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In a power plant that uses seawater as a coolant, a debris filter (DF) is required to remove foreign substances from the seawater, and differential pressure leads to a decrease in the coolant flow rate, leading to a decrease in the power generation efficiency. In this study, an analysis was performed for the cases wherein the initial flow velocity conditions of the DF used in the condenser tube cleaning system (CTCS) were 1.5 m/s, 2.0 m/s, and 2.5 m/s using Ansys Fluent 2021, and the flow characteristics were identified. The flow and differential pressure characteristics of a CTCS with an installed DF were considered in a comparative analysis of the velocity, pressure, and turbulence kinetic energy (TKE) distributions. The results confirmed that a vortex was generated in the pipe with the DF, apparently due to the collision of the flow with the bracket of the DF. As the flow rate increased, the range of the vortex increased, causing a loss in flow. [ABSTRACT FROM AUTHOR]

In a power plant that uses seawater as a coolant, a debris filter (DF) is required to remove foreign substances from the seawater, and differential pressure leads to a decrease in the coolant flow rate, leading to a decrease in the power generation efficiency. In this study, an analysis was performed for the cases wherein the initial flow velocity conditions of the DF used in the condenser tube cleaning system (CTCS) were 1.5 m/s, 2.0 m/s, and 2.5 m/s using Ansys Fluent 2021, and the flow characteristics were identified. The flow and differential pressure characteristics of a CTCS with an installed DF were considered in a comparative analysis of the velocity, pressure, and turbulence kinetic energy (TKE) distributions. The results confirmed that a vortex was generated in the pipe with the DF, apparently due to the collision of the flow with the bracket of the DF. As the flow rate increased, the range of the vortex increased, causing a loss in flow.

Abstract The standard model (e.g., Hocking in Earth Planets Space 51:525–541, 1999), $$\varepsilon = c_{0} \sigma^{2} N$$ ε=c0σ2N , (where $$\sigma$$ σ is the radar spectral width assumed to be equal to vertical turbulence velocity fluctuation $$\sqrt {\overline{{w^{2} }} }$$ w2¯ , N is the buoyancy frequency, and c 0 is a constant), derived from Weinstock (J Atmos Sci 35:1022–1027, 1978; J Atmos Sci 38:880–883, 1981) formulation, has been used extensively for estimating the turbulence kinetic energy (TKE) dissipation rate $$\varepsilon$$ ε under stable stratification from VHF radar Doppler spectral width $$\sigma$$ σ . The Weinstock model can be derived by simply integrating the TKE spectrum in the wavenumber space from the buoyancy wavenumber $$k_{\text{B}} = \frac{N}{\sigma }$$ kB=Nσ to $$\infty$$ ∞ . However, it ignores the radar volume dimensions and hence its spatial weighting characteristics. Labitt (Some basic relations concerning the radar measurements of air turbulence, MIT Lincoln Laboratory, ATC Working Paper NO 46WP-5001, 1979) and White et al. (J Atmos Ocean Technol 16:1967–1972, 1999) formulations do take into account the radar spatial weighting characteristics, but assume that the wavenumber range in the integration of TKE spectrum extends from 0 to $$\infty$$ ∞ . The White et al. model accounts for wind speed effects, whereas the other two do not. More importantly, all three formulations make the assumption that k −5/3 spectral shape of TKE spectrum extends across the entire wavenumber range of integration. It is traditional to use Weinstock formulation for $$k_{\text{B}}^{ - 1} < 2a,2b$$ kB-1 2a,2b$$ kB-1>2a,2b . However, there is no need to invoke these asymptotic limits. We present here a numerical model, which is valid for all values of buoyancy wavenumber $$k_{\text{B}}$$ kB and transitions from $$\varepsilon \sim\sigma^{2}$$ ε∼σ2 behavior at lower values of $$\sigma$$ σ in accordance with Weinstock’s model, to $$\varepsilon \sim\sigma^{3}$$ ε∼σ3 at higher values of $$\sigma$$ σ , in agreement with Chen (J Atmos Sci 31:2222–2225, 1974) and Bertin et al. (Radio Sci 32:791–804, 1997). It can also account for the effects of wind speed, as well the beam width and altitude. Following Hocking (J Atmos Terr Phys 48:655–670, 1986, Earth Planets Space 51:525–541, 1999), the model also takes into account contributions of velocity fluctuations beyond the inertial subrange. The model has universal applicability and can also be applied to convective turbulence in the atmospheric column. It can also be used to explore the parameter space and hence the influence of various parameters and assumptions on the extracted $$\varepsilon$$ ε values. In this note, we demonstrate the utility of the numerical model and make available a MATLAB code of the model for potential use by the radar community. The model results are also compared against in situ turbulence measurements using an unmanned aerial vehicle (UAV) flown in the vicinity of the MU radar in Shigaraki, Japan, during the ShUREX 2016 campaign.

