Tetsuya Senda

Experimental Investigation on Effects of Surface Roughness Geometry Affecting to Flow Resistance

Experimental investigation on effects of surface roughness geometry affecting to flow resistance has been carried out. The concentric cylinder device composed of outer cylinder and inner test cylinder was employed to the experiment. We prepared 24 different roughness models having various skewness of roughness profile as test inner cylinders. Surface of test cylinder has ridge and valley roughness whose shapes are isosceles right triangle V-shape. These ridge and valley are arranged at equal intervals. Therefore, RMS roughness of the surface and skewness of the surface roughness profile can be evaluated. In the experiment, inner cylinder is rotated but outer cylinder is stationary, torque of rotating inner cylinder was measured. Based on the torque measurement, we investigated the effect of skweness of the surface roughness on flow resistance. As a result, when the roughness profile has Gaussian distribution (skewness = 0), friction coefficient increases with increasing RMS roughness. Moreover, friction coefficient also increases with increasing skewness of surface roughness under same RMS roughness. In order to predict the friction coefficient from the geometric information of the surface, we estimated the equivalent sand grain roughness from surface roughness parameters. Results showed that it was clarified the relation among skewness of roughness profile, equivalent sand grain roughness and the root mean square of surface roughness.Copyright

Turbulent Drag Reduction by Polymer Containing Paint: Simultaneous Measurement of Skin Friction and Release Rate

Performance test for polymer containing trial antifouling paint was carried out experimentally. This trial paint is made by adding a polymer (PEO) to commercial antifouling paint for ship hull. Our developing paint has a function of leaching out the polymer and eventually reduces the skin frictional drag by the effect of dissolved polymer when the ship cruises. As the performance test, we examined the release rate of the polymer from the trial paint and measured the skin frictional drag at the same time. In addition, the velocity distribution near the painted wall was measured by Laser Doppler Velocimeter (LDV). As a result, in the first stage, the large drag reduction was obtained with releasing polymer. The Reynolds shear stress near the painted wall largely decreases comparing with the commercial antifouling paint in the water flow. However, after several hours, this drag reducing effect was hardly lost.Copyright

Experimental Study on Turbulent Drag Reduction and Polymer Concentration Distribution With Blowing Polymer Solution From the Channel Wall

Experimental study on turbulent drag reduction (DR) and polymer concentration distribution with blowing polymer solution from whole surface of the channel wall was carried out. A set of measurements for drag reduction were performed with blowing rate for the sintered porous metal plate (0.45m × 0.45m × 3) adjusted from 0.5 L/min to 4.0 L/min, and concentration of polymer solution varied from 10 ppm to 200 ppm. Reynolds number based on the channel height was chosen for 20000 and 40000 in this experiment. The polymer concentration distribution in the near-wall region (0.5 mm < y < 20 mm) at three locations of the downstream from the leading edge of the blower wall was also measured. Polymer concentration can be analyzed via Total Organic Carbon (TOC) analyzer. Through the analysis of mass transfer by polymer concentration distribution, we found that polymer which exists in buffer layer (10 < y+ < 70) has important influence on drag reduction.© 2010 ASME

Statistical Investigation on Coherent Vortex Structure in Turbulent Drag Reducing Channel Flow with Blown Polymer Solution

Coherent vortex structure in turbulent drag-reducing channel flow with blown polymer solution from the wall was investigated. As a statistical analysis, we carried out Galilean decomposition, swirling strength and linear stochastic estimation of the PIV data obtained by the PIV measurement in x – y plane. Reynolds number based on bulk velocity and channel height was set to 40000. As a result, the angle of shear layer that cleared up by using Galilean decomposition becomes small in the drag-reducing flow. Q3 events were observed near the shear layer. In addition, as a result of linear stochastic estimation (LSE) based on swirling strength, we confirmed that the velocity under the vortex core is strong in the water flow. This result shows Q2 (ejection) are dominant in the water flow. However, in the drag-reducing flow with blown polymer solution, the velocity above the vortex core become strong, that is, Q4 (sweep) events are relatively strong around the vortex core. This is the result of Q4 events to come from the channel center region because the polymer solution does not exist in this region. The typical structure like this was observed in the drag -reducing flow with blown polymer solution from the wall.

