Article

Large-eddy simulation of flow over a surface-mounted prism using a high-order finite-difference scheme

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Abstract

Large eddy simulation (LES) of the flow field over a surface-mounted prism under two different conditions, namely smooth and turbulent inflows, are carried out. A higher-order scheme, in which artificial dissipation is controllable, is used. The simulations are validated through comparison with experimental measurements. The results present new physical aspects and details regarding the development of the primary separation flow on the upwind face of the prism, the development of the horseshoe vortex flow, the primary and secondary separations of the reversed flow on the roof, and finally the locations of the highest suction pressures (in the mean) on the roof and the sides of the prism with respect to the secondary separation lines. The effects of the incident turbulence are determined by pointing out differences in the flow topologies between the two incident flow cases. Based on the validation with the experimental results, the compact upwind difference fifth-order scheme, used here, is recommended for performing LESs of complex flows.

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... In a study by Kwon and Kareem [6], they introduced the "Gust Front Factor" to account for transient aerodynamic effects in building codes. The effect of turbulence on the flow over surface-mounted prism using LES accompanied by velocity field measurements via PIV is examined by El-Okda et al., [7]. An experimental investigation was done by Lim et al., [8] where pressure measurements and smoke flow visualizations were done on a cube. ...
... Pilot pressure measurements were taken on a bare model without any modifications. The pressure distribution was compared to published results by El-Okda et al., [7]. The resulting pressure distribution, Figure 5, did not match any published results. ...
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... Numerical simulation of flows that exhibit complex characteristics such as separation, transition of the separated shear layer and vortex shedding can be performed with different levels of fidelity. High-fidelity simulations such as large eddy simulation (LES) (El-Okda et al., 2008;Ayed et al., 2015) and direct numerical simulation (DNS) require fine grids and are computationally expensive. A more common approach is to use the Reynolds-averaged navier-stokes (RANS) with different models for the Reynolds stresses. ...
... Numerical simulation of flows that exhibit complex characteristics such as separation, transition of the separated shear layer and vortex shedding can be performed with different levels of fidelity. High-fidelity simulations such as large eddy simulation (LES) (El-Okda et al., 2008;Ayed et al., 2015) and direct numerical simulation (DNS) require fine grids and are computationally expensive. A more common approach is to use the Reynolds-averaged navier-stokes (RANS) with different models for the Reynolds stresses. ...
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... Recent advances in hardware and software technology and numerical modeling are encouraging widespread applications of computational fluid dynamics (CFD) in wind engineering. Significant progress has been made in the application of computational wind engineering (CWE) to evaluate wind loads on short and tall buildings (to name some, Murakami and Mochida, 1988;Stathopoulos, 1997;Camarri et al., 2006;Tamura et al., 2008;Tutar and Celik, 2007;El-Okda et al., 2008;Tominaga et al., 2008;Dagnew et al., 2009 and others). Following similar principle, Shademan and Hangan (2009) employed a CFD simulation to estimate wind loads on stand-alone and arrayed solar panels engulfed in a turbulent wind field. ...
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The objective of this paper is to validate the large eddy simulation (LES) technique for predicting a flow around an obstacle under the condition that a turbulent flow is approaching the obstacle. The turbulent inflow data were generated for both a smooth surface and rough surfaces by the method we had proposed. A half-height cube was immersed in the turbulent boundary layers with several types of vertical velocity profile. With regard to the pressure distributions on the surface of the half-height cube, the computed time-averaged and rms values are in good agreement with previous experimental ones. However, the peak pressure coefficients are underestimated, especially compared to full-scale data.
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The suitability of high-order accurate, centered and upwind-biased compact difference schemes for large eddy simulation (LES) is evaluated through the static and dynamic analyses. For the static error analysis, the power spectra of the finite-differencing and aliasing errors are evaluated in the discrete Fourier space, and for the dynamic error analysis LES of isotropic turbulence is performed with various dissipative and non-dissipative schemes. Results from the static analysis give a misleading conclusion that both the aliasing and finite-differencing errors increase as the numerical dissipation increases. The dynamic analysis, however, shows that the aliasing error decreases as the dissipation increases and the finite-differencing error overweighs the aliasing error. It is also shown that there exists an optimal upwind scheme of minimizing the total discretization error because the dissipative schemes decrease the aliasing error but increase the finite-differencing error. In addition, a classical issue on the treatment of nonlinear term in the Navier–Stokes equation is revisited to show that the skew-symmetric form minimizes both the finite-differencing and aliasing errors. The findings from the dynamic analysis are confirmed by the physical space simulations of turbulent channel flow at Re=23000 and flow over a circular cylinder at Re=3900.
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The difference schemes for fluid dynamics type of equations based on third- and fifth-order Compact Upwind Differencing (CUD) are considered. To validate their properties following from a linear analysis, calculations were carried out using the inviscid and viscous Burgers' equation as well as the compressible Navier–Stokes equation written in the conservative form for curvilinear coordinates. In the latter case, transonic cascade flow was chosen as a representative example. The performance of the CUD methods was estimated by investigating mesh convergence of the solutions and comparing with the results of second-order schemes. It is demonstrated that the oscillation-free steep gradients solutions obtained without using smoothing techniques can provide considerable increase of accuracy even when exploiting coarse meshes.
Thesis
Stromingen van vloeistoffen en gassen die gehoorzamen aan de wetten van Newton worden beschreven door de Navier-Strokes vergelijkingen. Deze vergelijkingen bestaan uit drie behoudswetten: 1) de wet van behoud van massa, 2) de wet van behoud van impuls en 3) de wet van behoud van energie. Een belangrijke dimensieloze grootheid in de stromingsleer is het zogenaamde Reynoldsgetal (Re). Het Reynoldsgetal geeft de relatieve belangrijkheid aan van de convectie t.o.v. de diffusie. Hoe groter het Reynoldsgetal is, des te belangrijker is de convectie in vergelijking met de diffusie. Bij een laag Reynoldsgetal gedragen stromingen zich redelijk glad, we hebben dan te maken met een 'laminaire stroming'. ... Zie: Samenvatting.
Higher-order compact schemes for numerical simulation of incompressible flows. ICASE, NASA Langley Research Center, ICASE Report No. 98-13 A new filtered dynamic subgrid-scale model for large eddy simulation of indoor airflow
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Wilson, R.V., Demuren, A.O., Carpenter, M., 1998. Higher-order compact schemes for numerical simulation of incompressible flows. ICASE, NASA Langley Research Center, ICASE Report No. 98-13, Hampton, VA. Zhang, W., Chen, Q., 1999. A new filtered dynamic subgrid-scale model for large eddy simulation of indoor airflow. In: Proceedings of Building Simulation '99, Kyoto, Japan. ARTICLE IN PRESS Y.M. El-Okda et al. / J. Wind Eng. Ind. Aerodyn. 96 (2008) 900–912
Numerical simulation of wind loads on structures and effects of incident turbulence
  • M A K Elsayed
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Elsayed, M.A.K., Elokda, Y.M., Ragab, S.A., Hajj, M.R., 2005. Numerical simulation of wind loads on structures and effects of incident turbulence. In: Fourth European and African Conference on Wind Engineering, Prague, Czech Republic, July 11–15.