 196 ◽  
pp. 00028 ◽  
Author(s):  
Egor Palkin ◽  
Maxim Shestakov ◽  
Rustam Mullyadzhanov
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
Plane Channel ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Secondary Motion ◽  
Horseshoe Vortices

We report on Large-eddy simulations (LES) of flow around a short cylinder mounted in a narrow plane channel in a range of Reynolds numbers 1000, 2000, 3750 based on the bulk velocity of the flow and diameter of the cylinder supplemented with Particle image velocimetry (PIV) measurements for the highest considered Re. First two cases appear to be steady, however, for Re=3750 the flow becomes unsteady with the wake dominated by periodic vortex shedding. In front of the cylinder typical horseshoe vortices are identified intensifying the skin friction and heat transfer on the wall, while in the near wake we observe a quasiperiodic low-frequency secondary motion in the form of a pair of counterrotating eddies developing in the transverse direction. The Karman vortex street remains the dominant pattern, but further downstream from the cylinder the transport across the channel is associated with the secondary streamwise vortices, as also previously observed in slot jets. We observe their impact on heat transfer and skin friction on the wall of the channel.

Experimental Study of Three-Dimensional Laminar Wall Jets of Non-Newtonian Fluid

2009 ◽  
Author(s):  
Kofi K. Adane ◽  
Mark F. Tachie
Keyword(s):  
Newtonian Fluid ◽  
Open Channel ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Jet Flows ◽  
Wall Jet ◽  
Particle Image Velocimetry Technique ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Shear Thinning Fluid

A particle image velocimetry technique was employed to study three-dimensional laminar wall jet flows of a non-Newtonian shear-thinning fluid. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open channel. The Reynolds numbers based on the pipe diameter and jet exit velocity were varied from 250 to 800. The PIV measurements were performed in various streamwise-transverse and streamwise-spanwise planes. From these measurements, the velocity profiles, jet growth rate and spread rates were obtained to study the characteristics of three-dimensional wall jet flows of a non-Newtonian fluid.

scholarly journals APPLYING PIV MEASUREMENTS ON FLOW FIELD OF WAVES PROPAGATING OVER A SINGLE SUBMERGED POROUS ELASTIC BREAKWATER

2012 ◽  
Vol 1 (33) ◽  
pp. 29
Author(s):  
Tai-Wen Hsu ◽  
Yuan-Jyh Lan ◽  
Jian-Wu Lai ◽  
Yung-Han Cheng ◽  
Shan-Hwei Ou
Keyword(s):  
Flow Field ◽  
Wave Reflection ◽  
Surface Friction ◽  
The Other ◽  
Pressure Gradients ◽  
Wave Reflections ◽  
Reflection And Transmission ◽  
Submerged Breakwater ◽  
Piv Measurements ◽  
Image Velocimetry

The objective of the present study is to investigate the flow field for waves propagating over a submerged poro-elastic breakwater. Particle Image Velocimetry (PIV) measurements were performed in wave conditions with breakwaters made of different materials. The experimental results were compared for various rigid and impermeable, elastic and impermeable, as well as poro-elastic cases. Measurements of wave reflection and transmission induced by soft and permeable submerged breakwaters are both carried out. The results show that the oscillatory motion of elastic submerged breakwater can induce extra reflective waves and result in a larger reflection coefficient. Positive (counterclockwise) and negative (clockwise) vortices are generated due to corner separation and pressure gradients. The negative vortex obtained in a poro-elastic breakwater is generated by the surface friction at the top of the structure. Because of the permeability, it is found that the negative vortex at the upstream side of the elastic and permeable case is smaller than that of the rigid and impermeable one. In contrast, the positive vortex at the downstream side of the poro-elastic case is larger than that seen with the other two cases. It is concluded that a poro-elastic breakwater would induce different wave reflections and flow patterns from those seen with the other cases due to its particular wave and structure interactions.

scholarly journals Particle Image Velocimetry for in vitro characterization of Paravalvular Leakage of TAVR-sealing concepts

2021 ◽  
Vol 7 (2) ◽  
pp. 668-671
Author(s):  
Samuel Höing ◽  
Finja Borowski ◽  
Jan Oldenburg ◽  
Sabine Illner ◽  
Alper Öner ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Aortic Annulus ◽  
Piv Measurements ◽  
Paravalvular Leakage ◽  
Transcatheter Aortic Valve ◽  
Image Velocimetry

