European Journal of Mechanics B-fluids最新文献

{"title":"The linear stability of the Kazhikhov–Smagulov model","authors":"C. Jacques,&nbsp;B. Di Pierro,&nbsp;M. Buffat","doi":"10.1016/j.euromechflu.2024.04.001","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.04.001","url":null,"abstract":"<div><p>Using the Kazhikhov–Smagulov model, the linear stability of incompressible mixing layers and jets entailing large density variation is addressed analytically. The classical theorems of Squire, Rayleigh and Fjørtoft are extended to variable-density flows. It is shown that the bidimensional configuration is still the most unstable one, but the inflexion point is no longer a necessary condition for instability. Instead, a non trivial condition involving density and velocity gradient is identified. Dispersion relations are obtained for small wavenumbers as well as for piecewise linear base flow profiles. Additionally, an estimation of the threshold wavenumber that stabilises the flow is obtained. It is demonstrated that density variations modify the growth rate of the instability as well as the wavelength associated with the most unstable mode and the unstable wavenumber range. These results are in good agreement with numerical computations. Finally, it is observed that viscous effects are purely stabilising while molecular diffusion does not affect the stability.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0997754624000530/pdfft?md5=f482197308eef5090b2c7d7974d37782&pid=1-s2.0-S0997754624000530-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140539194","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 simulation of single-mode and multi-mode RTI regarding thixotropic effects by SPH","authors":"Mohammad Vahabi","doi":"10.1016/j.euromechflu.2024.04.002","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.04.002","url":null,"abstract":"<div><p>The Rayleigh-Taylor instability (RTI) between a heavier Newtonian liquid and a lighter thixotropic liquid is studied in this paper by weakly compressible smoothed particles (WC-SPH). It is assumed that the thixotropic liquid obeys the Moore rheological model. First, the developed code is verified against available Newtonian RTI cases. Then, it is applied to thixotropic RTI cases to investigate the effects of the different non-dimensional parameters, including the thixotropic number (destruction-to-rebuild ratio), Reynolds number, Bond number, and Deborah number. It is shown that <strong>Bo</strong> is the most paramount non-dimensional parameter (i.e., it determines whether the two-phase boundary is stable or unstable), while <strong>Re</strong>, <strong>De</strong>, and thixotropic numbers have secondary influences on RTI. Based on the obtained results, the behavior of the thixotropic case is similar to the Newtonian high viscous counterpart at initial times; however, it is different at long times. It is demonstrated that the value of the thixotropic number determines when the transition between the short-time and long-time phenomena occurs.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140535855","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":"Resonant water-waves in ducts with different geometries: Forced KdV solutions","authors":"U. Harlander ,&nbsp;F.-T. Schön ,&nbsp;I.D. Borcia ,&nbsp;S. Richter ,&nbsp;R. Borcia ,&nbsp;M. Bestehorn","doi":"10.1016/j.euromechflu.2024.03.008","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.03.008","url":null,"abstract":"<div><p>In a remarkable paper, Cox and Mortell (1986) (A.A. Cox, M.P. Mortell 1986. J. Fluid Mech. 162, pp. 99-116) showed that for an oscillating water tank, the evolution of small-amplitude, long-wavelength, resonantly forced waves follow a forced Korteweg–de Vries (fKdV) equation. The solutions of this model agree well with experimental results by Chester and Bones (1968) (W. Chester and J.A. Bones 1968. Proc. Roy. Soc. A, 306, 23 (Part II)). We compare the fKdV solutions with a number of channel flows with different geometry that have been studied experimentally and numerically. When sweeping the selected wide parameter range, extreme cases of the fKdV equation are covered: single soliton solutions as well as multiple solitons with a rather short wavelength challenging the long-wave fKdV assumption. The transition of solutions with a different number of solitons is rather abrupt and we show that the parameter values for transitions from single soliton towards multi-soliton solutions can be predicted and follow a simple exponential relation. In particular, we compare the fKdV model with solutions from a fully nonlinear Navier–Stokes model. We further consider a case for which the 2D assumption of the fKdV equation is strictly speaking violated.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0997754624000529/pdfft?md5=d0af53ed829b4469c89a655608a3f0c2&pid=1-s2.0-S0997754624000529-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140535856","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":"Slip length for a viscous flow over a plane with complementary lattices of superhydrophobic spots","authors":"Alexei T. Skvortsov ,&nbsp;Denis S. Grebenkov ,&nbsp;Leon Chan ,&nbsp;Andrew Ooi","doi":"10.1016/j.euromechflu.2024.03.007","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.03.007","url":null,"abstract":"<div><p>We propose an approximation for the functional form of the slip length for two complementary lattice configurations of superhydrophobic texture. The first configuration consists of the square lattice of the superhydrophobic spots employed on the no-slip plane. The second configuration is an ‘inverse’ of the first one and consists of the same lattice but of the no-slip spots on the superhydrophobic base. We validate our analytical results by a numerical solution of Stokes equation.