Turbulent Kinetic Energy Distribution Research Articles

Research on the Flow Characteristics in the Gap of a Variable-Speed Pump-Turbine in Pump Mode

A variable-speed pump-turbine is the core component of a hydraulic storage and energy generation station. When the pump-turbine operates at a constant speed, its response to the power grid frequency is poor. In order to improve the hydraulic efficiency of the pumped storage unit, variable-speed units are used. However, there has been no numerical study on the effect of the rotational flow characteristics within the gap of a variable-speed pump-turbine. This paper calculates the flow characteristics within the gap of a variable-speed pump-turbine under three typical pump modes (maximum head minimum flow condition, minimum head maximum flow condition, and maximum speed condition). The research results indicate that the rotational speed significantly affects the pressure distribution, velocity distribution, and turbulent kinetic energy distribution within the crown and band gaps. The higher the speed, the larger the area of the high-pressure region before the runner inlet compared to other operating conditions, and similarly, the low-pressure area after the runner outlet is also larger than in other operating conditions. The change in speed mainly affects the internal flow field of the crown gap, with the most noticeable changes occurring in the pressure and flow velocity at the inlet and outlet of the crown gap. There is a clear trend of pressure drop and velocity increase within the gap as the speed increases. However, with the increase in speed, the pressure distribution and flow velocity within the band gap remain almost the same. In addition to speed changes, it is observed that the pressure within the gap and the flow velocity within the passages are also related to the head, especially in the condition of maximum head, where this relationship becomes more noticeable.

An Experimental Investigation Of Local Thermo-Fluidic Heat Transfer In A U-Shaped Mini-Channel Sink

This study investigates experimentally a heated U-shaped mini-channel heat sink using Infrared Thermography and Particle Image Velocimetry for a water coolant flow of Reynolds numbers of 280, 650, and 1350 (based on the hydraulic channel diameter). The choice of this cell geometry is based on its role as a simplified unit of a serpentine heat exchanger, which is proved to be one of the most promising for cooling processes. The use of the infrared camera allows the detection of temperature fields on top of the external surface of the cell. Therefore, aiming to derive the temperature distribution on the channel roof, a dedicated transfer function is implemented. Moreover, we employed the lumped capacitance model for thermal analysis on both infrared measurements and thermocouple data. The latter are recorded to capture the cooling process of the aluminium base and water temperature at the end of the outlet tube. As a result, thermal transient rate, cooling magnitude and equilibrium temperature are obtained. These parameters indicate that higher Reynolds numbers correspond to increased thermal transient rates, enhanced cooling effects, and lower equilibrium temperatures. A non-uniform distribution of heat transfer along the channel is reported, with the most efficient cooling area localized close to the first 90-degree corner. These findings are consistent with numerical simulations and previous experimental observations. PIV results reveal the presence of two fluid acceleration zones following both 90-degree corners, which contribute to improve the water cooling ability in their respective regions. Additionally, the formation of two recirculating bubbles is reported at the inner wall from corners vertices, whose intensity is dependent on Reynolds number, pushing the main flow towards the outer channel wall and reducing the local heat transfer. Turbulent kinetic energy distributions are also investigated, pointing out the presence of intense areas that better match with regions of minimum equilibrium temperature than maximum velocity zones. This suggests the presence of local turbulent unsteadiness and three-dimensional phenomena, which contributes significantly to cooling enhancement.

