scholarly journals Error propagation dynamics of PIV-based pressure field calculation (3): What is the minimum resolvable pressure in a reconstructed field?

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Zhao Pan ◽  
Jarad P. Whitehead ◽  
Geordie Rechards ◽  
Barton L. Smith
Keyword(s):  
Spatial Resolution ◽  
Pressure Field ◽  
Analytical Framework ◽  
Field Calculation ◽  
Pressure Sensitivity ◽  
Reconstructed Field ◽  
Optimal Resolution ◽  
Theoretical Predictions ◽  
Flow Features ◽  
Numerical Solver

An analytical framework for the propagation of velocity errors into PIV-based pressure calculation is established. Based on this framework, the optimal spatial resolution and the corresponding minimum field-wide error level in the calculated pressure field are estimated. This minimum error is viewed as the smallest resolvable pressure. We find that the optimal spatial resolution is a function of the flow features, geometry of the flow domain, and the type of the boundary conditions, in addition to the error in the PIV experiments, making a general statement about pressure sensitivity is difficult. The minimum resolvable pressure is affected by competing effects from the experimental error due to PIV and the truncation error from the numerical solver. This means that PIV experiments motivated by pressure measurements must be carefully designed so that the optimal resolution (or close to the optimal resolution) is used. Flows (Re=1.27 × 104 and 5×104) with exact solutions are used as examples to validate the theoretical predictions of the optimal spatial resolutions and pressure sensitivity. The numerical experimental results agree well with the analytical predictions.

scholarly journals Assessment of CFD Model Performance for Flows around a Hydraulic Structure of Complex Geometry

2020 ◽  
Author(s):  
Péter Grivalszki ◽  
Gábor Fleit ◽  
Sándor Baranya ◽  
János Józsa
Keyword(s):  
Turbulence Modeling ◽  
Hydraulic Structure ◽  
Complex Geometry ◽  
Model Performance ◽  
Cfd Modeling ◽  
Source Modeling ◽  
Extensive Experience ◽  
Flow Features ◽  
Model Setup ◽  
Numerical Solver

Computational Fluid Dynamics (CFD) modeling has become a widely used research tool in the hydraulic engineering community, however, for many problems the numerical model setup and even the selection of the suitable hydrodynamic solver is still a challenging task. This is the case for fine scale analysis of flow features around hydraulic structures of complex geometry, where generation of the 3D grid, application of the correct turbulence modeling approach, or modeling of the free surface all require extensive experience and knowledge. The aim of this paper is to perform a numerical hydrodynamic experiment for a hydraulic structure with complex geometry to assess the model performance, in terms of grid resolution, grid refinement methods as well as turbulence modeling. The open source modeling environment of OpenFOAM is tested and validated against laboratory measurements, moreover, practical recommendations are made for future applications of the numerical solver.

scholarly journals Evaluations on a Pressure-Field Calculation Method using PIV Synthetic Image

2016 ◽  
Vol 14 (2) ◽  
pp. 46-51
Author(s):  
Chang Je Lee ◽  
Gyong Rae Cho ◽  
Uei Kan Kim ◽  
Dong Hyuk Kim ◽  
Deog Hee Doh
Keyword(s):  
Calculation Method ◽  
Pressure Field ◽  
Synthetic Image ◽  
Field Calculation

scholarly journals How sperm competition shapes the evolution of testes and sperm: a meta-analysis

2020 ◽  
Vol 375 (1813) ◽  
pp. 20200064
Author(s):  
Stefan Lüpold ◽  
Raïssa A. de Boer ◽  
Jonathan P. Evans ◽  
Joseph L. Tomkins ◽  
John L. Fitzpatrick
Keyword(s):  
Sperm Competition ◽  
Meta Analysis ◽  
Empirical Studies ◽  
Reproductive Behaviour ◽  
Analytical Framework ◽  
Sperm Length ◽  
Other Information ◽  
Theoretical Predictions ◽  
Testes Size ◽  
Sperm Size

Females of many species mate with multiple males, thereby inciting competition among ejaculates from rival males for fertilization. In response to increasing sperm competition, males are predicted to enhance their investment in sperm production. This prediction is so widespread that testes size (correcting for body size) is commonly used as a proxy of sperm competition, even in the absence of any other information about a species' reproductive behaviour. By contrast, a debate about whether sperm competition selects for smaller or larger sperm has persisted for nearly three decades, with empirical studies demonstrating every possible response. Here, we synthesize nearly 40 years of sperm competition research in a meta-analytical framework to determine how the evolution of sperm number (i.e. testes size) and sperm size (i.e. sperm head, midpiece, flagellum and total length) is influenced by varying levels of sperm competition across species. Our findings support the long-held assumption that higher levels of sperm competition are associated with relatively larger testes. We also find clear evidence that sperm competition is associated with increases in all components of sperm length. We discuss these results in the context of different theoretical predictions and general patterns in the breeding biology and selective environment of sperm. This article is part of the theme issue ‘Fifty years of sperm competition’.

