Kinetic Energy Profiles Research Articles

The Effect of the Number of Baffles on the Performance of Solar Updraft Tower: A Numerical Study

Enhancing the amount of flow field and heat transfer characteristic is an effective way to increase the performance of SUT plants. The velocity magnitude and heat transfer characteristic can be increased by adding passive flow control in the form of baffles. This study investigated the SUT prototype's flow field and heat transfer characteristics numerically using one, two, and three baffle variations through 2D axisymmetric analysis with the standard k-epsilon turbulence model using a Computational Fluid Dynamics (CFD) method. The results of the CFD solution obtained profiles of temperature distribution, velocity, streamline, kinetic power, and turbulent kinetic energy of each baffle variation. SUT with two-baffle variation is superior to the others by having a maximum air velocity of 6.248 m/s and increasing SUT performance by 104.769 %, while the three-baffle variation has the highest temperature profile and the most circulating flow effect with an increase in SUT performance of 51.524%. As the number of baffles in the SUT increases, the pressure drop also increases, but the effect of the pressure drop is not significant.

CFD Simulation of the Influence of the Type of Gas Distribution in the Burners on Thermal Aerodynamic Processes in the DKVR 10-13 Boiler

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power stations. However, in Asian countries, the ease of using natural gas as the main fuel and its environmental friendliness compared to coal made it possible to widely use natural gas in industry and energy sector. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion that it has the most attractive characteristics for its use in industry, including energy facilities, can be drawn. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy sector in the near future. The paper is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal one and at 60% capacity. The study was carried out using numerical methods with the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single-row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NOx generation in jet-niche systems was obtained. The authors of the paper believe that replacing the regular burners of the DKVR-10-13 water heating boiler with a jet-niche ones can contribute to better mixing of fuel and air and ensure more complete combustion. In this paper, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of combustion products spraying. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NOx. Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Modeling of thermo-aerodynamic and environmental parameters on the example of a two-pipe water heating boiler that has worked out the park resource

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power station. However, in Asian countries, the ease of using natural gas in industry as the main fuel, its environmental friendliness compared to coal, made it possible to widely use natural gas in industry and energy. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion can be drawn that it has the most attractive characteristics for its use in industry, including energy. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy industry in the near future. The presented work is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal and at 60% capacity. The study was carried out using numerical methods using the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single- row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NO x generation in SNS was obtained. In this work, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of spraying of combustion products. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NO x . Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Numerical analysis of a parallel triple-jet of liquid-sodium in a turbulent forced convection regime

In the present study, we have applied a combined wall-resolving dynamic Large-Eddy Simulation (LES) (for the velocity field) and Direct Numerical Simulation (DNS) (for the temperature field) approach for mixing of parallel triple-jets with different temperatures of liquid sodium in a turbulent forced convection regime. Because of the high thermal conductivity of sodium (a low-Prandtl fluid), we adopted the dynamic Smagorinsky subgrid closure for the unresolved velocity scales, while the thermal scales are fully resolved. Furthermore, the Time-dependent Reynolds-Averaged Navier-Stokes (T-RANS) approach with the high-Reynolds number variant (i.e. with the wall functions as boundary conditions along solid boundaries) of the four-equation eddy viscosity model (k−ε−kθ−εθ) was applied. The fine-mesh LES/DNS provided a close agreement with the experimental data for both velocity and temperature fields (for both first- and second-moments). In contrast, the coarse-mesh LES/DNS overestimated the turbulent kinetic energy profiles at different distances from the inlet plane. The T-RANS results confirmed a good agreement with the mean streamwise velocity and turbulent kinetic energy, as well as the mean temperature profiles. Finally, the analysis of power spectral density distributions of the temperature signal revealed that all simulation techniques captured a dominant flow frequency originating from the induced Kelvin-Helmholtz instabilities between the side and central jets. The presented combined dynamic LES/DNS approach is recommended for future simulations of the turbulent forced convection flows of low Prandtl fluids, especially if thermal fatigue effects need to be predicted correctly.

