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Application of Laser Doppler Anemometry to estimate turbulent power spectra inside an urban canopy

Herpin, Sophie and Perret, Laurent and Mathis, Romain and Tanguy, Christian and Lasserre, Jean-Jacques Application of Laser Doppler Anemometry to estimate turbulent power spectra inside an urban canopy. (2018) In: 19th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics, 16 July 2018 - 19 July 2018 (LISBON, Portugal).

(Document in English)

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In the present contribution, we propose to make use of Laser Doppler Anemometry to investigate the dynamics of the flow inside an urban canopy immersed into a thick turbulent boundary layer. Previous studies dedicated to such flows (Castro et al. 2006; Reynolds and Castro 2008) have focused the core of their analysis on the roughness sublayer region or on the inertial region. In contrast, the region below the canopy interface have received little attention so far, and only mean velocity or Reynolds stresses data can be found in the literature. Indeed, getting access to the dynamics of the flow inside the canopy represents a real experimental challenge: the flow is turbulent, 3-dimensionnal, and due to the tight clearance, only non-intrusive laser-based techniques such as LDA or PIV can be used. In this contribution, for the first time, a spectral analysis of the flow is carried out inside the canopy region. This is made possible thanks to very thorough LDA measurements as well as the use of advanced post-processing algorithm to compute temporal power spectra. Indeed, LDA measurement yields non-equidistantly spaced data points, and standard FFT algorithms cannot be used. A detailed comparison of various algorithms is undertaken, and a slight improvement is proposed to reduce the impact of measurement noise. Finally, the power spectra inside the canopy are analyzed and the main implications on the flow dynamics are discussed.

Item Type:Conference or Workshop Item (Paper)
HAL Id:hal-02363973
Audience (conference):International conference proceedings
Uncontrolled Keywords:
Institution:Other partners > Agrocampus Ouest (FRANCE)
French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Other partners > Ecole Centrale de Nantes (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
Other partners > Dantec Dynamics (FRANCE)
Laboratory name:
Agence Nationale pour la Recherche
Deposited On:14 Nov 2019 15:18

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