Direct numerical simulation of supersonic boundary layer transition induced by gap-type roughness

The transition of the supersonic boundary layer induced by roughness is a highly intricate process. Gaining a profound understanding of the transition phenomena and mechanisms is crucial for accurate prediction and control. In this study, to delve into the flow mechanisms of a transition in a supersonic boundary layer induced by the medium gap-type roughness, direct numerical simulation is employed to capture and analyze the transition process. Research indicates that as the flow over the flat plate passes the gap, the spanwise convergence effect leads to the formation of both upper and lower counter-rotating vortex pairs. As the flow progresses, these counter-rotating vortex pairs in the central region exhibit attenuation, with streamwise vortices developing on both sides. At a certain downstream distance, the boundary layer becomes unstable, triggering the formation of streamwise vortex legs. These streamwise vortex legs undergo further evolution, transforming into hairpin vortices and leg-buffer vortices. The formation of the central low-speed zone downstream of the roughness element is mainly attributed to the lift-up effect of the low-speed flow propelled by the central counter-rotating vortex pairs. The low-speed streaks on both sides are primarily influenced by the streamwise vortices. Through a meticulous analysis of the turbulent kinetic energy distribution and its generation mechanisms during the transition phase, this study infers that the primary sources of turbulent kinetic energy are the hairpin vortices, leg-buffer vortices, and their consequent secondary vortices. Combined with modal analysis, the study further elucidates the generation and breakdown of hairpin and leg-buffer vortices.

Numerical evaluation of the bubble dynamic influence on the characteristics of multiscale cavitating flow in the bluff body wake

Unsteady cavitating flow around the bluff body widely existed in practical engineering fields. This paper aims to investigate the physics involved in the multi-scale cavitating flow in the wake of a wedge-shaped bluff body, with special emphasis on the bubble effects. Numerical simulation is conducted using the traditional Eulerian-Eulerian (E-E) and newly developed Eulerian-Lagrangian (E-L) methods in OpenFOAM. It is found that, compared with the experimental results, the E-L method can predict more accurate cavitation characteristics than the E-E method due to the contribution of discrete bubbles. Bubbles can significantly influence the behaviors of the multi-scale cavitating flow. Specially, analysis of pressure fluctuations indicates that the bubbles induce a stronger power spectral density in the middle- and high-frequency regions. With the bubble effects considered, the vortex structure is stretched and more extensive in the near wake regions. The strength of time-averaged vorticity distribution decreases in the far wake region. Further analysis of the vortex transport equation shows that bubble dynamics significantly increase the intensity of the stretching term by enhancing the spanwise velocity fluctuations. The intensity of the baroclinic torque term predicted by the E-L method is higher than that by the E-E method near the center line due to the influence of bubbles. On the other hand, the analysis of turbulent kinetic energy distribution indicates that bubbles can induce turbulence by increasing cross-stream velocity fluctuations. The increment of the shear Reynold stress, u′xu′y‾, suggests that the bubbles intensify the coupling between the streamwise and cross-stream velocity fluctuations.

Analysis of the airflow features and ventilation efficiency of an Ultra-Clean-Air operating theatre by qDNS simulations and experimental validation

Ultra-Clean-Air (UCA) operating theatres aim to minimise surgical instrument contamination and wound infection through high flow rates of ultra-clean air, reducing the presence of Microbe Carrying Particles (MCPs). This study investigates the airflow patterns and ventilation characteristics of a UCA operating theatre (OT) under standard ventilation system operating conditions, considering both empty and partially occupied scenarios. Utilising a precise computational model, quasi-Direct Numerical Simulations (qDNS) were conducted to delineate flow velocity profiles, energy spectra, distributions of turbulent kinetic energy, energy dissipation rate, local Kolmogorov scales, and pressure-based coherent structures. These results were also complemented by a tracer gas decay analysis following ASHRAE standard guidelines. Simulations showed that contrary to the intended laminar regime, the OT’s geometry inherently fosters a predominantly turbulent airflow, sustained until evacuation through the exhaust vents, and facilitating recirculation zones irrespective of occupancy level. Notably, the occupied scenario demonstrated superior ventilation efficiency, a phenomenon attributed to enhanced kinetic energy induced by the additional obstructions. The findings underscore the critical role of UCA-OT design in mitigating MCP dissemination, highlighting the potential to augment the design to optimise airflow across a broader theatre spectrum, thereby diminishing recirculation zones and consequently reducing the propensity for Surgical Site Infections (SSIs). The study advocates for design refinements to harness the turbulent dynamics beneficially, steering towards a safer surgical environment.