Improvements for the DDES model with consideration of grid aspect ratio and coherent vortex structures

The delayed detached eddy simulation (DDES) model has achieved great success in simulations of massive separations, but has been found to significantly delay the Kelvin-Helmholtz (K-H) instability in weak separations due to the “grey area” problem. A new DDES model was proposed by considering the grid aspect ratio and local coherent vortex structures, named the DDES with an adaptive grid-scale and adaptive coefficient (DDES-AGAC). The DDES-AGAC model was examined in detail by computing four typical types of turbulent flows: fully attached turbulent boundary layer, massive separation, weakly unstable flow with a fixed separation point, and weak separation over a smooth surface due to pressure gradient. The results confirm the advantages of the new DDES-AGAC model over the standard DDES. It exhibits high efficiency and insensitivity to spanwise or circumferential grid spacing in flow simulations of quasi-three-dimensional flows. For the weakly unsteady separation, it helps to accelerate the rapid switch from Reynolds-averaged Navier-Stokes equations to large eddy simulation, unlock the K-H instability in the shear layer, and hence accurately resolve the turbulent structures, profiles of velocity and turbulent kinetic energy, and spectra in the separation regions. Furthermore, it does not result in a noticeable drag or skin friction reduction in the fully attached flow simulations. The DDES-AGAC model is expected to be widely used in simulations of engineering flows with separations.

Examining relative impacts of atmospheric and oceanic factors on offshore wind farms

Accurate understanding and prediction of how ocean waves affect offshore wind farms are critical to their siting, design, and operation. This study presents a computational framework for simulating finite offshore wind farms using Large Eddy Simulation (LES) and a Dynamic Wave Spectrum Model (Dyn-WaSp). Implementation of the Dyn-WaSp with and without a correction for swell modes is compared to a static roughness (wave phase-averaged) model, which has a similar computational cost. Impacts of the different wave models on the wind’s mean velocity and turbulent kinetic energy profiles in the finite offshore wind farm are examined, and ideal available power at hub height is compared. The dynamic wave spectrum model is shown to predict lower mean velocities in comparison to the phase-averaged approach and predicts higher shear and turbulent kinetic energy, suggesting that loading on turbines is greater than would be estimated by a static roughness model.

Deciphering the Internal Conversion Processes Involved in the Photochemical Ring-Opening of 1,3-Cyclohexadiene by Symmetric sp2-Carbon Substitutions.

Chemical substituents hold the potential to markedly influence the photochemical behavior in molecular systems and assist in gaining a comprehensive understanding of nonadiabatic phenomena. In this study, we have conducted a comparative analysis of the influence of chemical substituents on the photochemical ring-opening of 1,3-cyclohexadiene (CHD), considering four systems: CHD, 2,3-dimethylcyclohexadiene (CHD-Me2-1), 1,4-dimethylcyclohexadiene (CHD-Me2-2), and 1,2,3,4-tetramethylcyclohexadiene (CHD-Me4), using electronic structure theory calculations and nonadiabatic molecular dynamics simulations. Employing extended multistate complete active space second-order perturbation (XMS-CASPT2) theory, we optimized reactants, S1 states, conical intersections (CIns), and products, revealing structural and energetic variations consistent with prior research. Nonadiabatic molecular dynamics simulation was used to gain insights into photochemical dynamics at state-averaged complete active space self-consistent field (SA-CASSCF) theory. CHD-Me4 exhibited reduced carbon-carbon single bond rupture rates, responsible for ring-opening, due to substituent proximity. Further, CHD-Me2-2 and CHD-Me4 displayed prolonged excited-state relaxation times, highlighting notable substituents' impact. Analysis of kinetic energy profiles of specific carbon atoms also revealed restrained atomic displacements, particularly in CHD-Me2-2 and CHD-Me4. These findings advance our understanding of how substituents modulate photochemical reactions in cyclohexadiene derivatives, guiding new molecular design and future research.

