DIGITAL IMAGE MEASUREMENT OF BUBBLE MOTION IN AERATED WATER FLOWS

Digital image measurement method, as an extension of Particle Image Velocimetry of single-phase flow measurement, was investigated for application to air-water two-phase flows. The method has strong potential ability in measuring bubble geometrical features and moving velocities for complex bubble motion in aerated water flow. Both diluted and dense bubble rising flows are measured using the digital image method. Measured bubble shapes and sizes, and bubble velocities are affected by threshold selection for binary image. Several algorithms for selecting threshold are compared and methods for calculating the time-averaged void fraction are discussed.

NUMERICAL SIMULATION FOR THE STEPPED SPILLWAY OVERFLOW WITH TURBULENCE MODEL

Stepped spillways have increasingly become a very important measure for flood discharge and energy dissipation. Therefore, the velocity, pressure and other characteristics of the flow on the stepped spillway should be known clearly. But so far the study for the stepped spillway overflow is only based on the model test. In this paper, the stepped spillway overflow was simulated by the Reynolds stress turbulence model. The simulation results were analyzed and compared with measured data, which shows they are satisfactory.

NUMERICAL SIMULATION OF TURBULENT FLOW THROUGH THROAT-TYPE ENERGY-DISSIPATORS

The flow through the throat-type energy-dissipators is calculated by using an axis-symmetrical K-Ε turbulence model. The velocity field, the pressure field and the distributions of turbulent energy and its dissipation rate are acquired. The energy dissipation through the throat-type energy-dissipators can be seen in detail. The calculated pressure distribution is compared with the measured and is in good agreement. The results are useful to understand deeply the flow characteristics of the throat-type energy-dissipators.

NUMERICAL SIMULATION OF 3-D FLOW FIELD IN ARCIFORM PLUNGE POOL

The 3-D complex turbulent flow fields in a plunge pool with arciform bottom are simulated by using the k-Ε model in body-fitted coordinates. The calculated results reveal the flow characteristics in the arciform plunge pool under the different flood discharge conditions, which can not be easily obtained in the physical model test because the measurement of the complex velocity is very difficult. The calculated flow fields are helpful to understand the hydraulic characteristics of plunge pool deeply. The calculated and the measured pressure distributions on the pool bottom are compared and in good agreement.

TRANSPORTATION CHARACTERISTIC OF BED LOAD FOR NON-UNIFORM SEDIMENT WITH EQUIVALENT GRAIN

The incipient velocity of sediment is one of the most important basic theoretical problems of hydraulic engineering. The initial motion of sediment is a random process. Based on the combination methods of classical mechanics with statistics theory the formula to calculate the incipient motion of sediment was established. According to the standard of incipient motion, motion status, relative degree of expose for sediment and equivalent grain were defined. The coefficient in the formula included the flow fluctuation and relative degree of exposition. The value of the coefficient was calculated by using some parameters value. The results show that the value of dimensionless shear stress coefficient is not a constant, but locating in a range from 0.022 to 0.063 for weak and middle motion status, and varying with the relative degree of sediment expose. The value of dimensionless Shields numbers that put forward in the text can explain the reason that why the coefficients in difference formulas have wide scatter. The theoretical formula has been verified with amount of data collected from both natural rivers and flumes. The results can reflect the motion characteristic of the sediment.

EXPERIMENTAL INVESTIGATION OF EMERGENCY GATE SHUTTING FOR ORIFICE TUNNEL

In the process of the emergence gate shutting of one orifice tunnel, a big noise and great vibration may be observed in the mid gate chamber. In order to guarantee the working safety of orifice tunnels, an experimental investigation is carried out in Sichuan University. In the investigation, the fluctuation pressure along the tunnel and the wind velocity in the entry of emergency gate are measured. In the mean time, the fluid state in orifice tunnel is carefully observed and analyzed. The reasons of the noise and vibration in the mid gate chamber are found out and some countermeasures are presented in this paper. The conclusions are useful to the orifice tunnels with high water head and huge discharge.

PERIODIC BOUNDARY CONDITION IN SIMULATION OF TURBULENT FLOW

The simulations of the three-dimensional turbulent flows through hydraulic turbine components[1] were conducted based on the standard k-Ε turbulent model with body-fitted coordinates and staggering grid system. The SIMPLEC algorithm was adopted in the numerical procedure. A new method to treat the periodic boundary condition was used. The calculated results of the new method were compared with those of traditional ones. These results indicate that the new method can give much better results, and can be used in simulating flow through rotational impellers. The presented method can be combined with alternative turbulent model or employed in large eddy simulation.