Potential improvement in combustion performance of a natural gas rotary engine mixed with hydrogen by novel bluff-body

Hydrogen/natural gas blends fuel is considered one of the ideal alternative fuels for improving the thermal efficiency and reducing carbon emissions of rotary engine. In order to further enhance the combustion and power performance of rotary engine, a new method of the setting of bluff bodies in the cylinder was proposed. The influence of bluff-body settings in the cylinder on the combustion, power performance, and NO generation was numerically studied under different ignition timings. The results indicated that in-cylinder bluff-body settings could influence flame propagation by affecting the turbulent kinetic energy and mixture distribution during the process from the late compression stroke to the combustion stroke. Further, for any fixed bluff-body shape in the cylinder, there is a trade-off relationship between the non-blockage ratio and squish velocity at the cylinder block center section as the ignition timing is progressively advanced or delayed. Consequently, considering the above trade-off relationship, the triangular slotted bluff-body in combination with an ignition timing of 30° CA (BTDC) could be used to achieve the maximum improvement in the combustion and power performance of rotary engine. The peak pressure exhibited a growth of 4.83%, and the indicated mean effective pressure increased by 1.46%.

Numerical Analysis of Three Vertical Axis Turbine Designs for Improved Water Energy Efficiency

A hydrokinetic turbine with a vertical axis is specifically designed to harvest the kinetic energy from moving water. In this study, three vertical axis water turbines, namely Gorlov, Darrieus, and Savonius turbines, were compared for their efficiency via numerical modeling for steady-state conditions via the ANSYS 2022 R2 Fluent model. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) was implemented with an SST k-ω turbulence model. The dynamic mesh technique, which allows modeling according to changes in angular velocity at each time step, was used to simulate flow around the turbines for six different velocities (from 0.5 to 3 m/s). The efficiency of the turbines was compared and the results were analyzed. The pressure, velocity, and turbulence kinetic energy distributions around the rotor were measured at different rotational angles and results indicated a wider operating range for the Darrieus and Gorlov turbines compared to the Savonius turbine. The highest power coefficient of 0.293 was achieved in the model featuring a Darrieus turbine, corresponding to a TSR value of 1.34, compared to 0.208 for the Gorlov and 0.257 for the Savonius turbine, at TSR values of 1.3 and 1.06, respectively. Numerical modeling results pointed to a significantly higher self-starting capacity for the Savonius turbine compared to the others.

Study of dielectric-based thermal management of second-life battery packs with rectangular vortex generators

The performance of lithium-ion battery (LiB) is influenced by the operational temperature. The thermal management of the battery module depends upon the interaction between coolant and battery surface. The study focuses on analysis of vortex interactions as a commercial dielectric coolant (FC 3283) circulates within battery module. The analysis indicates that the arrangement reduces the maximum average temperature by 26 °C in comparison with the conventional methods. However, a maximum temperature difference of 4 °C persists at final row of battery cells. Therefore, the vortex generators (V.G.) are deployed to alter the flow behavior to achieve uniform cooling of LiB. Rectangular V.G. alleviates the temperature difference by stretching primary vortices. The V.G.s promote smaller induced vortices, enabling a multiscale distribution of turbulent kinetic energy, reducing the concentration of turbulence near central region of the cell. The induced vortices ensure uniform heat transfer along the cell length. Furthermore, a 15% increase in vorticity magnitude and a 33% rise in an average Nusselt number in the region near the last-row cells is achieved. Overall, employment of V.G.s results in a 2.5 °C reduction in maximum cell temperature difference. A novel metric, the operational effectiveness factor (OEF), is coined to assess the combined effect of heat transfer enhancement and additional pumping requirements resulting from the different positions of the V.G. A high OEF value implies the ability of the configuration to maintain a more uniform cell temperature while ensuring lower parasitic power. Middle V.G. configuration achieved highest OEF of 1.35, while bottom V.G. configuration exhibited lowest OEF of 1.11.

