scholarly journals PIV investigation of cavitating flows around circular cylinders with hydrophobic coatings

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Konstantin Dobroselsky ◽  
Anatoliy Lebedev ◽  
Alexey Safonov ◽  
Sergey Starinskiy ◽  
Vladimir Dulin
Keyword(s):  
Test Section ◽  
Pressure Sensors ◽  
Circular Cylinders ◽  
Bulk Velocity ◽  
Water Tunnel ◽  
Slip Effect ◽  
Long Distance ◽  
Hydrophobic Coatings ◽  
Heating Section ◽  
Near Wall

The treatment of the hydrophobic properties of solid surfaces is considered as a passive method to reduce the drag in water flows (Rothstein, 2010) and to potentially affect the flow separation and vortex shedding (Sooraj et al., 2020). The manufacturing of surfaces with micro- and nano-scale roughness allows to extend the hydrophobicity towards superhydrophobicity with the contact angle close to 180°. In such conditions the solid surface is not wetted completely and the air-water interphase partially remains on the surface texture. This results in so-called flow slip effect. Therefore, a local phase transition during the flow cavitation or gas effervescence in near-wall low-pressure regions may additionally affect the slip effect for hydrophobic surfaces. The present work is focused on the comparison between cavitating and noncavitating flows around circular cylinders with lateral sectors with hydrophobic and non-hydrophobic coatings. The experiments are performed in a water tunnel, which consists of a water outgassing and cooling/heating section, honeycomb, contraction section, test section and diffuser. The water flow is driven by an electric pump, providing a bulk velocity up to 10 m/s in the transparent test section with 1 m length and 80×150 mm2 rectangular cross-section. The facility is equipped with an ultrasonic flowmeter, temperature and pressure sensors. Besides, the static pressure inside the water tunnel can be varied by using a special shaft section. The measurements are performed by using high-repetition and low-repetition PIV systems. The former is used for the analysis of large-scale flow dynamics in the wake region, whereas the latter one is used for high-resolution measurements in near-wall regions by using a long-distance microscope. The Reynolds number based on the bulk velocity of the flow, diameter of the cylinders (D = 26 mm) and kinematic viscosity of the water is varied up to 2×105..

Characterization of the Custom-Designed, High Reynolds Number Water Tunnel

2016 ◽  
Author(s):  
Yasaman Farsiani ◽  
Brian R. Elbing
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Test Section ◽  
High Reynolds Number ◽  
Layer Growth ◽  
Water Tunnel ◽  
Freestream Velocity ◽  
Section Design ◽  
High Reynolds

This paper reports on the characterization of the custom-designed high-Reynolds number recirculating water tunnel located at Oklahoma State University. The characterization includes the verification of the test section design, pump calibration and the velocity distribution within the test section. This includes an assessment of the boundary layer growth within the test section. The tunnel was designed to achieve a downstream distance based Reynolds number of 10 million, provide optical access for flow visualization and minimize inlet flow non-uniformity. The test section is 1 m long with 15.2 cm (6-inch) square cross section and acrylic walls to allow direct line of sight at the tunnel walls. The verification of the test section design was accomplished by comparing the flow quality at different location downstream of the flow inlet. The pump was calibrated with the freestream velocity with three pump frequencies and velocity profiles were measured at defined locations for three pump speeds. Boundary layer thicknesses were measured from velocity profile results and compared with analytical calculations. These measurements were also compared against the facility design calculations.

Forces on Cylinders Near a Plane Boundary in a Sinusoidally Oscillating Fluid

1976 ◽  
Vol 98 (3) ◽  
pp. 499-503 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Reynolds Number ◽  
Least Squares ◽  
Least Squares Method ◽  
Lift Coefficient ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Plane Boundary ◽  
Water Tunnel ◽  
Inertia Coefficient ◽  
Line Force

The in-line and transverse forces acting on circular cylinders placed near a plane boundary in a sinusoidally oscillating fluid in a U-shaped vertical water tunnel have been measured. The period parameter UmT/D was varied from about 2 to 40, the Reynolds number from 4000 to 25,000, and the gap between the cylinder and the plane boundary from 0.01 D to 1.0D. The drag and inertia coefficients for the in-line force have been determined through the use of the Morison’s equation and the Fourier analysis, least squares method, and a modified least squares method. The transverse force coefficients have been obtained for the forces toward the wall and away from the wall. The results show that the in-line and transverse forces could acquire very large magnitudes and give rise to serious oscillations. For very small values of the period parameter, effects of flow separation become negligible and the inertia coefficient for the in-line force and the lift coefficient for the transverse force approach those predicted by the potential theory.

