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Ramis Orlu - One of the best experts on this subject based on the ideXlab platform.
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A description of turbulence intensity profiles for boundary layers with adverse pressure gradient
European Journal of Mechanics B-fluids, 2020Co-Authors: A. Dróżdż, Ramis Orlu, Ricardo Vinuesa, Witold Elsner, Paweł Niegodajew, Philipp SchlatterAbstract:Abstract The paper presents an extension of the Diagnostic-Plot scaling (Alfredsson et al., 2012) of the turbulence-intensity profiles for the outer region of adverse-pressure-gradient (APG) turbulent boundary layers (TBLs). An extended formula including the shape factor is proposed, which allows the Diagnostic-Plot scaling to be used in strong APGs at high Reynolds numbers. The validity of the new formulation is verified using several available databases. We demonstrate that the new formula allows to scale profiles in cases where the Clauser–Rotta pressure-gradient parameter β is below 14 even in presence of very strong flow-history effects. In order to extend the scaling to the near-wall region of TBLs the adapted complete difference function is proposed. The proposed scaling yields a unified description of the turbulence-intensity profiles regardless of their flow history (as opposed to other previously proposed scalings), and is valid for a wider range of cases not only for the outer but also for the inner region.
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On the identification of well-behaved turbulent boundary layers
Journal of Fluid Mechanics, 2017Co-Authors: C. Sanmiguel Vila, Ricardo Vinuesa, Stefano Discetti, Andrea Ianiro, Philipp Schlatter, Ramis OrluAbstract:This paper introduces a new method based on the Diagnostic Plot (Alfredsson et al., Phys. Fluids, vol. 23, 2011, 041702) to assess the convergence towards a well-behaved zero-pressure-gradient (ZPG ...
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On determining characteristic length scales in pressure gradient turbulent boundary layers
Journal of Physics: Conference Series, 2016Co-Authors: Ricardo Vinuesa, Ramis Orlu, Philipp SchlatterAbstract:In the present work we analyze three methods used to determine the edge of pressure gradient turbulent boundary layers: two based on composite profiles, the one by Chauhan et al. (Fluid Dyn. Res. 41:021401, 2009) and the one by Nickels (J. Fluid Mech. 521:217–239, 2004), and the other one based on the condition of vanishing mean velocity gradient. Additionally, a new method is introduced based on the Diagnostic Plot concept by Alfredsson et al. (Phys. Fluids 23:041702, 2011). The boundary layer developing over the suction side of a NACA4412 wing profile, extracted from a direct numerical simulation at Rec = 400,000, is used as the test case. We find that all the methods produce robust results with mild or moderate pressure gradients, but stronger pressure gradients (with β larger than around 7) lead to inconsistent results in all the techniques except the Diagnostic Plot. This method also has the advantage of providing an objective way of defining the point where the mean streamwise velocity is 99% of the edge velocity, and shows consistent results in a wide range of pressure gradient conditions, as well as flow histories. Therefore, the technique based on the Diagnostic Plot is a robust method to determine the boundary layer thickness (equivalent to δ99) and edge velocity in pressure gradient turbulent boundary layers.
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generalization of the Diagnostic Plot to higher order moments in turbulent boundary layers
5th International Conference on Jets Wakes and Separated Flows ICJWSF2015 15 June 2015 through 18 June 2015, 2016Co-Authors: Ramis Orlu, Antonio Segalini, Joseph Klewicki, Henrik P AlfredssonAbstract:The present work extends the Diagnostic Plot concept for the streamwise turbulence intensity in wall-bounded turbulent flows [Alfredsson and Orlu, Eur. J. Mech. B/Fluids 42, 403 (2010)], and generalizes it for higher-order (even and odd) moments, thereby providing a general description of the probability density distribution of streamwise velocity fluctuations. Turbulent boundary layer data up to a friction Reynolds number of 20000 are employed and demonstrate the feasibility of the Diagnostic Plot to scale data throughout the logarithmic and wake regions.