The numerical investigation of turbulence and scour interaction around the permeable groynes at the channel bend

Turbulence, particularly Reynolds Stress, plays a significant role in the flow field surrounding groynes, causing local scour. A limited number of studies have comprehensively analyzed the flow and turbulence structures encompassing a series of groynes in channel bends. This study numerically investigated the interplay between turbulence, sediment deposition, and scouring in a sharp channel bend with permeable groynes. The results show that the inner bank maintained high velocity, while permeable groynes decreased longitudinal velocity near the outer bank. Implementing permeable groynes structures reduced bottom velocity and increased flow separation. Turbulent kinetic energy distribution across the bend, particularly streamwise, influenced scour development more than vertical motion.

Numerical Investigations of Outer-Layer Turbulent Boundary Layer Control for Drag Reduction Through Micro Fluidic-Jet Actuators

Drag reduction through turbulent boundary layer control (TBLC) is an essential way to develop green aviation technologies. Compared with traditional approaches for drag reduction, turbulence drag reduction is a relatively new technology, particularly for skin friction drag reduction, and it is becoming a hotspot problem worldwide. This paper focuses on the research of micro fluidic-jet actuators used for outer-layer boundary layer control with high-performance computing (HPC). This study aims to reduce turbulent drag by reshaping the flow structure within the turbulent boundary layer. To ensure the calculation accuracy of the core region and reduce the consumption of computing resources, a zonal LES/RANS strategy and WMLES method are proposed to simulate the effects of fluidic-actuators for outer-layer boundary control, in which high-performance computing has to be involved. The studies are performed on the classical zero-gradient turbulent flat plate cases, in which three different control strategies named “W-control,” “V-control,” and “VW-control” are used and compared to study the effects of drag reduction under a low Reynolds number at Reτ = 470 and a higher Reynolds number at Reτ = 4700. The mechanism for drag reduction is analysed via a pre-multiplied spectral method and a parallel dynamic mode decomposition (DMD) method. The results show that the present approach can effectively simulate the outer-layer turbulent boundary control where the “V-control” with the fluidic-jet actuator array behaves well to achieve an average drag reduction (DR) rate of more than 5% for the high Reynolds number case of the flat plate boundary layer. The high Reynolds shear stress and turbulent kinetic energy distribution in the boundary layer region show an obvious uplift under the effects of actuators, which is the main mechanism for drag reduction.

Roughness effects on compressible turbulent boundary layers under different Mach numbers and wall temperature conditions

Compressible turbulent boundary layers over a zero-pressure gradient flat plate with three-dimensional sinusoidal roughness are simulated by direct numerical simulation. The roughness effects on surface drag, velocity transformation, and turbulence fluctuation characteristics are analyzed in a wide range of Mach numbers (Ma∞ = 2.25–7.25) and different ratios of wall-to-recovery temperature (Tw/Taw = 0.43 and 0.84) conditions. It is found that the roughness significantly amplifies the surface drag coefficient due to the extra pressure drag induced by roughness, and the relative increase in surface drag induced by the roughness rises by 31.1% when Ma∞ changes from 2.25 to 7.25. Current compressible velocity transformations cannot make the logarithmic region of velocity profiles independent of Tw/Taw conditions for rough cases due to the strong wall heat transfer effect below roughness peak. Therefore, a new velocity transformation (Uρt+) is proposed to make the logarithmic region of Uρt+ profiles and roughness induced a downward shift of Uρt+ profiles (ΔUρt+) in a logarithmic region independent of Ma∞ and Tw/Taw conditions. Further numerical experiments validate that, in hypersonic boundary layers, the relation between ΔUρt+ and equivalent sand-grain roughness height Reynolds number still satisfies the roughness function proposed earlier for incompressible flows. Moreover, roughness significantly changes the distribution of mean turbulent kinetic energy (TKE) in compressible turbulent boundary layers: TKE is suppressed at the bottom of roughness, while reaching its maximum at the roughness peak, which is 50%–60% larger than that in smooth case. Finally, the expansion/compression wave patterns induced by roughness alter the turbulence fluctuations in outer layer.

