Flow, Turbulence and Combustion最新文献

{"title":"Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence","authors":"Kosuke Nakagawa,&nbsp;Takahiro Ishida,&nbsp;Takahiro Tsukahara","doi":"10.1007/s10494-024-00616-5","DOIUrl":"10.1007/s10494-024-00616-5","url":null,"abstract":"<div><p>Laminar-turbulent transitions in boundary layers are one of the major research topics in fluid dynamics. In this study, we focused on a three-dimensional boundary layer formed on a swept flat plate. In this boundary layer, the crossflow instability is dominant, and the instability induces crossflow vortices (CFVs). Many studies have focused on the dependency of the transition process on the intensities of steady or unsteady disturbances, which correspond to a roughness element and freestream turbulence (FST), respectively. On the other hand, the effects of the FST wavelength are still unclear. Moreover, there is a lack of knowledge about the transition processes caused by both steady and unsteady disturbances. We investigated how the transition process of a stationary structure caused by cylindrical roughness changes depending on the FST wavelength using direct numerical simulations. We classified transition processes into two types: processes in which stationary structures grow into CFVs and processes in which hairpin vortices are generated on the stationary structures. The former is further classified into four types depending on the presence or absence of FST and on the FST wavelength. We revealed the contributions of different FST wavelengths to the transition process changes. The short-wavelength FST provides hairpin vortices to the stationary structure at low roughness height conditions because of its high-frequency components. The long-wavelength FST changes the process due to unsteady fluctuations influencing the stationary structure. In summary, the transition processes undergo different mechanisms between short- and long-wavelength FST.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 Heat and Mass Transfer","pages":"827 - 855"},"PeriodicalIF":2.0,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10494-024-00616-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143612160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Equivalence Ratio Gradient Effects on Locally Lean, Stoichiometric and Rich Propane/Air and N-Heptane/Air Turbulent Bluff Body Flames","authors":"Evangelos-Panagiotis Mitsopoulos,&nbsp;Stavros-Marios Panou,&nbsp;Michalis Manoudakis,&nbsp;Konstantinos Souflas,&nbsp;Panayiotis Koutmos","doi":"10.1007/s10494-024-00621-8","DOIUrl":"10.1007/s10494-024-00621-8","url":null,"abstract":"<div><p>The effect of inlet mixture stratification was investigated in propane/air and prevaporised n-heptane/air flames stabilized in the near wake region of a bluff-body burner. The employed axisymmetric burner can sustain flame anchoring at global equivalence ratio values in the range of 0.09 ÷ 0.1 independently of fuel type and permits the variation of fuel concentration along the radial direction. Three distinct stratification gradients were studied for the two fuels considered; One burning from rich to lean, one burning from stoichiometric to lean and one burning from stronger lean to weaker lean mixtures. Particle Image Velocimetry, Mie scattering and OH ∗ and CH* Chemiluminescence were used to investigate flame stabilization characteristics of the two fuels and three stratification gradients, while Fourier – Transform Infrared Spectroscopy was performed to assess the equivalence ratio disposition under non-reacting conditions in the near wake region. 2D hydrodynamic strain rates, Damköhler (Da) and Karlovitz (Ka) numbers and flame brush thickness distributions were estimated and analyzed to elucidate the effects of turbulence, mixture composition and fuel type on the investigated flames. Also, the characteristic size of the reacting fluid pockets was assessed using a two-point sample autocorrelation methodology on the OH* chemiluminescence images. Results suggest that supplying the vicinity of the anchoring region with lean peak equivalence ratio mixtures with Lewis numbers greater than unity reduces the flame’s resistance to strain, while supplying it with rich peak equivalence ratio mixtures of Lewis number ≈1, independently of fuel type, favors resistance to strain, suggesting a connection with preferential diffusion effects.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 2","pages":"487 - 518"},"PeriodicalIF":2.0,"publicationDate":"2024-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143430933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Binary Droplet Collisions in Bioprinting: Influence of Material Properties on Mixing and Repeatability","authors":"Élfego Ruiz-Gutiérrez,&nbsp;Josef Hasslberger,&nbsp;Markus Klein,&nbsp;Kenny Dalgarno,&nbsp;Nilanjan Chakraborty","doi":"10.1007/s10494-024-00606-7","DOIUrl":"10.1007/s10494-024-00606-7","url":null,"abstract":"<div><p>The study of suspended binary droplet collisions is an active research topic that has gathered interest due to its complexity and its industrial applications such as bioprinting. For many techniques that rely on the collision of two droplets, the quality of the outcome depends on the mixing process that begins when the droplets come in contact with each other. In this work, we study how the