Shear Stress Transport K-omega Turbulence Research Articles

Numerical study on the effect of smoke emitted from the vents on the roof of a diesel train on the intake of downstream air-conditioning units

Constrained by economic development and geographical features, numerous railway lines remain unelectrified, underscoring the expansive potential of diesel trains. Diesel engine emissions discharged from the roof of trains pose a challenge as some of the smoke infiltrates the cabin through the intake of roof-mounted air-conditioning units (ACUs). This intrusion diminishes the indoor air quality, posing health risks to passengers and potentially jeopardizing their safety. This study employs the shear stress transport k-omega turbulence model to formulate a multiphase flow model for simulating smoke diffusion in diesel trains. Additionally, we conducted an optimization design to minimize smoke entry into the ACUs. This study defined six cases based on variations in the shape and height of the cover and the spacing of the smoke vents. The results show that the effect of the diffusion characteristics decreased with the cover height. With the progression of airflow diffusion, the effect of the smoke vent structure on the concentration diminished farther from the vents. The minimum smoke mass flow rate into the intake occurred with the vent spacing of 2.14 m and without a cover, resulting in a 57.0% decrease compared with the maximum. Thus, a smoke vent spacing of 2.14 m without a cover was deemed to be the optimal configuration. The research results provide certain engineering guidance significance for the design and operation of train-smoke vent structures.

Quantitative evaluation on the suitable flow region inside the shielding device of submersible aquaculture facility

The primary purpose of the aquaculture facility is to provide a comfortable living environment and achieve welfare aquaculture for cultured fish in the open sea. Nevertheless, it has been a challenge to accurately assess the suitable flow region of the cultured fish inside the aquaculture facility for the severe ocean environment, which is a pressing concern for aquaculture farmers. First, the maximum domed swimming speed (MDSS) is used as an indicator to assess the swimming ability of Sciaenops ocellatus in this study, which can be measured through a vertical circulation water channel. Subsequently, the porous media theory is adopted and applied to predict the flow field inside the shielding device of the submersible aquaculture facility based on the shear stress transport k-omega turbulence model using the computational fluid dynamics (CFD) approach. In addition, combining the swimming ability of Sciaenops ocellatus and current speed distribution inside the shielding device of a submersible aquaculture facility, the suitable flow region is quantitatively assessed. The results indicate that when middle height, the inclined angle and net solidity are 0.4 m, 3π/12 and 0.65, respectively, the current speed inside the shielding device attenuates below the maximum domed swimming speed of Sciaenops ocellatus - 0.76 m/s and meets the survival of Sciaenops ocellatus for the actual sea condition with an incident current speed of 1.5 m/s. In addition, a suitable flow region for Sciaenops ocellatus, which is 204.512 m3 and accounts for 17.76% of the total aquaculture volume, is formed and located inside the shielding device, close to the downstream sides, and gradually extends towards the middle of the shielding device. Based on the swimming ability of Sciaenops ocellatus, using numerical means to describe the suitable flow region in detail is to provide clear and macroscopic guidance for aquaculture farmers.

Hydrodynamic assessment of a semi-submersible aquaculture platform in uniform fluid environment

Predicting the distribution of flow velocity inside a semi-submersible aquaculture platform and taking measures to optimize the flow field are critical to provide a dependable inhabit for farmed fish. This paper examines the hydrodynamics of a semi-submersible fish farm under current using the porous media method combined with a rigid wall based on the shear stress transport k-omega turbulence model. The results show that the presence of nets expands the low flow area and provides a better inhibit for farmed fish in the severe currents. The increase of net solidity enhances the damping effect on the flow, and it also simultaneously increases the current loads acting on the net. The attenuation caused by different net solidities produces a 66.10 % deficit of the flow velocity in maximum inside aquaculture platform. A maximum increase of 36.82 % for the drag force acting on the aquaculture platform is obtained. Furthermore, the distribution of drag force acting on the aquaculture platform in current is also assessed. Although the drag force of the frame-only is approximately twice compared to the net-only case, the improvement in the strength of the net structure under the action of flow should not be ignored.

