Unsteady RANS and detached-eddy simulations of flow around a circular cylinder in ground effect

Nishino, Takafumi; Roberts, G.T.; Zhang, X.

doi:10.1016/j.jfluidstructs.2007.06.002

Cited by 82 publications

(35 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The concept of URANS is based on the triple decomposition of time-dependent variables, where each instantaneous variable, such as velocity and pressure, is decomposed into longtime averaged, periodic, and turbulent components [10,11]. Typical RANS equations are solved in an unsteady way, even if the boundary conditions are steady [9].…”

Section: Uransmentioning

confidence: 99%

See 1 more Smart Citation

Numerical study on wake characteristics of high-speed trains

et al. 2013

View full text Add to dashboard Cite

Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the

show abstract

Section: Uransmentioning

confidence: 99%

“…For the latter one, it is realized by replacing the turbulence length scale factor with the function min[n, 0.65∆ max ], in which: ∆ max = max[∆x, ∆y, ∆z], where ∆x, ∆y, ∆z are the length of the side of the controlling volume respectively. As a result, the transition between URANS and LES could be achieved [10].…”

Section: Desmentioning

confidence: 99%

Numerical study on wake characteristics of high-speed trains

et al. 2013

View full text Add to dashboard Cite

show abstract

“…the adiabatic/protected wall surfaces) are constructed with quality meshes, typically a near-wall resolution of Δy + < 0.5, as addressed by Nishino et al [34] in an effort to assure a sufficiently fine spatial resolution for unsteady flow phenomenon at the mixing region. As suggested by Spalart et al [35][36] and Joo et al [37], the grid should be refined in the x, y and z directions in order to keep the consistency of local grid spacing in the 3-D domain, which is important to control the F DES factor in the SST model (see the equation (9)).…”

Section: Mesh Generationmentioning

confidence: 99%

DES study of blade trailing edge cutback cooling performance with various lip thicknesses

Effendy

Yao

et al. 2016

Applied Thermal Engineering

View full text Add to dashboard Cite

Highlights Detached-eddy simulation of the mixing process between mainstream flow and coolant;  Effects of various t/H ratios on blade trailing-edge cutback cooling performance;  Vortex shedding behind the lip plays an important role in near wall cooling efficiency;  Discharge coefficient and adiabatic film-cooling effectiveness agree with experiment;  Thermal mixing has been greatly intensified with the increase of the t/H ratio. ABSTRACTThree-dimensional detached-eddy simulation (DES) study has been carried out to evaluate the cooling performance of a trailing-edge cutback turbine blade with various lip thickness to slot height ratios (t/H). By adopting the shear-stress transport (SST) k-ω turbulence model, the numerical investigations were performed at two successive steps: first, to validate simulation results from an existing cutback turbine blade model with staggered circular pin-fins arrays inside the cooling passage against experimental measurements and other available numerical predictions; second, to understand the effects of the lip thickness to the slot height ratio on the blade trailing-edge cooling performance. It was found from the model validations that at two moderate blowing ratios of 0.5 and 1.1, DES predicted film cooling effectiveness are in very good agreement with experimental data. Further comparisons of four various t/H ratios (t/H = 0.25, 0.5, 1.0, 1.5) have revealed that the thermal mixing process between the 'cold' coolant gas and the 'hot' mainstream flow in the near wake region of the exit slot has been greatly intensified with the increase of the t/H ratio. As a result, it causes a rapid decay of the adiabatic film cooling effectiveness downstream of the blade trailing-edge. The observed vortex shedding and its characteristics in the near wake region are found to play an important role in determining the dynamic process of the 'cold' and the 'warm' airflow mixing, which in turn have significant influences on the prediction accuracy of the near-wall heat transfer performance. As the four t/H ratio increases from 0.25 to 1.5, DES predicts the decrease of main shedding frequencies as f s = 3.69, 3.2, 2.21, and 1.49 kHz, corresponding to Strouhal numbers S t = 0.15, 0.20, 0.23, and 0.22, respectively. These results are in good agreement with available experimental measurements.

show abstract

“…The detached eddy simulation (DES) is a hybrid method which combines RANS and LES together [14,15], and benefits a lot in solving large separation problems with high Reynolds numbers. DES usually keeps high accuracy in predicting aerodynamic drag and separation locations for large separation flows around ground transport vehicles.…”

Section: Desmentioning

confidence: 99%

“…For the latter one, it is realized by replacing the turbulence length scale factor n with the function, in which: D max = max[Dx, Dy, Dz], where Dx, Dy, Dz are the lengths of the sides of the controlling volume respectively. As a result, the transition between URANS and LES could be achieved [14].…”

Section: Desmentioning

confidence: 99%

Optimization design for aerodynamic elements of high speed trains

et al. 2014

View full text Add to dashboard Cite

a b s t r a c tThe complex wake flow of high speed trains severely influences the running safety and amenity of the trailing car. In this paper, based on the streamlined shape of CRH380A high speed train, taking the aerodynamic lift force of the trailing car and the volume of the streamlined head as the objectives, an efficient multi-objective optimization process based on the response surface has been constructed. The Kriging model has been constructed based on the cross-validation method and genetic algorithm (GA). This approach could decrease the number of training samples and improve the optimization efficiency while without decreasing its generalization. After the Pareto optimal solutions being obtained, four design points are chosen for comparative study with the original shape, and one of these points is chosen for the unsteady aerodynamic study together with the original shape. The results reveal that the variation trends of the lift force and the side force of the trailing car are the same as that of the drag of the whole train. After optimization, the volume of the streamlined head is almost the same as that of the original shape. Compared to the original shape, the lift force of the trailing car decreases by 27.86% of and the drag of the whole train decreases by 3.34% in conditions without crosswind, and the lift force of the trailing car decreases by 5.43%, the side force of the whole train decreases by 72.09% and the drag of the whole train decreases by 2.1% in the crosswind conditions. The optimal train benefits from low fluctuations of lift and side force of the trailing car. Besides, better wake flow could be obtained, and the wake vortices are suppressed, too. Consequently, the running safety and amenity of HST are improved a lot after optimization.

show abstract

Unsteady RANS and detached-eddy simulations of flow around a circular cylinder in ground effect

Cited by 82 publications

References 22 publications

Numerical study on wake characteristics of high-speed trains

Numerical study on wake characteristics of high-speed trains

DES study of blade trailing edge cutback cooling performance with various lip thicknesses

Optimization design for aerodynamic elements of high speed trains

Contact Info

Product

Resources

About