2D experiments and numerical simulation of the oscillatory shallow flow in an open channel lateral cavity

Steady shallow flows past an open channel lateral cavity can induce the excitation of an eigenmode of a gravity standing wave inside the cavity, called seiche, which may be coupled with the shedding of vortices at the opening of the cavity. The presence of the seiche is of fundamental interest as it enhances the mass exchange between the main channel and the cavity. Measurements of the time evolution of the water surface are not often found in the literature for this type of flows. In this work, an experimental and numerical study of a shallow flow past a channel lateral cavity is carried out. The main novelty is the use of a pioneering non-intrusive experimental technique to measure the water surface at the channel-cavity region. This optical technique offers high resolution 2D data in time and space of the water surface evolution, allowing to determine the relevant features of the seiche oscillation. Such data are supplemented with Particle Image Velocimetry measurements. Furthermore, the experiments are numerically reproduced using a high-resolution depth-averaged URANS shallow water model, under the assumption that shallow water turbulence is mainly horizontal. The experimental and numerical results are analyzed in the frequency domain. High-resolution two-dimensional amplitude oscillation maps of the seiche phenomenon, as well as velocity fields, are presented. The high quality of the experimental data reported in this work makes this data set a suitable benchmark for numerical simulation models in order to evaluate their performance in the resolution of turbulent resonant shallow flows

High order simulation models for the resolution of wave propagation phenomena in turbulent free surface flows

[EN] A depth-averaged large eddy simulation (DA-LES) model, based on the unsteady Reynolds averaged Navier Stokes approach for the shallow water equations, is herein presented. The simulation model aims at the resolution of free surface shallow flows where large-scale turbulence is mainly two-dimensional. The keystone of the model is the combination of a high order of accuracy in space and time with a suitable turbulence modelling that accounts for the effect of the unresolved eddies in the mean flow. The proposed model ensures the well-balanced property (i.e. quiescent equilibrium with machine precision) thanks to the use of augmented Riemann solvers, which include the bed slope source term in the definition of the derivative Riemann problem. The performance of the proposed model is assessed using experimental data from the literature. In particular, a laboratory experiment involving a shallow water flow over a submerged conical island is considered. The numerical results evidence that the proposed model is able to reproduce transient turbulent phenomena, providing a higher level of information and resolution than other models based on the traditional RANS (Reynolds averaged Navier Stokes) approach.[ES] En este trabajo se presenta una herramienta de simulación basada en la resolución transitoria de grandes remolinos (URANS o DA-LES) para flujos turbulentos de aguas poco profundas en los que la turbulencia es predominantemente horizontal. El aspecto fundamental del modelo es la combinación de una discretización de alto orden en espacio y tiempo con una modelización de los efectos en el flujo promedio de las escalas turbulentas no resueltas. El modelo propuesto garantiza con precisión de máquina el equilibrio hidrostático (propiedad well-balanced) gracias a la utilización de una formulación del flujo numérico que incluye los términos fuente en la resolución del problema de Riemann derivativo en las paredes de las celdas. Se presenta una validación del modelo utilizando datos de literatura para un experimento de laboratorio que involucra un flujo de aguas poco profundas sobre una isla cónica, que da lugar a la generación de una calle de vórtices aguas abajo de la isla. Los resultados numéricos muestran que el modelo propuesto es capaz de reproducir fenómenos turbulentos bidimensionales, proporcionando un mayor nivel de detalle que la aproximación RANS tradicional.Este trabajo ha sido financiado por el Ministerio de Ciencia e Innovación (proyecto PGC2018-094341-B-I00). También ha sido financiado por el Gobierno de Aragón (Referencia Grupo T32_17R) y cofinanciado con Feder 2014-2020 “Construyendo Europa desde Aragón”. Los autores agradecen los comentarios constructivos, correcciones y observaciones de los revisores, que han ayudado a mejorar la calidad de este trabajo.Navas-Montilla, A.; Murillo, J.; García-Navarro, P. (2019). Modelos de simulación de alto orden para la resolución de fenómenos de propagación de ondas en flujos de lámina libre con turbulencia. Ingeniería del Agua. 23(4):275-287. https://doi.org/10.4995/ia.2019.12169SWORD27528723

A family of well-balanced WENO and TENO schemes for atmospheric flows

We herein present a novel methodology to construct very high order well-balanced schemes for the computation of the Euler equations with gravitational source term, with application to numerical weather prediction (NWP). The proposed method is based on augmented Riemann solvers, which allow preserving the exact equilibrium between fluxes and source terms at cell interfaces. In particular, the augmented HLL solver (HLLS) is considered. Different spatial reconstruction methods can be used to ensure a high order of accuracy in space (e.g. WENO, TENO, linear reconstruction), being the TENO reconstruction the preferred method in this work. To the knowledge of the authors, the TENO method has not been applied to NWP before, although it has been extensively used by the computational fluid dynamics community in recent years. Therefore, we offer a thorough assessment of the TENO method to evidence its suitability for NWP considering some benchmark cases which involve inertia and gravity waves as well as convective processes. The TENO method offers an enhanced behavior when dealing with turbulent flows and underresolved solutions, where the traditional WENO scheme proves to be more diffusive. The proposed methodology, based on the HLLS solver in combination with a very high-order discretization, allows carrying out the simulation of meso- and micro-scale atmospheric flows in an implicit Large Eddy Simulation manner. Due to the HLLS solver, the isothermal, adiabatic and constant Brunt-Väisälä frequency hydrostatic equilibrium states are preserved with machine accuracy