Uncertainty calculations of pressure sensitivity of one inch microphones using pressure field method at the National Metrology Institute of Egypt

2015 ◽  
Vol 138 (3) ◽  
pp. 1827-1827
Author(s):  
Rabab S. Ahmed ◽  
Hany A. Shawky ◽  
Rabab S. Youssef ◽  
Tarek M. El-Basheer ◽  
Hatem K. Mohamed
Keyword(s):  
Pressure Field ◽  
Field Method ◽  
National Metrology Institute ◽  
Pressure Sensitivity

scholarly journals Flow Features of the Near Wake of the Australian Boobook Owl (Ninox boobook) During Flapping Flight Suggest an Aerodynamic Mechanism of Sound Suppression for Stealthy Flight

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Jonathan Lawley ◽  
Hadar Ben-Gida ◽  
Krishnan Krishnamoorthy ◽  
Erin E Hackett ◽  
Gregory A Kopp ◽  
...  
Keyword(s):  
High Speed ◽  
Pressure Field ◽  
Near Wake ◽  
Calidris Mauri ◽  
Long Duration ◽  
Image Velocimetry ◽  
Western Sandpiper ◽  
Wake Patterns ◽  
Flow Features ◽  
The Subject

Synopsis The mechanisms associated with the ability of owls to fly silently have been the subject of scientific interest for many decades and may be relevant to bio-inspired design to reduce noise of flapping and non-flapping flying devices. Here, we characterize the near wake dynamics and the associated flow structures produced during flight of the Australian boobook owl (Ninox boobook). Three individual owls were flown at 8 ms−1 in a climatic avian wind tunnel. The velocity field in the wake was sampled at 500 Hz using long-duration high-speed particle image velocimetry (PIV) while the wing kinematics were imaged simultaneously using high speed video. The time series of velocity maps that were acquired over several consecutive wingbeat cycles enabled us to characterize the wake patterns and to associate them with the phases of the wingbeat cycle. We found that the owl wake was dramatically different from other birds measured under the same flow conditions (i.e., western sandpiper, Calidris mauri and European starling, Sturnus vulgaris). The near wake of the owl did not exhibit any apparent shedding of organized vortices. Instead, a more chaotic wake pattern was observed, in which the characteristic scales of vorticity (associated with turbulence) are substantially smaller in comparison to other birds. Estimating the pressure field developed in the wake shows that owls reduce the pressure Hessian (i.e., the pressure distribution) to approximately zero. We hypothesize that owls manipulate the near wake to suppress the aeroacoustic signal by controlling the size of vortices generated in the wake, which are associated with noise reduction through suppression of the pressure field. Understanding how specialized feather structures, wing morphology, or flight kinematics of owls contribute to this effect remains a challenge for additional study.

scholarly journals The Unsteady Pressure Field Over a Turbine Blade Surface: Visualisation and Interpretation of Experimental Data

1997 ◽  
Author(s):  
Roger W. Moss ◽  
Roger W. Ainsworth ◽  
Colin D. Sheldrake ◽  
Robert Miller
Keyword(s):  
Pressure Field ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Surface Flow ◽  
Pressure Transducers ◽  
Root Region ◽  
Flow Features ◽  
Extensive Surface ◽  
Absolute Frame

The unsteady static pressure field over a turbine rotor has been measured in the Oxford Rotor Facility using 78 flush-mounted miniature pressure transducers. This extensive surface coverage allows ensemble-averaged data to be displayed as an animated image. At the mid-height plane the fluctuations are well predicted using the UNSFLO 2-D unsteady code: away from mid-height the data shows large fluctuations. 12 transducers mounted on the blade leading edge show the relative total pressure field entering the blade row; these plus area traverse measurements at rotor exit are used to interpret the surface flow features. Rotor-mounted hot wires show large variations in blade incidence during the wake-passing cycle and allow conversion of blade-relative data into the absolute frame. Large pressure fluctuations in the root region may be explained in terms of a loss core associated with the NGV wake.

