On the Circulating Water Channel Newly Constructed at the National Defence Academy

Abstract

Performance and chracteristics of the circulating water channel newly constructed at the National Defence Academy, the observation part is 5m length, 1.8m breadth, 1m water depth, is reported. The maximum speed reaches above 2.5m/s but somewhat device is desirable to be set for decreasing the air-bubble mixing in the high-speed region. The variance of velocity distribution at a measuring section is about less than ±4 percents and less than ±2 percents in the main part. The heights of the steady waves generated on the water surface are about ±2mm. The mean inclination of the water surface increases as the speed becomes high and the maximum value is less than 1/200. From measuring results of the pressure distribution and the drag for a vertical circular cylinder it is obtained that the critical Reynolds number is 2.2×10^5 and the intensity of turbulence is less than 2 percents. Resistance test and flow observation for a flat plate at zero incidence is conducted to confirm the transition of the boundary layer from laminar to turbulent and the Reynolds number is 1.5×10^6 for full turbulent flow condition. The effect of a trip wire is also confirmed to stimulate the transition to turbulence. The tank is evaluated to have a very high performance for its scale and the construction costs