Profiling the molecular destruction rates of temperature and humidity as well as the turbulent kinetic energy dissipation in the convective boundary layer

Abstract. A simultaneous deployment of Doppler, temperature, and water-vapor lidars is able to provide profiles of molecular destruction rates and turbulent kinetic energy (TKE) dissipation in the convective boundary layer (CBL). Horizontal wind profiles and profiles of vertical wind, temperature, and moisture fluctuations are combined, and transversal temporal autocovariance functions (ACFs) are determined for deriving the dissipation and molecular destruction rates. These are fundamental loss terms in the TKE as well as the potential temperature and mixing ratio variance equations. These ACFs are fitted to their theoretical shapes and coefficients in the inertial subrange. Error bars are estimated by a propagation of noise errors. Sophisticated analyses of the ACFs are performed in order to choose the correct range of lags of the fits for fitting their theoretical shapes in the inertial subrange as well as for minimizing systematic errors due to temporal and spatial averaging and micro- and mesoscale circulations. We demonstrate that we achieve very consistent results of the derived profiles of turbulent variables regardless of whether 1 or 10 s time resolutions are used. We also show that the temporal and spatial length scales of the fluctuations in vertical wind, moisture, and potential temperature are similar with a spatial integral scale of ≈160 m at least in the mixed layer (ML). The profiles of the molecular destruction rates show a maximum in the interfacial layer (IL) and reach values of ϵm≃7×10-4 g2 kg−2 s−1 for mixing ratio and ϵθ≃1.6×10-3 K2 s−1 for potential temperature. In contrast, the maximum of the TKE dissipation is reached in the ML and amounts to ≃10-2 m2 s−3. We also demonstrate that the vertical wind ACF coefficient kw∝w′2‾ and the TKE dissipation ϵ∝w′2‾3/2. For the molecular destruction rates, we show that ϵm∝m′2‾w′2‾1/2 and ϵθ∝θ′2‾w′2‾1/2. These equations can be used for parameterizations of ϵ, ϵm, and ϵθ. All noise error bars are derived by error propagation and are small enough to compare the results with previous observations and large-eddy simulations. The results agree well with previous observations but show more detailed structures in the IL. Consequently, the synergy resulting from this new combination of active remote sensors enables the profiling of turbulent variables such as integral scales, variances, TKE dissipation, and the molecular destruction rates as well as deriving relationships between them. The results can be used for the parameterization of turbulent variables, TKE budget analyses, and the verification of large-eddy simulations.

Design of parabolic conic gas cyclones for coarse particle classification: A CFD study with Response Surface Methodology

Gas cyclones have traditionally been used as particle separators to remove dust from gas streams, with the goal of achieving a dust-free gas flow at the exit pipe and recovering particles to the dust outlet. Typically, the particle size for removal to the dust outlet is less than 1 μm. However, gas cyclones can also be targeted for particle classification rather than particle removal. In this study, the effect of the shape of the curved conical wall, specifically the parabolic concave and convex conic designs, on particle classification in a 31 mm diameter gas cyclone was evaluated using Computational Fluid Dynamics (CFD). The CFD model predictions for standard small-scale gas cyclones were validated using experimental data available in the literature for various inlet flow rates. The curvature of the conical wall varied from convex to concave, resulting in the observation of sharper and coarser cut sizes for the parabolic conic designs. The cut size increases to 4.91 μm for the concave design at a flow rate of 30 liters per minute, compared to 3.38 μm and 2.65 μm for the convex and standard design cyclones, respectively. The axial, tangential, pressure, and turbulent kinetic energy profiles were used to provide an explanation for the observed results. The interaction effects between the parameters were explored using the Response Surface Methodology. Further, Monte Carlo simulations are performed to observe the trends in predictions by exploring the design space.