In the present study, we performed an extensive laboratory investigation to quantify the turbulence characteristics of 45° inclined dense jets using Particle Image Velocimetry (PIV) over a wide range of Densimetric Froude Number. The objective was to provide benchmark data to guide high resolution turbulence numerical simulations for dense jets in the future. The PIV measurements were sampled at a relatively high frequency of 50 Hz, which enabled the analysis of second order turbulence statistics as well as the turbulence kinetic energy spectrum (including the inertial subrange) along the curvilinear jet trajectory, which has hitherto not been reported. The measurements showed that the spectral profile was flat near the discharge port with the potential core, since the Kelvin-Helmholtz shear-induced turbulence at the jet boundaries had not fully penetrated to the core. The spectral profile then evolved along the trajectory with progressive steepening towards the higher frequencies, and a fully-developed profile appeared beyond the terminal rise with a clearly identifiable inertial subrange for the energy cascade. In parallel, we also performed numerical simulations using the Large Eddy Simulations (LES) approach with the Dynamic Smagorinsky sub-grid model for the specific discharge conditions as in the experiments. The LES approach followed that of Zhang et al. (Environ Fluid Mech 16(1):101-121, 2016, J Hydro Environ Res 15:54-66, 2017) using GCI as the grid convergence criteria. The comparison showed that the time-averaged first order mixing characteristics of the inclined dense jet can be simulated reasonably well comparing to the experimental data. In terms of the turbulence kinetic energy spectrum, the low frequencies of the production range were also well captured by the simulations. However, the simulated transitional spectra towards the inertial subrange decayed substantially faster than the experiments. The discrepancy was attributed to the fact that the grid resolution was not sufficiently fine in the simulations (which were constrained by the available computational resources and time), such that stratified effects remained present inside the sub-grids producing additional turbulence energy that were not represented by the Dynamic Smagorinsky model. Thus, the numerical investigation showed that further improvement in sub-grid models that can incorporate the stratified effects would be desirable in the future for engineering simulations. [ABSTRACT FROM AUTHOR]

Solid particles can be transported along a pipeline in the form of trains of individually shaped lenticular deposits (LDs) when the concentration of solids is less than 1 vol% and the transport velocity is below the critical value required for full suspension. Such special bed transport, observed as rippled sand dune patterns, may occur in petroleum production lines transporting oil and gas produced from unconsolidated sand reservoirs under turbulent flow conditions, and during sediment transport by rivers and winds. The primary objective of this study was to investigate how the occurrence of lenticular bed deposits affects near-wall turbulent activities at the sand/fluid ("wavelike") interface and frictional pressure drop during pipeline transportation of solids. Particle image velocimetry (PIV) measurements were used to quantify the velocity field, the turbulence kinetic energy (TKE), and the coherent structures associated with surface morphology change and LD formation near the bed deposits/fluid interface. A 7-8% reduction in frictional pressure drop was consistently observed during the transition from continuous sand bed to LDs. Results also indicate that the formation of naturally shaped LDs reduces the intensity and frequency of near-wall turbulent coherent structures (burst-sweep events). Moreover, TKE associated with flow over the LDs was found to be lower than that of continuous bed and water (only) flow. [ABSTRACT FROM AUTHOR]

The main objectives of this paper are to investigate the performance and emissions of a compression ignition (CI) engine run with biodiesel when guide vanes are installed in front of the intake runner. The simulation method is used to determine the optimum vane angle by analyzing the turbulence kinetic energy (TKE), velocity, vorticity and swirling strength developed by the guide vanes using varied angles between 3° and 60°. Based on the simulation results, the airflow characteristics were mostly improved between vane angles of 25.8° and 42.9°, and 35° was found to be the optimum vane angle. Based on the simulation results, five guide vane models with the vane angles varied between 25° and 45° were fabricated, installed and tested one by one on a generator CI engine run constantly at 1500 rpm. The experimental results of brake-specific fuel consumption (BSFC), engine efficiency, torque, air/fuel ratio and exhaust temperature as well as carbon dioxide (CO 2 ), oxygen (O 2 ), nitrogen oxide (NO x ), carbon monoxide (CO) and hydrocarbon (HC) emissions were presented and discussed. Based on the experimental results, the simulation results were validated. This research also found that using guide vanes improved the engine performance and reduced the exhaust emissions in general when compared with the engine run on biodiesel without guide vanes. Finally, the 35° vane angle was found to be the optimum vane angle as it had the best results of brake specific fuel consumption (BSFC), engine efficiency, and the emissions of NO x and HC. [ABSTRACT FROM AUTHOR]

