EXPERIMENTAL AND COMPUTATIONAL STUDY OF A FLOW OVER A HILL COVERED WITH FOREST O. Agafonova 1 , A. Mityakov 2,3 , A. Chaudhari 4 , S.Lupuleac 5 , and J.Hämäläinen 4 1 Department of Mathematics and Physics, Lappeenranta University of Technology, Skinnarilankatu 34, P.O.Box 20, FI-53851 Lappeenranta, Finland. Tel.: + 358 44 938 9029 2 Department of Thermodynamics and Heat Transfer, Saint Petersburg State Polytechnical University , St. Petersburg, 195251, Polytechnicheskaya Str., 29, Russia 3 LUT Energy, Lappeenranta University of Technology 4 Centre of Computational Engineering and Integrated Design (CEID) and Department of Mathematics and Physics, Lappeenranta University of Technology 5 Department of Applied Mathematics, Saint Petersburg State Polytechnical University Oxana.Agafonova@lut.fi Abstract An experiment conducted in wind tunnel, numerical results, and a comparison between them are considered in the article. The experiment was conducted over a physical model of a hill covered by forest. Forest was modeled numerically using a porous medium. Parameters of the porous medium were selected using the experimental data. Keywords: CFD, flow over a hill, physical experiment, PIV, turbulence modeling, vegetation modeling. Nomenclature H [m] height of the hill U [m/s] x component of mean velocity  U [m/s] velocity inlet from experiment a [m/s] slope of the hill p [Pa] pressure v [m/s] absolute velocity vector δ ij [-] Kronecker delta μ [Pa·s] dynamic viscosity ρ [kg/m 3 ] density inlet at the inlet of the test section outlet at the outlet of the test section LES Large-Eddy Simulation LIDAR Light Detection And Ranging RANS Reynolds-averaged Navier-Stokes Equations SST shear stress transport turbulence model x, z axial (along the wind tunnel axis), transversal (coordinate) 1 Introduction The research subject is related to the theoretical justification of a possible installation of wind turbines beside forested hills. The project enables receiving clean energy and avoiding cutting out forest. This topic is especially relevant because of the natural features of Finland and the north- western regions of the Russian Federation. There are many articles which are devoted to a numerical and experimental study of an air flow over a smooth hill (e.g. [1], [2], [4]). Those computational results are usually compared with the experimental data which was obtained by Kurshydian et al. ([3]) in 1981. The goal of this work is to understand how the vegetation on a hill affects the air flow over the hill. This research work was carried out in both Lappeenranta University of Technology (LUT, Finland) and St. Petersburg State Polytechnical University (SPbSPU, Russia). 2 Experimental methods 2.1 Description of the wind tunnel experiment Own physical experiment using the Particle Image Velocimetry (PIV) technique was conducted in the wind tunnel of Department of Thermodynamics and Heat Transfer of SPbSPU  in order to determine flow behavior and find the parameters of the porous medium model imitating the properties of vegetation. The wind tunnel has the diameter and length of the test section about 450 and 780 mm correspondingly. And it is able to conduct an experiment with the flow velocities 0.3…55 m/s. The scale model (see in Figure 1) especially prepared for this experiment reproduces the hill covered by forest. The slope shape was  S. Soloviev, A. Guzeev (Krylov Shipbuilding Research Institute), and V. Mityakov (SPbSPU) also participated in the conduction of the series of experiments in the wind tunnel of Thermodynamics and Heat Transfer Department of SPbSTU at 08.07.2011.