Blind Comparison

The Bolund experiment has been the basis for a blind comparison of flow models.

The figure above shows wind flow in complex terrain.

Background for Blind Comparison

The Bolund Experiment is a field campaign that provides a new dataset for validating models of flow in complex terrain. An increasing number of wind farms are being installed in complex terrain. However, many of the CFD tools used to predict the wind flow have only been developed for simple terrain and are often evaluated against such. In order to validate the numerical models, full scale field experiments with realistic complex terrain forms are necessary. The Bolund dataset allows just such a validation. The Bolund hill, though relatively small (12m high), has a geometrical shape that is characteristic for many complex sites e.g. a well-exposed, almost vertical upstream escarpment. Additionally, Bolund is located with a well-defined inflow from the sea. During the campaign in 2007 and 2008, velocity and high frequency turbulence data were collected simultaneously from 35 anemometers distributed on 10 masts, thereby generating a large database designed to validate CFD codes.

Blind Comparison

The blind comparison has been a unique opportunity to assess the accuracy of present day flow models. Modelers were challenged to predict the wind over Bolund based on the conditions of the free wind and the orography. To broaden the types of models participating, modelers were invited worldwide from research institutes, universities and industry. More than 40 groups participated in the blind comparison with well over 50 model predictions. Thank you! If you want to simulate the wind over Bolund, please download the description of the simulation cases and the Bolund orography.


80 participants joined the workshop to discuss the results of the blind comparison. The workshop was held at Risø DTU Denmark on 3-4 December 2009. We want to thank you all for your positive and constructive attitudes and for making it a memorable event. Below we have added two links where you can download the presentations from the two workshop days.

The photo above shows the participants at the workshop in 2009.

Publications on the Blind Comparison:

- The Bolund Experiment, Part II: Blind Comparison of Microscale Flow Models (2011). Boundary-Layer Meteorol. doi:10.1007/s10546-011-9637-x (open access)

For more information please download:
Technical Report (Ris-R-1658.pdf) 
The Bolund Orography ( 
Bolund_Measurements ( 
Bolund_Questionnaire (
Presentation1 (34 mb) 
Presentation2 (27 mb)

... or contact:
Andreas Bechmann,

Senior Scientist

Andreas Bechmann
Senior Scientist
DTU Wind
+45 46 77 59 67