OPENFOAM COMPUTATIONAL FLUID DYNAMICS SIMULATIONS OF THERMAL WIND GENERATION IN MOUNTAIN/VALLEY CONFIGURATIONS

Thermal winds appear in mountainous areas and valleys due to temperature gradients caused by the buoyancy effects associated with the diurnal heating-cooling cycle of the lower atmosphere. These winds develop over complex topographies of multiple scales, and reverse their direction twice a day, driven by formation and dissipation of temperature inversions. Winds may flow up-slope (anabatic winds), up-valley, or from the plain to the mountain massif during day-time. Conversely, during night-time, winds may flow down-slope (katabatic winds), down-valley, or from the mountain massif to the plain. Previous investigations have shown that such winds can reach relatively high speeds [1], which can be interesting for wind energy applications. Moreover, thermal winds showing higher regularity and periodicity than synoptic winds [1], can thus be more predictable, which is of special interest to the current energy market, aiming to match the energy demand with the renewable energy production, given the fact that wind energy and solar energy production cannot be controlled at will. In this work, thermal wind generation is analysed using OpenFOAM, which is an open source computational fluid dynamics software. For this analysis, an idealized numerical model of a mountain-valley system with a mountain slope angle of 20º is used. Anabatic and katabatic winds are generated imposing altitude-dependent temperature boundary conditions on the slope. OpenFOAM’s solver buoyantBoussinesqPimpleFoam is used, and validation of different turbulence models and initial conditions is done by comparing OpenFOAM simulations with results from the literature. The effects of the fluid domain height and of the valley width on the flow behaviour are also discussed. Conclusion on anabatic and katabatic wind formation and on their possible application to wind energy generation is finally drawn

Comparison of OpenFOAM turbulence models for numerical simulation of thermally-driven winds

Commercial computational fluid dynamics (CFD) codes have often been used for simulation of atmospheric boundary layer (ABL) flows. The present work explores the potential of the open-source CFD software OpenFOAM for simulating thermally-driven winds, by comparing several turbulence models. Indeed, in ABL and other large-scale flows, turbulence is critical to the mixing process of momentum and buoyancy, and simulations with commercial CFD codes have usually been done with Reynolds-Averaged Navier-Stokes (RANS) turbulence modelling. In this work, the formation of thermally-driven winds is studied in an idealised mountain-valley system, with realistic values of parameters such as the slope angle, the diurnal temperature cycle, etc. Performances of various OpenFOAM RANS turbulence models (k–e, re-normalisation group (RNG) k–e, k–¿ shear stress transport (SST)) are compared. A preliminary study of LES using Smagorinsky closure is also contemplated. Velocity contours, velocity and temperature profiles, the shapes of vortexes/convective cells, and the computational times are presented for all the studied turbulence models, to help identify the most suitable one for simulation of thermally-driven winds.This work is supported by the project PID2019-105162RB-I00 funded by MCIN/AEI/10.13039/501100011033 and by the project 2017 SGR 1278 from the AGAUR Generalitat de Catalunya.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.1 - Per a 2030, garantir l’accés universal a serveis d’energia assequibles, confiables i modernsObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaPostprint (published version

Simulations of wind formation in idealised mountain–valley systems using OpenFOAM

An OpenFOAM computational fluid dynamics model setup is proposed for simulating thermally driven winds in mountain–valley systems. As a first step, the choice of Reynolds Averaged Navier–Stokes k-e turbulence model is validated on a 3D geometry by comparing its results vs. large-eddy simulations reported in the literature. Then, a numerical model of an idealised 2D mountain–valley system with mountain slope angle of 20° is developed to simulate thermally driven winds. A couple of top surface boundary conditions (BC) and various combinations of temperature initial conditions (IC) are tested. A transient solver for buoyant, turbulent flow of incompressible fluids is used. Contrary to classical approaches where buoyancy is set as a variable of the problem, here temperature linearly dependent with altitude is imposed as BC on the slope and successfully leads to thermally driven wind generation. The minimum fluid domain height needed to properly simulate the thermally driven winds and the effects of the different setups on the results are discussed. Slip wall BC on the top surface of the fluid domain and uniform temperature IC are found to be the most adequate choices. Finally, valleys with different widths are simulated to see how the mountain–valley geometry affects the flow behaviour, both for anabatic (daytime, up-slope) and katabatic (nighttime, down-slope) winds. The simulations correctly reproduce the acceleration and deceleration of the flow along the slope. Increasing the valley width does not significantly affect the magnitude of the thermally driven wind but does produce a displacement of the generated convective cell.This research was funded by AGAUR/Generalitat de Catalunya, with grant number 2017 SGR 1278, and by the Spanish Science and Innovation Ministry (MCIN) within the project TABL4CW, with grant number PID2019-105162RB-I00, funded by MCIN/AEI/10.13039/501100011033.Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaPostprint (published version

Simulations of Wind Formation in Idealised Mountain–Valley Systems Using OpenFOAM