This research investigated the effect of guide vanes installed in front of the intake runner of a compression ignition (CI) engine run with biodiesel. Firstly, the simulation method used SolidWorks and ANSYS-CFX to determine the optimum vane height of the guide vane from among 10 variation models with different vane heights between 0.10 and 1.00 times the radius of the intake runner ( R ) (called 0.10 R for 0.10 times R , etc.). The simulation results of in-cylinder turbulence kinetic energy (TKE), velocity, vorticity and swirling strength were presented and discussed. Based on these results, 0.70 R was found to be the optimum guide vane height as it improved TKE, mostly improved velocity and partly improved vorticity, swirling strength within the fuel injection region from crank angles before the start of injection up to the first part of expansion stroke. Five guide vane models (0.10 R , 0.30 R , 0.50 R , 0.70 R , and 0.90 R ) were then fabricated and tested on a CI generator diesel engine run with biodiesel coupled with a load bank. Based on the experimental results, 0.70R guide vane model showed the most improvements as it reduced the brake-specific fuel consumption (BSFC), carbon monoxide (CO) and hydrocarbons (HC) as well as increased engine efficiency compared to the run without the guide vanes when ran with biodiesel. Hence, this research found that using guide vanes can improve the performance and reduce the emissions of CI engine run with biodiesel. [ABSTRACT FROM AUTHOR]

• Two SSTC models in submerged vegetation flow are derived based on SSTR and energy concept, respectively. • The flow above vegetation transports the majority of the suspended sediment, which increases with discharge and vegetation density. • An increase in TKE dissipation term due to submerged vegetation leads to a decrease in SSTC, which is why submerged vegetation promotes sediment deposition. Quantifying suspended sediment transport capacity (SSTC) in submerged vegetation flow is vital to predicting the topographical changes of a river channel with vegetation and the effect of ecological restoration projects. Based on the definition of suspended sediment transport rate (SSTR) and the assumption that the energy maintaining sediment suspension (suspension work) comes from the turbulence kinetic energy (TKE) of flow, two models for estimating SSTC in submerged vegetation flow were proposed in this study. The SSTR-based model calculated SSTR by taking the depth-integral average of the product of local velocity and suspended sediment concentration and dividing it by discharge per unit width. The Energy-based model introduced suspension work to the double-averaging TKE budget equation as a sink term. That is to say, the production of TKE is used for sediment suspension and viscous dissipation. In the open channel without vegetation, a fixed proportion of the TKE production term is used to maintain the sediment suspension, but the proportion falls and is no longer a constant for the reason that the presence of submerged vegetation raises the viscous dissipation term. To represent this influence, an equivalent ratio coefficient was introduced. Thus, the SSTC model was derived. Then, a series of experiments in suspension capacity flow through submerged vegetation were carried out to verify the two models. Results showed that the two models could estimate the SSTC in flow with submerged vegetation well. Moreover, it was found that the suspended sediment is mostly transported by the water flow above the vegetation layer, and the proportion of which rises as discharge and vegetation density increase. Furthermore, compared with the bared-bed channel, the increase of TKE dissipation term in submerged vegetation flow leads to the decrease of SSTC, which is why submerged vegetation promotes sediment deposition. [ABSTRACT FROM AUTHOR]

A non-hydrostatic, Boussinesq, and three-dimensional large eddy simulation (LES) model was used to study the impact of the Earth's rotation on turbulence and the redistribution of energy in turbulence kinetic energy (TKE) budget. A set of numerical simulations was conducted, (1) with and without rotation, (2) at different latitudes (10°N, 30°N, 45°N, 60°N, and 80°N), (3) with wave breaking and with Langmuir circulation, and (4) under different wind speeds (5, 10, 20, and 30 m/s). The results show that eddy viscosity decreases when rotation is included, indicating that rotation weakens the turbulence strength. The TKE budget become tight with rotation and the effects of rotation grow with latitude. However, rotation become less important under Langmuir circulation since the transport term is strong in the vertical direction. Finally, simulations were conducted based on field data from the Boundary Layer and Air-Sea Transfer Low Wind (CBLAST-Low) experiment. The results, although more complex, are consistent with the results obtained from earlier simulations using ideal numerical conditions. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a comprehensive review of the challenges encountered in stereoscopic PIV measurements when applied to the characterization of complex and interacting systems of turbulent supersonic streamwise vortices. Emphasis is given to the proper selection of critical parameters, their impact on the observability of the flowfield of interest and the accuracy of the derived results. Specifically, the discussion is centered on the guidelines underlying the requirements related to the choice of the interrogation area, laser pulse separation time and flow tracers in response to the necessity to probe the coherent structures under the constraints imposed by the investigated flow. Peak locking and its impact on the accuracy of the experiment are addressed and indications are given on how to recognize the resulting errors. All the aforementioned parameters are also analyzed with respect to each other as an ideal selection of some of them often produces contrasting effects on the others, affecting the calculations of the flowfields. The design and the results of a stereoscopic PIV experiment for the characterization of interacting, turbulent streamwise vortices in a Mach 2.5 freestream are included in this work in order to provide a practical application of the selection process of the critical experimental parameters and highlight the identification of the aforementioned contrasting requirements. [Copyright &y& Elsevier]

