scholarly journals Time-resolved velocity and pressure field quantification in a flow-focusing device for ultrafast microbubble production

2021 ◽  
Vol 6 (11) ◽  
Author(s):  
Sarah Cleve ◽  
Christian Diddens ◽  
Tim Segers ◽  
Guillaume Lajoinie ◽  
Michel Versluis
Keyword(s):  
Pressure Field ◽  
Flow Focusing ◽  
Time Resolved

Investigation of the 3D Unsteady Rotor Pressure Field in a HP Turbine Stage

2002 ◽  
Author(s):  
E. Valenti ◽  
J. Halama ◽  
R. De´nos ◽  
T. Arts
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Pressure Field ◽  
Pressure Ratio ◽  
Turbine Stage ◽  
Time Resolved ◽  
Mach Number Distribution ◽  
Rotor Surface ◽  
Exit Mach Number ◽  
Unsteady Pressure Measurements

This paper presents steady and unsteady pressure measurements at three span locations (15, 50 and 85%) on the rotor surface of a transonic turbine stage. The data are compared with the results of a 3D unsteady Euler stage calculation. The overall agreement between the measurements and the prediction is satisfactory. The effects of pressure ratio and Reynolds number are discussed. The rotor time-averaged Mach number distribution is very sensitive to the pressure ratio of the stage since the incidence of the flow changes as well as the rotor exit Mach number. The time-resolved pressure field is dominated by the vane trailing edge shock waves. The incidence and intensity of the shock strongly varies from hub to tip due to the radial equilibrium of the flow at the vane exit. The decrease of the pressure ratio attenuates significantly the amplitude of the fluctuations. An increase of the pressure ratio has less significant effect since the change in the vane exit Mach number is small. The effect of the Reynolds number is weak for both the time-averaged and the time-resolved rotor static pressure at mid-span, while it causes an increase of the pressure amplitudes at the two other spans.

scholarly journals Shear-free mixing to achieve accurate temporospatial nanoscale kinetics through scanning-SAXS: ion-induced phase transition of dispersed cellulose nanocrystals

Lab on a Chip ◽  
2021 ◽  
Author(s):  
Tomas Rosén ◽  
Ruifu Wang ◽  
HongRui He ◽  
Chengbo Zhan ◽  
Shirish Chodankar ◽  
...  
Keyword(s):  
Phase Transition ◽  
Reaction Kinetics ◽  
Cellulose Nanocrystals ◽  
Study Time ◽  
Free Flow ◽  
Nanoscale Materials ◽  
Flow Focusing ◽  
Time Resolved ◽  
Kinetics Of

We present a shear-free flow-focusing mixing experiment to study time-resolved reaction kinetics of nanoscale materials through scanning-SAXS.

Influence of Rim Seal Purge Flow on the Performance of an Endwall-Profiled Axial Turbine

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
P. Schuepbach ◽  
R. S. Abhari ◽  
M. G. Rose ◽  
J. Gier
Keyword(s):  
Static Pressure ◽  
Pressure Field ◽  
Leading Edge ◽  
Streamwise Vortex ◽  
Suction Side ◽  
Total Efficiency ◽  
Time Resolved ◽  
Axial Turbine ◽  
Baseline Case ◽  
Purge Flow

Nonaxisymmetric endwall profiling is a promising method to reduce secondary losses in axial turbines. However, in high-pressure turbines, a small amount of air is ejected at the hub rim seal to prevent the ingestion of hot gases into the cavity between the stator and the rotor disk. This rim seal purge flow has a strong influence on the development of the hub secondary flow structures. This paper presents time-resolved experimental and computational data for a one-and-1/2-stage high work axial turbine, showing the influence of purge flow on the performance of two different nonaxisymmetric endwalls and the axisymmetric baseline case. The experimental total-to-total efficiency assessment reveals that the nonaxisymmetric endwalls lose some of their benefit relative to the baseline case when purge is increased. The first endwall design loses 50% of the efficiency improvement seen with low suction, while the second endwall design exhibits a 34% deterioration. The time-resolved computations show that the rotor dominates the static pressure field at the rim seal exit when purge flow is present. Therefore, the purge flow establishes itself as jets emerging at the blade suction side corner. The jet strength is modulated by the first vane pressure field. The jets introduce circumferential vorticity as they enter the annulus. As the injected fluid is turned around the rotor leading edge, a streamwise vortex component is created. The dominating leakage vortex has the same sense of rotation as the rotor hub passage vortex. The first endwall design causes the strongest circumferential variation in the rim seal exit static pressure field. Therefore, the jets are stronger with this geometry and introduce more vorticity than the other two cases. As a consequence the experimental data at the rotor exit shows the greatest unsteadiness within the rotor hub passage with the first endwall design.

scholarly journals 3D pressure field reconstruction from time-resolved stereoscopic PIV measurements by relaxation of Taylor's hypothesis

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Dominique Fratantonio ◽  
John James Charonko
Keyword(s):  
Pressure Field ◽  
National Laboratory ◽  
Reconstruction Algorithm ◽  
Turbulent Channel Flow ◽  
Reconstruction Method ◽  
Time Resolved ◽  
Material Derivative ◽  
Stereoscopic Piv ◽  
Air Jet ◽  
Taylor’S Hypothesis

This work presents reconstructions of 3D pressure fields starting from 2D3C stereoscopic-PIV (SPIV) measurements. In Fratantonio et al. (2021), we presented a new reconstruction algorithm, the “Instantaneous convection” method, capable of producing 3D velocity fields from time-resolved SPIV measurements. For reconstructions in flows with strong shear layers and high turbulence intensity, this method is able to provide time-resolved 3D velocity volumes that are more accurate than those that can be obtained from the more frequently employed reconstruction method based on the Taylor’s hypothesis and on the use of a mean convective field. Here we investigate the possibility of reconstructing the 3D pressure field from the timeresolved series of reconstructed 3D velocity data. A pseudo-tracking method is employed for computing the velocity material derivative, and the pressure field is then reconstructed by solving the 3D Poisson equation. The velocity and pressure reconstructions are validated on the Direct Numerical Simulation data of the turbulent channel flow taken from the John Hopkins Turbulence Database (JHTDB), and an application to experimental SPIV measurements of an air jet flow in coflow carried out at the Turbulent Mixing Tunnel (TMT) facility at Los Alamos National Laboratory is presented.