An OpenFOAM computational fluid dynamics model setup is proposed for simulating thermally driven winds in mountain–valley systems. As a first step, the choice of Reynolds Averaged Navier–Stokes k−ε turbulence model is validated on a 3D geometry by comparing its results vs. large-eddy simulations reported in the literature. Then, a numerical model of an idealised 2D mountain–valley system with mountain slope angle of 20° is developed to simulate thermally driven winds. A couple of top surface boundary conditions (BC) and various combinations of temperature initial conditions (IC) are tested. A transient solver for buoyant, turbulent flow of incompressible fluids is used. Contrary to classical approaches where buoyancy is set as a variable of the problem, here temperature linearly dependent with altitude is imposed as BC on the slope and successfully leads to thermally driven wind generation. The minimum fluid domain height needed to properly simulate the thermally driven winds and the effects of the different setups on the results are discussed. Slip wall BC on the top surface of the fluid domain and uniform temperature IC are found to be the most adequate choices. Finally, valleys with different widths are simulated to see how the mountain–valley geometry affects the flow behaviour, both for anabatic (daytime, up-slope) and katabatic (nighttime, down-slope) winds. The simulations correctly reproduce the acceleration and deceleration of the flow along the slope. Increasing the valley width does not significantly affect the magnitude of the thermally driven wind but does produce a displacement of the generated convective cell

Annealing-induced changes in wear resistance and nanomechanical properties of CuZr metallic glass thin films

Over recent years, metallic glass thin films (MGTFs) have found extensive applications in advanced micro-engineering systems. Consequently, there is a need to thoroughly assess the nanomechanical and tribological behaviors of MGTFs to optimize the design of efficient components. In this study, we employed the nanoindentation technique in various modes to investigate the elastic heterogeneity, tribological response, and mechanical properties of CuZr amorphous films. Before conducting the mechanical tests, annealing treatments at 500 K and 600 K were performed to create samples with different stored energies. The thermal history analysis revealed that the annealing process reduced the stored energy in the microstructure. Furthermore, the pre-annealing treatment resulted in increased hardness and Young’s modulus of the thin films. Additionally, higher annealing temperatures significantly improved the wear resistance of the MGTFs. Observing the serration dynamics in the scratching test, we noticed that the annealing treatment induced larger shear bands on the wear track side. Moreover, the increase in annealing temperature led to a reduction in elastic heterogeneity, which was consistent with the enthalpy relaxation values in the samples. This suggests that the annealing temperature enhanced the densely packed atomic structure, leading to the stabilization of the thin films

OpenFOAM computational fluid dynamics simulations of thermal wind generation in mountain/valley configurations

Thermal winds appear in mountainous areas and valleys due to temperature gradients caused by the buoyancy effects associated with the diurnal heating-cooling cycle of the lower atmosphere. These winds develop over complex topographies of multiple scales, and reverse their direction twice a day, driven by formation and dissipation of temperature inversions. Winds may flow up-slope (anabatic winds), up-valley, or from the plain to the mountain massif during day-time. Conversely, during night-time, winds may flow down-slope (katabatic winds), down-valley, or from the mountain massif to the plain. Previous investigations have shown that such winds can reach relatively high speeds [1], which can be interesting for wind energy applications. Moreover, thermal winds showing higher regularity and periodicity than synoptic winds [1], can thus be more predictable, which is of special interest to the current energy market, aiming to match the energy demand with the renewable energy production, given the fact that wind energy and solar energy production cannot be controlled at will. In this work, thermal wind generation is analysed using OpenFOAM, which is an open source computational fluid dynamics software. For this analysis, an idealized numerical model of a mountain-valley system with a mountain slope angle of 20º is used. Anabatic and katabatic winds are generated imposing altitude-dependent temperature boundary conditions on the slope. OpenFOAM’s solver buoyantBoussinesqPimpleFoam is used, and validation of different turbulence models and initial conditions is done by comparing OpenFOAM simulations with results from the literature. The effects of the fluid domain height and of the valley width on the flow behaviour are also discussed. Conclusion on anabatic and katabatic wind formation and on their possible application to wind energy generation is finally drawn.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.a - Per a 2030, augmentar la cooperació internacional per tal de facilitar l’accés a la investigació i a les tecnolo­gies energètiques no contaminants, incloses les fonts d’energia renovables, l’eficiència energètica i les tecnologies de combustibles fòssils avançades i menys contaminants, i promoure la inversió en infraestructures energètiques i tecnologies d’energia no contaminantPostprint (author's final draft

An OpenFOAM set-up for simulating thermal winds in mountain/valley configurations

Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantPostprint (published version

Mechanical and thermal characterization of coir/hemp/polyester hybrid composite for lightweight applications

Individual applications of coir and hemp as reinforcement in composites have been exhaustively studied; however, their hybridization must also be investigated. In this context, this research investigates the utilization of coir and hemp fibers as reinforcements in a polyester-based hybrid composite system. The primary objective is to find out how these reinforcements affect the hybrid composites' mechanical (tensile, flexural, and impact) and thermo-gravimetric properties. To accomplish this, composite samples with varying weight proportions of coir and hemp fibers were fabricated, and extensive mechanical testing was performed. The findings from the tensile, flexural, and impact tests revealed an enhancement in the mechanical characteristics of the fabricated composites as the proportion of coir fiber grew and the proportion of hemp fiber reduced. The hybrid composite, containing 15% coir and 5% hemp fibers, had superior mechanical properties to the binary composite system. In addition, thermogravimetric analysis was performed to determine the thermal stability of the hybrid composites. Within a temperature range of 30 °C–800 °C, weight loss was observed, confirming the overall thermal resistance of the materials. Fourier Transform InfraRed Spectroscopy (FTIR) was used to determine the composite's chemical composition, revealing the presence of functional groups that contribute to the composite's performance. Utilizing Scanning Electron Microscopy (SEM), the surface morphology of hybrid composites was investigated, yielding valuable insights into the fiber-matrix interaction and composite structure. The results of this study demonstrate the potential of the coir/hemp/polyester hybrid composite as a lightweight material in a variety of industries