CFD Simulation and Experimental Validation of a New Closed Circuit Wind/Water Tunnel Design

1998 ◽  
Vol 120 (2) ◽  
pp. 311-318 ◽  
Author(s):  
Robert Gordon ◽  
Mohammed S. Imbabi
Keyword(s):  
Test Section ◽  
Cfd Simulation ◽  
Decisive Role ◽  
Cost Effective ◽  
Closed Circuit ◽  
Working Fluid ◽  
Water Tunnel ◽  
Measured Velocity ◽  
Tunnel Design ◽  
Set Up

A new closed-circuit wind/water tunnel to support flow visualization research was designed and constructed at The University of Aberdeen. Review of existing closed-circuit tunnel designs revealed that they are large, expensive, difficult to set up and maintain, and typically employ a single working fluid. Key objectives of the work reported here were to reduce the overall cost and size of the tunnel, facilitate the use of alternative working fluids (air or water), and provide high quality flow within the test section. Conventional design methods were used initially, and computational fluid dynamics (CFD) was then employed to simulate the flow within critical sections of the tunnel. The results from CFD played a decisive role in identifying the modifications needed to achieve the compact, cost-effective tunnel design eventually built and tested. Flow quality within the test section was established using measured velocity profiles, and these are also presented.

Hydrodynamic Performance of the Large Cavitation Channel (LCC)

2003 ◽  
Author(s):  
Joel T. Park ◽  
J. Michael Cutbirth ◽  
Wesley H. Brewer
Keyword(s):  
Test Section ◽  
Single Point ◽  
Temporal Stability ◽  
Hydrodynamic Performance ◽  
Water Tunnel ◽  
Axial Velocity Component ◽  
Pump Speed ◽  
Additional Information ◽  
Spatial Uniformity ◽  
Contour Plots

The U. S. Navy William B. Morgan Large Cavitation Channel (LCC) in Memphis, Tennessee, is the world’s largest water tunnel. Its hydrodynamic performance is outlined in this paper. Three key characteristics of tunnel velocity were measured: temporal stability, spatial uniformity, and turbulence. Temporal stability and spatial uniformity were measured by laser Doppler anemometer (LDA), while the turbulence was measured with a conical hot-film and constant temperature anemometer (CTA). The velocity stability at a single point for run times greater than 2 hours was measured as ±0.15% at the 95% confidence level for velocities from 0.5 to 18 m/s. The spatial non-uniformity for the axial velocity component was ±0.34 to ±0.60% for velocities from 3 to 16 m/s. The non-uniformity in the vertical velocity was nominally 2%. The turbulence or relative turbulence intensity, which is the commonly reported performance characteristic for water tunnels, was measured as 0.2 to 0.5% depending on tunnel velocity. Additional information includes calibration of the LDA and CTA, test section velocity as a function of pump speed, acceleration of the test section velocity, velocity spectra, and color contour plots of the axial and vertical components for velocity uniformity. The measurements demonstrate that the LCC is a high-quality world-class water tunnel.

ДАТЧИК ДАВЛЕНИЯ НА ПОВЕРХНОСТНЫХ АКУСТИЧЕСКИХ ВОЛНАХ С ЗЕРКАЛЬНОЙ ТОПОЛОГИЕЙ

2020 ◽  
Vol 96 (3s) ◽  
pp. 389-391
Author(s):  
И.Г. Анцев ◽  
С.В. Богословский ◽  
Г.А. Сапожников
Keyword(s):  
Acoustic Waves ◽  
Wireless Sensors ◽  
Surface Acoustic Waves ◽  
Pressure Sensors ◽  
Pressure Measurements ◽  
Delay Lines ◽  
Long Distance ◽  
Passive Devices ◽  
Linear Dimensions ◽  
Passive Wireless Sensors

Предложена новая конструкция датчиков давления, реализующая зеркальную топологию чувствительного элемента. Применение линий задержки позволяет создавать пассивные устройства, работающие на больших дальностях. Предлагаемое решение расширяет область применения зеркальных топологий для измерений давления. The liquid and gas pressure sensor is one of the most required sensors. Usually, resonator circuits are used in the passive wireless sensors based on surface acoustic waves. Wide application of pressure measurements resonators is caused by their small dimensions and, accordingly, by possibility to choose the part with low irregularity of parameter on the membrane (first of all a surface acoustic waves velocity). The sensitive elements based on surface acoustic waves delay lines have bigger linear dimensions than those with resonators. However, delay lines are less sensitive to irregularity of surface acoustic waves velocity distribution along acoustic way, and in practice to reach a long distance with a considerable number of random echo it is necessary to provide the significant (up to 4 |xs) delay of the sensor information response. The paper presents a new design, which implements the mirror topology of the sensitive element of pressure sensors. The use of delay lines allows the creation of passive devices operating at long ranges. The proposed solution extends the field of application of mirror topologies for pressure measurements.

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