The Bolund experiment has been reproduced in a neutral boundary layer wind tunnel (WT) at scale 1:115 for two Reynolds numbers. All the results have been obtained for an incoming flow from the 270° wind direction (transect B in the Bolund experiment jargon). Vertical scans of the velocity field are obtained using non-time resolved two components particle image velocimetry. Time-resolved velocity time series with a three component hot-wire probe have been also measured for transects at 2 and 5 m height and in the vertical transects at met masts M6, M3 and M8 locations. Special attention has been devoted to the detailed characterization of the inflow in order to reduce uncertainties in future comparisons with other physical and numerical simulations. Emphasis is placed on the analysis of spectral functions of the undisturbed flow and those of the flow above the island. The result's reproducibility and trustworthiness have been addressed through redundancy measurements using particle image velocimetry, two and three components hot-wire anemometry. The bias in the prediction of the mean speed is similar to the one reported during the Bolund experiment by the physical modellers. However, certain reduction of the bias in the estimation of the turbulent kinetic energy is achieved. The WT results of spectra and cosprectra have revealed a behaviour similar to the full-scale measurements in some relevant locations, showing that WT modelling can contribute to provide valid information about these important structural loading factors.KEYWORDS atmospheric boundary layer; wind tunnel simulation; complex terrain; wind energy Correspondence Yeow, TSL IDR/UPM, E.TS.I. Aeronauticos,

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This paper presents the development of the UPMSat-2 sun sensor, from the design to on-orbit operation. It also includes the testing of the instrument, one of the most important tasks that needs to be performed to operate a sensor with precision. The UPMSat-2 solar sensor has been designed, tested, and manufactured at the Universidad Politécnica de Madrid (UPM) using 3D printing and COTS (photodiodes). The work described in this paper was carried out by students and teachers of the Master in Space Systems (Máster Universitario en Sistemas Espaciales—MUSE). The solar sensor is composed of six photodiodes that are divided into two sets; each set is held and oriented on the satellite by its corresponding support printed in Delrin. The paper describes the choice of components, the electrical diagram, and the manufacture of the supports. The methodology followed to obtain the response curve of each photodiode is simple and inexpensive, as it requires a limited number of instruments and tools. The selected irradiance source was a set of red LEDs and halogen instead of an AM0 spectrum irradiance simulator. Some early results from the UPMSat-2 mission have been analyzed in the present paper. Data from magnetometers and the attitude control system have been used to validate the data obtained from the sun sensor. The results indicate a good performance of the sensors during flight, in accordance with the data from the ground tests.

We have determined the normal Reynolds stresses and spectra of the wind velocity over a 1:115 scale mock-up of the Bolund hill. The experiment was run in a neutral boundary layer wind tunnel using 3-component hot-wire velocimetry, 2-component particle image velocimetry, and a high-precision traversing system. Spectra have been determined at different points along transects at 2 and 5 m height above ground level. The experiment was run for 270 • wind direction and for two Reynolds numbers, Re h 1 = 4.25×10 4 and Re h 2 = 8.21×10 4 , based on the maximum height of the hill and the free wind speed at this height. Our results show how the normalized power spectral density S ii = fS ii ∕u 2 i changes over the hill. The analysis of the normalized streamwise spectrum at 2 m height, just after the escarpment, reveals that part of the energy is concentrated in the interval of normalized frequencies n h ≈ 0.01 − 0.02, which could be a signature of a weakened "flapping" phenomenon described in the literature for flows over forward facing steps. The departure of the spectra slope in the inertial subrange, from the value −5/3, was found to be correlated with the hill geometry. KEYWORDS atmospheric boundary layer, complex terrain, wind energy, wind tunnel simulation 1 INTRODUCTION The Bolund experiment, run by RISØ-DTU in 2007, is probably the most relevant test case of flow models oriented to wind energy analysis over highly complex terrains, in neutral conditions and nonaffected by Coriolis forces. 1,2 Bolund is a reference case to identify flow patterns and to validate numerical and physical models, due to the number and quality of sensors installed on the full-scale hill and the amount of numerical and physical analyses available such as literature. 1-6 Bolund is a small hill of about 130 m × 75 m × 12 m, surrounded by water with a long uniform fetch for most of the upstream directions of interest (see Figure 1-left). A large amount of periods with nearly neutral atmospheric conditions can be found in the full-scale database provided by RISØ-DTU. These characteristics convert Bolund into an ideal case for wind tunnel modeling without considering flow stratification effects.The escarpment facing westerly winds is one of the main geometric characteristics of Bolund (see Figure 1). The escarpment height varies slightly for the 200 • to 295 • wind direction interval, being roughly equal to the maximum height of the island, h = 11.73 m. Flow detachment at the escarpment has been observed in the full-scale experiment 1,7 and in wind tunnel tests. 4,8 Reproducing the flow characteristics in this region has revealed to be a challenge, particularly at lower heights, where the interaction between the turbulent inflow and the detachment dynamics is highly complex. Most of the numerical and physical models have failed to reproduce the high reduction in the mean wind speed and the high increment in the turbulent kinetic energy (TKE) found in the full-scale experiment in met mast M6 at 2 m height for 270 • wind direction, see Figure 2. ...