Gravity Waves due to Discontinuity Decay Over an Open-Channel Bottom Drop

Experimental data are given on wave shapes and propagation speeds and characteristic headwater and tailwater depths after removal of a shield producing an initial free-surface level drop and located above a bottom drop in a rectangular open channel. Check is performed of self-similar solutions of the problem obtained earlier using a hydraulic approximation. It has been established that in certain ranges of time, longitudinal coordinate, and problem parameters, these solutions are supported by experimental results.     

等波高双孤立波直墙爬高的数值模拟

基于RANS方程、VOF方法以及修正的Goring造波方法建立了模拟活塞式推波板运动的二维数值波浪水槽,实现了双孤立波直墙爬高的数值模拟．利用动边界技术模拟造波机推波板的运动,有效地实现了不同波峰间距双孤立波的造波方法．在验证单孤立波直墙爬高的基础上,模拟了不同相对波高、相对波峰间距的等波高双孤立波的直墙爬高过程,给出了波面、速度场及波动能量的变化规律．数值模拟结果表明：对于等波高的双孤立波,当入射波波高较大及两个波峰间距相对较小时,跟随在后孤立波的爬高放大系数小于先导孤立波的爬高放大系数;双孤立波在直墙爬高过程中,波动场的势能时间过程线呈现三峰形态,其中居中的最大势能峰值出现在第二个孤立波与经直墙反射后反向传播的第一个孤立波完全对撞的时刻．     

Impingement heat transfer at a circular cylinder due to a submerged slot jet of water

An experimental investigation was carried out on the heat transfer due to a submerged slot jet of water impinging on a circular cylinder in crossflow. The cylinder diameter and the slot width are of the same order of magnitude, specifically D_s = 2.0 and 3.0 mm and D_c = 2.5 and 3.0 mm. The experimental apparatus allowed variation of the slot width, the cylinder diameter, and the distance from nozxle exit to heater. Conditions of impingement from the bottom (ascending flow) were taken into consideration as well as impingement from above (descending flow). The Nusselt number was determined as a function of Reynolds and Prandtl numbers in the range 1.5 × 10³ < Re < 2.0 × 10⁴, 2.7 < Pr < 7.0, and 1.5 ≤ z/D_s ≤ 10. The experimental data were correlated with a simple equation that fits 90% of the data with a precision of 20%.     

Dependence of the force action of a water wave on the shape of its leading front

The results of experiments in which bore-type waves with various leading front shapes propagated first above an even horizontal bottom, then above a rising bottom, then again above a horizontal bottom segment, and were finally reflected from a vertical wall are presented. It is shown that the impact force is greatest if the leading front breaks directly on approaching the wall. This force is much greater than the impact force of smooth waves or waves that break before they reach the wall.     

Force action of discontinuous waves on a vertical wall

This paper presents the results of an experimental study of the dynamic action exerted on the vertical end wall of a rectangular channel by the wave propagating in the tailwater region after total dam break. It is shown that the results of calculations using the first shallow-water approximation differ from experimental data by not more than 5%. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 129–135, March-April, 2009.     

用三分量LDV测量壁湍流边界层

本文用三分量激光多普勒测速仪对壁湍流边界层进行了测量，经过数据处理后，给出了各湍流参数的分布曲线，并与Ｄｊｅｎｉｄｉ等的测量结果进行了比较，吻合得很好。结果表明，用３Ｄ－ＬＤＶ研究湍流是可行的     

Experimental study of extreme thrust on a tidal stream rotor due to turbulent flow and with opposing waves

Time-varying thrust has been measured on a rotor in shallow turbulent flow at laboratory scale. The onset flow has a turbulence intensity of 12% at mid depth and a longitudinal turbulence length scale of half the depth, about 5 times the vertical scale, typical of shallow flows. The rotor is designed to have thrust and power coefficient variations with tip speed ratio close to that of a full-scale turbine. Three extreme probability distributions give similar thrust exceedance values with the Type 1 Pareto in mid range which gives 1:100, 1:1000 and 1:10 000 exceedance thrust forces of 1.38, 1.5 and 1.59 times the mean value. With opposing waves superimposed the extreme thrust distribution has a very similar distribution to the turbulent flow only. Exceedance forces are predicted by superposition of a drag force with drag coefficient of 2.0 based on the wave particle velocity only and with an unchanged mean thrust coefficient of 0.89. These values are relevant for the design of support structures for marine turbines.