The numerical computation of near-wall turbulent flow over a steep hill

Loureiro, Juliana; Alho, Alexandre T. P.; Freire, Atila P. Silva

doi:10.1016/j.jweia.2008.01.011

Cited by 38 publications

(14 citation statements)

References 28 publications

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“…It is referred to as a model of SST model which was associated to benefits of k-ω turbulence model for simulation of features of the k-ε turbulence model and the near-wall boundary layer, wherein small dependence concerning conditions of the far-field boundary was involved. Hence, its accuracy and reliability of prediction are higher [ 22 – 24 ]. The eddy viscosity and k equation and ω equation of the SST model can be written into the following form: …”

Section: Methodology and Toolsmentioning

confidence: 99%

Numerical simulation of unsteady aerodynamic interactions of contra-rotating axial fan

Luan¹,

Weng²,

Luan³

2018

PLoS ONE

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This paper describes the investigations performed to better understand unsteady effect that develop in a contra-rotating axial fan. More specifically, this study focuses on rotor-rotor interactions effects on unsteady characteristic and blade aerodynamic force. The investigation method is based on three-dimensional URANS simulations, in conjunction with SST turbulence model. At first, the experimental measurements are compared to evaluate ability of the numerical method in estimation of unsteady flows. The results show that rotor-rotor interaction in the contra-rotating fan played an important role in aerodynamic efficiency. Unsteady effect increased flow losses of rotor 1, but effectively inhibited flow losses of rotor 2. The inhibition effect was mainly caused by wake recovery effect of upstream wakes in the flow passage of rotor 2. Meanwhile, negative jet flow enhanced boundary layer energy of the blade of rotor 2, so that flow separation was postponed. Different configurations consider five sets of axial spacing dimensions. Specific survey of flows under the same operation conditions indicates that axial spacing is responsible for the unsteady interaction effect. The blade aerodynamics analysis shows that the influence of the downstream potential flow disturbance on rotor 1 is greater than the effect of the upstream wake on rotor 2.

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Section: Methodology and Toolsmentioning

confidence: 99%

Numerical simulation of unsteady aerodynamic interactions of contra-rotating axial fan

Luan¹,

Weng²,

Luan³

2018

PLoS ONE

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“…Regarding the experiment of an incoming turbulent boundary layer flow over a single hill model, Loureiro et al [10] recently examined the nearwall turbulent statistics, including the wall shear stress, using a one-component LDV with a forward-scatter mode in a water tunnel. The detailed near-wall data were used for assessment of various turbulence models [25].…”

Section: Introductionmentioning

confidence: 99%

Turbulent Heat and Fluid Flow over a Two-Dimensional Hill

Houra

Nagano

2009

Flow Turbulence Combust

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Experimental investigation has been made on the flow and thermal fields over a heated two-dimensional hill with a cosine-squared shape. The detailed turbulent characteristics are measured by a backscatter-type two-component LDV, a PIV system, a fine thermocouple and a cold-wire probe. In the reverse-flow region on the leeward side of the hill, the turbulence intensities and the Reynolds shear stress show much larger values than in a canonical wall-bounded shear flow. The mean temperature maintains a relatively high value below the location where the horizontal mean velocity rapidly decreases. At the outer edge of the reverse-flow region, there exists a second maximum intensity of temperature fluctuations. The instantaneous temperature waveforms near the heated surface show very large amplitude consisting of high-frequency fluctuations superimposed on the low-frequency motions. Simultaneous measurement of velocity and temperature is also done using a combination of a two-component LDV and a fine-wire thermocouple together with digital response compensation. In the downstream region of the hill, the horizontal and vertical turbulent heat fluxes become maximum at the hill-top height, and tend to diffuse in the vertical direction. On the other hand, in the reverse-flow region formed behind the hill, both of the heat fluxes decrease remarkably. In particular, it is worth noting that the horizontal turbulent heat flux near the surface becomes opposite in sign to that in the forward flow region. This is mainly due to the reversal of the mean flow direction. Nomenclature C pwall static pressure coefficient,height of a two-dimensional hill L half width of a two-dimensional hill P probability density function P mean pressure P 0 reference inlet pressure R θ Reynolds number based on momentum thickness T, T instantaneous and mean temperatures T w , T ∞ wall and ambient temperatures t fluctuating temperature, t = T − T t fluctuating temperature normalized by rms value,t = t/t rms

