The Budget of Turbulent Kinetic Energy in the Urban Roughness Sublayer

Christen, Andreas; Rotach, Mathias W.; Vogt, Roland

doi:10.1007/s10546-009-9359-5

Cited by 79 publications

(71 citation statements)

References 52 publications

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“…Roth (2000) summarized the studies on urban turbulence in the twentieth century and found that velocity spectra show good agreement with reference spectra. Later, Feigenwinter et al (1999), Roth et al (2006), Vesala et al (2008), Christen et al (2009) confirmed general agreement between the shape of the spectrum over built-up terrain and a flat, homogeneous surface. Less documented is the dependence of the spectrum on the stability parameter, and the location of the spectrum peak.…”

Section: Introductionsupporting

confidence: 52%

“…Our results for a w /a u (a w /a u = 1.11 and a w /a u = 1.13) are lower than predicted by isotropy, but they are consistent with other works. Values of a w /a u lower than 4/3 were observed in many studies, especially for rough surfaces such as forest (Anderson et al 1986;Amiro 1990;Su et al 2004) or (sub)urban areas, where the values of a w /a u range from 1.03 to 1.20 as reported by Roth and Oke (1993), Roth et al (2006), and Christen et al (2009). Högström et al (1982) found in Uppsala the a w /a u ratio close to 4/3 for measurements at a height of 50 m, and 1.15 and 1.06 for sensors mounted at lower heights.…”

Section: The Spectra Of Velocity Componentsmentioning

confidence: 82%

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Selected Spectral Characteristics of Turbulence over an Urbanized Area in the Centre of Łódź, Poland

Fortuniak

Pawlak

2014

Boundary-Layer Meteorol

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We present the turbulence spectra and cospectra derived from more than five years of eddy-covariance measurements at two urban sites in Łódź, central Poland. The fast response wind velocity components were obtained using sonic anemometers placed on narrow masts at 37 and 42 m above ground level. The analysis follows Kaimal et al. (Q J R Meteorol Soc 98:563-589, 1972) who established the spectral and cospectral properties of turbulent flow in atmospheric surface layer on the basis of the Kansas experiment. Our results illustrate many features similar to those of Kaimal et al., but some differences are also observed. The velocity (co)spectra from Łódź show a clear inertial subrange with −2/3 slope for spectra and −4/3 slope for cospectra. We found that an appropriate stability function for the non-dimensional dissipation of turbulent kinetic energy calculated from spectra in the inertial subrange differs from that of Kaimal et al., and it can be satisfactorily estimated with the assumption of local equilibrium using standard functions for the non-dimensional shear production. A similar function for the cospectrum corresponds well to Kaimal et al. for unstable and weakly stable conditions. The (co)spectra normalized by their spectral values in the inertial subrange are in general similar to those of Kaimal et al., but they peak at lower frequencies in strongly stable conditions. Moreover, our results do not confirm the existence of a clear "excluded region" at low frequencies for the transition from stable to unstable conditions, for longitudinal and lateral wind components. The empirical models of Kaimal et al. with adjusted parameters fit well to the vertical velocity spectrum and the vertical momentum flux cospectrum. The same type of function should be used for longitudinal and lateral wind spectra because of their sharper peak than occurs for the Kansas data. Finally, it should be stressed that the above relationships are well-defined for averaged values. The results for individual 1-h periods are very scattered and can be significantly different from the generalized functions.

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Section: Introductionsupporting

confidence: 52%

Section: The Spectra Of Velocity Componentsmentioning

confidence: 82%

Selected Spectral Characteristics of Turbulence over an Urbanized Area in the Centre of Łódź, Poland

Fortuniak

Pawlak

2014

Boundary-Layer Meteorol

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“…Finally, we validated our model with data from two different experiments: an LES study from Coceal et al, (2007) and with data from the Bubble experiment (Rotach et al, 2005;Christen et al, 2009). Although, there were some discrepancies in the wind speed close to the ground, the simulation results were in very good agreement with the measured data, especially when taking into account the computational time and the fact that CIM is a 1D column module resolving the flow in 2 directions only.…”

