On the simulation of thick non-neutral boundary layers for urban studies in a wind tunnel

Marucci, Davide; Carpentieri, Matteo; Hayden, Paul

doi:10.1016/j.ijheatfluidflow.2018.05.012

Cited by 27 publications

(48 citation statements)

References 35 publications

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“…The averaging time for each measurement was set to 2.5 minutes, in line with previous work both in neutral (Castro et al, 2017) and non-neutral (Marucci et al, 2018;Marucci and Carpentieri, 2019b) conditions. The standard error for first and second order statistics was evaluated at each measurement point.…”

Section: Measurementsmentioning

confidence: 99%

“…Surface quantities in stratified UBLs were estimated following the methodology described by Marucci et al (2018). It assumed that the spatially averaged profiles for the Reynolds shear stress and vertical heat flux were approximately linear in both the roughness sub-layer (RSL) and the region immediately above.…”

Section: Scaling and Estimation Of Surface Propertiesmentioning

confidence: 99%

“…The same geometry was already studied by Castro et al (2017) and Fuka et al (2018) for neutral stratification. Great emphasis has also been dedicated to the characteristics of the approaching flow, as described in details by Marucci et al (2018). This paper deals mainly with the modifications in the flow, turbulence and temperature fields introduced by a non-neutral stratification on an urban array.…”

Section: Introductionmentioning

confidence: 99%

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Stable and convective boundary-layer flows in an urban array

Marucci

Carpentieri

2020

Journal of Wind Engineering and Industrial Aerodynamics

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In this paper non-neutral approaching flows were employed in a meteorological wind tunnel on a regular urban-like array of rectangular buildings. As far as stable stratification is concerned, results on the flow above and inside the canopy show a clear reduction of the Reynolds stresses and an increment of the Monin-Obukhov length up to 80%. The roughness length and displacement height were also affected, with a reduction up to 35% for the former and an increment up to 12% for the latter. A clear reduction of the turbulence within the canopy was observed. In the convective stratification cases, the friction velocity appears increased by both the effect of roughness and unstable stratification. The increased roughness causes a reduction in the surface stratification, reflected in an increase of the Monin-Obukhov length, which is double over the array compared to the approaching flow. The effect on the aerodynamic roughness length and displacement height are specular to the SBL case, an increase up to 50% of the former and a reduction of the same amount for the latter.

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Section: Measurementsmentioning

confidence: 99%

Section: Scaling and Estimation Of Surface Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stable and convective boundary-layer flows in an urban array

Marucci

Carpentieri

2020

Journal of Wind Engineering and Industrial Aerodynamics

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“…where Θ symbols represent temperatures, U velocities, the subscripts δ and H, respectively, the boundary-layer depth and the buildings' height, g is the gravitational acceleration and Θ 0 is a reference temperature measured close to the floor (at z = 10 mm). Stable boundary layers were generated by imposing a non-uniform inlet temperature profile, cooling the floor at a desired temperature and adjusting the maximum inlet temperature (∆Θ M AX is defined as the difference between this maximum temperature and the floor temperature) and reference velocity (U REF ) to set the required stratification strength (Marucci et al, 2018). It should be noted that Ri app δ in the table is the nominal (or desired) bulk Richardson number of the approaching flow, which sometimes differs slightly from the one actually measured (also reported in the table).…”

Section: Approaching Flow and Boundary Layer Over The Arraymentioning

confidence: 99%

“…It was a first attempt to bridge the identified gap in the literature about the lack of experimental data in non-neutral conditions. Initially, new methodologies were developed and optimised to simulate either stable or convective conditions in a meteorological wind tunnel, producing a boundary layer that was thick enough for urban studies (Marucci et al, 2018). The non-neutral boundary layers produced in that first phase were then applied to a single heated/cooled street canyon (Marucci and Carpentieri, 2019a) and to an array of rectangular buildings (Marucci and Carpentieri, 2019b).…”

Section: Introductionmentioning

confidence: 99%

Dispersion in an array of buildings in stable and convective atmospheric conditions

Marucci

Carpentieri

2020

Atmospheric Environment

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Wind tunnel experiments were conducted to study the impact of atmospheric stratification on flow and dispersion within and over a regular array of rectangular buildings. Three stable and two convective incoming boundary layers were tested with a Richardson number ranging from −1.5 to 0.29. Dispersion measurements were carried using a fast response flame ionisation detector. The results show that the stratification effect on the plume width is significantly lower than the effect on the vertical profiles. Stable stratification did not affect the plume central axis inside the canopy, but in the unstable case the axis appeared to deviate from the neutral case direction. Above the canopy both stratification types caused an increase in the plume deflection angle compared to the neutral case. Measured mean concentrations in stable stratification were up to two times larger in the canopy compared to the neutral case, while in convective conditions they were to three times smaller. The proportionality between the vertical turbulent fluxes and the vertical mean concentration gradient was also confirmed in the stratified cases. The high-quality experimental data produced during this work may help developing new mathematical models and parametrisation for non-neutral stratified conditions, as well as validating existing and future numerical simulations.

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Neutrally- and stably-stratified boundary layers adjustments to a step change in surface roughness

et al. 2023

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In this work, we study the development of the internal boundary layer (IBL) induced by a surface roughness discontinuity, where the downstream surface has a roughness length greater than that upstream. The work is carried out in the EnFlo meteorological wind tunnel, at the University of Surrey, in both thermally neutral and stable cases with varying degrees of stability. For the neutrally-stratified boundary layer, the IBL development in the log-law region shows good agreement with the diffusion model proposed by Panofsky and Dutton (Atmospheric turbulence, Wiley, New York, 1984) provided that a modified origin condition is introduced and its growth rate is dictated by a constant diffusion term. However, the model over-predicts the growth of the IBL in the outer layer, where the IBL depth grows slowly with fetch following a power function with exponent n being 0.61 (whereas the original model prescribes $$n\approx 0.8$$ n ≈ 0.8 ). For the stably-stratified boundary layers, n is found to further reduce as the bulk Richardson number, $$\textrm{Ri}_\textrm{b}$$ Ri b , increases. The analysis of the top region of the IBL shows that the slow growth rate is due to a combination of the decay of the diffusion term and a significantly negative mean wall-normal velocity, which transports fluid elements towards the wall. Considering these two effects, a modified diffusion model is proposed which well captures the growth of the IBL for both neutrally and stably-stratified boundary layers. Graphical abstract

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On the simulation of thick non-neutral boundary layers for urban studies in a wind tunnel

Cited by 27 publications

References 35 publications

Stable and convective boundary-layer flows in an urban array

Stable and convective boundary-layer flows in an urban array

Dispersion in an array of buildings in stable and convective atmospheric conditions

Neutrally- and stably-stratified boundary layers adjustments to a step change in surface roughness

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