Impact of the Confinement Plate on the Velocity of Synthetic Jet

In the paper, the impact of the limitation of the environment around the office of synthetic jet actuators were tested. One short and three length orifices were tested and compared with and without confinement plate. In total, seven different synthetic jet actuators were investigated. The constant temperature anemometer was used for the velocity measurements. The synthetic jet was tested for the Reynolds number in the range of 2300 < Re < 19,500, and the Stokes number in the range of 46 < S < 62. The confinement plate decreased the velocity of synthetic jet depending on the actuator supply power even around 5%. However, the differences in axial velocity profile are slight and the impact of the confinement plate was visible only in the distance x/d < 4.

RECONSTRUCTING THE AXIAL VOID VELOCITY PROFILE IN BWRs FROM MEASUREMENTS OF THE IN-CORE NEUTRON NOISE

The problem of determining the axial velocity profile from the in-core neutron noise measurements is revisited, with the purpose of developing an objective method for the determination of the void fraction. Until now it was assumed that in order to determine a realistic velocity profile which shows an inflection point and hence has to be at least a third order polynomial, one needs four transit times and hence five in-core detectors at various axial elevations. However, attempts to determine a fourth transit time by adding a TIP detector to the existing four LPRMs and cross-correlate it with any of the LPRMs were unsuccessful so far. In this paper we thus propose another approach, where the TIP detector is only used for the determination of the axial position of the onset of boiling. By this approach it is sufficient to use only three transit times. Moreover, with another parametrisation of the velocity profile, it is possible to reconstruct the velocity profile even without knowing the onset point of boiling, in which case the TIP is not needed. In the paper the principles are explained and the strategy is demonstrated by concrete examples.

Computational Analyses of Flow and Heat Transfer at 60° Position of 180° Curved Duct of Square Cross-Section

3D computational analyses are achieved to predict seriously the influences of thermal buoyancy strength and Dean number on Dean vortices, flow behavior and the rate heat transfer through 180° curved channel of square cross-sectional form. The work shows many results, so this paper emphasizes only on the results of 60° cross-sectional position of the bend duct. The principal partial equations of continuity, momentum and energy are considering in three dimensions under the following assumptions: flow is incompressible and laminar, and it is solved in steady-state. The aforementioned equations are subjected to suitable boundary conditions under following range as: Dean number of De = 125 to 150, Richardson number of Ri = 0 to 2 at fixed value of Prandtl number Pr = 1. The principal results of this work are illustrated as streamline and isotherm contours to draw to flow patterns and temperature distributions respectively. The axial velocity profile is shown versus above conditions, the local Nusselt number is also presented along the wall of 60° cross-sectional position. The results show that the thermal buoyancy can balance the effect of centrifugal force of fluid particles at the angular position of 60°.

Self-similar properties of decelerating turbulent jets

The flow in a decelerating turbulent round jet is investigated using direct numerical simulation. The simulations are initialised with a flow field from a statistically stationary turbulent jet. Upon stopping the inflow, a deceleration wave passes through the jet, behind which the velocity field evolves towards a new statistically unsteady self-similar state. Assumption of unsteady self-similar behaviour leads to analytical relations concerning the evolution of the centreline mean axial velocity and the shapes of the radial profiles of the velocity statistics. Consistency between these predictions and the simulation data supports the use of the assumption of self-similarity. The mean radial velocity is predicted to reverse in direction near to the jet centreline as the deceleration wave passes, contributing to an approximately threefold increase in the normalised mass entrainment rate. The shape of the mean axial velocity profile undergoes a relatively small change across the deceleration transient, and this observation provides direct evidence in support of previous models that have assumed that the mean axial velocity profile, and in some cases also the jet spreading angle, remain approximately constant within unsteady jets.

A Numerical Study on Flow Characteristics Through Orifice Flowmeter and Measurement Accuracy Depending on Upstream Straight Length

In this numerical study, Commercial CFD (Computational Fluid Dynamics) code, ANSYS CFX ver. 17.1, is used to analyze the 3-Dimensional flow characteristics through orifice plate (β = 0.6) with two 90 degree bends in different planes. The purpose of this numerical study is to evaluate measurement accuracy and flow characteristics of orifice flowmeter depending on upstream straight length from 12D to 56D. Thus, numerical calculations of pressure drop caused by swirling flow and distortion of axial velocity profile on orifice plate are performed by using numerical analysis. In addition, numerical analysis results are compared with recommended upstream straight length of ASME Performance Test Codes 19.5 for orifice plates and nozzles. The results show that if upstream straight length of orifice flowmeter is more than 40D, there is a little deviation of differential pressure. Moreover, it is found that up-down asymmetry of recirculation zones is relatively attenuated as the upstream straight length increases.

On the compressible bidirectional vortex in a cyclonically driven Trkalian flow field

In this study, the Bragg–Hawthorne equation (BHE) is extended in the context of a steady, inviscid and compressible fluid, thus leading to an assortment of partial differential equations that must be solved simultaneously. A solution is pursued by implementing a Rayleigh–Janzen expansion in the square of the reference Mach number. The corresponding formulation is subsequently used to derive a compressible approximation for the Trkalian model of the bidirectional vortex. The approximate solution is compared to a representative computational fluid dynamics simulation in order to validate the modelling assumptions under realistic conditions. The latter is found to exhibit an appreciable steepening of the axial velocity profile, which is accompanied by an axial dependence in the mantle location that is somewhat reminiscent of the radial shifting of mantles reported in some experimental trials and simulations. In this context, flows with a strong swirl intensity do not seem to be significantly affected by the introduction of compressibility. Rather, as the swirl intensity is reduced the effects of compressibility become more noticeable, especially in the axial and radial velocity components. It may also be realized that imparting a progressively larger swirl component stands to promote the axisymmetric distribution of flow field properties, and these include an implicit resistance to dilatational effects in the tangential direction. From a broader perspective, this study provides a viable approximation to the Trkalian motion associated with cyclonic flows, while serving as a limited proof of concept for the compressible Bragg–Hawthorne procedure applied to a steady, axisymmetric and inviscid fluid.

An Exact Solution for a Boundary Value Problem with Application in Fluid Mechanics and Comparison with the Regular Perturbation Solution

The exact solution for any physical model is of great importance in the applied science. Such exact solution leads to the correct physical interpretation and it is also useful in validating the approximate analytical or numerical methods. The exact solution for the peristaltic transport of a Jeffrey fluid with variable viscosity through a porous medium in an asymmetric channel has been achieved. The main advantage of such exact solution is the avoidance of any kind of restrictions on the viscosity parameterα, unlike the previous study in which the restrictionα≪ 1 has been put to achieve the requirements of the regular perturbation method. Hence, various plots have been introduced for the exact effects of the viscosity parameter, Daray’s number, porosity, amplitude ratio, Jeffrey fluid parameter, and the amplitudes of the waves on the pressure rise and the axial velocity. These exact effects have been discussed and further compared with those approximately obtained in the literature by using the regular perturbation method. The comparisons reveal that remarkable differences have been detected between the current exact results and those approximately obtained in the literature for the axial velocity profile and the pressure rise.