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The combined effect of an internal slot in an airfoil and transverse leading-edge tubercles on its performance is studied. The internal slot allows flow ventilation from the pressure face to the suction face of the airfoil, effectively delaying flow separation and stall. Previous studies have demonstrated good stall characteristics of airfoils with leading-edge tubercles. It is shown here that the slot results in further improvement of the post-stall performance. The performance characteristics are investigated both numerically and experimentally, with angles of attack in the range of 0°-30° at a chord-Reynolds number of 105 lift and drag coefficients of slotted airfoils with leading-edge tubercles predicted from the computational fluid dynamics study correlate well with the corresponding coefficients determined via experiments. The experimental results show that the lift and drag coefficients of airfoils with leading-edge tubercles are significantly improved for angles of attack exceeding 10° with the inclusion of the internal slot. The slotted airfoil with small leading-edge tubercles outperformed others for angles of attack in the range of 10°-20° with the most improved maximum lift coefficient and maximum lift-to-drag ratio, whereas the slotted airfoil with larger tubercles achieved the best performance for angles of attack in the range of 20°-30°, including more favorable stall characteristics. [ABSTRACT FROM AUTHOR]

This paper presents visible experimental results of three-dimensional scour beneath pipelines. A miniature camera installed inside a transparent pipeline was used to observe the scour propagation process under a pipeline in steady currents. The data showed that the average scour hole propagation rate decreased nonlinearly with increasing pipeline embedment. The scour propagation rate increased with the Froude number at an increasing climb rate. The critical flow velocity for scour propagation was investigated. The critical velocity increased with increased pipeline embedment and the flow depth. It was lower than the critical velocity of sediment incipient motion. An empirical equation for the variation of the Froude number with the scour propagation rate was proposed for pipeline embedment ratios 0.045 = e=D = 0.1 and relative flow depths 2.73 = y0=D = 4.08. [ABSTRACT FROM AUTHOR]

Determination of the horizontal planar scale of local scour (HSLS) at a submerged monopile in water flow conditions is necessary for site selection and the intuitive effectiveness-evaluation of upstream protection projects. A simplified experimental method for the prediction of HSLS is proposed and validated with a set of indoor experiments. High efficiency was obtained by modelling the erodible bed in a thin layer at the millimeter scale, which is much smaller than the centimeter or meter scale for the prediction of scour depth. The experiment was conducted under steady, uni-directional flow in non-cohesive sand-bed conditions. A 15 cm diameter cylindrical monopile submerged 0.2 cm was rigidly fixed on a flume bed. The complete 5-minute process the HSLS undergoes to reach its equilibrium shape and size was observed. A comparison of the HSLS with other research show good agreement. Compared with the conventional method for the observation of the complete scour-hole process, which includes reaching maximum scour depth which may take days, the proposed method significantly improves the model-test efficiency. The fundamental mechanism of this high-efficiency in the HSLS' development process to reach its equilibrium state is that the HSLS is mainly influenced by the wake vortices, which are dependent on the cylinder-diameter Reynolds number instead of scour depth. [ABSTRACT FROM AUTHOR]