1 Ankara International Aerospace Conference 10 th ANKARA INTERNATIONAL AEROSPACE CONFERENCE AIAC-2019-151 18-20 September 2019 - METU, Ankara TURKEY A NUMERICAL ASSESSMENT OF ATMOSPHERIC BOUNDARY LAYER SIMULATION INSIDE TWO DIFFERENT BOUNDARY LAYER WIND TUNNELS Anas Abdulrahim 1 Middle East Technical University Ankara, Turkey Munir Elfarra 2 Ankara Yıldırım Beyazıt University Ankara, Turkey Oğuz Uzol 3 Middle East Technical University Ankara, Turkey ABSTRACT A new large scale wind tunnel is under development at METU Center for Wind Energy (RÜZGEM). This wind tunnel is a closed-loop multi-purpose wind tunnel with a 3 m x 7 m x 20 m boundary layer test section. Inside this test section the atmospheric boundary layer (ABL) will be simulated using the spire-roughness element technique in order to represent different terrain exposures (or categories) as defined by American Society of Civil Engineers (ASCE). Since no experimental data are available yet, Computational Fluid Dynamics (CFD) will be implemented as a tool in order to provide an initial assessment for the simulation of the ABL. However, in order to validate the CFD approach, another wind tunnel test case from literature will be used for comparison. This wind tunnel has 1.82 m x 1.82 m x 9.8 m test section. Four different test cases have been simulated and the results show reasonable agreement between the experiments and numerical results in terms of velocity profiles, power law exponents and boundary layer parameters. INTRODUCTION In order to correctly simulate the atmospheric boundary layer (ABL) inside a wind tunnel test section, certain conditions need to be met such as the velocity profile, turbulence intensity as well as turbulent length scales and power spectrum that represent a certain terrain category. According to ASCE7-10 (2010), there are four different terrain categories (A, B, C & D) classified according to the power law exponent ( α) ranging from 0.4 for terrain A to 0.05 for terrain D. Wind tunnel simulation of the ABL could be achieved using either passive or active techniques. Passive techniques include vortex generators such as spires, array of roughness elements, grids as well as a combination of these devices [Counihan, 1969 & 1973; Cook, 1973; Irwin, 1981]. On the other hand, active techniques include active grids, multiple fans, or oscillating spires [Cao et al., 2002; Pang and Lin, 2008]. Both techniques require intensive research and investigation in order to find the appropriate combination of these devices to properly simulate a certain terrain or exposure category. Therefore, in order to save time and cost, CFD has been implemented to provide initial assessment for such experiments. For instance, Shojaee et al., (2009 & 2014), conducted CFD simulations in the Ankara Wind Tunnel using different combinations of spires and roughness elements in order to represent different terrain 1 PhD Candidate. Department of Aerospace Engineering, METU. Lecturer, Faculty of Air Transportation, University of Turkish Aeronautical Association (UTAA.) Email: anas.abdulrahim@metu.edu.tr 2 Assistant Professor. Department of Aerospace Engineering, Ankara YBU. Email: monierelfarra@hotmail.com 3 Professor. Department of Aerospace Engineering, METU. Head, METU Center for Wind Energy (RÜZGEM). Email: uzol@metu.edu.tr