Understanding the effects of inhaler resistance on particle deposition behaviour – A computational modelling study

Background and objectiveUnderstanding the impact of inhaler resistance on particle transport and deposition in the human upper airway is essential for optimizing inhaler designs, thereby contributing to the enhancement of the therapeutic efficacy of inhaled drug delivery. This study demonstrates the potential effects of inhaler resistance on particle deposition characteristics in an anatomically realistic human oropharynx and the United States Pharmacopeia (USP) throat using computational fluid dynamics (CFD). MethodMagnetic resonance (MR) imaging was performed on a healthy volunteer biting on a small mockup inhaler mouthpiece. Three-dimensional geometry of the oropharynx and mouthpiece were reconstructed from the MR images. CFD simulations coupled with discrete phase modelling were conducted. Inhaled polydisperse particles under two different transient flow profiles with peak inspiratory flow rates (PIFR) of 30 L/min and 60 L/min were investigated. The effect of inhaler mouthpiece resistance was modelled as a porous medium by varying the initial resistance (Ri) and viscous resistance (Rv). Three resistance values, 0.02 kPa0.5minL−1, 0.035 kPa0.5minL−1 and 0.05 kPa0.5 minL−1, were simulated. The inhaler outlet velocity was set to be consistent across all models for both flow rate conditions to enable a meaningful comparison of models with different inhaler resistances. ResultThe results from this study demonstrate that investigating the effect of inhaler resistance by solely relying on the USP throat model may yield misleading results. For the geometrically realistic oropharyngeal model, both the pressure and kinetic energy profiles at the mid-sagittal plane of the airway change dramatically when connected to a higher-resistance inhaler. In addition, the geometrically realistic oropharyngeal model appears to have a resistance threshold. When this threshold is surpassed, significant changes in flow dynamics become evident, which is not observed in the USP throat model. Furthermore, this study also reveals that the impact of inhaler resistance in a geometrically realistic throat model extends beyond the oral cavity and affects particle deposition downstream of the oral cavity, including the oropharynx region. ConclusionResults from this study suggest that key mechanisms underpinning the working principles of inhaler resistance are intricately connected to their complex interaction with the pharynx geometry, which affects the local pressure, local variation in velocity and kinetic energy profile in the airway.

Advances and Future Challenges in Aircraft Fuselage Section Crashworthiness: A Critical Review

Background: Crashworthiness studies the safety qualification of a vehicle (both airborne and road transports) to protect its occupants during an impact. Before an aircraft can receive transport certification, it must meet a number of crashworthiness requirements, such as the structure's deformation pattern, absorbed kinetic energy profile, and acceleration responses experienced by the components and human body models. Therefore, in recent times, crashworthiness has emerged as a crucial field of study during the early design stages of aircraft, along with other key parameters like weight reduction, load factor, fatigue life estimation, etc. Objective: The main objective of the present article is to undertake an in-depth analysis of the developments in crashworthiness related to the civil aircraft fuselage section. Furthermore, it aims to identify and address the future challenges that must be overcome to ensure the utmost safety of the occupants. Methods: Based on the research objectives, the available literature is categorized into three major groups: (i) finite element code validation; (ii) improvement of the crashworthiness criteria; and (iii) impact on different surface models. A methodology to solve fuselage section crashworthiness is briefly described. A review of the research articles discussing general purpose energy absorbers for crashworthy design without any implementation to the fuselage structure is out of the scope of this article. Results: Experimental testing of fuselage section crashworthiness is expensive and non-repeatable. Furthermore, the intricate structure of the fuselage, with its numerous components, makes it nearly impossible to devise crashworthy design solutions through classical hand calculations alone. As a result, commercial software codes play a crucial role in the development of fuselage section crashworthiness, offering valuable assistance in overcoming these limitations. Conclusion: Future challenges of crashworthy design involve exploring novel materials and devices to mitigate injury during controlled crash conditions. An intriguing area of study would be the analysis of lattice components, as they have the potential to enhance crashworthiness. Furthermore, as newly designed fuselage sections emerge, it will be crucial to investigate and establish the necessary requirements to ensure compliance with crashworthiness certification standards.