The unsteady approaching flow (UAF) and its influence upon the flow pattern within street canyon are investigated from a perspective of mechanism in this study. Based on wind tunnel test (WTT) measurements, the boundary conditions for the approaching flow over 2D street canyons (H/W = 2.4) are described in continuous functions of reference velocity and height. The turbulence kinetic energy (TKE) profiles present a normal-log distribution in WTT; the turbulence eddy dissipation rate (TED) profiles are modified according to WTTs and basic governing equations. With a sinusoidally varying reference velocity, these novel boundary conditions are then applied to study the influence of UAF (with periodic sinusoidal fluctuations) upon the flow pattern within 2D street canyons. CFD simulations with proposed scenario agree well with WTT for steady and unsteady approaching flows regarding velocity magnitude, vortex position and TKE. UAF can also enhance street canyon's ventilation as pollutant decays faster than that under steady approaching flow. The proposed scenario is finally extended to the investigation of Re independence and shows the larger normalized TKE at the periphery prolongs the procedure of reaching Re independence. Once it reaches Re independence, the flow pattern under a larger TKE has a higher eddy centre and velocity magnitude. • Flows in 2D street (H/W = 2.4) under steady/unsteady inlet flows are studied by CFD. • Wind tunnel tests by PIV with periodic boundary are adopted to validate CFD data. • Global optimization method is used to reproduce steady/unsteady inlet flows in CFD. • Pollutant dispersion can be enhanced by unsteady approaching flow than steady type. • The Reynolds-number-independence and impacts of TKE at domain inlet are studied. [ABSTRACT FROM AUTHOR]

The standard model (e.g., Hocking in Earth Planets Space 51:525-541, 1999), ε=c0σ2N, (where σ is the radar spectral width assumed to be equal to vertical turbulence velocity fluctuation w2¯, N is the buoyancy frequency, and c0 is a constant), derived from Weinstock (J Atmos Sci 35:1022-1027, 1978; J Atmos Sci 38:880-883, 1981) formulation, has been used extensively for estimating the turbulence kinetic energy (TKE) dissipation rate ε under stable stratification from VHF radar Doppler spectral width σ. The Weinstock model can be derived by simply integrating the TKE spectrum in the wavenumber space from the buoyancy wavenumber kB=Nσ to ∞. However, it ignores the radar volume dimensions and hence its spatial weighting characteristics. Labitt (Some basic relations concerning the radar measurements of air turbulence, MIT Lincoln Laboratory, ATC Working Paper NO 46WP-5001, 1979) and White et al. (J Atmos Ocean Technol 16:1967-1972, 1999) formulations do take into account the radar spatial weighting characteristics, but assume that the wavenumber range in the integration of TKE spectrum extends from 0 to ∞. The White et al. model accounts for wind speed effects, whereas the other two do not. More importantly, all three formulations make the assumption that k−5/3 spectral shape of TKE spectrum extends across the entire wavenumber range of integration. It is traditional to use Weinstock formulation for kB-1<2a,2b (where a and b are radar volume dimensions in the horizontal and vertical directions) and White et al. formulation (without wind advection) for kB-1>2a,2b. However, there is no need to invoke these asymptotic limits. We present here a numerical model, which is valid for all values of buoyancy wavenumber kB and transitions from ε∼σ2 behavior at lower values of σ in accordance with Weinstock's model, to ε∼σ3 at higher values of σ, in agreement with Chen (J Atmos Sci 31:2222-2225, 1974) and Bertin et al. (Radio Sci 32:791-804, 1997). It can also account for the effects of wind speed, as well the beam width and altitude. Following Hocking (J Atmos Terr Phys 48:655-670, 1986, Earth Planets Space 51:525-541, 1999), the model also takes into account contributions of velocity fluctuations beyond the inertial subrange. The model has universal applicability and can also be applied to convective turbulence in the atmospheric column. It can also be used to explore the parameter space and hence the influence of various parameters and assumptions on the extracted ε values. In this note, we demonstrate the utility of the numerical model and make available a MATLAB code of the model for potential use by the radar community. The model results are also compared against in situ turbulence measurements using an unmanned aerial vehicle (UAV) flown in the vicinity of the MU radar in Shigaraki, Japan, during the ShUREX 2016 campaign. [ABSTRACT FROM AUTHOR]