Vortex-corner interactions in a cavity shear layer elucidated by time-resolved measurements of the pressure field

2013 ◽  
Vol 728 ◽  
pp. 417-457 ◽  
Author(s):  
Xiaofeng Liu ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Pressure Field ◽  
Vertical Wall ◽  
Feedback Mechanism ◽  
Pressure Gradients ◽  
Direct Role ◽  
Time Resolved ◽  
Number Range ◽  
Cavitation Inception

AbstractThe flow structure and turbulence in an open cavity shear layer has been investigated experimentally at a Reynolds number of$4. 0\times 1{0}^{4} $, with an emphasis on interactions of the unsteady pressure field with the cavity corners. A large database of time-resolved two-dimensional PIV measurements has been used to obtain the velocity distributions and calculate the pressure by spatially integrating the material acceleration at a series of sample areas covering the entire shear layer and the flow surrounding the corners. Conditional sampling, low-pass filtering and time correlations among variables enable us to elucidate several processes, which have distinctly different frequency ranges, that dominate the shear layer interactions with the corners. Kelvin–Helmholtz shear layer eddies have the expected Strouhal number range of 0.5–3.2. Their interactions with the trailing corner introduce two sources of vorticity fluctuations above the corner. The first is caused by the expected advection of remnants of the shear layer eddies. The second source involves fluctuations in local viscous vorticity flux away from the wall caused by periodic variations in the streamwise pressure gradients. This local production peaks when the shear layer vortices are located away from the corner, creating a lingering region with peak vorticity just above the corner. The associated periodic pressure minima there are lower than any other point in the entire flow field, making the region above the corner most prone to cavitation inception. Flapping of the shear layer and boundary layer upstream of the leading corner occurs at very low Strouhal numbers of ∼0.05, affecting all the flow and turbulence quantities around both corners. Time-dependent correlations of the shear layer elevation show that the flapping starts in the boundary layer upstream of the leading corner and propagates downstream at the free stream speed. Near the trailing corner, when the shear layer elevation is low, the stagnation pressure in front of the wall, the downward jetting flow along this wall, the fraction of shear layer vorticity entrained back into the cavity, and the magnitude of the pressure minimum above the corner are higher than those measured when the shear layer is high. However, the variations in downward jetting decay rapidly with increasing distance from the trailing corner, indicating that it does not play a direct role in a feedback mechanism that sustains the flapping. There is also low correlation between the boundary/shear layer elevation and the returning flow along the upstream vertical wall, providing little evidence that this returning flow affects the flapping directly. However, the characteristic period of flapping, ∼0.6 s, is consistent with recirculation time of the fluid within the cavity away from boundaries. The high negative correlations of shear/boundary layer elevation with the streamwise pressure gradient above the leading corner introduce a plausible mechanism that sustains the flapping: when the shear layer is low, the boundary layer is subjected to high adverse streamwise pressure gradients that force it to widen, and when the shear layer is high, the pressure gradients decrease, allowing the boundary layer to thin down. Flow mechanisms that would cause the flapping-induced pressure changes, and their relations to the flow within the cavity are discussed.

Wake, Shock, and Potential Field Interactions in a 1.5 Stage Turbine—Part I: Vane-Rotor and Rotor-Vane Interaction

2003 ◽  
Vol 125 (1) ◽  
pp. 33-39 ◽  
Author(s):  
R. J. Miller ◽  
R. W. Moss ◽  
R. W. Ainsworth ◽  
N. W. Harvey
Keyword(s):  
High Pressure ◽  
Potential Field ◽  
Pressure Field ◽  
Fast Response ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Time Resolved ◽  
Pressure Transducers ◽  
Unsteady Pressure ◽  
The Individual

The composition of the time-resolved surface pressure field around a high-pressure rotor blade caused by the presence of neighboring blade rows is investigated, with the individual effects of wake, shock and potential field interaction being determined. Two test geometries are considered: first, a high-pressure turbine stage coupled with a swan-necked diffuser exit duct; secondly, the same high-pressure stage but with a vane located in the downstream duct. Both tests were conducted at engine-representative Mach and Reynolds numbers, and experimental data was acquired using fast-response pressure transducers mounted on the mid-height streamline of the HP rotor blades. The results are compared to time-resolved computational predictions of the flowfield in order to aid interpretation of experimental results and to determine the accuracy with which the computation predicts blade interaction. The paper is split into two parts: the first investigating the effect of the upstream vane on the unsteady pressure field around the rotor (vane-rotor interaction), and the second investigating the effect of the downstream vane on the unsteady pressure field around the rotor (rotor-vane interaction). The paper shows that at typical design operating conditions shock interaction from the upstream blade row is an order of magnitude greater than wake interaction and that with the design vane-rotor inter-blade gap the presence of the rotor causes a periodic increase in the strength of the vane trailing edge shock. The presence of the potential field of the downstream vane is found to affect significantly the rotor pressure field downstream of the Mach one surface within each rotor passage.

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.

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