Computational Fluid Dynamics and Particle Image Velocimetry Supported Examination of Bidirectional Velocity Probes for Measurements in Flames

2013 ◽  
Vol 6 (1) ◽  
Author(s):  
Nadir Yilmaz ◽  
Brian C. Hogan ◽  
Humberto Bocanegra ◽  
A. Burl Donaldson ◽  
Walt Gill
Keyword(s):  
Fluid Dynamics ◽  
Experimental Study ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Pressure Difference ◽  
Particle Image ◽  
Amplification Factor ◽  
Local Velocity ◽  
Bernoulli’S Equation ◽  
Image Velocimetry

The bidirectional velocity probe has been used in various flames to measure local velocity. The device is based on the pressure difference between a closed forward facing cavity and a closed rearward facing cavity. The probes have been noted to indicate a pressure difference greater than that which would be predicted based on Bernoulli's equation. Each device must be experimentally calibrated in a wind tunnel at similar Reynolds number to determine its “amplification factor.” This study uses PIV, flow visualization and CFD to examine the flow field around the probe, as well as an experimental study which compares various probe configurations for measurement of velocity by pressure differential. The conclusion is that the amplification factor is indeed greater than unity but use of the wind tunnel for calibration is questionable.

scholarly journals Examination of the Bi-Directional Velocity Probe Used in Flames

2009 ◽  
Author(s):  
Brian C. Hogan ◽  
Humberto Bocanegra ◽  
Ramiro Chavez Alarcon ◽  
Nadir Yilmaz ◽  
A. Burl Donaldson ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Particle Image ◽  
Amplification Factor ◽  
Probe Design ◽  
Pressure Measurements ◽  
Bernoulli’S Equation ◽  
Image Velocimetry ◽  
Visualization Techniques ◽  
The Impact ◽  
Measured Pressure

The bidirectional probe has been used in combustion environments to measure localized flame velocities. The device measures the pressure difference between a closed forward-facing cavity, and a closed rearward-facing cavity. Each device must be experimentally calibrated to determine the “amplification factor,” which is unity if the measured differential pressures match Bernoulli’s equation. It is hypothesized that the probe design disrupts the flow, creating turbulence and irreversibilities, resulting in measured pressure differences. This study uses computational fluid dynamics, particle image velocimetry, and flow visualization techniques to examine the flow field around the probe, as well as an experimental study exploring the impact of minor changes in probe design on differential pressure measurements for velocity calculations.

Features of a Laminar Separated Boundary Layer Near the Leading-Edge of a Model Airfoil for Different Angles of Attack: An Experimental Study

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
K. Anand ◽  
S. Sarkar
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Particle Image ◽  
Leading Edge ◽  
Viscous Effect ◽  
Reattachment Point ◽  
Bubble Bursting ◽  
Image Velocimetry ◽  
Random Fluctuations

The evolution of a separated boundary layer over a model airfoil with semicircular leading-edge has been illustrated for angles of attack (α) varying from −3 deg to 10 deg, where the Reynolds number (Rec) based on chord is 1.6 × 105 and the inlet freestream turbulence (fst) being 1.2%. The features of boundary layer are described through measurements of velocity and surface pressure besides the flow visualization using a planar particle image velocimetry (PIV). Freestream perturbations are amplified because of enhanced receptivity of the separated boundary layer resulting in pockets of disturbances, which then propagate downstream attributing to random fluctuations near the reattachment. The separation and reattachment locations including the onset and end of transition are identified for changing α. The reattachment point changes from 18.8% to 47.7% of chord with the onset of separation at almost 7%, whereas the onset of transition moves upstream from 13.2% to 9% with increasing α. The bubble bursting occurs at α = 10 deg. The transition in the separated boundary layer occurs through Kelvin–Helmholtz (K–H) instability for α = 0 deg and 3 deg, whereas the K–H mechanism is bypassed for higher α with significant viscous effect.

