Journal of Wind Engineering and Industrial Aerodynamics 85 (2000) 163}176 The microscale model MIMO: development and assessment J. Ehrhard*, I.A. Khatib, C. Winkler, R. Kunz, N. Moussiopoulos, G. Ernst Institut fu ( r Technische Thermodynamik, Universita ( t Karlsruhe, D-76128 Karlsruhe, Germany Laboratory of Heat Transfer and Environmental Engineering, Aristotle University Thessaloniki, GR-54006 Thessaloniki, Greece Abstract The numerical model MIMO is a three-dimensional model for simulating microscale wind #ow and dispersion of pollutants in built-up areas. It solves the Reynolds averaged conserva- tion equations for mass, momentum and energy. Additional transport equations for humidity, liquid water content and passive pollutants can be solved. The Reynolds stresses and turbulent #uxes of scalar quantities can be calculated by several linear and nonlinear turbulence models. A staggered grid arrangement is used and coordinate transformation is applied to allow non- equidistant meshsize in all three dimensions in order to achieve a high resolution near the ground and near obstacles. The model was validated for a variety of test cases and it was applied successfully to air pollution problems.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Urban atmosphere; Pollutant dispersion; Turbulence modeling; Numerical simulation; Coupling 1. Introduction The increasing interest in the prediction of wind #ow and pollutant dispersion over built-up areas and major advances in computer technologies have led to the develop- ment of e$cient numerical models as an alternative or complementary approach to laboratory and "eld experiments. The microscale model MIMO [1] was developed at the Institut fu K r Technische Thermodynamik on the basis of the non-hydrostatic * Corresponding author. Present address: ABB ALSTOM POWER Technology Ltd., CH-5405 Baden- Da K ttwil, Switzerland. Tel.: #41-56-486-70-04; fax: #41-56-486-73-18. E-mail address: jan.ehrhard@ch.abb.com (J. Ehrhard) 0167-6105/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 6 7 - 6 1 0 5 ( 9 9 ) 0 0 1 3 7 - 3