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140327684","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":"PREFACE for THESIS-2019 Special Issue of the EJMFLU","authors":"","doi":"10.1016/j.euromechflu.2024.03.006","DOIUrl":"10.1016/j.euromechflu.2024.03.006","url":null,"abstract":"","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.5,"publicationDate":"2024-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140406769","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":"Absolute instability of the boundary-layer flows due to rotating a spheroid","authors":"S. Khan,&nbsp;A. Samad","doi":"10.1016/j.euromechflu.2024.03.005","DOIUrl":"10.1016/j.euromechflu.2024.03.005","url":null,"abstract":"<div><p>This paper explores local absolute instability in the boundary layer flow over two distinct families of rotating spheroids (prolate and oblate). While convective instability was established in earlier work by Samad and Garrett <span>[1]</span>, this study delves into the potential occurrence of local absolute instability. Some results of local convective instability under the assumption of stationary vortices are reproduced for a more comprehensive investigation. The analysis considers viscous and streamline curvature effects, demonstrating that the localized mean flow within the boundary layer over either family of the rotating spheroid is absolutely unstable for each fixed value of the eccentricity parameter <span><math><mrow><mi>e</mi><mo>∈</mo><mrow><mo>[</mo><mn>0</mn><mo>,</mo><mn>0</mn><mo>.</mo><mn>8</mn><mo>]</mo></mrow></mrow></math></span>. For certain combinations of Reynolds number <span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span> and azimuthal wave number <span><math><mi>β</mi></math></span>, a third branch (Branch 3) of the dispersion relation intersects Branch 1 at a pinch point, indicating absolute instability. Neutral curves depict regions that are absolutely unstable, while below critical Reynolds numbers, the region is either convectively unstable or stable. The paper also illustrates the effect of increasing eccentricity on spatial branches within both convectively and absolutely unstable regions. From lower to moderate latitudes, the stabilizing effect of <span><math><mi>e</mi></math></span> on the onset of absolute instability is robust for the prolate family and almost negligible for the oblate family. At high latitudes of the prolate spheroid, the stabilizing effect of <span><math><mi>e</mi></math></span> is fainter but persists until close to the equator. Conversely, at high latitudes of the oblate spheroid, the stabilizing effect of <span><math><mi>e</mi></math></span> is more pronounced. The paper discusses the implications of the parallel flow assumption employed in the analyses.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140279071","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":"A continuous non-ergodic theory for the wave set-up","authors":"Saulo Mendes","doi":"10.1016/j.euromechflu.2024.03.001","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.03.001","url":null,"abstract":"<div><p>Inhomogeneities in the wave field due to wave groups, currents, and shoaling among other ocean processes can affect the mean water level. In this work, the classical and unsolved problem of continuously computing the set-down and the following set-up induced by wave breaking on a shoal of constant finite slope is tackled. This is possible by using available theoretical knowledge on how to approximate the distribution of wave random phases in finite depth. Then, the non-homogeneous spectral analysis of the wave field allows the computation of the ensemble average by means of the phase distribution and the inversion of the integral of the second moment for the special case of a shoaling process with uniform phase distribution. In doing so, I am able to obtain a direct effect of the slope magnitude on the phases distribution. Therefore, an analytical and slope-dependent mean water level with continuity over the entire range of water depth is provided.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0997754624000451/pdfft?md5=e0bd63a001032ab1fd1431fd09802b9e&pid=1-s2.0-S0997754624000451-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140320950","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":"Improved self-adaptive turbulence eddy simulation for complex flows and stall prediction using high-order schemes","authors":"Wenchang Wu ,&nbsp;Xingsi Han ,&nbsp;Yaobing Min ,&nbsp;Zhen-guo Yan ,&nbsp;Yankai Ma ,&nbsp;Xiaogang Deng","doi":"10.1016/j.euromechflu.2024.03.003","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.03.003","url":null,"abstract":"<div><p>It is challenging to apply numerical simulations to accurately predict the stall behavior of aircraft equipped with high-lift devices. Simulations with Reynolds-Averaged Navier<img>Stokes (RANS) models suffer from lack of the reliability at high angles of attack with separated and reattached boundary layers, whereas wall-resolved Large Eddy Simulations (LES) of wall-bounded flows at high Reynolds numbers currently costs too much computational resources. A new unified hybrid turbulence modeling approach, denoted the Self-Adaptive Turbulence Eddy Simulation (SATES), is proposed and applied for complex turbulent flows combining with high-order numerical scheme of the Weighted Compact Nonlinear Scheme (WCNS) in the present study. It enables a seamless evolution from unsteady RANS to LES and finally approaches Direct Numerical Simulation (DNS) depending on the turbulent scales. In