Abstract
Five triangular riblets longitudinal in the streamwise direction have been studied experimentally. The riblets have pick to pick spaced (s) equal to 1000 μm and with groove height to space ratio (h/s) 0.4, 0.6, 0.8 and 1. The tests were conducted in a full turbulence water channel on a flat plate for Reynolds numbers 13000 to 53000 based on channel hydraulic diameter. Pressure drop was measured using pressure transmitter gauge with pressure tap points of 12.7 mm in diameter were provided at the bottom of the channel. The main purpose of the present study is to investigate the response of turbulent flow to longitudinal grooves of triangular shaped riblets and compare the effect of the turbulence structure over smoothed and grooved surfaces with pressure drop measurements. 10.20 was the maximum drag reduction appear at h/s equal to (1).
Highlights
The effects of rib surfaces on the turbulent flow in rectangular channels and circular tubes have been extensively studied in literature [1,2,3,4,5,6,7,8,9,10]
The second experiment has been in 6-inch diameter pipe line system. 3M vinyl riblets have been used in both systems with height and spacing of V-groove h=s=76.2μm. the results shows a maximum drag reduction 8.1% several challenges face surface textures and disabling this technology to be translated into industrial applications
The effect of longitudinal grooved surfaces on wall-pressure fluctuations can be estimated by calculating the effect first on smooth flat plate and on ribbed plate
Summary
The effects of rib surfaces on the turbulent flow in rectangular channels and circular tubes have been extensively studied in literature [1,2,3,4,5,6,7,8,9,10]. Several challenges face surface textures and disabling this technology to be translated into industrial applications. Choi [11] studied the wall pressure fluctuations in a wind tunnel to modified turbulent boundary layer with riblets. The tunnel had a test section of (4.8m x 2.4 m x 15 m) and 0.5 % flow speed controlled by a feedback control system. The reduction appeared as a result of decrease in turbulence intensity within a small volume near a riblet surface. Reidy [12] and Reidy and Anderson[13], conducted experimental studies in 3M riblets in a high speed water tunnel over a flat plate in turbulent flow. The results shows a maximum drag reduction 8.1% several challenges face surface textures and disabling this technology to be translated into industrial applications. Triangular riblets will be designed, fabricated and tested in a closed loop liquid circulation system. the flow rate will be the controlled variable and the pressure drop across the rib surface will be measured to evaluate the drag reduction performance
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