Instantaneous measurements of forces and moments on pv modules scaled as flat plates
Date
2012
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Abstract
Inclined flat plates of aspect ratios, ARs, between 1 and 10 are the fundamental geometry for a number of wind engineering systems. Our particular interest is in photovoltaic (PV) modules and arrays mounted on flat roofs at the high angles required for optimum energy production in high latitudes. Usually PV modules are mounted of a number of similar units. However, wind loads on an isolate PV module are useful to determine the baseline performance. The wind loads on these structures can be very high and any correlation between, say, the instantaneous lift and drag can cause overturning moments that are not obvious from knowing only the mean drag and lift. This report describes a detailed examination of the three instantaneous forces and moments acting on an isolate module over a wide range of angles and at varying distances from the wind tunnel floor which represents a flat roof, in order to get a comprehensive set of mean lift, drag, and moment data for wind engineering purposes. The measurements were undertaken in the 0. 76 m x 1.3 7 m environmental wind tunnel at the University of Calgary. The nominal wind speed was 19 mis and the model sizes were chosen to keep the blockage below 3 .5 %. The flat plates with maximum AR=9 were attached to a sting to simulate an open support structure as distinct from the molded plastic pods that are becoming common for mounting modules at low angles. The forces and moments were measured by an ATI multi-axis force/torque sensor holding the sting to a solid frame. Forces and Moments acting on the sting were measured prior the tests with the flat plate to account for the effect of the sting drag on the measurements. The experimental set-up was checked by measurements of normal plates in the free stream for which the drag coefficient is well established. Results are in good agreement with the literature. The AR showed to be an important parameter affecting wind loads. Drag and lift are mainly due to pressure rather than shear stresses at all distances above the wind tunnel floor. The level of fluctuation of Co increased as o. increased and as the distance between the model and the wall decreased. In the free stream position, high values of CL for AR '.S 1 at 25° :S o. '.S 55° are related with high values of C0. The location of COP is close to the centre of the plate for all AR at 25° :So. '.S 55° in the free stream position, but in proximity to the wall, the COP is located close to the centre of the plate for AR :S 2.5 at all a. The estimation of both instantaneous COP and correlation coefficients were adversely affected by the fluctuations in the sting drag.
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Bibliography: p. 130-138
Many pages are in colour.
Many pages are in colour.
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Citation
Ortiz, X. F. (2012). Instantaneous measurements of forces and moments on pv modules scaled as flat plates (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/4881