Evaluation of Two-Phase Turbulence Closure Models Modifications in Near Wall Region of Boundary Layer

Previous study of authors showed that kappa-taf turbulence model has a good accuracy for prediction of hydrodynamic behaviour of near wall turbulence in a gas-solid boundary layer flow. In that study two-phase kappa-taf model was derived from Yokomine et al. modified kappa-epsilon model. In the present study, a new version of two phase kappa-taf turbulence model has been presented. In this model we use Adeniji et.al. modifications to account for the effect of solid particles both on the turbulence kinetic energy and it's dissipation rate. The new modified kappa-taf has been compared with the later version of kappa-taf for prediction of flow behaviour in near wall region of two-phase boundary layer. The governing equations for two-phase boundary layer flow with Eulerin-Eulerian approach by two different modified kappa-taf turbulence models have been solved numerically using finite volume method. In comparison with available experimental data, the obtained results by modified kappa-taf, based on Yokomine et al. modifications, have better agreement than modified kappa-taf based on Adeniji et al. model

A Finite Volume Study on the Effects of Electro-Hydro-Dynamic Fluid Acceleration on Airflow Around a Cylinder at Low Reynolds Numbers

Applying a high-voltage electric field in a flow (electro-hydrodynamics or EHD) is a highly effective approach to locally accelerate a fluid to a desired speed. In this paper, a finite volume implementation is used to study the fluid flow around a fixed cylinder at a low Reynolds number. Two pairs of wire-plate electrodes are used to generate the electric field for fluid acceleration. Two Reynolds numbers are considered: Re=40, 100. We show that by increasing the Reynolds number, the relative effect of EHD is decreased. Further, we study the change in drag force due to EHD actuation. Finally, we showed that under certain voltage, electrode placement and Reynolds number the EHD fluid acceleration does not increase the total drag on the cylinder and yet leads to an increase in the total streamwise momentum transfer by augmenting the velocity at the top of the boundary layer

Experimental Investigation of Flow and Coherent Properties of Excited Non-Circular Liquid Jets

Non-circular jet is identified as an efficient passive flow-control technique that attracts many research topics. The existence of twine-vortexes is the main reason for dissimilarity between circular and non-circular jets. Which also influences the production of droplets and satellites as well as the jet instability. This investigation presents instability analysis of liquid-gas interface as an applicable conception in free-jet flows. We experiment different jet geometries within a gas ambient in order to study their hydrodynamic behavior. These studies give an appropriate perception about contributing forces that play essential roles in fluid instability. We focus on varying viscosity and surface tension as our excitation techniques. These methods are vital to examine the key properties of non-circular jets such as breakup and decay length, axis-switching wavelength as well as produced droplets and satellites characteristics. First, instabilities of charged liquid jets are investigated by considering the interaction between electric and inertial forces. Also, the viscosity effect was studied for its interaction with the inertial and surface tension forces. In each case, liquid jet in-stability for various nozzle geometries over a specific range of jet velocity is examined. The obtained results illustrate that the geometry of nozzle has an important effect on jet instability. In addition, by increment of We number, the breakup and decay length as well as the axis-switching wavelength are raising. However, by the rise of twin-vortex number, the breakup length increases but the decay length and axis-switching wavelength decrease

Ensemble Kalman Methods With Constraints

Ensemble Kalman methods constitute an increasingly important tool in both state and parameter estimation problems. Their popularity stems from the derivative-free nature of the methodology which may be readily applied when computer code is available for the underlying state-space dynamics (for state estimation) or for the parameter-to-observable map (for parameter estimation). There are many applications in which it is desirable to enforce prior information in the form of equality or inequality constraints on the state or parameter. This paper establishes a general framework for doing so, describing a widely applicable methodology, a theory which justifies the methodology, and a set of numerical experiments exemplifying it

Immunohistochemical and bacteriological investigations of mannheimia haemolytica in sheep bronchopneumonia

Mannheimia haemolytica infection is one of the most common etiologic agents of sheep pneumonia almost all over the world. Ovine pneumonic Mannheimiosis is characterized by severe fibrinous pleuropneumonia. Subacute to chronic cases progress to purulent bronchopneumonia and its squeals include abscessation and fibrous pleural adhesions. In the present study, lungs of 8986 sheep were inspected grossly in the Ahvaz abattoir and totally 65 lungs with visible signs of bronchopneumonia were selected for pathological and bacteriological examinations. Mannheimia haemolytica antigens were detected in 63.07% of immunoperoxidase stained tissue sections while 52.30% of the lungs were positive in bacteriological culture. Suppurative, necrotic and fibrinous types of bronchopneumonia were the most abundant lesions and right cranial lobes, specifically their cranial portions, were the most affected areas. McNemar test showed a significant difference between the diagnostic power of immunohistochemistry (IHC) and bacterial culture in detection of M. haemolytica (κ=0.66). Considering IHC as a golden test, sensitivity and specificity of bacterial culture were estimated as 78.05 and 91.67%, respectively. Chi- squared test showed significant correlations between the distribution of the lesions and bacterial isolation (P=0.04), types of lesions and IHC results (P=0.01), and also types of bronchopneumonia and mixed/pure isolation (P=0.008). This study showed the significant role of Mannheimia haemolytica in causing pneumonic lesions of studied sheep