the framework of SATES, a new SATES-σ model with an adaptive model coefficient is developed by extending the underlying LES mode based on an enhanced sub-grid-scale model of the σ-model. The new SATES-σ is first examined in two benchmark cases of channel flow and flow past a square cylinder. Then, it is validated in supercritical flow past a circular cylinder to assess the performance of turbulent models. The results show significant improvements over the previous SATES and IDDES in the predictions of boundary layer flow. Finally, successful application is achieved in the accurate prediction of the stall of the MD-30P30N airfoil at a Reynolds number of 9×10⁶ with wide angles of attack. The simulation results show good agreement with experimental results for surface pressure even for the challenging cases of 21 and 23 deg angles of attack. Again, the SATES-σ shows better results than the previous SATES and IDDES. The presented method has considerable potential for the challenging stall predictions.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140190746","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":"Three dimensional interface normal prediction for Volume-of-Fluid method using artificial neural network","authors":"Jinlong Li ,&nbsp;Jia Liu ,&nbsp;Kang Li ,&nbsp;Shuai Zhang ,&nbsp;Wenjie Xu ,&nbsp;Duanyang Zhuang ,&nbsp;Liangtong Zhan ,&nbsp;Yunmin Chen","doi":"10.1016/j.euromechflu.2024.03.004","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.03.004","url":null,"abstract":"<div><p>In the numerical simulations of multi-phase flow using Volume-of-Fluid (VOF) method, the calculation of the interface normal is a crucial point. In this paper, a machine learning method is used to develop an artificial neural network (ANN) model to make more accurate prediction of the local normal vector from neighboring volume fractions. Spherical surfaces with different radii are intersected with a structural background grid to generate 84328 groups of data: 3×3×3 neighboring volume fractions are used as input, and normal vector as output. Using 90% data as training dataset, the ANN model is well trained by optimizing the number of hidden layers and the number of neurons on each layer. Using the remaining 10% data, normal predictions are made using ANN-VOF and the most used YOUNG and HEIGHT-FUNCTION methods. The RMSE of the ANN-VOF/YOUNG/ HEIGHT-FUNCTION methods are 0.008/0.022/0.045 respectively. In the reconstruction of a sinusoidal surface, the MSE of the ANN-VOF/YOUNG/ HEIGHT-FUNCTION methods are 0.008/0.018/0.041. It is demonstrated that the ANN-VOF method has better performance for interface normal prediction. The proposed method has a simple computational logic and does not need to deal with complex geometric topology, which lays the foundation for application in other more complex grids.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140163426","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":"Optimization of Reynolds stress model coefficients at multiple discrete flow regions for three-dimensional realizations of fractal-generated turbulence","authors":"Michael Chee Hoe Mok,&nbsp;Chin Vern Yeoh,&nbsp;Ming Kwang Tan,&nbsp;Ji Jinn Foo","doi":"10.1016/j.euromechflu.2024.03.002","DOIUrl":"https://doi.org/10.1016/j.euromechflu.2024.03.002","url":null,"abstract":"<div><p>The quantification of global turbulence statistical moments generated by grid turbulators is crucial for the enhancement of conjugate heat transfer in industrial thermo-fluid systems. As such, there is a need for precise, low-cost alternatives to numerically model three-dimensional flow dynamics of fractal-generated turbulence (FGT) behind multilength-scale square fractal grids (SFGs), in contrast to previously-reported direct numerical simulations. In this study, a numerical framework consisting of multiple applications of the Reynolds stress model (RSM), each employing its own distinct set of optimized coefficient values, is developed by segregating an FGT flow domain into its production and decay regions with Nelder-Mead optimization on key coefficients then performed independently for each region. The flow fields predicted by such RSM framework achieved overall disparities below 3% and 13% <em>w.r.t.</em> reported experimental measurements of mean velocity and turbulence intensity, respectively, considering the evolution in the flow domain along the streamwise, vertical, and spanwise directions. This is therefore the first documentation of any RANS-turbulence model being validated for mean velocity and turbulence intensity predictions of FGT in <em>all</em> three-dimensions<em>.</em> Thereafter, this proposed RSM framework is generalized to predict industry-relevant turbulence statistical moments of four additional FGT flows. The predicted centerline-statistics are verified against reported experiments, and the findings potentially enable realizations of FGT induced by arbitrary SFGs without relying on <em>a posteriori</em> validation while eliminating further reliance on the Nelder-Mead optimization algorithm on a case-by-case basis. The findings indicate a potential to apply the model coefficients as continuous functions of space to simulate the entire FGT domain. Overall, the accurate and numerically sustainable realizations of FGT in 3D provide valuable insights to engineer potent fluid-solid heat transfer via passive turbulence management within HVAC systems.</p></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0997754624000463/pdfft?md5=8f3e555619645c50ea60c19a18c506f4&pid=1-s2.0-S0997754624000463-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140190851","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}