Physical Modeling of Ski-Jump Spillway to Evaluate Dynamic Pressure

The effects of changes in the angle of pool impact plate, plunging depth, and discharge upon the dynamic pressure caused by ski-jump buckets were investigated in the laboratory. Four impact plate angles and four plunging depths were used. Discharges of 67, 86, 161, and 184 L/s were chosen. For any discharge, plunging depth and impact plate angle were regulated, and dynamic pressures were measured by a transducer. The results showed that with the increase in the ratio of drop length of the jet to its break-up length (H/Lb), and with an increase in the impact plate angle, the mean dynamic pressure coefficient decreased. An inspection of the plunging depth (Y) ratio to the initial thickness of the jet (Bj) revealed that when Y/Bj > 3, the plunging depth of the downstream pool reduced dynamic pressure. At the angle of 60°, the dynamic pressure coefficient due to increasing in plunging depth varied from 34% to 95%.

Numerical and Experimental Analysis of Impinging Synthetic Jets for Cooling a Point-Like Heat Source

High power light emitting diodes (LEDs) being used for low and high beam in automotive lighting need active cooling of their heat sinks by radial or axial fans. But the moving elements of the fan cause abrasion, noise, and high energy consumption. Synthetic jets can replace conventional fans with their disadvantages and allow the directed cooling of LEDs. Therefore, in this paper, flow and heat transfer characteristics of impinging synthetic jets are investigated numerically and experimentally as an alternative to cooling LEDs with fans. It is shown that the impact plate brings forward the laminar-turbulent transition of the jets temporally and spatially. The impact plate itself should not be positioned in the region of the free jet's transition height. Increasing the frequency of the synthetic jet has a greater influence on the heat transfer compared to an increase in amplitude. The maximum cooling performance is achieved for all jet configurations with moderate distances between the orifice and the impact plate. In this case, the jet reaches its highest mass flow and impulse and its lowest temperature.

Application of the wavelet transform to sediment grain sizes analysis with an impact plate for bedload monitoring in sediment bypass tunnels

An impact plate (IP) is a bedload transport monitoring device developed for a part of the sediment bypass tunnels management. In the measurement, the impact produced by bedload is recorded as the number of impulses (Ip) which is widely used in Japan. Ip, however, has several shortcomings attributed to the insufficient raw signal denoising. In this study, the discrete wavelet transform (DWT), an advanced signal processing technique especially for noisy, non-periodical, and transient signals, was introduced to devise an improved Ip count system solving the problems in the original signal denoising process. The presented results revealed that the DWT is useful for water noise reduction, signal overlap reduction, and mitigating Ip saturation at grain sizes Ds = 50 and 100 mm compared to the original Ip counting system.