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A new formulation for the streamwise turbulence intensity distribution in wall-bounded turbulent flows
European Journal of Mechanics B-fluids, 2012Co-Authors: P. Henrik Alfredsson, Ramis Orlu, Antonio SegaliniAbstract:Abstract The distribution of the streamwise velocity turbulence intensity has recently been discussed in several papers both from the viewpoint of new experimental results as well as attempts to model its behavior. In the present paper numerical and experimental data from zero pressure-gradient turbulent boundary layers, channel and pipe flows over smooth walls have been analyzed by means of the so called Diagnostic Plot introduced by Alfredsson & Orlu [P.H. Alfredsson, R. Orlu, The Diagnostic Plot–a litmus test for wall bounded turbulence data, Eur. J. Mech. B Fluids 29 (2010) 403–406]. In the Diagnostic Plot the local turbulence intensity is Plotted as function of the local mean velocity normalized with a reference velocity scale. Alfredsson et al. [P.H. Alfredsson, A. Segalini, R. Orlu, A new scaling for the streamwise turbulence intensity in wall-bounded turbulent flows and what it tells us about the outer peak, Phys. Fluids 23 (2011) 041702] observed that in the outer region of the boundary layer a universal linear decay of the turbulence intensity independent of the Reynolds number exists. This approach has been generalized for channel and pipe flows as well, and it has been found that the deviation from the previously established linear region appears at a given wall distance in viscous units (around 120) for all three canonical flows. Based on these results, new empirical fits for the streamwise velocity turbulence intensity distribution of each canonical flow are proposed. Coupled with a mean streamwise velocity profile description the model provides a composite profile for the streamwise variance profile that agrees nicely with existing numerical and experimental data. Extrapolation of the proposed scaling to high Reynolds numbers predicts the emergence of a second peak of the streamwise variance profile that at even higher Reynolds numbers overtakes the inner one.
Antonio Segalini - One of the best experts on this subject based on the ideXlab platform.
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generalization of the Diagnostic Plot to higher order moments in turbulent boundary layers
5th International Conference on Jets Wakes and Separated Flows ICJWSF2015 15 June 2015 through 18 June 2015, 2016Co-Authors: Ramis Orlu, Antonio Segalini, Joseph Klewicki, Henrik P AlfredssonAbstract:The present work extends the Diagnostic Plot concept for the streamwise turbulence intensity in wall-bounded turbulent flows [Alfredsson and Orlu, Eur. J. Mech. B/Fluids 42, 403 (2010)], and generalizes it for higher-order (even and odd) moments, thereby providing a general description of the probability density distribution of streamwise velocity fluctuations. Turbulent boundary layer data up to a friction Reynolds number of 20000 are employed and demonstrate the feasibility of the Diagnostic Plot to scale data throughout the logarithmic and wake regions.
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A new formulation for the streamwise turbulence intensity distribution in wall-bounded turbulent flows
European Journal of Mechanics B-fluids, 2012Co-Authors: P. Henrik Alfredsson, Ramis Orlu, Antonio SegaliniAbstract:Abstract The distribution of the streamwise velocity turbulence intensity has recently been discussed in several papers both from the viewpoint of new experimental results as well as attempts to model its behavior. In the present paper numerical and experimental data from zero pressure-gradient turbulent boundary layers, channel and pipe flows over smooth walls have been analyzed by means of the so called Diagnostic Plot introduced by Alfredsson & Orlu [P.H. Alfredsson, R. Orlu, The Diagnostic Plot–a litmus test for wall bounded turbulence data, Eur. J. Mech. B Fluids 29 (2010) 403–406]. In the Diagnostic Plot the local turbulence intensity is Plotted as function of the local mean velocity normalized with a reference velocity scale. Alfredsson et al. [P.H. Alfredsson, A. Segalini, R. Orlu, A new scaling for the streamwise turbulence intensity in wall-bounded turbulent flows and what it tells us about the outer peak, Phys. Fluids 23 (2011) 041702] observed that in the outer region of the boundary layer a universal linear decay of the turbulence intensity independent of the Reynolds number exists. This approach has been generalized for channel and pipe flows as well, and it has been found that the deviation from the previously established linear region appears at a given wall distance in viscous units (around 120) for all three canonical flows. Based on these results, new empirical fits for the streamwise velocity turbulence intensity distribution of each canonical flow are proposed. Coupled with a mean streamwise velocity profile description the model provides a composite profile for the streamwise variance profile that agrees nicely with existing numerical and experimental data. Extrapolation of the proposed scaling to high Reynolds numbers predicts the emergence of a second peak of the streamwise variance profile that at even higher Reynolds numbers overtakes the inner one.