THREE-DIMENSIONAL NUMERICAL SIMULATION OF BOD-DO FOR LARGE RESERVOIR

With a large reservoir as an example, a 3-D Biological Oxygen Demand (BOD) and Dissolved Oxygen (DO) model for large deep reservoirs was investigated by considering the effects of low concentration of dissolved oxygen and stratified temperature structure. A dissolved oxygen saturability equation was initially developed in the model. The influences of temperature on interfacial mass transfer coefficient and degradation rate coefficient and the restrained effects of low DO concentration on the degrading process were included in the model. The model is of great importance to accurate simulation of the temperature influential characteristics of water quality and the degrading law of organic pollutants in a large and deep reservoir.

HYDRODYNAMIC UPLIFT FORCE AND STABILITY OF ARCIFORM PLUNGE POOL

Compared with general trapeziform plunge pools, an arciform plunge pool has its advantages, e.g. less excavate quantity, higher stability, etc. In this paper, the hydrodynamic pressure distribution on the soleplate of the arciform plunge pool is measured under a relatively dangerous condition of operation. The result is helpful to the design of the arciform plunge pool. The result also shows that the difference between the maximum and the minimum pressures on the upward surface of the soleplate may cause an additional uplift force on the soleplate under certain condition and should be taken into consideration in the uplift force calculation of the soleplate. The scour experiment verifies the higher stability of the arciform plunge pool.

CHARACTERISTICS OF CORRELATION AND SPECTRUM BETWEEN WALL FLUCTUATING PRESSURE AND FLUCTUATING VELOCITY OF IMPINGING JET

The correlation, between wall fluctuating pressure and fluctuating velocity, on the bed of plunging pool under the action of single and twin impinging jet, and their spectrum and turbulent scale are investigated in the paper by using 2-D LDA and the dynamic pressure scanning system of multiple points. It is found that the cross correlation between the horizontal fluctuating velocity and the fluctuating pressure of twin jet is bigger than that of single jet, and the spectrums of horizontal fluctuating velocity and fluctuating pressure obviously have approximately same dominant frequency. The relationship between the fluctuation pressure coefficient on wall and the turbulent intensity near the wall can be described with logarithmic curve.

AERATION EFFECT OF SUBMERGED JET ON HYDRAULIC CHARACTERISTICS

A water-air two-phase turbulence mathematical model was proposed, The mass-weighted average was adopted for velocity, air mass fraction and turbulent parameters. The algebraic stress equation was used to calculate the Reynolds stress. The pulsating flux of air mass fraction was simulated by employing the concept of the eddy viscosity. The numerical simulation of aerated flow in plunge pool shows that, for the same depth, aeration may decrease the time-averaged pressure on pool floor and increase slightly the turbulent intensity. The computed concentration and pressure distributions coincide with the experimental data.

SUBMERGED IMPINGING JETS WITHIN A FINITE WATER DEPTH

By use of the sheet of laser light and the tracing particle technology, flow visualization tests of complex flow structures for submerged impinging jets within finite water depths are conducted. Typical flow patterns of submerged impinging jets are analysed by the singular topology method. In order to reveal the mechanism of these flows, the diffusive characteristics and turbulent fluctuations of submerged impinging jets are measured by the hot-film anemometer.

THEORETICALLY AND NUMERICALLY ASSESSING THE VALIDITY OF EULERIAN TRUNCATION IN STOCHASTIC GROUNDWATER MODELING

A theoretical and numerical assessment of the validity of Eulerian truncation in stochastic modeling is presented. Specifically, we analyze and compare theoretically various existing Eulerian-based first-order techniques with and without invoking Eulerian truncation and quantify the terms truncated and retained in the stochastic perturbation equations using high resolution Monte Carlo simulations. We also analyze and compare numerically various existing Eulerian-based first-order techniques and Monte Carlo simulation. The obtained results have demonstrated theoretically and numerically that existing Eulerian-based stochastic perturbation techniques are equivalent. The terms truncated are indeed one order higher than those retained. Therefore, we conclude that Eulerian truncation is mathematically consistent and asymptotic.

REVIEW OF REGIME THEORY OF ALLUVIAL CHANNELS

One of the most important problems in river engineering is to determine a stable cross section geometry and slope for an alluvial channel. This has been the subject of considerable research for about a century and continues to be of great practical interest. Ignoring plan geometry, an alluvial channel can adjust its slope, depth and width, to develop a dynamic stable condition in which it can transport a certain amount of water and sediment. The brief history of regime theory and its new development are reviewed in this paper.

NUMERICAL SIMULATION OF UPLIFT FORCES ON SLAB IN PLUNGE POOL

The mechanism of the fluid-solid coupled vibration is analyzed as the fluctuating pressure acts on the inlet and the outlet slits of a slab. The parameter multinomial method was exploited to calculate the pressure field within the joints of the slabs by solving the basic equations of the oscillation flow. The calculated result shows that the time-averaged uplift increases with the increase of the length of the slab and is large in the middle and is small in both sides. The time-averaged uplift reduces with the increase of water depth, and the fluctuating uplift reduces rapidly with the increase of the thickness of the slit. The calculated result is in agreement with the experimental results.