Research on the Internal Flow Difference between Peak and Valley Conditions of Water Jet Propulsion Pump during Working at Hump Region

When we tested the water jet propulsion pump, we found that there were significant vibrations in the pump, especially at small flow points that deviated from the design conditions. The water jet propulsion pump is a mixed-flow pump with guide vane, which is commonly employed for water jet propulsion. However, the guide vane mixed-flow pump is susceptible to a phenomenon known as “hump”, which can cause flow disturbances, increased vibration, and noise when the pump operates within the hump region. According to the vibration phenomenon found in our experiment, the mechanism of vibration needs to be revealed. This study focuses on vorticity and turbulence distributions of a mixed flow water jet propulsion pump under the valley and peak operating conditions of the hump region. The research is conducted using experimental and numerical simulation methods. The SST k-ω turbulence model is employed for turbulence calculations. The experiments are conducted on a closed test rig for axial (mixed) flow pumps. A comparison of experimental and numerical simulation results of hydraulic performance curves are conducted to validate the accuracy of the numerical simulation. Cavitation flow structures of the critical cavitation stage under valley conditions and under peak conditions are compared. A comparative analysis is conducted to examine the differences in internal vortex core distribution and turbulence kinetic energy distribution between the valley and peak operating conditions when working within the hump region. The pressure and velocity vectors of the pump impeller blades and the velocity streamline distribution between the impeller and the guide vane blades are compared. To further analyze the flow state in different flow channels under valley and peak conditions, the streamline distribution at Span = 0.5 in the impeller and diffuser basin is extracted. This study provides theoretical foundations and technical support for the design of high-performance, low-vibration water jet propulsion pumps.

Direct numerical simulation of laminar, transitional and turbulent radially inward flow between closely spaced corotating disks

This study describes direct numerical simulation (DNS) of radially inward spiralling corotating disk flow with a narrow disk spacing, using the open source solver Nek5000 and the supercomputer SuperMUC-NG at Leibniz Supercomputing Centre. Knowledge about laminar and turbulent regime boundaries in this flow scenario is important for modelling and performance prediction of friction turbines. Simulations are performed in differently sized sections of the flat annulus that is formed by two opposing corotating disk surfaces. Three sets of operating conditions are covered, from the laminar, transitional and turbulent region of a previously determined stability chart respectively. Directly downstream of the inlet boundary, the flow is artificially perturbed with a random body force acting normal to the disk surfaces. Fourier analysis of the DNS flow field reveals that the artificial perturbation is dampened across all wavenumbers for the laminar conditions, while at the transitional conditions a small range of modes is weakly amplified towards the outlet. The identified unstable modes were previously correctly predicted by linear stability analysis. Comparison to experimental velocity profile measurements from a previous study at the same transitional operating conditions suggests strongly perturbed flow during the experiment. For inflow conditions leading to turbulent flow, average velocity profiles from DNS coincide with those from experiment and from commercial fluid simulation software with turbulence modelling (ANSYS CFX). Close to the walls, turbulent dissipation and turbulent kinetic energy distributions do not agree with the ANSYS CFX results. Friction Reynolds number settles at about 118 after turbulent flow has developed from the initial perturbation. Two point correlations and corresponding energy spectra are presented.

