Vol 26, No 3 (2019)

A new composite phase change material based on porous diatomite, saturated with paraffin by immersion method, has been developed. The results of the study of heat propagation in this material heated from one side with a constant power source are presented. On the basis of the enthalpy model, numerical computations were carried out, a comparison with the experimental results was made, and the influence of the properties of the composite material on the thermal processes in it was analyzed. In the computations, the heat flux power, the phase transition temperature range, and the characteristics of the phase change material were varied. The analysis of the computation results has shown that the use of the phase change material allows not only increasing the heat-storage capacity of the composite material, but also controlling the heat fluxes. As a result, it becomes possible to reduce the peak values of the heat flux passing through the material and to limit the material temperature range during heating for a long time.

Using the recently developed explicit anisotropic algebraic Reynolds-stress model, calculations were performed to study the stable boundary layer dynamics according to the well-known test case of the GABLS1 (Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study) project, where the Richardson number Ri > 1. The model includes the effect of gravity waves, which allows taking into account the momentum maintenance under strong stability conditions. The model shows good agreement with the results of LES simulation. The study aims at obtaining a much more realistic boundary layer, shallower in depth than in traditional first-order models. The case of a constant surface cooling rate is considered. Some interesting features of the model are related to its deduction based on physical principles. In particular, the use of a larger number of prognostic equations in the model makes it possible to obtain more realistic dynamic behavior.

In this paper, a numerical investigation of airfoil flow control using passive air jet is presented. The study of generate a passive jet from pressure side to suction side was conducted in order to improve the airfoil characteristics. Such characteristics include boundary layer separation and stall inception. The numerical simulations conducted using CFDRC software. Different structured and unstructured finite volume technique is used to solve the steady compressible Navier—Stokes equations. The code results were validated with the experimental testing results for different turbulence model. Parametric study is performed for the location, slot width and angle of a synthetic jet on the suction side of a subsonic flow over a NACA 23012C airfoil. The maximum lift is achieved with the jet flow being normal to suction side surface but this come with penalty of the high drag. The maximum lift to drag ratio was accompanying with synthetic jet being located at 43% chord and 30° jet angle. Finally, optimum geometry of jet is obtained using simplex algorithm with initial shape obtained from the parametric study.

The paper studies the process of liquid atomization in high-speed gas jets with application to a subject of high-rate fuel nozzles. Experiments were carried out for gas-liquid jet with the central-axis feeding of liquid to the outlet of a confuser-type nozzle with pumping of air in subsonic and supersonic flow regimes. The energy balance approach was developed for describing a gas-liquid jet. This provided us the needed data for comprehensive description of the gasliquid jet: gas velocity field without liquid, shadow visualization of geometry and wavy structure of a jet with liquid and with pure gas, velocity profiles for liquid phase, spray droplet size, spray concentration and spatial distribution. The gas-liquid flow was characterized by Weber number from the time of liquid jet breakup till the final spray.

The experimental values of the effective thermal conductivity of water at transverse streamlining of the in-line rod bundles with square packing have been obtained. The effective thermal conductivity of water was measured in the direction parallel to the axes of the rods. The measurement method implied mixing of two flat parallel water flows in the working area; the latter moved at the same velocities, but had different temperatures. By measuring the flow temperatures before and after the mixing area, the amount of heat transferred from the hot to the cold flow was determined and the effective thermal conductivity of the liquid was calculated. In the investigated range of Reynolds numbers (from 7·10³ to 8·10⁴), calculated by the velocity in a narrow section, the experimental effective thermal conductivity of water showed a linear increase with increasing velocity and good agreement with the results of calculations by the integral turbulence model. The obtained experimental data have confirmed the possibility of using an integral turbulence model to calculate the parameters of the anisotropic porous solid model, used in CFD codes simulating thermal-hydraulic processes in the active zones of nuclear reactors and heat exchangers.

The influences of Hall current and velocity slip on MHD Casson nanofluid flow and heat transfer over a stretching sheet have been analyzed numerically. The Casson fluid model is applied to characterize the non-Newtonian fluid behavior. Physical mechanisms responsible for Brownian motion and thermophoresis with non-uniform internal heat generation/absorption are accounted for in the model. A recently proposed boundary condition requiring zero nanoparticle mass flux is applied to achieve practically applicable results. The partial differential equations are transformed into the system of ordinary differential equations by applying similarity transformation, which is then solved numerically. A validation of the work is presented by comparing the current results with existing literature. The results have revealed that the axial skin friction, the transverse skin friction, the heat, and mass transfer rates are significantly boosted with an increase in Hall parameter.

This paper presents a numerical investigation on the concept for enhancing film cooling performance by placing shaped vortex generators (VG) upstream of the film hole. Nine cases with different shapes of vortex generators are investigated, including the rectangular shape, triangular shape, parallelogram shape, and trapezoid shape. The film cooling performance is evaluated at the density of 0.97 with the blowing ratios ranging from 0.5 to 1.5. Results obtained show that the film cooling performance is greatly improved by the upstream VG. The twisted flow rotates in the opposite direction of kidney vortices, attenuating its effect. Furthermore, the case with rectangular VG shows the most uniform coolant layer in the spanwise direction and the highest averaged adiabatic cooling effectiveness while the total pressure loss increases a bit as a penalty.