Structure of Low-Speed Streaks in Drag Reducing Flow With Polymer Solution Blown From the Channel Wall

For the investigation of turbulent structure in drag reducing flow with polymer solution blown from the channel wall (wall blowing), instantaneous velocity field has been precisely measured in the x-z plane at different locations along the wall-normal direction via Particle Image Velocimetry (PIV). Polymer solutions with 25 ppm and 100 ppm of weight concentration were tested at a blowing ratio of 1.2×10−4 and at 20000 of Reynolds number. About 5% and 11% of drag reduction (DR) rate was obtained, respectively. As a result of this experiment, turbulent statistic data showed that the Root Mean Square (RMS) of streamwise velocity fluctuation increased and RMS of spanwise velocity fluctuation was suppressed comparing with water flow. We found that these low-speed streaks became relatively regular in the buffer layer, including an increase of both length and width, which indicated a depression of turbulence by polymer diffused in the buffer layer.© 2011 ASME

Relationship Between Vortex Structure and Reynolds Shear Stress of Turbulent Drag Reducing Flow With Blowing Polymer Solution From the Wall

Relation between vortex structure and Reynolds shear stress of turbulent drag reducing channel flow with blown polymer solution was investigated by using PIV in an x-y plane. Experiment was carried out at 20000 and 40000 of Reynolds number based on the bulk mean velocity and the channel height. Blowing rate of polymer solution from the channel wall was 2.0 L/min and concentration of the polymer solution was 10, 50 and 100pmm. In the present study, calculation of the vorticity and quadrant analysis were performed to clarify the relationship between the vortex structure and Reynolds shear stress. From the result of vorticty, we found low and high speed packets which have the interaction motion fluid (Q1 and Q3). On the other hand, interaction motion increases by the polymer solution with decreasing ejection and sweep. Therefore, Reynolds shear stress decreases in order to not only decreasing ejection and sweep, but also related to increasing interaction motions. Moreover, interaction motions are amplified various intensity motion against suppression of ejection and sweep are limited to weak intensity motion. But the frequency of the interaction motions stays unchanged with drag reduction rate. The result shows characteristic structure which affects decreasing of Reynolds shear stress exists in the near-wall region.Copyright

Wear Mechanism and Self Lubrication of Engineering Ceramics at Elevated Temperatures

Friction and wear tests of Al2O3 and SiC were conducted from room temperature to 1200°C both in air and in vacuum. Results show that the wear mechanism of Al2O3 is dominated by micro fracture, debris abrasive and delamination at temperatures below 600 °C, while is controlled by plastic deformation and recrystallization among 600~1200 °C, resulting in an obvious decrease of wear loss. The wear rate and surface microstructure of SiC are closely depending on the testing temperature, atmosphere and contact pressure. Oxidation of SiC at elevated temperatures plays important role on the wear rate. Self lubrication of both Al2O3 and SiC at high temperatures was observed, which is mainly depending on the formation of a specific surface layer composed of nano-particles or very thin glassy film.

A Method for Evaluating the Efficacy of Antifouling Paints Using Mytilus galloprovincialis in the Laboratory in a Flow-Through System

A laboratory test with a flow-through system was designed and its applicability for testing antifouling paints of varying efficacies was investigated. Six different formulations of antifouling paints were prepared to have increasing contents (0 to 40 wt.%) of Cu2O, which is the most commonly used antifouling substance, and each formulation of paint was coated on just one surface of every test plate. The test plates were aged for 45 days by rotating them at a speed of 10 knots inside a cylinder drum. A behavioral test was then conducted using five mussels (Mytilus galloprovincialis) that were pasted onto the coated surface of each aged test plate. The number of the byssus threads produced by each mussel generally decreased with increasing Cu2O content of the paint. The newly designed method was considered valid owing to the high consistency of its results with observations from the field experiment.

Examination of Effect of NOx Regulation by Diffusion Simulation

The International Maritime Organization (IMO) is working for the further advancement of regulation in NOx emission reduction for ships diesel engines. As for Tier III, which is assumed to be entering into force in 2015, two proposals were discussed at the 11th meeting of BLG Subcommittee in February 2008. One was a uniform regulation over the world with 40% to 50% reduction from the Tier I regulations. The other was a geographically controlled regulation with an 80%, or higher, reduction for a designated area. Tier II level for others are applied. In the present study, a simple diffusion model is employed to estimate the NOx concentration over the land area for the case that each regulation is applied. Simulation studies have revealed that an appropriate distance given as the boundary in the geographical regulation could reduce the NOx concentration over a land area, to a comparable level as the uniform regulation can be estimated to achieve.

Tribology of Titanium Boride Sliding against Silicon Carbide at Elevated Temperatures

Friction and wear tests of TiB2 sliding against SiC were conducted without lubricant from room temperature to 1200°C in air and in vacuum. The friction coefficient of the couple of TiB2/SiC is affected obviously by the oxidation of TiB2. It increases with the increase of temperature and reaches a maximum at some temperature in air, then decreases remarkably. The friction coefficient of TiB2/SiC in vacuum exhibites almost a constant and keeps smaller value than that in air. Transition of TiB2 onto the sliding surface of SiC was observed, which improved the wear resistance of SiC at high temperatures.