On Improvement of PIV Measurements in the High-Shear Layer of a Wall-Bounded Flow

2015 ◽  
Author(s):  
Richard S. Skifton ◽  
Ralph S. Budwig
Keyword(s):  
Velocity Measurement ◽  
Interrogation Window ◽  
Wall Layer ◽  
Particle Dispersion ◽  
Bias Error ◽  
High Shear ◽  
Flow Measurements ◽  
Geometric Center ◽  
Layer Flow ◽  
Measurement Location

The particles utilized in particle image velocimetry (PIV) form a biased dispersion near interfaces that, in turn, lead to biased velocity measurements. This lack of seeding in the high shear region of the flow always biases the velocity measurement high as the particles are, on average, towards the far end of an interrogation window (IW) — opposite of the wall. By observing the ensemble-averaged IW particle-dispersion centroid as the corrected measurement location against the industry standard of the geometric center of the IW, this paper puts forth a methodology to correct for the biased error in flow measurements very near the wall. A typical correction to the reported velocity measurement location within a wall layer flow was seen to be approximately 75% from the geometric center to the edge of an IW. This methodology can easily be implemented in any PIV code with the express purpose of removing a source of bias error that forms by reporting measurements at the geometric center of an IW.

scholarly journals Estimating the Optimal Velocity Measurement Time in Rivers’ Flow Measurements: An Uncertainty Approach

Water ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 1010
Author(s):  
Robert Clasing ◽  
Enrique Muñoz
Keyword(s):  
Stability Criterion ◽  
Velocity Measurement ◽  
Measurement Time ◽  
Optimal Time ◽  
Optimal Point ◽  
Flow Measurements ◽  
Central Chile ◽  
Optimal Velocity ◽  
South Central ◽  
Point Velocity

The gauging process can be very extensive and time-consuming due to the procedures involved. Since velocity measurement time (VMT) is one of the main variables that would allow gauging times to be reduced, this study seeks to determine the optimal point VMT and, thereby, reduce the overall gauging time. An uncertainty approach based on the USGS area-velocity method and the GLUE methodology applied to eight gauging samples taken in shallow rivers located in South-central Chile was used. The average point velocity was calculated as the average of 1 to 70 randomly selected instant velocity samples (taken every one second). The time at which the uncertainty bands reached a stability criterion (according to both width and slope stability) was considered to be the optimum VMT since the variations were negligible and it does not further contribute to a less uncertain solution. Based on the results, it is concluded that the optimum point VMT is 17 s. Therefore, a point velocity measurement of 20 s is recommended as the optimal time for gauging in shallow rivers.

scholarly journals Flow Measurements Behind the Inlet Guide Vane of a Centrifugal Compressor

1998 ◽  
Author(s):  
I. Kassens ◽  
M. Rautenberg
Keyword(s):  
Centrifugal Compressor ◽  
Total Pressure ◽  
Guide Vane ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Inlet Guide Vane ◽  
Flow Measurements ◽  
Flow Angle ◽  
Partial Load ◽  
Measurement Location

In a centrifugal compressor adjustable inlet guide vanes (IGV) in front of the impeller are used to regulate the pressure ratio and the mass flow. The stationary measurement of the velocity profile in front of the impeller with different angles of the IGV displays shock losses at the inlet edge of blade of the impeller. In the partial-load region (e.g. partial-load efficiency) the radial distribution of the flow influences considerably the performance of the impeller. The tested compressor consists of an adjustable IGV with straight vanes, a shrouded impeller and a vaneless, parallel diffuser. In the first measurement location, behind the IGV, total pressure, static pressure and flow angle were measured with a 5-hole cylinder probe. In the second measurement location, in front of the impeller, the measurement of the total pressure was carried out with a Kiel probe and the flow angle with a Cobra probe accordingly the static wall pressure was measured. Taking into consideration the fundamental thermodynamical equations it was possible to determine the velocity profiles because of the measured distributions of the flow angle in these two measurement locations. For different angles of the IGV and with various mass flows the distributions of the deflection defect behind the IGV are described. Starting with the measured distributions of the flow in front of the impeller the flow angles at the impeller inlet are calculated and the distributions of the incidence angle at the impeller inlet are figured out.

A Comparative Investigation of Round and Fan-Shaped Cooling Hole Near Flow Fields

2007 ◽  
Author(s):  
James S. Porter ◽  
Jane E. Sargison ◽  
Gregory J. Walker ◽  
Alan D. Henderson
Keyword(s):  
High Speed ◽  
Near Field ◽  
Steady State Solution ◽  
Comparative Investigation ◽  
Round Hole ◽  
High Shear ◽  
Cooling Hole ◽  
Turbulence Data ◽  
Shaped Hole ◽  
Layer Flow

This study presents velocity and turbulence data measured experimentally in the near field of a round and a laterally expanded fan-shaped cooling hole. Both holes are fed by a plenum inlet, and interact with a turbulent mainstream boundary layer. Flow is Reynolds number matched to engine conditions to preserve flow structure, and two coolant to mainstream blowing momentum ratios are investigated experimentally. Results clearly identify regions of high shear for the round hole as the jet penetrates into the mainstream. In contrast, the distinct lack of high shear regions for the fan shaped hole point to reasons for improvements in cooling performance noted by previous studies. Two different CFD codes are used to predict the flow within and downstream of the fan shaped hole, with validation from the experimental measurements. One code is the commercially available ANSYS CFX 10.0, and the other is the density-based solver with low Mach number preconditioning, HYDRA, developed in-house by Rolls-Royce plc for high speed turbomachinery flows. Good agreement between numerical and experimental data for the center-line traverses was obtained for a steady state solution, and a region of reversed flow within the expansion region of the fan-shaped hole was identified.

