Applicability of URANS and DES Simulations of Flow Past Rectangular Cylinders and Bridge Sections

Abstract

This paper discusses the results of computational fluid dynamics simulations carried out for rectangular cylinders with various side ratios of interest for many civil engineering structures. A bridge deck of common cross-section geometry was also considered. Unsteady Reynolds-averaged Navier-Stokes (URANS) equations were solved in conjunction with either an eddy viscosity or a linearized explicit algebraic Reynolds stress model. The analysis showed that for the case studies considered, the 2D URANS approach was able to give reasonable results if coupled with an advanced turbulence model and a suitable computational mesh. The simulations even reproduced, at least qualitatively, complex phenomena observed in the wind tunnel, such as Reynolds number effects for a sharp-edged geometry. The study focused both on stationary and harmonically oscillating bodies. For the latter, self-excited forces and flutter derivatives were calculated and compared to experimental data. In the particular case of a benchmark rectangular 5:1 cylinder, 3D detached eddy simulations were also carried out, highlighting the improvement in the accuracy of the results with respect to both 2D and 3D URANS calculations. All of the computations were performed with the Tau code, a non-commercial unstructured solver developed by the German Aerospace Center.

Numerical and experimental analysis of automotive turbocharger compressor aeroacoustics at different operating conditions

“…On average, each time step of the conducted detached eddy simulations took 20% more computational time than the correspondent one using URANS. As indicated by Mannini [34], the expected increase of computational effort when moving from URANS to DES is not mainly due to the greater cost of solving a set of discretized equations corresponding to one cell, but to the demand of better spatial and temporal resolution. In this work, the same computational grid and time-step size were used for both turbulence modeling approaches as suggested by the sensitivity studies conducted by Navarro [16].…”

The Turbulence Intensity Effect on the Flow Characteristics and Aerodynamics of a Circular Cylinder

“…] +(1-F 1 )CD kω (5) in which, G =min(G, c 1 * kω) and G=v t S 2 . F 1 is a blending that is described as…”

“…In addition to the experimental studies, numerical studies investigating flow structure the flow structure around bluff bodies has been increasing. Mannini et al [5] compared the flow structure around a rectangular cross section by using numerical method of Unsteady Reynolds Averaged Navier-Stokes (URANS) and Detached Eddy Simulation (DES) turbulence models at Reynolds number, Re=21600. According to the results, DES always provides results closer to the experimental studies and while URANS gave a partially good results when the edge ratios of rectangle were 5:1, neither 2D nor 3D URANS simulations could give as accurate results as 3D DES at edge ratios of rectangle, 1:5.…”

“…He showed that LES and DES models gave very close results in experimental study in all parameters examined comparing with URANS models. Norberg and Sunden [12] experimentally investigated the influence of the turbulence intensity and Reynolds number on the flow structure past a circular cylinder at Reynolds number within the range of 2×10 4 and 3×10 5 and turbulence intensities in free-stream flow as 0.1% and 0.4%. They pointed out that pressure forces increase when the turbulence intensity gets higher for Reynolds number smaller than, 10 5 , while reverse effect was detected for higher Reynolds numbers.…”

Silindir Etrafındaki Kararsız Akışın Farklı Türbülans Modelleri ile Sayısal Olarak İncelenmesi

“…[8] 2D URANS modellerinin Reynolds gerilmelerini doğru tahmin etmesinden kaynaklı olarak ölü akış bölgesini daha kısa ve sürükleme kuvvetini ise yüksek tahmin ettiğini göstermişlerdir. Mannini [9] Re= 21600'de dikdörtgen ve köprü kesiti etrafındaki akışı URANS ve DES ile kıyaslamışlardır. DES her zaman deneye daha yakın sonuçlar vermiş ve dikdörtgenin kenar oranları 5:1 oranında iken 2D URANS kısmen iyi sonuç verse de 1:5 oranında ne 2D ne de 3D URANS 3D DES kadar iyi sonuç verebilmiştir.…”