difference in material properties of colliding droplets, such as viscosity and surface tension, affect the mixing process. Employing multiphase direct numerical simulations, the distribution of the impinging liquids and the structure of the flow field have been analysed to find ways of mixing and process repeatability optimisation. To analyse the effects that differences in viscosity and surface tension have in the mixing process, the flows emerging from the collision are analysed. The differences in kinematic viscosity, in the range of <span>(1 times 10^{-7})</span> to <span>(1 times 10^{-5},text {m}^{2}text {s}^{-1})</span> and surface tension, in the range of 36 to <span>({82.7,mathrm{text {m}text {N} , text {m}^{-1}}})</span>, have also been demonstrated to affect the trajectory of the centre of mass and morphology of the droplets upon collision and thus could have implications from the point of view of process repeatability. In the parameter space considered here, it was found that differences in viscosity and surface tension enhance the mixing due to the departure from the symmetry in the collision.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 Heat and Mass Transfer","pages":"913 - 939"},"PeriodicalIF":2.0,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10494-024-00606-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143612060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical Prediction of Cavitation for a Horizontal Axis Tidal Turbine","authors":"Adriano Evangelisti,&nbsp;Giuliano Agati,&nbsp;Domenico Borello,&nbsp;Luca Mazzotta,&nbsp;Paolo Capobianchi,&nbsp;Paolo Venturini","doi":"10.1007/s10494-024-00615-6","DOIUrl":"10.1007/s10494-024-00615-6","url":null,"abstract":"<div><p>This paper aims at assessing cavitation in a scaled tidal turbine geometry through numerical simulations. Cavitation occurrence is predicted by using the Singhal cavitation model, based on the Rayleigh-Plesset equation, for treating bubble dynamics. Turbulence is modelled adopting a Reynolds Averaged Navier Stokes (RANS) approach, specifically employing the Shear Stress Transport (SST) <i>k-</i>ω model to simulate the fluid flow. The Reboud density function is applied to adjust the eddy viscosity computation in the cavitation region. Initially, cavitation and turbulence models are validated using a NACA 66 (mod) hydrofoil profile as a test case. Numerical and experimental pressure coefficients are compared on the hydrofoil suction side for a selected cavitation condition. A Mesh Sensitivity Analysis (MSA) is performed to ensure simulation accuracy, comparing numerical results with experimental data on the Horizontal Axis Tidal Turbine (HATT) scaled domain. Based on this analysis, the optimal computational grid is selected. Experimental and numerical power and thrust coefficients are then compared across different tip speed ratios. Finally, cavitation occurrence is evaluated for four different regimes, namely the cut-in, the peak-power, the curve highest velocity and the off-set tip speed ratios. Computational Fluid Dynamics (CFD) solutions reveal vapor formation around turbine components, highlighting regions most exposed to cavitation onset.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 Heat and Mass Transfer","pages":"887 - 912"},"PeriodicalIF":2.0,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143612041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessing the Multi-Regime Capability of the Super-Grid Linear Eddy Model (SG-LEM) Using the Darmstadt Multi-Regime Burner","authors":"Abhilash Menon,&nbsp;Alan Kerstein,&nbsp;Michael Oevermann","doi":"10.1007/s10494-024-00602-x","DOIUrl":"10.1007/s10494-024-00602-x","url":null,"abstract":"<div><p>Recent advances in combustion modelling for Large Eddy Simulation (LES) have increasingly utilised lower-dimensional manifolds, such as Flamelet Generated Manifolds and Flamelet/Progress Variable methods, due to their computational efficiency. These methods typically rely on one-dimensional representations of flame structures, often assuming premixed or non-premixed configurations. However, practical combustion devices frequently operate under partially-premixed conditions and present challenges due to mixture inhomogeneities and complex flow features. The Linear Eddy Model (LEM) offers an alternative by directly simulating turbulence-chemistry interactions without presuming specific flame structures. However, traditional LES-LEM approaches are computationally quite expensive due to the need for resolved LEM domains to be embedded in every LES cell.The authors developed the Super-Grid LEM (SG-LEM) method (Comb. Theor. Model.  28, 2024) to address these computational challenges by coarse-graining the LES mesh and embedding individual LEM domains within <i>clusters</i> of LES cells. This study evaluates SG-LEM in the context of the Multi-Regime Burner (MRB) introduced by Butz et al. (Combust. Flame, 210, 2019), which features both premixed and non-premixed flame characteristics. SG-LEM simulations of the MRB case demonstrate the method’s sensitivity to clustering parameters, with flow-aligned clusters significantly improving flame stability. LEM domains on the super-grid were able to represent the MRB flame topology while LES radial profiles including velocity, mixture fraction, temperature, and <span>({textrm{CO}})</span> mass fraction, were validated against experimental data and also reference simulations using standard combustion closures. The work also investigates discrepancies in CO profiles using conditional statistics and stand-alone LEM simulations. Finally, the work identifies areas of improvement for the SG-LEM framework, in particular relating to cluster generation, and (advective and diffusive) mass exchange between neighbouring LEM domains, as well as possible solutions for future SG-LEM implementations which could improve the model’s predictive capability.