The Relationship Between Frictional Resistance and Roughness for Surfaces Smoothed by Sanding

2002 ◽  
Vol 124 (2) ◽  
pp. 492-499 ◽  
Author(s):  
Michael P. Schultz
Keyword(s):  
Reynolds Number ◽  
Frictional Resistance ◽  
Resistance Coefficient ◽  
Polished Surface ◽  
Average Height ◽  
Freestream Velocity ◽  
Number Range ◽  
Test Fixture ◽  
Plate Length ◽  
The Relationship

An experimental investigation has been carried out to document and relate the frictional resistance and roughness texture of painted surfaces smoothed by sanding. Hydrodynamic tests were carried out in a towing tank using a flat plate test fixture towed at a Reynolds number ReL range of 2.8×106−5.5×106 based on the plate length and freestream velocity. Results indicate an increase in frictional resistance coefficient CF of up to 7.3% for an unsanded, as-sprayed paint surface compared to a sanded, polished surface. Significant increases in CF were also noted on surfaces sanded with sandpaper as fine as 600-grit as compared to the polished surface. The results show that, for the present surfaces, the centerline average height Ra is sufficient to explain a large majority of the variance in the roughness function ΔU+ in this Reynolds number range.

Frictional Resistance of Antifouling Coating Systems

2004 ◽  
Vol 126 (6) ◽  
pp. 1039-1047 ◽  
Author(s):  
Michael P. Schultz
Keyword(s):  
Roughness Length ◽  
Frictional Resistance ◽  
Resistance Coefficient ◽  
Length Scale ◽  
Average Height ◽  
Test Fixture ◽  
Antifouling Coating ◽  
Plate Length ◽  
Antifouling Coatings ◽  
Frictional Resistance Coefficient

An experimental study has been made to compare the frictional resistance of several ship hull coatings in the unfouled, fouled, and cleaned conditions. Hydrodynamic tests were completed in a towing tank using a flat plate test fixture towed at a Reynolds number ReL range of 2.8×106-5.5×106 based on the plate length and towing velocity. The results indicate little difference in frictional resistance coefficient CF among the coatings in the unfouled condition. Significant differences were observed after 287 days of marine exposure, with the silicone antifouling coatings showing the largest increases in CF. While several of the surfaces returned to near their unfouled resistance after cleaning, coating damage led to significant increases in CF for other coatings. The roughness function ΔU+ for the unfouled coatings showed reasonable collapse to a Colebrook-type roughness function when the centerline average height k=0.17Ra was used as the roughness length scale. Excellent collapse of the roughness function for the barnacle fouled surfaces was obtained using a new roughness length scale based on the barnacle height and percent coverage.

scholarly journals Numerical simulation of turbulent boundary layers of surfaces covered with foul release and antifouling coatings

2016 ◽  
Vol 13 (1) ◽  
pp. 17-26
Author(s):  
Sadra Kianejad ◽  
Naznin Ansarifard
Keyword(s):  
Frictional Resistance ◽  
Reynolds Numbers ◽  
Resistance Coefficient ◽  
Cfd Modeling ◽  
Test Plate ◽  
Plate Length ◽  
Numerical Studies ◽  
Antifouling Coatings ◽  
Coating Characteristics ◽  
Good Agreement

In order to compare the frictional resistance of three kinds of ship’s hull coatings (Foul Release, SPC copper, SPC TBT) in the unfouled conditions, the numerical studies have been made. Simulations have been carried out for different Reynolds numbers in the range of 2.85 ×  – 5.5 ×  based on the plate length and flow velocity. Antifouling coatings have a larger mean roughness than Foul Release. The results have indicated that frictional resistance coefficient of Foul Release test plate is lower than SPC copper and SPC TBT test plates. The total resistance obtained by computational fluid dynamics has been compared with the experimental data and good agreement in results has been found which those have shown the ability of CFD modeling in calculating of fluid flow resistance by considering the coating characteristics.

Study on the Resistance Characteristics of Heat Metering System Based on Electric Valve

2014 ◽  
Vol 492 ◽  
pp. 507-510
Author(s):  
Dong Jun Gong ◽  
Yao Zhang ◽  
Xing Ru Li ◽  
Li De Fang ◽  
Zi Hui Wei ◽  
...  
Keyword(s):  
Pressure Difference ◽  
Theoretical Calculations ◽  
Frictional Resistance ◽  
Resistance Coefficient ◽  
Experiment System ◽  
Average Value ◽  
Parallel Pipeline ◽  
Heat Metering ◽  
The Relationship ◽  
Resistance Coefficients