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A new formulation for the streamwise turbulence intensity distribution
Journal of Physics: Conference Series, 2011Co-Authors: P. Henrik Alfredsson, Ramis Orlu, Antonio SegaliniAbstract:Numerical and experimental data from zero pressure-gradient turbulent boundary layers over smooth walls have been analyzed by means of the so called Diagnostic Plot introduced by Alfredsson & Orlu [Eur. J. Fluid Mech. B/Fluids, 42, 403 (2010)]. In the Diagnostic Plot the local turbulence intensity is shown as a function of the local mean velocity normalized with a reference velocity scale. In the outer region of the boundary layer a universal linear decay of the turbulence intensity is observed independent of Reynolds number. The deviation from this linear region appears in the buffer region and seems to be universal when normalized with the friction velocity. Therefore, a new empirical fit for the streamwise velocity turbulence intensity distribution is proposed and the results are compared with up to date reliable high-Reynolds number experiments and extrapolated towards Reynolds numbers relevant to atmospherical boundary layers.
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the Diagnostic Plot a new way to appraise turbulent boundary layer data
Bulletin of the American Physical Society, 2009Co-Authors: Henrik P Alfredsson, Ramis Orlu, Antonio Segalini, Thomas Kurian, Jens H M Fransson, Jeandaniel Ruedi, Alessandro TalamelliAbstract:During the last decade there has been a renewed interest in how averaged quantities of the turbulent boundary layer vary in the direction normal to the wall, especially with regard to the mean and fluctuation velocity distributions (see e.g. [1, 2]). Comparing data from different facilities and/or different techniques are, however, often inconclusive since the inaccuracies of the measured quantities may be larger than the trends one wants to investigate.
Yongxin Xu - One of the best experts on this subject based on the ideXlab platform.
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the Diagnostic Plot analysis of artesian aquifers with case studies in table mountain group of south africa
Hydrogeology Journal, 2015Co-Authors: Yongxin XuAbstract:Parameter estimates of artesian aquifers where piezometric head is above ground level are largely made through free-flowing and recovery tests. The straight-line method proposed by Jacob-Lohman is often used for interpretation of flow rate measured at flowing artesian boreholes. However, the approach fails to interpret the free-flowing test data from two artesian boreholes in the fractured-rock aquifer in Table Mountain Group (TMG) of South Africa. The Diagnostic Plot method using the reciprocal rate derivative is adapted to evaluate the artesian aquifer properties. The variation of the derivative helps not only identify flow regimes and discern the boundary conditions, but also facilitates conceptualization of the aquifer system and selection of an appropriate model for data interpretation later on. Test data from two free-flowing tests conducted in different sites in TMG are analysed using the Diagnostic Plot method. Based on the results, conceptual models and appropriate approaches are developed to evaluate the aquifer properties. The advantages and limitations of using the Diagnostic Plot method on free-flowing test data are discussed.
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The Diagnostic Plot analysis of artesian aquifers with case studies in Table Mountain Group of South Africa
Hydrogeology Journal, 2015Co-Authors: Yongxin XuAbstract:A estimativa de parâmetros dos aquíferos artesianos onde os níveis piezométricos se encontram acima do nível do solo é, na maior parte das vezes, baseada nos caudais livres e em ensaios de recuperação. O método da linha reta proposto por Jacob-Lohman é muitas vezes usado para a interpretação da descarga medida em poços artesianos repuxantes. No entanto, a abordagem falha na interpretação dos dados do ensaio de caudal livre de dois poços artesianos no aquífero fraturado do Grupo de Table Mountain (GTM), na África do Sul. O método da projeção diagnóstica, que usa a derivada do recíproco do caudal, é adaptado para avaliar as propriedades do aquífero artesiano. A variação da derivada ajuda não só na identificação dos regimes de fluxo e no discernimento das condições de fronteira, como também facilita a concetualização do sistema aquífero e a seleção de um modelo adequado para a interpretação dos dados numa fase posterior. São analisados os dados de dois ensaios de caudal livre realizados em diferentes locais no GTM, usando o método da projeção diagnóstica. Com base nos resultados, são desenvolvidos modelos conceituais e abordagens adequadas para avaliar as propriedades do aquífero. São discutidas as vantagens e as limitações do uso do método da projeção diagnóstica com dados de ensaios de caudal livre. 