Analysis of local velocity gradients in rapid mixer using particle image velocimetry technique

2002 ◽  
Vol 2 (5-6) ◽  
pp. 47-55
Author(s):  
N.-S. Park ◽  
H. Park
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Velocity Fields ◽  
Local Velocity ◽  
Mixing Condition ◽  
Particle Image Velocimetry Technique ◽  
Velocity Gradients ◽  
Image Velocimetry ◽  
Current Design ◽  
G Value

Recognizing the significance of factual velocity fields in a rapid mixer, this study focuses on analyzing local velocity gradients in various mixer geometries with particle image velocimetry (PIV) and comparing the results of the analysis with the conventional G-value, for reviewing the roles of G-value in the current design and operation practices. The results of this study clearly show that many arguments and doubts are possible about the scientific correctness of G-value, and its current use. This is because the G-value attempts to represent the turbulent and complicated factual velocity field in a jar. Also, the results suggest that it is still a good index for representing some aspects of mixing condition, at least, mixing intensity. However, it cannot represent the distribution of velocity gradients in a jar, which is an important factor for mixing. This study as a result suggests developing another index for representing the distribution to be used with the G-value.

scholarly journals Aerodynamics of manoeuvring flight in brown long-eared bats ( Plecotus auritus )

2018 ◽  
Vol 15 (148) ◽  
pp. 20180441 ◽  
Author(s):  
Per Henningsson ◽  
Lasse Jakobsen ◽  
Anders Hedenström
Keyword(s):  
Particle Image Velocimetry ◽  
Wind Tunnel ◽  
High Speed ◽  
Particle Image ◽  
Future Studies ◽  
Image Velocimetry ◽  
Mechanistic Basis

In this study, we explicitly examine the aerodynamics of manoeuvring flight in animals. We studied brown long-eared bats flying in a wind tunnel while performing basic sideways manoeuvres. We used particle image velocimetry in combination with high-speed filming to link aerodynamics and kinematics to understand the mechanistic basis of manoeuvres. We predicted that the bats would primarily use the downstroke to generate the asymmetries for the manoeuvre since it has been shown previously that the majority of forces are generated during this phase of the wingbeat. We found instead that the bats more often used the upstroke than they used the downstroke for this. We also found that the bats used both drag/thrust-based and lift-based asymmetries to perform the manoeuvre and that they even frequently switch between these within the course of a manoeuvre. We conclude that the bats used three main modes: lift asymmetries during downstroke, thrust/drag asymmetries during downstroke and thrust/drag asymmetries during upstroke. For future studies, we hypothesize that lift asymmetries are used for fast turns and thrust/drag for slow turns and that the choice between up- and downstroke depends on the timing of when the bat needs to generate asymmetries.

Measurement of Velocity Profiles of Laminar to Turbulent Water Flows in a Tube Using Particle Image Velocimetry

2004 ◽  
Author(s):  
Meredith R. Martin
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Glass Tube ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Reynolds Number Flow ◽  
Image Velocimetry ◽  
Dye Visualization ◽  
Number Flow

The transition from laminar to turbulent in-tube flow is studied in this paper. Water flow in a glass tube with an inside diameter of 21.7 mm was investigated by two methods. First, a dye visualization test using a setup similar to the 1883 experiment of Osborne Reynolds was conducted. For the dye visualization, Reynolds numbers ranging from approximately 1000 to 3500 were tested and the transition from laminar to turbulent flow was observed between Reynolds numbers of 2500 and 3500. For the second method, a particle image velocimetry (PIV) system was used to measure the velocity profiles of flow in the same glass tube at Reynolds numbers ranging from approximately 500 to 9000. The resulting velocity profiles were compared to theoretical laminar profiles and empirical turbulent power-law profiles. Good agreement was found between the lower Reynolds number flow and the laminar profile, and between the higher Reynolds number flow and turbulent power-law profile. In between the flow appeared to be in a transition region and deviated some between the two profiles.

Experimental study on the wake fields of a Panamax Bulker based on stereo particle image velocimetry

2018 ◽  
Vol 165 ◽  
pp. 91-106 ◽  
Author(s):  
Chun-yu Guo ◽  
Tie-cheng Wu ◽  
Wan-zhen Luo ◽  
Xin Chang ◽  
Jie Gong ◽  
...  
Keyword(s):  
Experimental Study ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Image Velocimetry ◽  
Stereo Particle Image Velocimetry ◽  
Wake Fields
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