Flow structure in a compound channel: benchmarking 2D and 3D numerical models

The benchmarking test of 2D and 3D numerical models on a compound channel flow with a rectangular-shaped main channel and a rectangular-shaped floodplain was carried out by the IAHR Working Group on Compound Channels. The selected test case is the flume experiment by Nezu and Tominaga (1991). Nine depth-averaged 2D models and four 3D models participated in the benchmark. In the 2D models, the depth-averaged streamwise velocity profiles in the lateral direction were compared. In the 3D models, velocity components in three directions as well as the distribution of the turbulence kinetic energy in a cross-section were compared. Through the comparison, the applicability and limitations of each model are highlighted and discussed with regard to the model characteristics.Konferencija je održana na daljinu (on-line), bez fizičkog prisustva i sav materijal se nalazi na web-stranici organizatora skupa

Evaluación de esquemas de alto orden para la simulación numérica de fenómenos de transporte convectivo en flujos reales

Los flujos reales están determinados por características y fenómenos físicos muy complejos. En particular, la turbulencia del movimiento fluido es indescriptible analíticamente, así que es necesario afrontar su resolución mediante métodos numéricos. En la Dinámica de Fluidos Computacional, a la hora de resolver flujos turbulentos es conveniente conocer de manera muy detallada las propiedades de los esquemas numéricos que se van a utilizar. Dos propiedades relevantes de estos esquemas son la dispersión y la difusión numéricas, que pueden ser cuantificadas mediante el análisis espectral de von Neumann. En este trabajo se explora el estudio de varios esquemas numéricos, utilizando esta metodología, para evaluar su adecuación para la resolución de problemas de turbulencia. El análisis espectral de los esquemas numéricos se complementa con el estudio de un problema unidimensional descrito por la ecuación de Burgers con término fuente, que presenta características análogas a las de las ecuaciones de Navier-Stokes. Con las conclusiones obtenidas se propone un modelo de simulación para flujos de aguas poco profundas y se evalúan sus limitaciones.<br /

Depth-averaged unsteady RANS simulation of resonant shallow flows in lateral cavities using augmented WENO-ADER schemes

Turbulent shallow flows are characterized by the presence of horizontal large-scale vortices, caused by local variations of the velocity field. Apart from these 2D large vortices, small scale 3D turbulence, mainly produced by the interaction of the flowing water with the solid boundaries, is also present. The energy spectrum of turbulent shallow flows shows the presence of a 2D energy cascade at low wave numbers and a 3D energy cascade at high wave numbers, with a well-defined separation region between them. Horizontal flow movements (e.g. 2D large-scale vortical structures) at low wave numbers mostly determine the hydrodynamic behavior of these flows. Moreover, the generation of standing waves often occurs closely associated to the interaction of 2D horizontal flows with lateral boundaries, this is the case of seiches. To adequately reproduce these phenomena, a mathematical and numerical model able to resolve 2D turbulence is required. We herein show that depth-averaged (DA) unsteady Reynolds averaged Navier Stokes (URANS) models based on the Shallow Water Equations (SWE) are a suitable choice for the resolution of turbulent shallow flows with sufficient accuracy in an affordable computational time. The 3D small-scale vortices are modeled by means of diffusion terms, whereas the 2D large-scales are resolved. A high order numerical scheme is required for the resolution of 2D large eddies. In this work, we design a DA-URANS model based on a high order augmented WENO-ADER scheme. The mathematical model and numerical scheme are validated against observation of complex experiments in an open channel with lateral cavities that involve the presence of resonant phenomena (seiching). The numerical results evidence that the model accurately reproduces both longitudinal and transversal resonant waves and provides an accurate description of the flow field. The high order WENO-ADER scheme combined with a SWE model allows to obtain a powerful, reliable and efficient URANS simulation tool.Accepted Author ManuscriptRivers, Ports, Waterways and Dredging Engineerin

Depth-averaged unsteady RANS simulation of resonant shallow flows in lateral cavities using augmented WENO-ADER schemes

Turbulent shallow flows are characterized by the presence of horizontal large-scale vortices, caused by local variations of the velocity field. Apart from these 2D large vortices, small scale 3D turbulence, mainly produced by the interaction of the flowing water with the solid boundaries, is also present. The energy spectrum of turbulent shallow flows shows the presence of a 2D energy cascade at low wave numbers and a 3D energy cascade at high wave numbers, with a well-defined separation region between them. Horizontal flow movements (e.g. 2D large-scale vortical structures) at low wave numbers mostly determine the hydrodynamic behavior of these flows. Moreover, the generation of standing waves often occurs closely associated to the interaction of 2D horizontal flows with lateral boundaries, this is the case of seiches. To adequately reproduce these phenomena, a mathematical and numerical model able to resolve 2D turbulence is required. We herein show that depth-averaged (DA) unsteady Reynolds averaged Navier Stokes (URANS) models based on the Shallow Water Equations (SWE) are a suitable choice for the resolution of turbulent shallow flows with sufficient accuracy in an affordable computational time. The 3D small-scale vortices are modeled by means of diffusion terms, whereas the 2D large-scales are resolved. A high order numerical scheme is required for the resolution of 2D large eddies. In this work, we design a DA-URANS model based on a high order augmented WENO-ADER scheme. The mathematical model and numerical scheme are validated against observation of complex experiments in an open channel with lateral cavities that involve the presence of resonant phenomena (seiching). The numerical results evidence that the model accurately reproduces both longitudinal and transversal resonant waves and provides an accurate description of the flow field. The high order WENO-ADER scheme combined with a SWE model allows to obtain a powerful, reliable and efficient URANS simulation tool.The present work has been partially funded by Gobierno de Aragón through the Fondo Social Europeo (T32-17R). This research has also been supported by the Research Project CGL2015-66114-R, funded by the Spanish Ministry of Economy and Competitiveness (MINECO).Peer reviewe