Through theoretical calculations and derivation, the paper obtained the relationship between resistance coefficient and pressure difference, as well as flow rate. For the series pipeline, the flow in the series pipeline is the same, as a result, all the resistance in the series pipeline is the total resistance. For the parallel pipeline, the pressure difference is same, and the all the flow in parallel pipeline is the total flow. According to the real example, the paper identified the inlet pressure difference of the indoor system, the most unfavorable ring and the ratio frictional resistance. Based on the room heat load calculation, the paper determined the most unfavorable loop diameter of each pipe section. By calculating the resistance coefficients of the electric valve at opening, the resistance coefficients of the electric valve at closing were obtained. In the experiment system, the resistance coefficient average value when the electric valve is off was 101831.65, which is basically in line with the calculable value 10719.6, indicating that the existing parameters are much more reasonable.

Flow and Heat Transfer Characteristics in a Channel Periodically Fitted with Blocks and Inclined Plates

2011 ◽  
Vol 66-68 ◽  
pp. 299-306
Author(s):  
Jian Sheng Wang ◽  
Cui Wu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
The Self ◽  
Sustained Oscillation ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Plate Length ◽  
Cfd Method ◽  
Inclined Plates

A numerical investigation in the CFD method of the heat transfer characteristics and the self-sustained oscillation flow is conducted in a grooved channel with periodic mounted inclined plate.Control of low Reynolds number range(600-1600), two-dimensional, unsteady laminar flow was analyzed .Various physical and flow arrangements have been considered as plate length, plate position and Reynolds number .A comparison among different channels was made for streamlines、history of cartesian velocity component in the x-direction and Nusselt number(Nu)．Compared with the results got by the no plates case, the heat transfer has been enhanced in channel that installation of a inlined plate for all Reynolds number.At higher Reynolds number(Reynolds number over the critical Reynolds number), the enhancement of heat transfer is more marked ,that because it can not only modify the direction of the flow towards the obstacle faces to be cooled ,and activate the self-oscillations using inclined plates placed periodically.

scholarly journals Comparative modeling of hull form resistance for three ocean going vessels using methodical series

2015 ◽  
Vol 4 (4) ◽  
pp. 489 ◽  
Author(s):  
Nitonye Samson ◽  
Adumene Sidum
Keyword(s):  
Reynolds Number ◽  
Frictional Resistance ◽  
Comparative Modeling ◽  
Resistance Coefficient ◽  
Container Ship ◽  
Test Technique ◽  
Hull Form ◽  
Reynolds Number Increase ◽  
Friction Line ◽  
Resistance Coefficients

This paper presents a comparative estimation of the hull form resistance for Cargo ship, Ocean-going Tug and Container ship. The research study evaluates the influences of various ship hull parameters in relations to the vessel speeds and level of turbulence (Reynolds number). The modeling was done using MATLAB software and the model test technique based on the ITTC, ATTC, Granville and Hughes friction line application. The result shows that the hull form resistances follow the same trend in the ITTC, ATTC and Granville models, while the Hughes model gave a different trend with other techniques. It further revealed that as the speed increases by 10knots, the frictional resistance coefficients decrease by 11.86% for the ITTC & Granville models, and 12.03% for the Hughes model. For Ocean-going Tug and Container Ship, the frictional resistance coefficient decrease by 12.31% for the ITTC & Granville models, and 12.14% for the Hughes model. The Reynolds number increase by 62.52% for every 10knots increase in the speed of the Cargo ship and 62.23% for every 10knots increase in the speed of the Ocean going tug and Containership. At various experimental speeds, the results showed that for every 1 knots increase in the speed of the Containership, the effective power developed increases by 9.45%. This provides a technical and analytical guide on hull form resistance trend for engineers and ship operators.

Laser Velocity and Surface Measurements Toward the Prediction of Turbulent Frictional Resistance on Irregular Rough Surface in Higher Reynolds Number Range

2019 ◽  
Author(s):  
Kyohei Okubo ◽  
Shunpei Suzuki ◽  
Yusuke Kuwata ◽  
Yasuo Kawaguchi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Rough Surface ◽  
Empirical Formula ◽  
Rough Surfaces ◽  
Frictional Resistance ◽  
Frictional Stress ◽  
Mean Velocity ◽  
Number Range ◽  
High Reynolds

