Three-dimensional numerical modeling of flow upstream of a symmetric streamlined body mounted over a flat plate with tip gap

In this research activity numerical simulations are carried out to investigate the flow field upstream of a symmetric streamlined body mounted perpendicular to a flat plate with and without clearance gap between the tip of the streamlined body and the flat plate with laminar boundary layer. The developed numerical model successfully predicted the three-dimensional horseshoe vortex system upstream of the streamlined body with and without the tip gap. The resulting vortex system for the configuration with tip gap contains multiple vortices with characteristics similar to that of end-wall-flows of surface-mounted obstacles. The effects of varying tip gap clearance for various values of free stream Reynolds number are also investigated. It was found that the introduction of a gap between the streamlined body tip and flat surface caused shifting of the vortex structure system in the upstream direction. Moreover, it is observed that the free stream Reynolds number and the tip gap between the streamlined body and the flat plate substantially influences the unsteady character of the flow field and the vortex system structure. Results obtained from the numerical simulations are compared with experimental measurements of a blunt body configuration and have been found in good agreement.

The Influence of Boiling on the Streamlined Body Drag Force and Falling Velocity

This article presents the results of numerical investigation of the influence of the streamlined body temperature on drag force and on the falling velocity in a water channel. The experimental data reflecting the cooling dynamics and body temperature influence on the falling velocity are presented as well. k − ε turbulence model and homogenous heat transfer model were chosen for the numerical 3D simulation. Drag force changes induced by the alteration of the body temperature were investigated. Velocity of the streamlined body under different temperatures of water was investigated experimentally, and the results were compared to the data obtained during the numerical simulation. The increase of the falling velocity and decrease of drag force were found to have been affected by the increase of the body temperature, which had influence on the change of the water parameters (density, phase, etc.) near the surface of the body. Simulation showed that the drag force and a velocity also depended on the water temperature. The drag force of the streamlined body decreased by 32% in comparison to the cold body for the body temperature equal to 150 °C and water temperature close to the saturation temperature (98 °C). Experimentally, it was determined that the velocity of the streamlined body covered by vapor film depended on the falling time and increased by 10–30%. Velocity difference was very small for the cold and hot bodies at the initial moment of the drop; however, it reached 20% and more after 0.3 s of the falling process.

MODELING OF A VENTILATED CAVITY BEHIND A STREAMLINED BODY

The results of physical and numerical modeling of a ventilated air cavity behind a streamlined body are presented. The results of laboratory experiments to determine the amount of gas flowing from the ventilated cavity are presented. It is formed behind the cavitator depending on a number of geometric and dynamic parameters. Numerical simulation of non-stationary 3D two-phase flow was performed on the basis of open source software OpenFOAM. The influence of gas blowing parameters on the formation of an air cavity, size, shape and stability has been investigated. Good qualitative agreement with experimental data was obtained. It is shown that the thickness of the ventilated cavity is determined by the diameter of the cavitator regardless of the diameter of the blow hole, and the increase in velocity or gas flow rate has a positive effect on the length and stability of the formed cavity.

SIMULATION OF BODY FLOW WITH A SEPARATED LIQUID FLOW IN A COMSOL MULTIPHYSICS ENVIRONMENT

The article presents the results of using the COMSOL Multiphysics environment to perform one of the laboratory works of the Aerodynamics module of the Hydrogas and Aerodynamics discipline. In the COMSOL Multiphysics environment, it is proposed to simulate the process of a laminar flow of a viscous incompressible fluid around bodies of various geometric shapes, which allows you to visually visualize the boundary layer, its separation from the surface of the streamlined body.

ENHANCEMENTS OF THE THERMAL UNIFORMITY INSIDE A GAS-TURBINE DILUTION SECTION USING DIMENSIONAL OPTIMIZATION

In the dilution section of the gas turbine, the flow and thermal mixing between the cold radial jets and hot mainstream is always a matter of interest to generate a consistent thermal profile, extending the longevity of the turbine blades. Multiple researches explored the topic experimentally and numerically, and new designs have been evaluated, including a central streamlined body with swirlers inside the dilution zone. Moreover, the dimensional aspects (diameter, length, and position) of the streamlined body can help in generating more uniform thermal profiles, but with the cost of increased pressure drop. Various design iterations are needed to be tested and assessed based on minimizing the contradicting uniformity number and pressure drop. Such process is time and resources consuming if not wisely managed. The paper proposes a solution for the current problem by the integration of the “Design of Experiment/ Optimization Algorithms” generator with the computational fluid dynamics solver. The outcomes from three different algorithms (ULH, MOGA-II, and HYBRID) are statistically analyzed to understand inputs-outputs correlations, develop response surface methodology, and help in finding the optimal designs. The suggested HYBRID optimization provided a better optimal curve with improvements of 69% and 15% in the thermal uniformity and pressure drop respectively. The correlation coefficients stressed on the importance of the diameter as the highest influencer with inverse and direct correlations with uniformity and pressure drop, respectively. Finally, the Kriging response surface model enabled more optimal designs and a better understanding of the effective ranges of the three inputs.

Gliding performance is affected by cranial movement of abdominal organs

Swimming is an extremely popular sport around the world. The streamlined body position is a crucial and foundational position for swimmers. Since the density of lungs is low, the center of buoyancy is always on the cranial side and the center of gravity is always on the caudal side. It has been reported that the greater the distance between the centers of buoyancy and gravity, the swimmer’s legs will sink more. This is disadvantageous to swimming performance. However, the way to reduce the distance between the centers of buoyancy and gravity is yet to be elucidated. Here we show that swimmers with high gliding performance exhibit different abdominal cavity shapes in the streamlined body position, which causes cranial movement of the abdominal organs. This movement can reduce the distance between the centers of buoyancy and gravity, prevent the legs from sinking, and have a positive effect on gliding performance.

Morphology of the Genus Gymnocephalus (Pisces) from the Lower Danube River

The current study completed the information regarding the phenotypic variability in the Danube ruffe (Gymnocephalus baloni). We also assessed the phylogenetic relationship of G. baloni with the other two species of the genus Gymnocephalus from the Lower Danube River. Ten morphological characters were the most useful together for discriminating between G. baloni and G. cernua from the Lower Danube River. In addition, we found a more streamlined body shape in G. baloni compared with the described holotype, which could be in connection with fish phenotypic response to ecological characteristics of the Lower Danube River.