Numerical analysis of high-lift configurations with oscillating flaps

This study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport k-omega turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of 0.5 times 10^{6} the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of 20 times 10^6, reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

Numerical Study of Fluidic Thrust Vector Control Using Dual Throat Nozzle

Compared to a variety of mechanical vectoring nozzles, fluidic vectoring nozzles possess more research value nowadays. The dual throat nozzle is gradually developing into an outstanding technology to handle supersonic and hypersonic aircraft deflections. Three-dimensional, steady, compressible, and viscous flows in rectangular dual throat nozzles are numerically investigated by resolving Reynolds-averaged Navier-Stokes equations and shear stress transport k-omega turbulence model. Computational fluid dynamics results are verified against the existing experimental data, where a good consistency is gained. The impacts of nozzle pressure ratio, injection-to-mainstream momentum flux ratio, and setup angle of the slot injector on the systemic performance are examined. Useful conclusions are summarized for engineering designers. Firstly, pitching angles decline along with an increasing nozzle pressure ratio, while systemic thrust ratio and thrust efficiency increase. Secondly, thrust vector angles enlarge with an increase of the injection-to-mainstream momentum flux ratio, whereas both systemic thrust ratio and thrust efficiency decay. Finally, the setup angle of the slot injector impacts the systemic performance remarkably. Although the pitching angle for the setup angle of 120° is highest, comprehensive characteristics in terms of systemic thrust efficiency and systemic thrust ratio for the setup angle of 150° are more excellent.

Performance investigations of cross flow hydro turbine with the variation of blade and nozzle entry arc angle

Mistreatment of small hydropower sources requires the use of small turbines that combine efficiency and economy which can suitably provide the power requirements of rural and small societies. In this context, the cross flow hydro turbines are extensively used due to their simpler in design, ease of maintenance, low initial cost. Although the cross flow hydro turbine has moderated efficiency, but it has operated at low head and discharge. Hence, the objective of the present investigation is to increase the efficiency of a cross flow hydro turbine with the geometric modification. In the present study, the numerical investigation of cross flow hydro turbine has been carried out using multi-physics finite volume solver in ANSYS FLUENT. The three dimensional unsteady simulations have been conducted using shear stress transport k-omega turbulence model. The performance of cross flow hydro turbine has been investigated by changing the inlet blade angle from 5° to 40° and nozzle entry arc angle from 65° to 85° with the number of blades being 20. The rotational speed of the turbine has been varied from 200 rpm to 800 rpm. The total pressure and velocity field have been examined to evaluate the performance coefficients. From the unsteady results, the maximum efficiency has been found at the inlet blade angle, 5° and nozzle entry arc angle, 65° with the runner rotational speed of 600 rpm. However, with the consideration of the manufacturing feasibility inlet blade angle and nozzle entry arc angle have been considered as 10° and 65° respectively to be the most promising design configuration. The effect of temperature of the flowing water on performance of the turbine also has been studied. The maximum efficiency at inlet blade angle, 10° has been found to be 93.8% at 600 rpm. By incorporating the nozzle entry arc angle, maximum efficiency has been found to be 97.8% at nozzle entry arc angle, 65° with rotational speed 600 rpm and inlet blade angle, 10°. The efficiency of the current design configuration has been found 20% higher compare to the existing model.

Effects of Rib Shapes on the Entropy Generation in a Ribbed Duct

Ducts are often used in reactors and heat exchangers. Using rough surfaces in ducts is recognized as an effective technique to enhance heat transfer. In this research, an entropy generation analysis is carried out for turbulent flow inside a ribbed duct. Numerical simulations are performed to study the effects of rib shapes and flow Reynolds numbers on friction factor, Nusselt number, and different types of entropy generation containing the frictional and thermal ones. All simulations are performed for Reynolds number in the range of 20,000 to 60,000 and six rib shapes (rectangular, square, isosceles trapezoidal, rectangular trapezoidal, equilateral triangle, and nonequilateral triangle). A shear stress transport k-omega turbulence model is used for the numerical simulations. It was found that the ribs with no inclined surfaces such as square and rectangular shapes create more thermal irreversibility. Moreover, it was shown that among different rib shapes, the equilateral triangle rib has the highest frictional entropy generation over the entire range of the Reynolds number, whereas the rectangular rib has the lowest one.

A numerical simulation of wheel spray for simplified vehicle model based on discrete phase method

Road spray greatly affects vehicle body soiling and driving safety. The study of road spray has attracted increasing attention. In this article, computational fluid dynamics software with widely used finite volume method code was employed to investigate the numerical simulation of spray induced by a simplified wheel model and a modified square-back model proposed by the Motor Industry Research Association. Shear stress transport k-omega turbulence model, discrete phase model, and Eulerian wall-film model were selected. In the simulation process, the phenomenon of breakup and coalescence of drops were considered, and the continuous and discrete phases were treated as two-way coupled in momentum and turbulent motion. The relationship between the vehicle external flow structure and body soiling was also discussed.