Numerical Simulation of Turbulent Structure and Particle Deposition in a Three-Dimensional Heat Transfer Pipe with Corrugation

When colloidal particles are deposited in a heat transfer channel, they increase the flow resistance in the channel, resulting in a substantial decrease in heat transfer efficiency. It is critical to have a comprehensive understanding of particle properties in heat transfer channels for practical engineering applications. This study employed the Reynolds stress model (RSM) and the discrete particle model (DPM) to simulate particle deposition in a 3D corrugated rough-walled channel. The turbulent diffusion of particles was modeled with the discrete random walk model (DRW). A user-defined function (UDF) was created for particle–wall contact, and an improved particle bounce deposition model was implemented. The research focused on investigating secondary flow near the corrugated wall, Q-value standards, turbulent kinetic energy distribution, and particle deposition through validation of velocity in the tube and particle deposition modeling. The study analyzed the impact of airflow velocity, particle size, corrugation height, and corrugation period on particle deposition efficiency. The findings suggest that the use of corrugated walls can significantly improve the efficiency of deposition for particles less than 20 μm in size. Specifically, particles with a diameter of 3 μm showed five times higher efficacy of deposition with a corrugation height of 24 mm compared to a smooth surface.

Study of non-constant local cavitation suppression in micro-wedge structure

To alleviate the negative impacts of cavitation phenomenon on hydrodynamic machinery, such as mechanical vibration and noise, a hydrofoil model is established based on the micro-wedge structure, and numerical simulation of the hydrofoil is carried out by using the modified turbulence model k–omega shear stress transport (SST k–ω) to analyze the lift coefficient of drag, pressure pulsation, cavitation volume fraction, cavitation volume morphology, and turbulent kinetic energy distribution, and to reveal the inhibition of cavitation mechanism of the chord direction of the placement and the height of the micro-wedge structure coupling. The results show that the height of the micro-wedge structure determined by the thickness of the boundary layer is an important parameter affecting the cavitation performance, and the micro-wedge structure with a smaller height will produce better cavitation suppression, and the height of 0.05 mm has the best suppression effect, and the suppression of the main frequency of pulsation and the amplitude of pulsation shows a positive effect. The micro-wedge structure arranged on the hydrofoil can delay the change cycle of the cavitation volume to different degrees, in which the chordwise position of 3.5 mm has the best cavitation suppression effect, and the cavitation suppression rate is about 16.7%.

Numerical Study and Structural Optimization of Impinging Jet Heat Transfer Performance of Floatation Nozzle

A floatation nozzle can effectively transfer heat and dry without touching the substrate, and serves as a vital component for heat transfer to the substrate. Enhancing the heat transfer performance, and reducing its heat transfer unevenness to the substrate play an important role in improving product quality and reducing thermal stress. In this work, the effects of key structural parameters of the floatation nozzle on the heat transfer mechanism are systematically investigated by means of a numerical simulation of computational fluid dynamics. The findings demonstrate that the secondary vortex structure induced by the floatation nozzle with effusion holes increases heat transfer performance by 254.3% compared with the nozzle without effusion holes. The turbulent kinetic energy and temperature distribution between the jet and the target surface are affected by the jet angle and slit width respectively, which change the heat transfer performance of the float nozzle in different degrees. Furthermore, to improve the comprehensive heat transfer performance of the floatation nozzle structure, taking into account the average heat transfer capability and heat transfer uniformity, the floatation nozzle’s design is optimized by the application of the response surface method. The comprehensive heat transfer performance is increased by 26.48% with the optimized design parameters. Our work is of practical value for the design of floatation nozzles with high heat transfer performance to improve product quality in industrial systems.

Numerical study on the gaseous radioactive pollutant dispersion in urban area from the upstream wind: Impact of the urban morphology

The radioactive pollutant could migrate to the downstream urban area under the action of atmospheric dispersion due to the turbulent mixing under actual pollution accidents. A scenario in which radioactive contaminants from the upstream (for example, a nearshore nuclear power plant accident) migrates to the downstream urban blocks have been considered in this study. Numerical simulations using computational fluid dynamics (CFD) are then conducted to investigate the effects of the urban morphology (building packing density and layout) on the atmospheric dispersion of radioactive pollutants in this scenario. The building packing density and structure can significantly affect urban areas' mean flow pattern and the turbulent kinetic energy (TKE). The flow pattern and the TKE distribution influence the radioactive pollution dispersion. It is found that the radioactive pollution at the urban canyons is significantly affected by the vertical transport at the canyon. A comparison of the distributions of radioactive and traditional non-radioactive pollutants is also provided.

