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We introduce a modified tomographic PIV technique using four high-speed video cameras and a scanning pulsed laser-volume. By rapidly illuminating adjacent subvolumes onto separate video frames, we can resolve a larger total volume of velocity vectors, while retaining good spatial resolution. We demonstrate this technique by performing time-resolved measurements of the turbulent structure of a round jet, using up to 9 adjacent volume slices. In essence this technique resolves more velocity planes in the depth direction by maintaining optimal particle image density and limiting the number of ghost particles. The total measurement volumes contain between 1 ×106 and 3 ×106 velocity vectors calculated from up to 1500 reconstructed depthwise image planes, showing time-resolved evolution of the large-scale vortical structures for a turbulent jet of Re up to 10 000.

The i -V curve describes the current drawn from a flame as a function of the voltage difference applied across the reaction zone. Since combustion diagnostics and flame control strategies based on electric fields depend on the amount of current drawn from flames, there is significant interest in modeling and understanding i -V curves. We implement and apply a detailed model for the simulation of the production and transport of ions and electrons in one-dimensional premixed flames. An analytical reduced model is developed based on the detailed one, and analytical expressions are used to gain insight into the characteristics of the i -V curve for various flame configurations. In order for the reduced model to capture the spatial distribution of the electric field accurately, the concept of a dead zone region, where voltage is constant, is introduced, and a suitable closure for the spatial extent of the dead zone is proposed and validated. The results from the reduced modeling framework are found to be in good agreement with those from the detailed simulations. The saturation voltage is found to depend significantly on the flame location relative to the electrodes, and on the sign of the voltage difference applied. Furthermore, at sub-saturation conditions, the current is shown to increase * Corresponding author Email address: fbisetti@utexas.edu (Fabrizio Bisetti)Preprint submitted to Proceedings of the Combustion Institute July 17, 2016linearly or quadratically with the applied voltage, depending on the flame location. These limiting behaviors exhibited by the reduced model elucidate the features of i -V curves observed experimentally. The reduced model relies on the existence of a thin layer where charges are produced, corresponding to the reaction zone of a flame. Consequently, the analytical model we propose is not limited to the study of premixed flames, and may be applied easily to others configurations, e.g. nonpremixed counterflow flames.

This paper compares a number of probabilistic weather forecasting verification approaches. Forecasting skill scores from linear error in probability space and relative operating characteristics are compared with results from an alternative approach that first transforms probabilistic forecasts to yes/no form and then assesses the model forecasting skill. This approach requires a certain departure between the categorical probability from forecast models and its random expectation. The classical contingency table is revised to reflect the ''nonapplicable'' forecasts in the skill assessment. The authors present a verification of an Australian seasonal rainfall forecast model hindcasts for the winter and summer seasons over the period from 1900 to 1995. Overall skill scores from different approaches demonstrate similar features. However there are advantages and disadvantages in each of those approaches. Using more than one skill assessment scheme is necessary and is also of practical value in the evaluation of the model forecasts and their applications.

Current-voltage, or i−V , curves are used in combustion to characterize the ionic structure of flames. The objective of this paper is to develop a detailed modeling framework for the quantitative prediction of the i−V curves in methane/air flames. Ion and electron transport coefficients were described using methods appropriate for charged species interactions. An ionic reaction mechanism involving cations, anions and free electrons was used, together with up-to-date rate coefficients and thermodynamic data. Because of the important role of neutral CH species in the ion production process, its prediction by the detailed AramcoMech 1.4 mechanism was optimized by using available experimental measurements. Model predictions were evaluated by comparing to i-V curves measured in atmospheric-pressure, premixed, burner-stabilized flames. A detailed evaluation of the reliability of ion kinetic and transport parameters adopted was performed. The model provides good quantitative agreement with experimental data for various conditions.