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 2","pages":"395 - 420"},"PeriodicalIF":2.0,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10494-024-00602-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143430845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the Feasibility of a Self-adaptive Strategy for Hybrid RANS/LES Based on Physical Criteria and its Initial Testing on Low Reynolds Number Backward-Facing Step Flow","authors":"Martin David,&nbsp;Mahitosh Mehta,&nbsp;Rémi Manceau","doi":"10.1007/s10494-024-00583-x","DOIUrl":"10.1007/s10494-024-00583-x","url":null,"abstract":"<div><p>Hybrid RANS/LES methods can produce more reliable results than RANS with a reasonable computational cost. Thus, they have the potential to become the next workhorse in the industry. However, in continuous approaches, whether or not they depend on the grid step explicitly, the ability of the model to switch to a well-resolved LES depends on the mesh generated by the user, such that the results are user-dependent. The present paper proposes a self-adaptive strategy, in which the RANS and LES zones are determined using physical criteria, in order to mitigate the user influence. Starting from an initial RANS computation, successive HTLES are carried out and the mesh is refined according to the criteria. To demonstrate the feasibility of this strategy, the method is applied to the backward-facing step case with the Hybrid Temporal Large Eddy Simulation (HTLES) approach, but is suitable for any other hybrid approach. The results obtained show that the method reaches a fixed point after only a few simulations and significantly improves the predictions when compared to RANS, with no intervention from the user. Even though the process is still a long way from being applicable to a wide range of turbulent flows, this paper is a demonstrator of the applicability of this self-adaptive strategy.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 1","pages":"49 - 79"},"PeriodicalIF":2.0,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142995780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatiotemporal Characteristics of Turbulent Flows Around Partially Submerged Circular Cylinders","authors":"Mark K. Israel,&nbsp;Karen Dow,&nbsp;Shawn P. Clark,&nbsp;Mark F. Tachie","doi":"10.1007/s10494-024-00598-4","DOIUrl":"10.1007/s10494-024-00598-4","url":null,"abstract":"<div><p>This paper presents a time-resolved particle image velocimetry investigation of the spatiotemporal characteristics of the wake flow around a partially submerged horizontal circular cylinder with and without upstream ice cover. This study is applicable to offshore structures such as ice booms. In the experiments, the cylinder was submerged with 50% of its surface below the free surface and the Reynolds number was 10,000. A reference experiment was performed with the cylinder fully immersed in the uniform flow for comparison. Due to the absence of an upper shear layer, the recirculation length of the submerged cylinder is longer, but the turbulence levels are lower compared to the uniform case, and an upstream ice cover reduces the recirculation length and turbulence levels around the submerged cylinder compared to the open water case. The wake of the cylinders is highly anisotropic, regardless of boundary condition, with vertical fluctuating velocities being dominant over streamwise fluctuating velocities in the uniform case and vice versa in the submerged cases. In the uniform case, the turbulence production is maximum on the wake centerline, but in the submerged cases, the maximum turbulence production occurs within the shear layer. The frequency spectra of fluctuating velocities also showed that the wake of a submerged cylinder is characterized by multiple low, distinct frequencies indicative of a wide range of vortical structures, regardless of the upstream flow condition.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 Heat and Mass Transfer","pages":"995 - 1015"},"PeriodicalIF":2.