通过自流和恢复试验主要对压水头高于地面的自流含水层的参数进行了估算。Jacob-Lohman提出的直线法经常用于解译自流钻孔的流量。然而,该方法不能解译南非桌山山脉组断裂岩含水层中的自流试验数据。利用倒数率导数的诊断标绘方法适合评估自流含水层特性。导数变化不仅有助于确定水流动态、识别边界条件,而且还可以促进含水层的概念化及以后用于数据解译的合适模型的选择。对桌山山脉组不同地点进行的自流试验数据采用诊断标绘方法进行了分析。根据研究结果,开发了概念模型和适当方法用来评估含水层特性。探讨了分析自流试验数据所用的诊断标绘方法的优点和局限。 Les estimations des paramètres des aquifères artésiens, où la charge hydraulique est au-dessus du niveau du sol, sont largement réalisées au moyen d’essais de pompage en écoulement libre et de suivi de la remontée. La méthode de la droite proposée par Jacob-Lohman est souvent utilisée pour l’interprétation du débit mesuré au niveau de forages artésiens en écoulement. Cependant, l’approche ne parvient pas à interpréter les données d’un essai en écoulement libre réalisé au sein de deux forages artésiens de l’aquifère fracturé du groupe de la Montagne de la Table (TMG) en Afrique du Sud. La méthode du graphe de Diagnostic utilisant la dérivée de l’inverse du débit est adaptée pour évaluer les propriétés de l’aquifère artésien. La variation de la dérivée aide non seulement à identifier les régimes d’écoulement et discerner les conditions aux limites, mais elle facilite aussi la conceptualisation du système aquifère et la sélection d’un modèle approprié pour l’interprétation ultérieure des données. Les données de deux essais en écoulement libre conduits en différents sites du TMG sont analysées en utilisant la méthode du graphe de Diagnostic. Des modèles conceptuels et des approches appropriées sont développés sur la base de ces résultats, afin d’évaluer les propriétés des aquifères. Les avantages et limites de l’utilisation de la méthode du graphe de Diagnostic pour les données d’essais en écoulement libre sont discutés. Parameter estimates of artesian aquifers where piezometric head is above ground level are largely made through free-flowing and recovery tests. The straight-line method proposed by Jacob-Lohman is often used for interpretation of flow rate measured at flowing artesian boreholes. However, the approach fails to interpret the free-flowing test data from two artesian boreholes in the fractured-rock aquifer in Table Mountain Group (TMG) of South Africa. The Diagnostic Plot method using the reciprocal rate derivative is adapted to evaluate the artesian aquifer properties. The variation of the derivative helps not only identify flow regimes and discern the boundary conditions, but also facilitates conceptualization of the aquifer system and selection of an appropriate model for data interpretation later on. Test data from two free-flowing tests conducted in different sites in TMG are analysed using the Diagnostic Plot method. Based on the results, conceptual models and appropriate approaches are developed to evaluate the aquifer properties. The advantages and limitations of using the Diagnostic Plot method on free-flowing test data are discussed. La estimación de los parámetros de acuíferos artesianos donde la carga piezométrica está por encima del nivel del terreno, en gran medida, son realizados a través de ensayos de flujo libre y recuperación. El método de la línea recta propuesto por Jacob-Lohman se usa a menudo para la interpretación de las medidas de caudal en las perforaciones artesianas. Sin embargo, el enfoque es equivocada para la interpretación de los datos de ensayos de flujo libre a partir de dos perforaciones artesianas en un acuífero de rocas fracturadas en el Table Mountain Group (TMG) de Sudáfrica. El diagnóstico por el método gráfico usando la derivada de la tasa recíproca se adapta para evaluar las propiedades del acuífero artesiano. La variación de la derivada ayuda no solamente a identificar el régimen de flujo y discernir las condiciones de los límites, sino también que facilita la conceptualización del sistema acuífero y la selección de un modelo apropiado para la interpretación posterior de los datos. Se analizan los datos de dos ensayos de flujo libre realizados en diferentes sitios en TMG usando el método gráfico de diagnóstico. En base a los resultados se desarrollan modelos conceptuales y enfoques apropiados para evaluar las propiedades del acuífero. Se discuten las ventajas y limitaciones de usar el método gráfico de diagnóstico en datos de ensayos de flujo libre.
Claudia Becker - One of the best experts on this subject based on the ideXlab platform.