scholarly journals Effect of the boundary conditions, temporal, and spatial resolution on the pressure from PIV for an oscillating flow

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Nazmus Sakib ◽  
Alexander Mychkovsky ◽  
James Wiswall ◽  
Randy Samaroo ◽  
Barton Smith
Keyword(s):  
Boundary Conditions ◽  
Spatial Resolution ◽  
Temporal Resolution ◽  
Pressure Field ◽  
Interrogation Window ◽  
Window Size ◽  
Synthetic Jet ◽  
Frequency Noise ◽  
Time Resolved ◽  
Temporal Derivative

The pressure field of an impinging synthetic jet has been computed from time-resolved, three-dimensional, three-component (3D-3C) particle image velocimetry (PIV) velocity field data using a Poisson equationbased pressure solver. The pressure solver used in this work can take advantage of the temporal derivative of the pressure to enhance the temporal coherence of the calculated pressure field for time-resolved velocity data. The reconstructed pressure field shows sensitivity to the implementation of the boundary conditions, as well as to the spatial and temporal resolution of the PIV data. The pressure from a 3D Poisson solver that does not consider the temporal derivative of the pressure shows high random error. Invoking the temporal derivative of the pressure eliminates this high-frequency noise, however, the calculated pressure exhibits an unphysical temporal drift. This temporal drift is affected by both the temporal resolution of the PIV data and the spatial resolution of the PIV vector field, which was systematically evaluated by downsampling the instantaneous data and increasing the interrogation window size. It was observed that decreasing the temporal resolution increased the drift, while decreasing the spatial resolution decreased the drift.

Numerical simulation of droplet formation in different microfluidic devices

2020 ◽  
Vol 234 (19) ◽  
pp. 3776-3788
Author(s):  
Pooria Hadikhani ◽  
Sahand Majidi ◽  
Asghar Afshari
Keyword(s):  
Microfluidic Devices ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Strong Impact ◽  
Generation Process ◽  
Flow Solver ◽  
Computational Performance ◽  
Flow Features ◽  
Multi Phase Flow ◽  
Numerical Solver

This study aims to assess the droplet formation process in microfluidic devices using an all Mach-number multi-phase flow solver. Harten-Lax-van Leer-Contact (HLLC) Riemann solver is implemented for solving the discretized equations while Tangent of Hyperbola for INterface Capturing (THINC) method is applied to reduce the excessive diffusion of the method at the interface. The multi-block strategy is implemented in the flow solver to improve its capability of simulating flows in more complicated, multi-port droplet formation geometries. First, the computational performance of the numerical solver is validated through simulating the benchmark Rayleigh-Taylor instability problem and the droplet formation in a planar flow-focusing geometry. The comparison of numerical results with available analytical/experimental data indicates a precise prediction of flow features. Then, the droplet generation process in coflowing devices with Newtonian liquid is numerically studied. Finally, the shear-thinning effects of the dispersed and continuous phase on the drop formation characteristics are investigated. It is shown that deviation of the continuous phase from Newtonian behavior has a strong impact on droplet size, speed, and generation rate. On the other hand, assuming the dispersed phase as non-Newtonian does not strongly affect the aforementioned properties of the droplet formation regime.

Nonlinear dynamic pressure beneath waves in water of large and intermediate depth

2021 ◽  
Author(s):  
Anna Kokorina ◽  
Alexey Slunyaev ◽  
Marco Klein
Keyword(s):  
Gravity Waves ◽  
Pressure Field ◽  
Dynamic Pressure ◽  
Surface Displacement ◽  
Weakly Nonlinear ◽  
Pressure Fields ◽  
Component Theory ◽  
Theoretical Predictions ◽  
Weakly Nonlinear Waves ◽  
The Waves

<p>The data of simultaneous measurements of the surface displacement produced by propagating planar waves in experimental flume and of the dynamic pressure fields beneath the waves are compared with the theoretical predictions based on different approximations for modulated potential gravity waves. The performance of different theories to reconstruct the pressure field from the known surface displacement time series (the direct problem) is investigated. A new two-component theory for weakly modulated weakly nonlinear waves is proposed, which exhibits the best capability among the considered. Peculiarities of the vertical modes of the nonlinear pressure harmonics are discussed.</p><p> </p><p>The work was supported by the RFBR projects 19-55-15005 and 20-05-00162 (AK).</p>

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