Application of computational fluid dynamics for simulation of stirred bioreactors in Ansys Fluent

Stirred bioreactors are widely used in the pharmaceutical industry to produce various active substances for the treatment of cancer, heart and vascular diseases, viral and bacterial infections. Despite the widespread use of bioreactors with a stirrer, the optimization of mixing conditions remains an urgent task. In bioreactors of this type, continuous mixing of cells in a medium with a high rotation speed should be carried out. The manuscript considers an example of the use of computational fluid dynamics to study and model the process of cultivation Escherichia coli bacterial cells in a batch bioreactor (NLF, 30 l.). Computational fluid dynamics was used to analyze the hydrodynamic conditions in a bioreactor with a double Rushton turbine stirrer. To describe the movement of flows and evaluate turbulence in a batch bioreactor, the multiphase Euler model and the k-𝜀 turbulence model, respectively, were used, the built-in Ansys Fluent software package. A geometric model was built with the original dimensions of the bioreactor with an NLF 30 stirrer. Based on the geometric model, a computational grid was created for the working volume of the bioreactor and the optimal parameters for constructing the computational grid were selected. As a result of modeling the hydrodynamic regime, the distribution profiles of the turbulence kinetic energy over the volume of the bioreactor were obtained and the velocities of cell movement were found at different speeds of rotation of the stirrer. The obtained results show the possibility and applicability of the Ansys Fluent software package for calculating the hydrodynamic situation in a bioreactor with a stirrer at different stirring rates and at different cell volume fractions.

THE NUMERICAL ANALYSIS OF MIXING DEPTH AND THE THICKNESS OF BBL CONSIDERING THE SUBMERGED AQUATIC VEGETATION AND WIND STRESS

Mangrove forests, salt marshes, and seagrass meadows have a vital role in mitigating global warming (Duarte et al.,2013). They contribute about 50 percent of carbon burial in ocean sediments (Duarte et al., 2013). On the other hand, submerged aquatic vegetations (SAVs) significantly affect the mixing depth (the thickness of the upper layer), resulting in a change in carbon flux with the atmosphere. According to the numerical simulations in the previous studies, mixing depth becomes larger with increasing SAV's density and decreasing SAV’s height (Herb et al., 2005, Vilas et al., 2017). On the other hand, Coates et al. (2009) indicated that wind stress was not crucial for mixing depth in SAV’s meadow since it did not change the vertical turbulent kinetic energy (TKE) profile, except in the thin surface layer, thus mixing depth became similar even though wind speed varied under the effect of SAVs (Coates et al., 2009). In addition, it is crucial to estimate the thickness of the benthic boundary layer (BBL) because dissolved inorganic carbon elucidates from bottom sediments, affecting carbon flux. Therefore, we aim to clarify how wind stress impacts the mixing depth and thickness of BBL with SAVs.

Magnetic resonance velocity imaging of turbulent gas flow in a packed bed of catalyst support pellets

Compressed sensing magnetic resonance methods have been used to image the time-averaged velocity and turbulent kinetic energy in 3D for turbulent gas flowing through a bed of porous, hollow cylindrical catalyst support pellets. Velocity and turbulent kinetic energy images were acquired at a spatial resolution of 0.70 mm (x) × 0.70 mm (y) × 1.0 mm (z) for particle Reynolds numbers, Rep, of 500, 2500 and 6500 in a bed with a tube-to-particle diameter ratio of 4.7. These data represent the first full-field measurements of turbulent gas flow in packed beds of non-spherical pellets. The resulting images reveal several interesting features of the hydrodynamics in this system. A large degree of flow heterogeneity is observed in the bed, with regions of high-speed fluid observed near the walls and in large voids, and regions of backflow observed in the wake of pellets, between pellets, and within the pellet holes. For increasing Rep, the normalized axial velocity at the wall is found to increase, and the normalized turbulent kinetic energy becomes more homogeneous throughout the bed. The correlation between the turbulent kinetic energy and time-averaged velocity shows that the highest turbulent kinetic energy occurs in regions of intermediate time-averaged velocity. Further, the turbulent kinetic energy profile at the pellet-scale is substantially different from the case of simple channel flow for Rep≥ 2500. Overall, these measurements clearly demonstrate the ability of magnetic resonance methods for acquiring full-field flow data in packed bed systems using commercially-relevant pellets and flow conditions.