Abstract Paravalvular leakage (PVL), defined as the leakage between the aortic annulus and a transcatheter aortic valve replacement (TAVR), is verifiably associated with short- and long-term clinical outcome, especially with increased mortality. Therefore, with the ambition to reduce or even prevent PVL of next generation TAVR, it is necessary to extend the hemodynamic understanding of PVL. This study presents an in vitro flow measurement method to localize PVL during hydrodynamic characterization of TAVR and furthermore presents different design features, socalled outer skirt, to reduce PVL. Particle image velocimetry (PIV) measurements were performed for flow field assessment during hydrodynamic characterization of TAVR. Additionally, two different sealing concepts were developed to reduce PVL. The skirts were manufactured from polymeric-nonwoven and sued to pericardium-based TAVR-prototype. The prepared TAVR-prototypes were then deployed in a pathophysiological model of the aortic root with a calcification nodule of 2 mm according to ISO 5840:2021. To assess PVL, the flow field and the regurgitation volume was measured. The PIV measurements showed a clearly visible leakage jet between the TAVR-prototypes without skirt and the pathophysiological aortic annulus model. Jet velocities of up to 0.5 m/s were measured depending on presence or configuration of a PVL-preventing skirt. When implanted in the physiological annulus model without calcification nodule, PVL was hardly recognizable. The regurgitation volume of a TAVR-prototype without skirt at 5 l/min was 36.26±1.89 ml (n = 10). The developed and manufactured polymeric-nonwoven skirts reduced PVL from 37.67±1.17 ml to 18.36±1.8 ml (n = 10, TAVR-skirt-design1) and from 46.97±1.07 ml to 17.85±1.29 ml (n = 10, TAVR-skirt-design2) at 5 l/min. The localization of PVL during hydrodynamic characterization by means of PIV was successful. The sealing concepts developed in this work were very effective and led to a PVL-reduction of the tested TAVR prototypes of about 50% to 70%.

Experimental Investigation of an Acoustic Field Influence on a Development of the Plane Microjet by Particle Image Velocimetry (PIV)

2011 ◽  
Vol 6 (4) ◽  
pp. 42-50
Author(s):  
Yuriy Litvinenko ◽  
Maria Litvinenko ◽  
Mikhail Katasonov
Keyword(s):  
Particle Image Velocimetry ◽  
Acoustic Field ◽  
Vector Fields ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Laser Flash ◽  
Piv Measurements ◽  
Low Reynolds Numbers ◽  
Image Velocimetry ◽  
Field Influence

An acoustic field influence on a development of the plane microjet at low Reynolds numbers were investigated experimentally employing Particle Image Velocimetry (PIV). Measurements were performed at synchronization of an acoustic signal phase with a laser flash. Instantaneous velocity fields of different cross- and longitudinal sections are occurred. Receptivity of the plane microjet to transversal acoustic disturbances is shown. PIV-images, correspond to them vector fields and vorticity fields are presented

Characterization of Pulsating Submerged Jet—A Particle Image Velocimetry Study

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Harekrishna Yadav ◽  
Atul Srivastava ◽  
Amit Agrawal
Keyword(s):  
Particle Image Velocimetry ◽  
Critical Frequency ◽  
Particle Image ◽  
Near Field ◽  
Reynolds Numbers ◽  
Pulsation Frequency ◽  
Potential Core ◽  
Image Velocimetry ◽  
Pulsating Jet ◽  
Surrounding Fluid

An experimental investigation has been performed to determine the flow characteristics of an axisymmetric submerged water jet with superimposed periodically oscillating flow. The objective of the study is to quantify in detail the near field of a pulsating jet using the particle image velocimetry (PIV) technique. The amplitude and frequency of oscillations are varied separately and the effect of each parameter is determined for a range of Reynolds numbers (ReD = 1602, 2318, and 3600). The experimental results indicate that for a given Reynolds number and amplitude, with an increase in the frequency of pulsation, the vortex formation shifts toward the nozzle exit. The number of vortices also increases with an increase in the jet pulsation frequency. Broadening of the jet and shortening of the potential core length are also observed. This indicates that mixing with the surrounding fluid is higher with pulsating jet even at relatively low Reynolds numbers. It is observed that frequency up to a critical frequency helps increase entrainment of the surrounding fluid. An upper critical frequency beyond which pulsation does not affect the entrainment is also determined. These results should eventually lead to a better understanding of the physical phenomena responsible for enhanced heat transfer rates in the presence of pulsating jets.

The Effect of Reynolds Number on Microfan Performance

2004 ◽  
Author(s):  
David Quin ◽  
Ronan Grimes ◽  
Ed Walsh ◽  
Mark Davies ◽  
Stefan Kunz
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Electronic Systems ◽  
Piv Measurements ◽  
Flow Characterization ◽  
Image Velocimetry ◽  
Macro Scale

Miniaturisation of modern electronics means that future compact electronic systems are likely to be too hot to be held in the users hand. Simultaneous increases in heat dissipation will also require the development of novel compact cooling technologies. In systems such as mobile phones and palmtop computers, macro scale fans cannot be used to overcome this problem, as they are too large. As a solution, the implementation of micro fan technology is proposed. Previous investigators have shown that reduction of the Reynolds number of turbomachinery results in reduced efficiency. To experimentally investigate this predicted phenomenon, a series of geometrically similar axial flow fans have been fabricated. These range in size from the macro to the micro scale with the Reynolds numbers varying linearly with fan dimensions. Through detailed Particle Image Velocimetry (PIV) measurements and pressure flow characterization of these fans, this investigation aims to quantify the reduction in efficiency, which occurs as the Reynolds number is reduced. This paper concludes that the extent to which fan efficiency is reduced by Reynolds number is in surprisingly good agreement with relatively simple predictions developed by the authors in previous investigations. Reduced Reynolds number was also seen to alter the velocity distribution at the fan outlet. This is an important point as it indicates a change in the physics of the flow with reducing scale.

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