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143612102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Revisiting the Modelling of Mixing Time Scales for Lagrangian Filtered Density Function Methods","authors":"Sergio Gutiérrez Sánchez,&nbsp;Jacqueline Yang,&nbsp;Andreas Kronenburg,&nbsp;Thorsten Zirwes","doi":"10.1007/s10494-024-00612-9","DOIUrl":"10.1007/s10494-024-00612-9","url":null,"abstract":"<div><p>Mixing models for multiple mapping conditioning (MMC) methods are revisited as some details of their implementation have not yet been assessed. We use simulations of scalar mixing in non-reacting homogeneous isotropic decaying turbulence (HIT) such that (1) key modelling parameters can be taken from the direct numerical simulations without incurring additional modelling uncertainties and (2) direct validation is possible. Variants of Curl’s model are studied and direct comparison is sought with the variants’ performances in the context of standard (intensive) and sparse (such as MMC) particle approaches for the modelling of the probability density function (PDF). The second aim is to show the relative importance of micro-mixing and spatial diffusion in the presence of differential diffusion. The results demonstrate that MMC approximates the correct relaxation towards Gaussian independent of the mixing model’s variant. This is different from the standard PDF approach that requires a clear spatial localization given by the computational mesh to achieve a similar outcome. This spatial localization is not needed in MMC as the MMC mixing model already employs a localization in reference space. Differential diffusion effects can, however, only be accurately predicted if not only mixing but also spatial transport accounts for the differences in the molecular diffusion term. It is insufficient to adjust the mixing time scales only and future MMC models may require adjustments for accurate prediction capabilities.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 2","pages":"585 - 615"},"PeriodicalIF":2.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10494-024-00612-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143431051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Synthetic Turbulence with Prescribed Probability Density Function and Application to Scalar Quantities Occurring in Reactive Flows","authors":"Markus Klein","doi":"10.1007/s10494-024-00614-7","DOIUrl":"10.1007/s10494-024-00614-7","url":null,"abstract":"<div><p>Based on a (synthetic) turbulent signal which obeys a Gaussian probability density function (PDF) together with some form of prescribed two-point statistics (i.e. integral length or time scales or turbulent energy spectrum), a simple algorithm is proposed to transform the original signal, such that it follows a new target PDF. It is shown that for many practical applications the transformation does not change the integral length or time scale more than a few per cent. The algorithm can be combined with any turbulence generator. It has applications for prescribing boundary or initial conditions of non-Gaussian signals in scale resolving simulations of turbulent flows, such as passive scalars like temperature, bounded passive scalars occurring in reactive flows or velocity signals close to walls.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 2","pages":"387 - 393"},"PeriodicalIF":2.0,"publicationDate":"2024-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10494-024-00614-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143430782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Turbulence Structure and Mixing in Strongly Stable Couette Flows over Thermally Heterogeneous Surfaces: Effect of Heterogeneity Orientation","authors":"Dmitrii Mironov,&nbsp;Peter Sullivan","doi":"10.1007/s10494-024-00593-9","DOIUrl":"10.1007/s10494-024-00593-9","url":null,"abstract":"<div><p>Direct numerical simulations (DNS) of plane Couette flows over thermally heterogeneous surfaces at bulk Reynolds number <span>(Re=10^4)</span> and bulk Richardson number <span>(Ri=0.25)</span> are performed. The focus of the present study (that extends previous work by the authors) is the effect of surface heterogeneity orientation on boundary-layer structure. The temperature of the upper and lower walls is either homogeneous or varies sinusoidally, where the temperature-wave crests are either normal or parallel to the mean flow (HETx and HETy cases, respectively). Importantly, the horizontal-mean surface temperature is the same in all simulations. The stratification is strong enough to quench turbulence over a homogeneous surface, but turbulence survives over heterogeneous surfaces. In all heterogeneous cases, both molecular diffusion and turbulence transfer momentum down the gradient of mean velocity. The total (turbulent plus diffusive) heat flux is down-gradient, but quasi-organized eddy motions generated by the surface thermal heterogeneity induce heat transfer up the gradient of the mean temperature. Comparative analysis of HETx and HETy cases shows that the configuration with the spanwise heterogeneity is more turbulent and more efficient in transporting momentum and heat vertically than its counterpart with the streamwise heterogeneity. Vertical profiles of mean fields and turbulence moments differ considerably between the HETx and HETy cases, e.g., the streamwise heat flux differs not only in magnitude but also in sign. A close examination of the second-order turbulence moments, vertical-velocity and temperature skewness, and the flow eddy structure helps explain the observed differences between the HETx and HETy cases. The implications of our DNS findings for modelling turbulence in stably-stratified environmental and industrial flows with surface heterogeneity are discussed.</p></div>","PeriodicalId":559,"journal":{"name":"Flow, Turbulence and Combustion","volume":"114 Heat and Mass Transfer","pages":"967 - 994"},"PeriodicalIF":2.0,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10494-024-00593-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143612097","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}