Optimized reaction coordinates for analysis of enhanced sampling.

Atomistic simulations of biological processes offer insights at a high level of spatial and temporal resolution, but accelerated sampling is often required for probing timescales of biologically relevant processes. The resulting data need to be statistically reweighted and condensed in a concise yet faithful manner to facilitate interpretation. Here, we provide evidence that a recently proposed approach for the unsupervised determination of optimized reaction coordinate (RC) can be used for both analysis and reweighting of such data. We first show that for a peptide interconverting between helical and collapsed configurations, the optimal RC permits efficient reconstruction of equilibrium properties from enhanced sampling trajectories. Upon RC-reweighting, kinetic rate constants and free energy profiles are in good agreement with values obtained from equilibrium simulations. In a more challenging test, we apply the method to enhanced sampling simulations of the unbinding of an acetylated lysine-containing tripeptide from the bromodomain of ATAD2. The complexity of this system allows us to investigate the strengths and limitations of these RCs. Overall, the findings presented here underline the potential of the unsupervised determination of reaction coordinates and the synergy with orthogonal analysis methods, such as Markov state models and SAPPHIRE analysis.

Numerical Study of Flow Characteristics Inside Serrated Dodger Channels Using the Openfoam Program

The dodger building is one part of the dam component that serves to divert the flow of the river during construction work. One of the requirements for evasive buildings is to be able to drain river water well, so that the characteristics of the flow in the dodger channel need to be known to see how the flow conditions that occur in the dodge channel. This study aims to examine the flow characteristics of the Tapin Dam circumvention channel due to the design of the channel tunnel using a tooth shape, by modeling the relationship between the flow characteristics (velocity profile, pressure drop profile, and turbulent kinetic energy profile) of the jagged channel dimension shape using numerical computational analysis with the help of CFD (Computational Fluid Dynamics) software. From the modeling results, it will be known the influence of channel dimensions on flow characteristics in the dodger channel.

A Zero-Equation Model for External Aerodynamics

The zero-equation model (ZEM) has been generalized for aerodynamic applications by eliminating the thickness of boundary-layer (BL) dependency to construct the stress length parameter . The SED (Structural Ensemble Dynamics) postulate evaluates the using the order function based on universal multi-layer structures for wall turbulence. The SED concept is further employed to optimize the profiles of the turbulent kinetic energy and dissipation rate with turbulent BL flows. Results demonstrate that the multi-layer ZEM receives a remarkable achievement in the prediction of wall-bounded turbulence and thus, prevails over the drawbacks encountered in most algebraic turbulence models.

Field measurement of the erosion threshold of silty seabed in the intertidal flat of the Yellow River Delta with a newly-developed annular flume