Section: Resultsmentioning

confidence: 71%

“…To assess CIM's ability to reproduce vertical wind profile in an urban environment, we compare the profile obtained from CIM with those from an LES experiment designed for a regular arrays of cubes (Coceal et al, 2007;Xie et al, 2008) (see Table 2) and with data from the BUBBLE experiment (Rotach et al, 2005;Christen et al, 2009) (see Table 3). …”

Section: Cim Performance With Urban Obstaclesunder Neutral Conditionsmentioning

confidence: 99%

On the Coherence in the Boundary Layer: Development of a Canopy Interface Model

et al. 2017

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A 1D Canopy Interface Model (CIM) is developed to act as an interface between a meso-scale and a micro-scale atmospheric model and to better resolve the surface turbulent fluxes in the urban canopy layer. A new discretisation is proposed to solve the TKE equation finding solutions that remain fully concordant with the surface layer theories developed for neutral flows over flat surfaces. A correction is added in the buoyancy term of the TKE equation to improve consistency with the Monin-Obukhov surface layer theory. Obstacles of varying heights and dimensions are taken into account by introducing specific terms in the equations and by modifying the mixing length formulation in the canopy layer. The results produced by CIM are then compared with wind and TKE profiles simulated with a LES experiment and results obtained during the BUBBLE meteorological intensive observation campaign. It is shown that the CIM computations are in good agreement with the results simulated by the LES as well as the measurements from BUBBLE. The applicability of the correction term in an urban canopy layer and to further validate CIM in multiple stability conditions and various urban configurations is discussed.

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“…In the past few decades experimentalists have devoted significant efforts to measuring the relevant processes that drive mean flow and turbulence in the RSL over real cities (Grimmond and Oke 1999;Eliasson et al 2006;Christen et al 2007;Ramamurthy et al 2007;Christen et al 2009;Peng and Sun 2014;Wang et al 2014;Ramamurthy and Pardyjak 2015). However, such field studies are limited to measurements at a few points and cannot capture the full threedimensional flow field in its heterogeneous state.…”

Section: Introductionmentioning

confidence: 99%

Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface

Giometto

Christen

Meneveau

et al. 2016

Boundary-Layer Meteorol

144

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Single-point measurements from towers in cities cannot properly quantify the impact of all terms in the turbulent kinetic energy (TKE) budget and are often not representative of horizontally-averaged quantities over the entire urban domain. A series of large-eddy simulations (LES) is here performed to quantify the relevance of non-measurable terms, and to explore the spatial variability of the flow field over and within an urban geometry in the city of Basel, Switzerland. The domain has been chosen to be centered around a tower where single-point turbulence measurements at six heights are available. Buildings are represented through a discrete-forcing immersed boundary method and are based on detailed real geometries from a surveying dataset. The local model results at the tower location compare well against measurements under near-neutral stability conditions and for the two prevailing wind directions chosen for the analysis. This confirms that LES in conjunction with the immersed boundary condition is a valuable model to study turbulence and dispersion within a real urban roughness sublayer (RSL). The simulations confirm that mean velocity profiles in the RSL are characterized by an inflection point z γ located above the average building height z h . TKE in the RSL is primarily produced above z γ , and turbulence is transported down into the urban canopy layer. Pressure transport is found to be significant in the very-near-wall regions. Further, spatial variations of time-averaged variables and non-measurable dispersive terms are important in the RSL above a real urban surface and should therefore be considered in future urban canopy parametrization developments.

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The Budget of Turbulent Kinetic Energy in the Urban Roughness Sublayer

Cited by 79 publications

References 52 publications

Selected Spectral Characteristics of Turbulence over an Urbanized Area in the Centre of Łódź, Poland

Selected Spectral Characteristics of Turbulence over an Urbanized Area in the Centre of Łódź, Poland

On the Coherence in the Boundary Layer: Development of a Canopy Interface Model

Spatial Characteristics of Roughness Sublayer Mean Flow and Turbulence Over a Realistic Urban Surface

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