Single Pixel Evaluation of Microchannel Flows

2005 ◽  
Author(s):  
Steve Wereley ◽  
Carl Meinhart ◽  
Lichuan Gui ◽  
Derek Tretheway ◽  
Arjun Sud
Keyword(s):  
Correlation Analysis ◽  
Particle Concentration ◽  
Interrogation Window ◽  
Window Size ◽  
Bias Error ◽  
Zero Bias ◽  
Effective Particle ◽  
The Interrogation Window Size ◽  
Error Behavior ◽  
Single Pixel

Recently a new μPIV interrogation algorithm has been proposed in which the interrogation window size is reduced to a single pixel. Such small interrogation window sizes are possible using correlation averaging to increase the effective particle concentration to levels required for correlation analysis to succeed. The random error exhibits the expected behavior of decreasing roughly in proportion to N−1/2 while the bias error exhibits unexpected peak-locking behavior with zero bias error at integer and half integer pixel displacements and maximal errors at one-quarter and three-quarter pixel displacements. Accompanying experiments show the potential of this technique but have not yet been sufficiently refined to confirm this unexpected bias error behavior.

Physical Model Study of the Wind Turbine Array Boundary Layer

2014 ◽  
Author(s):  
Kyle Charmanski ◽  
John Turner ◽  
Martin Wosnik
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Hot Wire ◽  
Flow Measurements ◽  
Model Study ◽  
Power Rate ◽  
First Results ◽  
Upstream Part ◽  
Measurement Location

First results from an experimental investigation of the fully developed wind turbine array boundary layer are reported, using arrays of up to 100 model wind turbines with a diameter of 0.25 m. The wind turbine array was simulated by a combination of drag-matched porous disks, used in the upstream part of the array, and by a smaller array of realistically scaled 3-bladed wind turbines just upstream of the measurement location. The model array was placed in the 6.0 m × 2.7 m × 72.0 m test section of the UNH Flow Physics Facility. Power, rate of rotation and rotor thrust were measured for select turbines, and hot-wire anemometry was used for flow measurements. Development of a fully developed wind turbine array boundary layer was noted with increase in array size.

A Comparative Investigation of Round and Fan-Shaped Cooling Hole Near Flow Fields

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
James S. Porter ◽  
Jane E. Sargison ◽  
Gregory J. Walker ◽  
Alan D. Henderson
Keyword(s):  
High Speed ◽  
Near Field ◽  
Steady State Solution ◽  
Comparative Investigation ◽  
Round Hole ◽  
High Shear ◽  
Cooling Hole ◽  
Turbulence Data ◽  
Shaped Hole ◽  
Layer Flow

This study presents velocity and turbulence data measured experimentally in the near field of a round and a laterally expanded fan-shaped cooling hole. Both holes are fed by a plenum inlet, and interact with a turbulent mainstream boundary layer. Flow is Reynolds number matched to engine conditions to preserve flow structure, and two coolant to mainstream blowing momentum ratios are investigated experimentally. Results clearly identify regions of high shear for the round hole as the jet penetrates into the mainstream. In contrast, the distinct lack of high shear regions for the fan-shaped hole points to reasons for improvements in cooling performance noted by previous studies. Two different computational fluid dynamics codes are used to predict the flow within and downstream of the fan-shaped hole, with validation from the experimental measurements. One code is the commercially available ANSYS CFX 10.0, and the other is the density-based solver with low Mach number preconditioning, HYDRA, developed in-house by Rolls-Royce plc for high speed turbomachinery flows. Good agreement between numerical and experimental data for the center-line traverses was obtained for a steady state solution, and a region of reversed flow within the expansion region of the fan-shaped hole was identified.

PHYSICS OF COHERENT STRUCTURES OF TURBULENT FLOW IN NEAR-WALL REGION OF A VIBRATING PLATE

2010 ◽  
Vol 24 (13) ◽  
pp. 1433-1436
Author(s):  
L. X. ZHANG
Keyword(s):  
Boundary Layer ◽  
Coherent Structures ◽  
Boundary Layer Flow ◽  
Wall Layer ◽  
Basis Functions ◽  
Galerkin Projection ◽  
Wall Region ◽  
Layer Flow ◽  
Near Wall ◽  
Vibrating Plate

The focus of this paper is on physics of coherent structures in boundary layer flow in near-wall region of a vibrating plate. A dynamical model is developed based on Galerkin projection of the governing equation of the wall layer flow onto a subspace spanned by the orthogonal divergence-free Fourier basis functions. The interactive physics of the coherent structures with the wall vibration is studied with the established model truncated at any order. The compared results show that the prevailing coherent structures in the layer flow near a vibrating wall region are captured.

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