Accurately measuring the critical shear stress is crucial for numerous applications, such as sediment transport modeling, erosion prediction, and the design of sustainable coastal engineering structures. However, developing reliable and precise in-situ measurement devices faces significant challenges due to the harsh and dynamic nature of aquatic environments. Factors like turbulence and waves introduce complexities that must be considered when designing and calibrating these devices. The newly developed Openable Underwater Carousel In-situ Flume (OUC-IF) was used to determine the critical shear stress (τc) and quantify erosion rates. Acoustic Doppler Velocimeter (ADV) was employed to measure 3D near-bottom velocities, which were then used to estimate and pre-calibrate bed shear stress (τ) applied on the seabed in the annular flume. Three computation methods of shear stress were evaluated: turbulent kinetic energy (TKE), direct covariance (COV), and log profile (LP). In-situ erosion experiments were conducted for the first time at two sites in the tidal flat of the Yellow River Delta (site 1 with a water depth of 1.32 m and site 2 with a water depth of 0.75 m). The critical shear stress was found to be 0.10 Pa at site 1 and 0.19 Pa at site 2, and the erosion rates of the sediments were successfully measured. The effect of wave-seabed interactions on erosion resistance was explored by theoretically estimating the wave-induced pore pressure of the seabed based on the observed data. The max liquefaction degree of the seabed at site 1 and site 2 was 0.035 and 0.057, respectively, and the average erosion coefficient Me was 2.63E-05 kg m-2s-1 at site 1 and 3.48E-05 kg m-2s-1 at site 2.

A wave appropriate discontinuity sensor approach for compressible flows

In this work, we propose a novel selective discontinuity sensor approach for numerical simulations of the compressible Navier–Stokes equations. Since transformation to characteristic space is already a common approach to reduce high-frequency oscillations during interpolation to cell interfaces, we exploit the characteristic wave structure of the Euler equations to selectively treat the various waves that the equations comprise. The approach uses the Ducros shock sensing criterion to detect and limit oscillations due to shocks while applying a different criterion to detect and limit oscillations due to contact discontinuities. Furthermore, the method is general in the sense that it can be applied to any method that employs characteristic transformation and shock sensors. However, in the present work, we focus on the gradient-based reconstruction family of schemes. A series of inviscid and viscous test cases containing various types of discontinuities are carried out. The proposed method is shown to markedly reduce high-frequency oscillations that arise due to improper treatment of the various discontinuities; i.e., applying the Ducros shock sensor in a flow where a strong contact discontinuity is present. Moreover, the proposed method is shown to predict similar volume-averaged kinetic energy and enstrophy profiles for the Taylor–Green vortex simulation compared to the base Ducros sensor, indicating that it does not introduce unnecessary numerical dissipation when there are no contact discontinuities in the flow.

Numerical simulation of an idealised Richtmyer–Meshkov instability shock tube experiment

The effects of initial conditions on the evolution of the Richtmyer–Meshkov instability (RMI) at early to intermediate times are analysed, using numerical simulations of an idealised version of recent shock tube experiments performed at the University of Arizona (Sewell et al., J. Fluid Mech., vol. 917, 2021, A41). The experimental results are bracketed by performing both implicit large-eddy simulations of the high-Reynolds-number limit as well as direct numerical simulations (DNS) at Reynolds numbers lower than those observed in the experiments. Various measures of the mixing layer width $h$ , known to scale as ${\sim }t^\theta$ at late time, based on both the plane-averaged turbulent kinetic energy and volume fraction profiles are used to explore the effects of initial conditions on $\theta$ and are compared with the experimental results. The decay rate $n$ of the total fluctuating kinetic energy is also used to estimate $\theta$ based on a relationship that assumes self-similar growth of the mixing layer. The estimates for $\theta$ range between 0.44 and 0.52 for each of the broadband perturbations considered and are in good agreement with the experimental results. Decomposing the mixing layer width into separate bubble and spike heights $h_b$ and $h_s$ shows that, while the bubbles and spikes initially grow at different rates, their growth rates $\theta _b$ and $\theta _s$ have equalised by the end of the simulations. Overall, the results demonstrate important differences between broadband and narrowband surface perturbations, as well as persistent effects of finite bandwidth on the growth rate of mixing layers evolving from broadband perturbations. Good agreement is obtained with the experiments for the different quantities considered; however, the results also show that care must be taken when using measurements based on the velocity field to infer properties of the concentration field.