Homotopy analysis solutions for the asymmetric laminar flow in a porous channel with expanding or contracting walls

In this paper, the asymmetric laminar flow in a porous channel with expanding or contracting walls is investigated. The governing equations are reduced to ordinary ones by using suitable similar transformations. Homotopy analysis method （HAM） is employed to obtain the expres- sions for velocity fields. Graphs are sketched for values of parameters and associated dynamic characteristics, especially the expansion ratio, are analyzed in detail.

Numerical Study on the Effects of Contraction Ratio in a Two-Phase Flow Injection Nozzle

The Euler-Euler numerical method was used to investigate the effects of contraction ratio on twophase flow mixing with mass transfer in the flow injection nozzle. The geometric shape of the nozzle was modified to improve carbonation efficiency. A gas inlet hole was created to increase the flow mixing of CO2 with water. A nozzle throat was also introduced to increase the gas dissolution by increasing flow rates. Various contraction ratios of nozzle throat, inlet gas and liquid velocities, and gas bubble sizes were employed to determine their effects on gas hold-up, gas concentration, and mass transfer coefficient. Results revealed that the flow injection nozzle with high contraction ratios improved carbonation because of high gas hold-up. Gas concentration was directly related to contraction ratio and gas flow velocities. Carbonation reduced when high liquid velocities and large gas bubbles were employed because of inefficient flow mixing. This study indicated that flow injection nozzle with large contraction ratios were suitable for carbonation because of their ability to increase gas hold-up, gas concentration, and mass transfer coefficient.

Minimum wall pressure coefficient of orifice plate energy dissipater

Orifice plate energy dissipaters have been successfully used in large-scale hydropower projects due to their simple structure, convenient construction procedure, and high energy dissipation ratio. The minimum wall pressure coefficient of an orifice plate can indirectly reflect its cavitation characteristics： the lower the minimum wall pressure coefficient is, the better the ability of the orifice plate to resist cavitation damage is. Thus, it is important to study the minimum wall pressure coefficient of the orifice plate. In this study, this coefficient and related parameters, such as the contraction ratio, defined as the ratio of the orifice plate diameter to the flood-discharging tunnel diameter; the relative thickness, defined as the ratio of the orifice plate thickness to the tunnel diameter; and the Reynolds number of the flow through the orifice plate, were theoretically analyzed, and their relationships were obtained through physical model experiments. It can be concluded that the minimum wall pressure coefficient is mainly dominated by the contraction ratio and relative thickness. The lower the contraction ratio and relative thickness are, the larger the minimum wall pressure coefficient is. The effects of the Reynolds number on the minimum wall pressure coefficient can be neglected when it is larger than 10^5. An emoirical expression was presented to calculate the minimum wall oressure coefficient in this study.

Simulation on effect of throat contraction ratio and strake stagger angle on flow field and aerodynamic performance of scrampressor

The design methods of typical supersonic aircraft intakes and shock wave compression technology have been applied to ram-rotor,an attractive compression system.A ram-rotor is of a typical structure including the compression ramp,the throat and the subsonic diffuser;a scrampressor is similar to ram-rotor,the only difference is that scrampressor has no subsonic diffuser.The work was the continuation of the preparatory work.In order to further study the effect of throat contraction ratio and strake stagger angle on the flow field and performance of a scrampressor,the flow field of a scrampressor with a three-dimensional flow path was numerically simulated with different throat contraction ratios and strake stagger angles.Simulated results indicated that the optional aerodynamic performance of a scrampressor could be achieved with an adiabatic efficiency of 0.8413atotal pressure recovery coefficient of 0.8446,a total pressure ratio of 7.14 and a static pressure ratio of 5.17for a throat contraction ratio of 0.6 and a strake stagger angle of 12°.It was therefore concluded that an appropriate decrease in throat contraction ratio and an increase in strake stagger angle could help the comprehensive improvement of a scrampressor in performance.

THRESHOLD CONDITION FOR CHOCKING IN OPEN CHANNELS AND EXCAVATION OF TAILRACE

On the basis of energy and continuity equations a general threshold condition for chocking in open channels is obtained and a representation in terms of the Froude number at the upstream section and other parameters is given to predict whether the chocking phenomenon occurs or not at the downstream section. From the general threshold condition for chocking the limit contraction ratios of the channel width are introduced for both with and without the energy losses and a criterion for excavation of the tailrace to avoid chocking is derived. An example shows that using these criterion and the representation proposed for calculating flow depth it is very easy to determine the scheme of the excavation of the open channels.

Hydraulic Characteristics of Multi-Stage Orifice Plate

Energy dissipater of multi-stage orifice plate, as a kind of effective energy dissipater with characteristics of high energy dissipation ratio and low cavitations risk, has become welcomed more and more by hydraulics researchers. The relationship between the contraction ratio of upper stage orifice plate and the lower one's under the principle of equal-cavitation characteristics, and the reasonable distance between upper stage orifice plate and the lower one under the condition of complying with this principle, are two important factors to be considered for multi-stage energy dissipater design. In the present paper, these two factors were analyzed by theoretical consideration and numerical simulations, and solving methods were put forward. The conclusion in this paper was proved to be reasonable by model experiment.