Blind test comparison on the wake behind a yawed wind turbine

This article summarizes the results of the Blind test 5 workshop, which was held in Visby, Sweden, in May 2017. This study compares the numerical predictions of the wake flow behind a model wind turbine operated in yaw to experimental wind tunnel results. Prior to the workshop, research groups were invited to predict the turbine performance and wake flow properties using computational fluid dynamics (CFD) methods. For this purpose, the power, thrust, and yaw moments for a 30° yawed model turbine, as well as the wake's mean and turbulent streamwise and vertical flow components, were measured in the wind tunnel at the Norwegian University of Science and Technology (NTNU). In order to increase the complexity, a non-yawed downstream turbine was added in a second test case, while a third test case challenged the modelers with a new rotor and turbine geometry.Four participants submitted predictions using different flow solvers, three of which were based on large eddy simulations (LES) while another one used an improved delayed detached eddy simulation (IDDES) model. The performance of a single yawed turbine was fairly well predicted by all simulations, both in the first and third test cases. The scatter in the downstream turbine performance predictions in the second test case, however, was found to be significantly larger. The complex asymmetric shape of the mean streamwise and vertical velocities was generally well predicted by all the simulations for all test cases. The largest improvement with respect to previous blind tests is the good prediction of the levels of TKE in the wake, even for the complex case of yaw misalignment. These very promising results confirm the mature development stage of LES/DES simulations for wind turbine wake modeling, while competitive advantages might be obtained by faster computational methods.</p

Growth effect of trade and investment in Sub-Saharan Africa countries: Empirical insight from panel corrected standard error (PCSE) technique

The pre-eminence of trade and investment in the economic prosperity of developed and developing countries cannot be overemphasized. Many studies have shown a strong positive impact of trade on economic growth across developed and the emerging market. However, very little is known about the simultaneous effect of trade and investment on growth in SSA when institutional control variables are introduced in the model. Therefore, this study examines the role of trade and investment in the growth process in the SSA using trade openness (% GDP), export (% of GDP) and import (% of GDP) as a measure of trade. We embrace an ideographic perspective that allows methodology and design that are sensitive to the nature of the study by deploying panel corrected standard error (PCSE). In this paper, we draw on 35 countries within the SSA. The research outcomes reveal that trade domestic investment and import affect growth in the region positively while export affects growth negatively. A possible reason for this is the nature of export of sub-Saharan African economies which are mostly affected by price volatility in the global market among other factors such as low prices, vagaries of weather, etc.. We discuss the policy implication of the study