Numerical computations of wall-jet flowsCalcul numerique des jets parietauxNumerische berechnung von wandstrahlströmungenЧиcлeнныe pacЧeTы пpиcTeнныч cTpyй

Turbulent wall-jets on conical surfaces represent a practically useful situation and an important test for theoretical methods used for predicting turbulent transport. Experimental data on the velocity fields and the maximum concentration of a tracer gas have been obtained for turbulent wall-jets formed on conical surfaces of various angles. It is shown that the correct prediction of the data by a mixing-length hypothesis requires the mixing-length constant to be changed for each cone angle, A set of two-equation models of turbulence is then employed which solves two additional differential equations for the local properties of turbulence. These models correctly predict all the experimental data without the need for the adjustment of constants.     

Electro-orientation in particle light valves

Electro-orientation of rod-like particles in liquids, under the application of an external AC field, is analysed. A rod shape is suitable for particle light valve (PLV) applications. When they are aligned with their long axes parallel to the electric field (and the direction of light is assumed to be parallel to the applied electric field), then it can lead to good transmission of light. Various criteria to arrive at appropriate parameters for PLV applications are proposed. It is found that good electric conductors are excellent rod materials for PLV applications. They lead to an appropriate orientation of the rods and at the same time result in maximum orientational torque. Water-like liquids with higher values of permittivity are appropriate choices as suspending liquids since the Brownian dispersion in the presence of the electric field is minimized. The time it takes the rods to fully diffuse in the orientational space, once the electric field is turned off, decreases with decreasing liquid viscosity.     

Rheological characterization of filled polyamide 11 and polyamide 12 solutions in polyols

A thorough understanding of the rheological properties of real-world, formulated polymer melts and solutions is important to fabricate articles via typical melt processing techniques. Polyamides have been studied extensively in the area of water purification applications. In this work, the viscosity of these homogeneous polyamide 11 and polyamide 12 solutions in specific polyols was measured in the single phase region as a function of shear rate and temperature via capillary rheometry. In addition, the viscosity of the same polyamide solutions containing various levels of dispersed, nanoscale calcium carbonate particles was characterized in order to understand the rheology of the filled systems. Viscosity-reduced shear rate master curves were constructed by applying the principle of time–temperature superposition, and the activation energies were measured for the polyamide-polyol solutions. The observed increase in viscosity caused by the addition of nanofiller could not be explained by simply applying a vertical shift to the master curve, and a density exponent was required to account for the stiffening mechanism. Also, the dependence of the relative viscosity on the filler loading was shown to be consistent with the hypothesis that the filler particles were organized in the form of small fractal aggregates. The filled polyamide 11 systems exhibited higher relative viscosities than the filled polyamide 12 systems, indicating a higher level of particle aggregation and larger mean cluster size for the filled polyamide 11 systems. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48244.     

A tribute to D.B. Spalding and his contributions in science and engineering

This paper presents a summary of some of the scientific and engineering contributions of Prof. D.B. Spalding up to the present time. Starting from early work on combustion, and his unique work in mass transfer theory, Spalding’s unpublished “unified theory” is described briefly. Subsequent to this, developments in algorithms by the Imperial College group led to the birth of modern computational fluid dynamics, including the well-known SIMPLE algorithm. Developments in combustion, multi-phase flow and turbulence modelling are also described. Finally, a number of academic and industrial applications of computational fluid dynamics and heat transfer applications considered in subsequent years are mentioned.     

A methodology for the design of perforated tiles in raised floordata centers using computational flow analysis

An important aspect of the design of data centers involves sizing of the perforated floor tiles for return of cold air, the size of the space under the raised floor, and placement of the DP equipment and modular chillers. The flow through individual perforated tiles needs to fulfil the cooling requirements of the computer equipment placed adjacent to them. The novelty of this paper lies in the treatment of the volume under the raised floor as a uniformly pressurized plenum. The accuracy of the Pressurized Plenum model is demonstrated with reference to a computational fluid dynamics (CFD) analysis of the recirculating flow under the raised floor and the limits of its validity are also identified. The simple model of the volume under the raised floor enables use of the technique of flow network modeling (FNM) for the prediction of the distribution of flow rates exiting from the various tiles. An inverse design method is proposed for one-step design of the perforated tiles and flow balancing plates for individual chillers. Subsequent use of the FNM technique enables assessment of the performance of the actual system. Further, required design changes to an existing system can also be evaluated using the FNM analysis in a simple, quick, and accurate manner. The resulting design approach is very simple and efficient, and is well suited for the design of modern data centers     

Fully coupled solution of the equations for incompressible recirculating flows using a penalty-function finite-difference formulation

This paper describes two new solution algorithms for steady recirculating flows that use a penalty formulation to eliminate the pressure from the finite difference form of the governing equations. One algorithm uses successive substitution to linearize the equations, while the other employs the Newton-Raphson linearization. In both cases, the equations are solved in a fully coupled manner using a sparse matrix form of LU decomposition. The D'Yakonov iteration is used to avoid unnecessary factorizations of the coefficient matrix, significantly improving the computational efficiency. The Newton-Raphson linearization leads to faster convergence, but the execution times of the two methods are comparable. The algorithms converge rapidly and are robust to changes in grid size and Reynolds number. In a number of laminar two-dimensional flows, the new methods proved to be two to ten times faster than some conventional iterative methods.List of symbols A coefficient matrix - A _e area of east control-volume face - a coefficient in the discretization equations - â coefficients in the modified momentum equations in the penalty formulation, Eqs. (13) - b constant term in the discretization equations - F symbolic form of nonlinear system of equations, F ₍₎=A –b=0 - H characteristic length - J Jacobian matrix - n iteration number - P dimensionless pressure - p pressure - Re Reynolds number - U dimensionless u velocity - u x-direction velocity - V dimensionless v velocity - v y-direction velocity - X, Y dimensionless coordinates, X=x/H, Y=y/H - x, y physical coordinates - x x-direction width of the control volume - normalized error in the unconverged solution, Eqs. (19) - dimensionless penalty parameter, Eq. (7) - dimensional penalty parameter, Eq. (10) - viscosity - density