Numerical Simulation of Heat Transfer Enhancement in the Presence of an Electric Field at Low Reynolds Numbers

One way for optimization of the rational use of energy in thermal systems is to increase their rate of heat transfer. In this study, the effects of an electric field on the fluid flow and temperature field as an active method of enhancement is numerically investigated. The hydrodynamics and heat transfer behaviors of laminar duct flow with specific boundary conditions in the presence of an EHD actuator was taken into consideration. The partial difference equations of flow field and electric field namely continuity, momentum and energy equations for fluid flow and electric current and Poisson’s equations for electric field was numerically solved with finite volume method. At first, the electric equations were solved and then their results were imported to the fluid field for improvement of the body forces. The aim of this study is an application of the EHD actuator on local heat transfer enhancement by using wire-plate electrodes in laminar duct flow. The obtained results show for the flows with R

Experimental Study of Plasma Actuator Effects on Flow Field Separation Bubble around Blunt Flat Plate

In this paper, the air flow around a blunt flat plate with a rounded leading edge has been experimentally examined with and without the presence of a plasma actuator. Tests have been conducted with Reynolds numbers ranging from 104 to 105. Significant phenomena in this flow field is the flow separation at the leading edge of the body, which called separation bubble. There are two considerably dimensionless parameters in this experiment. One of them is the leading edge radius ratio to body thickness and other one is the ratio of maximum velocity induced by plasma actuator to free stream velocity. Geometries with the values of R/D=0, 1/16, 2/16, 4/16 were tested. For each geometry, the effectiveness of plasma actuator on the separation bubble is studied in different values of velocity ratio. The results show that, the effect of plasma actuator for the geometry with sharp edge (R/D=0), is negligible, while in geometry with rounded edge, the plasma actuator has significant effect on the separation bubble domain. This effectiveness is enhanced, by increasing of leading edge radius and velocity ratio, so that in rounded edge geometry (R/D=4/16) length of separation bubble is reduced about 75%

Heat Transfer Enhancement in a Stagnant Dielectric Liquid by the Up and Down Motion of Conductive Particles Induced by Coulomb Forces

When charged particles are exposed to an electric field the well-known Coulomb force acts on them. In this investigation, this force is utilized to induce vertical motion of spherical steel particles submerged in a dielectric liquid. The interelectrode space of a two parallel electrode system is filled with the liquid and dispersed steel particles, which become charged after contact with the electrodes. Experiments were carried out to measure the effect of this particle motion on the heat transfer between an electrode surface and an adjacent stagnant dielectric liquid. In order to interpret the experimental data, the dynamics of particles was analytically studied for low particle volume concentrations. Experimental results demonstrate significant heat transfer enhancement on low viscosity dielectric liquids. A detailed discussion is presented on the possible mechanisms responsible for such an enhancement

Inverse dynamics-based motion control of a fluid-actuated rolling robot

In this paper, the rest-to-rest motion planning problem of a fluid-actuated spherical robot is studied. The robot is driven by moving a spherical mass within a circular fluid-filled pipe fixed internally to the spherical shell. A mathematical model of the robot is established and two inverse dynamics-based feed-forward control methods are proposed. They parameterize the motion of the outer shell or the internal moving mass as weighted Beta functions. The feasibility of the proposed feed-forward control schemes is verified under simulations

Echocardiographic evaluation of mitral geometry in functional mitral regurgitation

<p>Abstract</p> <p>Objectives</p> <p>We sought to evaluate the geometric changes of the mitral leaflets, local and global LV remodeling in patients with left ventricular dysfunction and varying degrees of Functional mitral regurgitation (FMR).</p> <p>Background</p> <p>Functional mitral regurgitation (FMR) occurs as a consequence of systolic left ventricular (LV) dysfunction caused by ischemic or nonischemic cardiomyopathy. Mitral valve repair in ischemic MR is one of the most controversial topic in surgery and proper repairing requires an understanding of its mechanisms, as the exact mechanism of FMR are not well defined.</p> <p>Methods</p> <p>136 consecutive patients mean age of 55 with systolic LV dysfunction and FMR underwent complete echocardiography and after assessing MR severity, LV volumes, Ejection Fraction, LV sphericity index, C-Septal distance, Mitral valve annulus, Interpapillary distance, Tenting distance and Tenting area were obtained.</p> <p>Results</p> <p>There was significant association between MR severity and echocardiogarphic indices (all p values < 0.001). Severe MR occurred more frequently in dilated cardiomyopathy (DCM) patients compared to ischemic patients, (p < 0.001). Based on the model, only Mitral valve tenting distance (TnD) (OR = 22.11, CI 95%: 14.18 – 36.86, p < 0.001) and Interpapillary muscle distance (IPMD), (OR = 6.53, CI 95%: 2.10 – 10.23, p = 0.001) had significant associations with MR severity.</p> <p>Mitral annular dimensions and area, C-septal distance and sphericity index, although greater in patients with severe regurgitation, did not significantly contribute to FMR severity.</p> <p>Conclusion</p> <p>Degree of LV enlargement and dysfunction were not primary determinants of FMR severity, therefore local LV remodeling and mitral valve apparatus deformation are the strongest predictors of functional MR severity.</p