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“…Adopting LES, a constant mixing-length assumption was found not to be strictly valid within the canopy by Ross [14], the same conclusion reached in a recent study by Okaze et al [15], and the structure of the turbulence over a forested hill was found to be broadly similar to that over flat ground, with sweeps and ejections dominating. Then, Loureiro et al developed a consistent theory on the flow over rough ground using water-tank experiments [5,16]. Furthermore, the surface roughness was found to have a great influence on the flow separation point which occurs earlier with rougher surface leading to a larger recirculation area, in the studies by Takahashi et al [17], Cao and Tamura [12], Tamura et al [18], Loureiro et al [5], and Cao et al [19].…”

Section: Introductionmentioning

confidence: 99%

“…Flow structures over complex topographies are featured by the flow separations and reattachments which strongly depend on the topographic aspects, including surface roughness conditions, slopes, and shapes. On the other hand, the turbulent flow fields over complex terrain are of a great interest for many applications, such as wind turbine sittings [1], pollution diffusions [2], estimation of aerodynamic loadings on structures [3], identifications of tree damage [4], and forest fire propagation [5]. As a starting point modeling flow fields over real complex terrains, great efforts have been made to clarify the turbulent boundary layer (TBL) over simplified isolated hills.…”

Section: Introductionmentioning

confidence: 99%

“…Then, Loureiro et al developed a consistent theory on the flow over rough ground using water-tank experiments [5,16]. Furthermore, the surface roughness was found to have a great influence on the flow separation point which occurs earlier with rougher surface leading to a larger recirculation area, in the studies by Takahashi et al [17], Cao and Tamura [12], Tamura et al [18], Loureiro et al [5], and Cao et al [19]. Most recently, Liu et al concluded that with intent to capture the turbulent characteristics accurately the horizontal gird size should be at least as large as the height of the roughness canopy [20].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Large Eddy Simulations of the Flow Fields over Simplified Hills with Different Roughness Conditions, Slopes, and Hill Shapes: A Systematical Study

Liu

Wang

2019

Energies

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Turbulent flow fields over topographies are important in the area of wind energy. The roughness, slope, and shape of a hill are important parameters affecting the flow fields over topographies. However, these effects are always examined separately. The systematic investigations of these effects are limited, the coupling between these effects is still unrevealed, and the turbulence structures as a function of these effects are still unclear. Therefore, in the present study, the flow fields over twelve simplified isolated hills with different roughness conditions, slopes, and hill shapes are examined using large eddy simulations. The mean velocities, velocity fluctuations, fractional speed-up ratios, and visualizations of the turbulent flow fields are presented. It is found that as the hill slope increases, the roughness effects become weaker, and the roughness effects will further weaken as the hill changes from 3D to 2D. In addition, the fractional speed-up ratio at the summit of rough hills can even reach to three times as large as that over the corresponding smooth hills. Furthermore, the underestimation of the ratios of spanwise fluctuation to the streamwise fluctuation by International Electrotechnical Commission (IEC) 61400-1 is quite obvious when the hill shape is 3D. Finally, coherent turbulence structures can be identified for smooth hills, and as the hill slope increases, the coherent turbulence structures will experience clear evolutions. After introducing the ground roughness, the coherent turbulence structures break into small eddies.

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The numerical computation of near-wall turbulent flow over a steep hill

Cited by 38 publications

References 28 publications

Numerical simulation of unsteady aerodynamic interactions of contra-rotating axial fan

Numerical simulation of unsteady aerodynamic interactions of contra-rotating axial fan

Turbulent Heat and Fluid Flow over a Two-Dimensional Hill

Large Eddy Simulations of the Flow Fields over Simplified Hills with Different Roughness Conditions, Slopes, and Hill Shapes: A Systematical Study

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