Large Eddy Simulation of Transitional Separated-Reattached Flow over Geometries Characterized by Different Aspect Ratios and with Different Intensities of Free Stream Turbulence

In the current study, changes in the physics of transitional separated-reattached flow due to changes of a geometry nature and an increase of intensity of free stream turbulence have been investigated numerically using the large eddy simulation approach. Numerical simulations have been carried out using the Open FOAM tool box. Six case studies are selected and divided into two groups of the flows: a low level of intensity of free stream turbulence (< 0.2%) and a high level of intensity of free stream turbulence (3.7%). Each group involves three geometrical shapes: a two-dimensional flat plate, a three-dimensional geometry with an aspect ratio value of 1 and a three-dimensional geometry with an aspect ratio value of 2. To the best of the author’s knowledge, the current study is the first work to explore transitional separated-reattached flow over three-dimensional geometries. In a comparison among the case studies, the separation bubble that formed on the flat plate is longer than that on other geometries, leading to longer temporal and spatial evolution of the transition. In addition, maximum values of the Reynolds stresses in the flat plate are larger than that in other geometries. Furthermore, all case studies show that the transition in the free shear layer is driven by the Kelvin-Helmholtz instability mechanism. Spectral analysis is carried out to cover all the computational domains employing both Fourier transform and wavelet power transform methods. In the current geometries for both incoming flows (with high and low levels of intensity of free stream turbulence), the regular shedding frequencies are in a good agreement with that reported in the literature. In addition, these frequencies are compatible with the Kelvin-Helmholtz instability conditions. Moreover, the spectral analysis indicates that the low frequency of the free shear layer flapping is absent. The evolution of coherent structures is identified by performing flow visualisation techniques. Different evolution processes of transformation of large-scale structures from Kelvin-Helmholtz rolls to hairpin structures are observed depending on the geometry shapes and on the level of intensity of free stream turbulence. The development of the turbulent boundary layer after the reattachment is also examined. For all case studies used here, a dominant observation is that there is no apparent effect of the geometry nature on the delay in the recovery of the reattached turbulent boundary layer.Iraq Governmen

A numerical investigation of the enhancement of single-slope single-basin solar still productivity

Enhancement of pure water productivity is necessary to keep human life, especially in the regions where people straggling of finding drinking water. The current work investigates numerically the increase in the productivity of the single-slope single-basin solar still by creating a new design of the absorbent base to increase the evaporation surface area. The new suggested design of the absorbent base is the use of stainless steel geometries which are different in shape and size in order to highlight their effect on solar still productivity. Results showed that using of stainless steel geometries increased the evaporation rate and enhanced the still productivity. In addition, the change in the geometry shape has a limited effect on the solar still productivity; whereas, changing the geometry size has a significant increase in productivity. The calculated data of the conversional solar still productivity was 2.987 kg/m2 with maximum temperatures of still water and the inner surface of the glass cover 63.6 °C and 54.2 °C respectively The maximum freshwater productivity was obtained by using cones, where the produced water was 4.13 kg/m2 with an enhancement ratio of 38.2%. In this case, the maximum temperatures of still water and the inner surface of the glass cover were 72.9 °C and 61.9 °C, respectively

Performance study on a solar concentrator system for water distillation using different water nanofluids

The rapid growth in the world–population urges the need for potable water in various regions, especially in hot and dry regions. The main challenge in the productivity of potable water is the cost and availability of water sources. Thus, it is crucial to develop effective methods to overcome this global need. Utilizing solar power is proven to be a promising path to implementing thermal solar radiation in solar distillation applications. This work investigates the effectiveness of using concentrated solar power to irradiate heat exchange to evaporate water in a receiver, which will be collected as pure water in a condenser later. The thermal performance of the proposed model and its productivity are tested experimentally by using tap water only, and the test was repeated twice using two nanofluids namely, (aluminium oxide (Al2O3) and zinc oxide (ZnO)). The results showed that using (Al2O3) has a superior influence on the productivity of the solar unit, where the productivity is increased by 43.53% and 21.89% when compared to tap water and zinc oxide (ZnO) nanofluid respectively. The thermal efficiency of the solar unit was also increased by 9.91% (maximum) when using (aluminium oxide (Al2O3) as a working fluid compared to tap water. The model has simple components and is easy to install with a compact size, which can be developed be utilized in urban and desert areas