Interaction of a heavy fluid flow in a channel with a transverse jet barrier

An experimental and numerical analysis of the interaction between a plane horizontal water flow in a rectangular channel (free water current) and a plane thin water jet (water jet curtain) is presented; the jet flows out vertically from either a slot nozzle in the bottom of the channel or the crest of a rigid spillway at a velocity appreciably (several times) greater than the water velocity in the channel. Numerical calculations were carried out using the STAR-CD software package preliminarily tested against the experimental data obtained. The dependence of the water level in the channel at a certain distance ahead of the jet barrier on the main jet parameters and the water flow rate in the horizontal channel is studied. It is found that in the region of the interface between the flows both steady and unsteady (self-oscillatory) flow patterns can be realized. Steady stream/jet interaction patterns of the “ejection” and “ejection-spillway” types are distinguished and a criterion separating these regimes is obtained. The notion of a rigid spillway equivalent to a jet curtain is introduced and an approximate dependence of its height on the relevant parameters of the problem is derived. The possibility of effectively controlling the water level ahead of a rigid spillway with a sharp edge by means of a plane water jet flowing from its crest is investigated. The boundary of transition to self-oscillation interaction patterns in the region of the flow interface is determined. The structure of these flows and a possible mechanism of their generation are described. Within the framework of the inviscid incompressible fluid model in the approximate formulation for a “thin” jet, an analytical dependence of the greatest possible depth of a reservoir filled with a heavy fluid at rest and screened by a vertical jet barrier on the jet parameters is obtained.     

Numerical investigation of the effects of sluice spillway roof profiles on the hydraulic characteristics

There is a need for evolving hydraulically efficient roof profile of bellmouth for high head sluice spillways, as sluice roof is susceptible to cavitation damage. In this paper, formulation and development of a numerical model for simulating the spillway flow and its application to a sluice spillway are presented. The main focus of the simulation study is to apply the developed model to investigate the effects of sluice roof profile geometry on the pressure distribution, the discharge coefficient and the nature of flow regime within the sluice bellmouth. From the analysis of results for eight different roof profiles by varying the entry and exit angles of elliptic bellmouth transition, some important observations have been suggested, which are of practical relevance to hydraulic design engineers. The numerical model results are compared for one profile with physical model study. The simulated results are in close agreement with the measured values. Copyright © 2007 John Wiley & Sons, Ltd.     

台阶式溢洪道掺气水流水深的试验研究

根据紊流边界层理论,整理分析了前人对台阶式溢洪道掺气位置的研究成果,提出了掺气发生点的计算方法。通过模型试验,研究了坡度分别为30°、51．3°、60°台阶式溢洪道上掺气水深的分布规律。研究结果表明当台阶尺寸一定时,掺气水深主要与堰上流能比、台阶坡度、台阶以上总水头有关;流能比越小,单宽流量越小,台阶上的水层越薄,掺气越充分,相对掺气水深越大;随着坡度的变陡,来流速度增加,掺气发生点前移,水流破碎严重,水深增加越大;沿程相对掺气水深随流程的增加而增加。     

Self-entrainment of air on stepped spillways

The pseudo-bottom-inception point related to air entrainment is located further upstream on stepped spillways than on smooth spillways, for otherwise identical conditions. Its position is relevant concerning cavitation aspects, flow losses and flow depths. This Paper presents and discusses visual observations made with a high-speed camera and air concentration measurements in the vicinity of the pseudo-bottom air inception point on a stepped model spillway. Insight into the bottom aeration processes is provided, pointing at the effects of dynamic and turbulent air-phase surface troughs instantaneously protruding to the pseudo-bottom. In addition, the measured data were analyzed with regard to the extensions of these surface troughs. The trough bases were found to reach approximately 70–80% of the mixture flow depth upstream of the inception point, to 60–70% at the inception point and to 40–50% at the equilibrium flow region downstream of the inception point. The highly-turbulent character of developed flow is described and the general air transport process specified on the basis of air concentrations and related parameters.     

Stepped chutes: Pre-aeration and spray reduction

Stepped chutes are a standard element in hydraulic engineering. Among others, two basic problems have not yet been addressed so far. These include the direct spray reduction on stepped chutes for relatively small discharges by an improved step edge geometry, and the cavitation damage up to the point of self-aeration for relatively large discharges. This research adds to these two items by systematic observations on a stepped chute of definite slope and step size. The test data were analyzed resulting in preliminary recommendations for an improved performance of stepped chutes. It was concluded that the present knowledge applies also for stepped chutes extended with an aerator as proposed herein. The latter may be easily added to existing designs, of which the design discharge is increased.     

考虑边界层影响时溢流坝动水压强分布规律的研究

根据溢流坝反弧段水流运动的基本方程,考虑水流边界层的影响,在流线曲率同心圆假设条件下,得到了溢流坝反弧段水流压强计算的表达式。通过引入近壁薄流层要领和缓和过渡流线假设,在水工模型试验的基础上,得到了溢流坝反弧段水流流线曲率半径的计算公式,使反弧段离心力影响范围内的水流流线曲率光滑连续,从而得到反弧段水流压强分布规律的统一表达式,该表达式能够反映水流压强沿反弧法线方向及切线方向的变化规律。