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rdela a delaunay triangulation based location and covariance estimator with high breakdown point
Statistics and Computing, 2013Co-Authors: Steffen Liebscher, Thomas Kirschstein, Claudia BeckerAbstract:We propose an approach that utilizes the Delaunay triangulation to identify a robust/outlier-free subsample. Given that the data structure of the non-outlying points is convex (e.g. of elliptical shape), this subsample can then be used to give a robust estimation of location and scatter (by applying the classical mean and covariance). The estimators derived from our approach are shown to have a high breakdown point. In addition, we provide a Diagnostic Plot to expand the initial subset in a data-driven way, further increasing the estimators' efficiency.
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RDELA—a Delaunay-triangulation-based, location and covariance estimator with high breakdown point
Statistics and Computing, 2013Co-Authors: Steffen Liebscher, Thomas Kirschstein, Claudia BeckerAbstract:We propose an approach that utilizes the Delaunay triangulation to identify a robust/outlier-free subsample. Given that the data structure of the non-outlying points is convex (e.g. of elliptical shape), this subsample can then be used to give a robust estimation of location and scatter (by applying the classical mean and covariance). The estimators derived from our approach are shown to have a high breakdown point. In addition, we provide a Diagnostic Plot to expand the initial subset in a data-driven way, further increasing the estimators’ efficiency.
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RDELA-a Delaunay-triangulation-based, location and covariance estimator with high breakdown point
Statistics and Computing, 2013Co-Authors: Steffen Liebscher, Thomas Kirschstein, Claudia BeckerAbstract:We propose an approach that utilizes the Delaunay triangulation to identify a robust/outlier-free subsample. Given that the data structure of the non-outlying points is convex (e.g. of elliptical shape), this subsample can then be used to give a robust estimation of location and scatter (by applying the classical mean and covariance). The estimators derived from our approach are shown to have a high breakdown point. In addition, we provide a Diagnostic Plot to expand the initial subset in a data-driven way, further increasing the estimators' efficiency. © 2012 Springer Science+Business Media, LLC.
Henrik P Alfredsson - One of the best experts on this subject based on the ideXlab platform.
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generalization of the Diagnostic Plot to higher order moments in turbulent boundary layers
5th International Conference on Jets Wakes and Separated Flows ICJWSF2015 15 June 2015 through 18 June 2015, 2016Co-Authors: Ramis Orlu, Antonio Segalini, Joseph Klewicki, Henrik P AlfredssonAbstract:The present work extends the Diagnostic Plot concept for the streamwise turbulence intensity in wall-bounded turbulent flows [Alfredsson and Orlu, Eur. J. Mech. B/Fluids 42, 403 (2010)], and generalizes it for higher-order (even and odd) moments, thereby providing a general description of the probability density distribution of streamwise velocity fluctuations. Turbulent boundary layer data up to a friction Reynolds number of 20000 are employed and demonstrate the feasibility of the Diagnostic Plot to scale data throughout the logarithmic and wake regions.
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the Diagnostic Plot a litmus test for wall bounded turbulence data
European Journal of Mechanics B-fluids, 2010Co-Authors: Henrik P Alfredsson, Ramis OrluAbstract:A Diagnostic Plot is suggested that can be used to judge wall bounded turbulence data of the mean and the rms of the streamwise velocity in terms of reliability both near the wall, around the maximum in the rms as well as in the outer region. The important feature of the Diagnostic Plot is that neither the wall position nor the friction velocity needs to be known, since it shows the rms value as a function of the streamwise mean velocity, both normalized with the free stream velocity. One must remember, however, that passing the test is a necessary, but not sufficient condition to prove good data quality.
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the Diagnostic Plot a new way to appraise turbulent boundary layer data
Bulletin of the American Physical Society, 2009Co-Authors: Henrik P Alfredsson, Ramis Orlu, Antonio Segalini, Thomas Kurian, Jens H M Fransson, Jeandaniel Ruedi, Alessandro TalamelliAbstract:During the last decade there has been a renewed interest in how averaged quantities of the turbulent boundary layer vary in the direction normal to the wall, especially with regard to the mean and fluctuation velocity distributions (see e.g. [1, 2]). Comparing data from different facilities and/or different techniques are, however, often inconclusive since the inaccuracies of the measured quantities may be larger than the trends one wants to investigate.