Abstract In this research, we consider the relationship between roughness of the wall and frictional resistance in the range of high-Reynolds number regime which is important for practical use, and its goal is to build a more accurate and highly versatile formula for predicting the frictional resistance acting on the complex surface with irregular roughness. In addition to the parameter corresponding to the distribution of the roughness used in a conventional and empirical formula, we aim to construct an empirical formula including the parameter representing the wavelength of the rough surface. In this study, we conduct laboratory experiments of Taylor-Couette flow, using the cylindrical test specimens roughly sprayed with an actual ship paint, and investigate the influence of irregular roughness on flow field and the surface frictional stress based PIV (Particle Image Velocimetry) measurements and torque measurements in high Reynolds numbers. The azimuthal mean velocity for rough surfaces increased in the entire flow field in comparing to the flow for a smooth surface, and this tendency is remarkable in a bulk region. Also, we measure the rough surfaces of the specimens using a laser type one-shot three-dimensional measurement device. Based on the results of above measurements, we propose the direct relationship between the parameter of a rough surface and frictional resistance.

scholarly journals Influence of Vegetation Coverage on Hydraulic Characteristics of Overland Flow

Water ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1055
Author(s):  
Zekang Cai ◽  
Jian Wang ◽  
Yushuo Yang ◽  
Ran Zhang
Keyword(s):  
Reynolds Number ◽  
Soil Erosion ◽  
Vegetation Cover ◽  
Overland Flow ◽  
Resistance Coefficient ◽  
Vegetation Coverage ◽  
Hydraulic Characteristics ◽  
The Loess Plateau ◽  
Artificial Grass ◽  
The Relationship

Soil erosion is a major problem in the Loess Plateau (China); however, it can be alleviated through vegetation restoration. In this study, the overland flow on a slope during soil erosion was experimentally simulated using artificial grass as vegetation cover. Nine degrees of vegetation coverage and seven flow rates were tested in combinations along a 12° slope gradient. As the coverage degree increased, the water depth of the overland flow increased, but the flow velocity decreased. The resistance coefficient increased with increasing degree of coverage, especially after a certain point. The resistance coefficient and the Reynolds number had an inverse relationship. When the Reynolds number was relatively small, the resistance coefficient decreased faster; however, when it exceeded 600, the resistance coefficient decreased at a slower rate. A critical degree of vegetation cover was observed in the relationship between the resistance coefficient and submergence degree. When the degree of coverage was greater than 66.42%, the resistance coefficient first decreased and then increased with a higher submergence degree. Finally, the formula for the resistance coefficient under vegetation coverage was derived. This formula has a relatively high accuracy and can serve as a reference for predicting soil erosion.

Evaluation of Various Channel Shapes of a Microchannel Heat Sink

2016 ◽  
Vol 24 (03) ◽  
pp. 1650018 ◽  
Author(s):  
Aatif Ali Khan ◽  
Kwang-Yong Kim
Keyword(s):  
Reynolds Number ◽  
Thermal Resistance ◽  
Heat Sink ◽  
Stokes Equations ◽  
Hydraulic Diameter ◽  
Navier Stokes ◽  
Average Height ◽  
Microchannel Heat Sink ◽  
Navier Stokes Equations ◽  
Number Range

Thermal and hydraulic performances of various geometric shapes of a microchannel heat sink were evaluated numerically using Navier–Stokes equations. A heat sink comprised of a [Formula: see text][Formula: see text]cm2 silicon wafer was investigated with water as the cooling fluid. The performances of seven microchannel shapes were compared at the same microchannel hydraulic diameter and the same average height of the bottom silicon substrate. The thermal resistance, friction coefficient, and Nusselt number were calculated for a Reynolds number range of 50 to 500. The results show that an inverse trapezoidal shape gives the lowest thermal resistance for a Reynolds number up to 300. The values of [Formula: see text]Re are almost similar for all the shapes because of the constant hydraulic diameter.

Vortex shedding from spheres

1974 ◽  
Vol 62 (2) ◽  
pp. 209-221 ◽  
Author(s):  
Elmar Achenbach
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Critical Reynolds Number ◽  
Measurement Techniques ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Present Measurement ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
The Relationship

Vortex shedding from spheres has been studied in the Reynolds number range 400 < Re < 5 × 106. At low Reynolds numbers, i.e. up to Re = 3 × 103, the values of the Strouhal number as a function of Reynolds number measured by Möller (1938) have been confirmed using water flow. The lower critical Reynolds number, first reported by Cometta (1957), was found to be Re = 6 × 103. Here a discontinuity in the relationship between the Strouhal and Reynolds numbers is obvious. From Re = 6 × 103 to Re = 3 × 105 strong periodic fluctuations in the wake flow were observed. Beyond the upper critical Reynolds number (Re = 3.7 × 105) periodic vortex shedding could not be detected by the present measurement techniques.The hot-wire measurements indicate that the signals recorded simultaneously at different positions on the 75° circle (normal to the flow) show a phase shift. Thus it appears that the vortex separation point rotates around the sphere. An attempt is made to interpret this experimental evidence.

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