Oscillatory Flow Conditions Research Articles

Wave Action in Pumping Station Storm Overflow

A method of analysis of tidal flap doors under oscillatory flow conditions is presented. Hydrodynamic data for flap doors is given for use in numerical simulation of door movement. Application of the data is illustrated by considering the case of a pumping station overflow that includes twin tidal flap doors. Boundary conditions for the numerical model are the inflow to the pumping station and the time history of pressure at the outfall determined from wave-climate measurements offshore. Computations were undertaken with a threefold purpose: to establish peak water levels in the pumping station for selection of safe machinery levels, to determine the closure rate of flap doors to assess risk of slamming; and to quantify airflow rates to and from access chambers to provide adequate venting arrangements.

A study of oscillatory flow in curved pipes. 3rd report. Visualization and velocity measurement of secondary flow.

Visualization, by the tracer method, was made of the secondary flow in the fully-developed region of a curved pipe under oscillatory laminar flow conditions. In the experiment, photographs were taken systematically of traces on nylon particles suspended in water flowing in the range of Womersley number α=5.5 to 28 and oscillatory Dean numbers D= 40 to 500. The experimental results, i. e. the instantaneous or time-averaged velocity profiles, and the locations of the center of vortices, are compared with those of the numerical analysis and descriptions are given for the transition of the secondary flow pattern due to Dean and Womersley numbers.

Reflooding With Steady and Oscillatory Coolant Injection: Part 2—Quench Front and Liquid Carryover Behavior

The reflooding of a tubular test section under oscillatory inlet flow conditions has been investigated experimentally for initial wall temperatures from 316° C to 760°C, oscillation periods from 2 to 6 s, and test section liquid level amplitudes up to 0.76 m. Compared to constant-injection reflooding, the oscillations always increase the liquid carryover rate in the early stages of reflooding. As reflooding progresses, the enhancement diminishes and becomes negative. The crossover point roughly coincides with saturation of the liquid at the quench front. The higher initial liquid carryover increases downstream heat transfer and speeds up quench front propagation, but it also reduces the test section mass accumulation rate, and for this reason delays quench front propagation at later stages. These effects are accentuated at higher oscillation amplitude and frequency. Large oscillations change the reflooding behavior substantially. Quantitative comparisons of quench front velocities and heat transfer immediately downstream of the quench front, obtained through the use of empirical local-condition correlations representing the steady-reflooding rate data, are presented.

Studies on Wells turbine for wave power generator. (4th report, Starting and running characteristics in periodically oscillating flow)

In order to clarify the starting and runnning characteristics of Wells turbine in oscillating flow, an experimental investigation has been made by a newly deviced turbine equipment in which the oscillating flow condition is simulated. The results have been compared with the analytical results. In the analysis, both starting and running characteristics were calculated on the basis of the experimental results obtained from steady unidirectional flow conditions. The comparison between the experiment and analysis has shown that the effects of hysteresis and Reynolds number on torque coefficient should be considered in the analysis. Furthermore, running characteristics have been investigated from a viewpoint of the method of load control.

Field investigations of the threshold of grain motion by ocean waves and currents

Instrumented tripods were deployed on three occasions at continental shelf sites: twice in the United States (December, 1978, and March, 1979) and once in Australia (December, 1979). A total of 37 days of data were collected. Data included measurements of current speed and direction 100 cm off the seabed; mean bottom pressure and pressure fluctuations; water turbidity with nephelometer or transmissometer; and photographs of the seabed. Bottom sediment samples were also collected prior to each deployment. These data were analyzed to estimate the vector-averaged velocity ( U 100), tides, gravity waves, near-bottom sediment concentration, bed configuration, and bottom sediment texture. During the sampling period, sediment resuspension occurred frequently as a result of oscillatory currents due to surface gravity waves. The field data have been used to evaluate several existing relationships for predicting the threshold of grain motion under oscillatory flow conditions. The first method is an evaluation of the Shields (1936) entrainment function for unidirectional flows in which the boundary shear stress is computed using the wave friction factor of Jonsson (1966). The second is an equation presented by Komar and Miller (1973, 1975) that is based on the laboratory investigations of Bagnold (1946) and Manohar (1955). The third method computes the boundary shear stress as a nonlinear combination of stresses due to waves and currents as proposed by Grant and Madsen (1979) and further developed in this paper. The results show that the Shields diagram, in which the Shields entrainment function for unidirectional currents is plotted with respect to a grain Reynolds number, adequately predicts the threshold of grain motion on the continental shelf. Although the results of all three computational methods were within the scatter of results of the laboratory studies upon which the predictive relationships were based, the wave-current model of Grant and Madsen is preferred because it includes the influence of currents in the computation of boundary shear stress.

An Investigation of Heat Transport In Oscillatory Turbulent Subcooled Flow

An experiment has been conducted to investigate transient radial heat transport effects created by oscillatory flow in uniformly heated tubes. Departures from one-dimensional, quasi-steady-state behavior have been quantified in the frequency range of density-wave oscillations. The data show a substantial radial dependence of both the amplitude and the phase of the liquid temperature perturbations even at frequencies as low as 0.1 Hz. The orderly axial enthalpy perturbation propagation breaks down at frequencies above 0.5 Hz. These effects must be taken into consideration in predicting the behavior of the point of net vapor generation in a boiling channel under oscillatory flow conditions.

Viscosity of oscillating non-newtonian fluids--an empirical approach as applied to blood.

The viscosity of blood varies with tube radius, viscosity of suspending medium, flow amplitude, hematocrit, and frequency, under oscillatory flow conditions. Various factors affecting the viscosity of blood were related by an empirical relation. The

Flow and frequency dependent viscosity of blood and blood-dextran mixtures

To evaluate quantitatively the viscosity of blood under pulsatile conditions in vivo, steady flow viscosity is inadequate, since the oscillatory viscosity of blood is ignored. A comparison was, therefore, made between steady flow apparent viscosity and the equivalent viscosity (the viscosity under oscillatory flow conditions). It was found that the equivalent viscosity of blood and blood-dextran mixture was significantly higher than the steady flow apparent viscosity, at all frequencies.

Mass transport under oscillatory fluid flow conditions

Mass transport under oscillatory fluid flow conditions

Transmission of Power by Sinusoidal Wave Motion through Hydraulic Oil in a Uniform Pipe

An analysis is made of the viscous power losses in a liquid-filled pipe under oscillatory compressible flow conditions, particular attention being paid to Shell Tellus 27 oil in a 7/8 in diameter pipe, 80 ft long. Using an effective friction coefficient to take into account oscillating flow, the efficiency and the power-carrying capacity of the pipe are calculated for four discrete values of resistive output load. It is shown that if the load is not equal to the characteristic impedance of the pipe, then the efficiency is reduced and the power capacity depends upon the frequency of operation of the pipeline. A mismatched load should be resistive with the pipe preferably tuned to the quarter wavelength frequency supplied from a constant pressure generator. Relative power output increases under these conditions are achieved at the expense of efficiency and increased pipe pressure. Agreement between theory and experiment for the load conditions considered is good.