Turbulent Kinetic Energy Distribution Research Articles

Turbulence and sediment deposition in a channel with floating vegetation

Floating canopies of vegetation alter the vertical profile of flow velocity within and below canopies, which in turn impacts sediment deposition below canopies. This study explored the impacts of channel-average velocity (U0), vegetation density (a), and relative flow depth (hg/H, where hg is the height of the free flow region below the floating canopy and H is the entire flow depth) on the longitudinal distributions of near-bed turbulent kinetic energy (TKE) and sediment deposition in a channel with a floating vegetation canopy. Below a floating canopy, sediment deposition was correlated with the near-bed TKE. For the low-density and low-velocity cases, sediment deposition was spatially uniform across the entire channel because the near-bed TKE was lower than the critical value for sediment resuspension. As the vegetation density and channel-average velocity increased, the near-bed TKE increased and surpassed the critical TKE, which caused resuspension and reduced deposition below the canopy relative to the upstream reference. For the same vegetation density and channel-average velocity, a lower relative flow depth (hg/H) produced a higher below-canopy depth-averaged velocity and near-bed TKE, resulting in less deposition below the canopy. A model was proposed for predicting the longitudinal evolution of near-bed TKE based on the predicted flow velocity below the canopy throughout the channel. The longitudinal evolution of deposition below a floating canopy was predicted by combining the predicted near-bed TKE with the deposition probability. The predicted near-bed TKE and deposition matched laboratory measurements. Finally, the proposed model can be used to predict the longitudinal profile of deposition below a real Eichhornia crassipes canopy.

Vertical flow structures on a vegetated immobile bed under wave-current conditions: Laboratory experiments

Natural revegetation alters local hydrodynamic conditions in coastal lagoons. To investigate vertical flow structures in revegetated lagoons, a series of flume experiments are implemented on an immobile bed with Phragmites australis by a certain staggered configuration. Six incident wave heights and five inflow discharges are considered. The experimental results demonstrate that wave dominates turbulent kinetic energy (TKE) distributions under wave-current conditions. Vegetation morphology plays an important role in wave-current-vegetation interactions, which regulates TKE distributions by diminishing wave effects within 70% of water depth especially (0.3 < z/h < 1). The increasing inflow discharge has positive effects on diminishment of wave effects, while the reduction of mean streamwise flow velocity is stable under the present vegetation configuration. Moreover, the practical values of vertical mean flow velocity can be obtained from the empirical equation, which includes wave effects by a quadratic polynomial relationship between the ratio of experimental values to theorical values (U/Up) and the relative wave height H0/h. Furthermore, two relationships are established between the reduction of mean streamwise flow velocity r and z/h, involving a logarithmical relationship in the lower layer (0 < z/h < 0.3), and a cubic polynomial relationship in the upper layer (0.3 < z/h < 0.7).

Numerical simulation of hydraulic characteristics and pollutant transport in the channels with different ice coverages

ABSTRACT In winter, rivers at high latitudes often freeze and an ice cover emerges at the free surface of the river. According to the coverage degree of the ice cover, rivers can be divided into free-flowing, partially frozen, and completely frozen. The presence of ice cover can greatly alter the hydraulic conditions of rivers, complicating the transport of pollutants in river channels. The distribution of pollutants in rivers with different ice coverages was simulated using the Detached Eddy Simulation (DES) model in this paper. The velocity distribution, the pollutant diffusion coefficient distribution, the turbulent kinetic energy distribution, and the vortex distribution with different ice coverages were analyzed. The velocity in the ice cover zone is at a lower rate than in the open flow zone. With the increase of the ice coverage, the turbulent kinetic energy of the ice cover area in partially frozen conditions gradually increases, which makes the water flow turbulence increase. The diffusion coefficient of pollutants in the ice cover area is greater than that in the open flow area, so pollutants disperse more quickly in the ice cover area. The turbulence energy and the diffusion coefficient have similar distribution characteristics beneath the ice cover. The presence of the ice cover promotes the movement of the vortex from the open flow area to the ice cover area, which may be the reason for the larger turbulence energy and the diffusion coefficient. The simulation results can provide a reference for ice disasters and water quality remediation.

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.

Suitability of 2D depth-averaged simulations to support predictions of cyprinids passage through Vertical Slot Fishways

Fishways are a key measure to recover longitudinal connectivity. Among them, Vertical Slot Fishways (VSFs) have undergone extensive studies. However, very few numerical studies have included coupled hydrodynamics and ecological simulations. We investigated the impact of using three-dimensional (3D RANS) and two-dimensional (2D SWE) flow simulations in a Eulerian Lagrangian Agent-based Model (ELAM) for VSFs. Spatial distribution of turbulent kinetic energy ( k ), velocity magnitude ( | u i | ) , and velocity strain rate ( S ij ) were evaluated. While the | u i | was consistent across simulations, k was overestimated by the 2D SWE simulations. The frequency of S ij highest values was different between 3D RANS and 2D SWE. Also, the influence of these variables on the agent’s cognitive response was inconsistent. 2D SWE displayed an influence of around 0%, 35%, and 25% for k , | u i | and S ij , respectively. 3D RANS resulted in percentages of around 80% of k , 10–20% of | u i | and 0–10% of S ij . All cases were validated, demonstrating that both approaches are suitable to reproduce experimental observations. We demonstrated that the 2D SWE might serve as a good input to simulate fish movement in VSF. Nonetheless, hydrodynamic variables’ influence on agents’ decision making might be biased from real fish experience.

Numerical Investigation on internal flow characteristics of a mixed-flow pump with Tandem malposed blades

Abstract Mixed-flow pump plays an important role in national major projects and national economic construction. In this paper, a mixed-flow pump is taken as the research object, and the internal flow characteristics and the distribution of turbulent kinetic energy in the pump under different malposed angles of blade are studied by using numerical simulation and blade modification method. The results show that the pump efficiency and head are higher when the tandem blade angles (α) are 15° and 45°, and the pump head is the largest at the α =15°, increasing by 4.37%. Meanwhile, the high-pressure area inside the impeller was large, which had a higher pressurization performance. Under the rated flow condition, the velocity curve of α =15° changes most gently, which is close to the prototype velocity curve, and the single hump zone is not obvious. The tandem malposed blades can restrain the velocity fluctuation and improve the flow field in the impeller. At α =45°, the turbulent kinetic energy dissipation and the velocity fluctuation were the smallest; the flow field was the most stable. The research results have reference significance for the optimal design and selection of mixed flow pump.

Hydrodynamic characterization of the surfacing attitude of the manned deep-sea submersible

Hydrodynamic characteristics of manned deep-sea submersibles are important for optimizing design, increasing safety, and improving handling and control. To study the hydrodynamic characteristics of manned deep-sea submersibles in different surfacing attitudes, this paper carries out hydrodynamic tests on the scaled-down simplified model of “Jiaolong” submersible of 1:36. The drag, lift, and pitching moment of the manned deep-sea submersible in different surfacing attitudes are obtained by six-component sensors, and the time-averaged streamlines, turbulence kinetic energy, normal velocity and Reynolds stress distribution are obtained by photographing the wake flow field of the submersible using PIV particle image velocimetry. The results show that compared with the vertical surfacing attitude, the drag decreased by 38.2%, the lift magnitude rose by 98.9%, the pitching moment decreased by 20.8%, the vortex disappeared in the stern wake area, and the maximum turbulent kinetic energy decreased by 33.6% when surfacing at a 30° rake angle.

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.