Vortex dynamics characteristics in the tip region based on Wray–Agarwal model

In order to solve the blockage effect and energy dissipation phenomenon caused by cavitation in the low-pressure vortex core region, this paper analyzes the spatial evolution of vorticity intensity and turbulent kinetic energy intensity under different cavitation conditions based on the Wray–Agarwal (WA) model. First, the tip leakage flow characteristics are studied, the evolution of vorticity and vorticity intensity is analyzed, then the distribution of turbulent kinetic energy distribution in the blade tip region is studied, and finally, the vorticity transport characteristics of the tip region are analyzed. It is found that the tip leakage rate is less affected by the vortex cavitation of the tip leakage, and there is a strong interaction between the leakage flow at the tip leading edge and the trailing edge, and the separation vortices and low-speed regions formed in the end-wall region cause blockage of the flow passage. Low pressure causes cavitation to cover most regions of the suction surface, inhibiting the formation and development of the tip leakage vortices. The distribution range of high turbulent kinetic energy region is almost the same as that of high-vorticity region, and there is a positive correlation between the two intensities. Severe cavitation causes the high turbulent kinetic energy region at the outlet of the flow passage to develop in the radial and axial directions of the impeller, which increases the turbulent dissipation and energy loss. The change of vorticity transport intensity caused by cavitation is mainly reflected in the expansion contraction term, and the Coriolis force term plays a dominant role in the vorticity transport process. This paper provides a reference for further improving the performance of mixed-flow pumps.

Numerical simulation of a novel small water turbine generator for installation in a deep-flow hydroponics system

Hydroponics systems are crucial for providing sustainable and cost-effective choices when soils are unavailable for conventional farming. The application of water flow rates within hydroponics systems to generate electricity is another idea that can be used in the field of power generation. This paper presents the determination of the mechanical power efficiency of a novel small water turbine generator for use in a deep-flow hydroponics system (DFT). The system was designed, analysed, and calculated for the most suitable geometries of the water pipeline inlet, DFT system, main structure of the PVC Tee Pipe Fitting, and a water turbine wheel using computational fluid dynamics software. The diameter of the water turbine wheel in this research was 48 mm. A DFT hydroponic system was modelled for the purposes of this research. We conducted a numerical simulation with water flow rates of 6, 8, and 10 l/min to evaluate the turbulent kinetic energy distribution in the DFT hydroponic system. The numerical simulation employed the control volume methodology, and the k-epsilon turbulence model was applied to obtain the computational conclusions. The highest torque and power that a novel small water turbine for installation in a DFT system could generate at a maximum flow rate of 0.000167 m3/s were 0.082 N.m. and 1.9568 watts, respectively. The forces generated by the fluid's speed and pressure can then be transferred to the building process of a novel small water turbine wheel. The FEA numerical result shows that the maximum value of the total deformation at a wheel speed of 228 rpm is 7.0 x 10-5 mm. The numerical simulations used in this study could potentially be used to further develop prototypes for innovative miniature water turbines that generate commercial electricity.

Numerical Study of Bottom Shape Effect on the Mixing for Stirred Tank

Abstract In this work, computational fluid dynamics (CFD) was used to investigate the effect of the bottom shape on the flow field and mixing characteristics in an agitated vessel stirred by six-pitched blade turbine (PBT6). The simulation was based on the resolution of the Navier-Stokes equations using standard k-ε turbulence model. Hydrodynamic behavior of the stirred vessel with four types of bottom shapes was investigated, a flat bottom and three different semi-elliptical bottoms. The results show reasonably satisfactory agreement with the experimental data. The CFD simulation also showed that the semi-elliptical bottom shapes had a significant influence on the velocity profiles and on the turbulent kinetic energy distributions of the local flow generated at the bottom region of the vessel.