1.2 Outline

In this section the research set-up and goals are explained along the outline of the present study.

Chapter 2 (Theory) introduces definitions of the considered quantities and the models on driving rain. There are two (though closely related) models described in the chapter. The so-called theoretical model is about the calculation of individual raindrop trajectories. This model is applied for driving rain calculations with CFD, and its details are presented in chapter 6 (CFD simulations). The second model is an empirical model, and is rather based on over-all rain quantities (i.e. no individual raindrops are considered but their volumes are taken together). The empirical model serves mainly the full-scale measurements, as measurement techniques detect over-all rain quantities.

The Main Building of the Eindhoven University of Technology (TUE) is used as test object for the full-scale measurements of wind and (driving) rain. This building, its surroundings, the instrumentation and the data processing techniques are described in chapter 3. The site is interesting because the Main Building has an relatively simple geometry and is much higher than the average surroundings. Moreover, an intermediate reference position is easily defined. Much attention is paid to the design of the driving rain gauges. Two driving rain gauges were developed at the TUE and, thanks to collaboration with the Chalmers University of Technology (CTH) and the Technical University of Denmark (DTU), two other driving rain gauges were included in a full-scale comparison test. We did not expose the driving rain gauges to artificial driving rain, because preliminarily we did not have real driving rain data with corresponding raindrop spectra, rain intensities and wind speeds. Moreover, realistic artificial driving rain is probably very difficult to generate.

Chapter 4 presents results of the full-scale comparison test of the driving rain gauges on a façade of the Main Building. The experiences from this test contribute to the formulation of design rules for driving rain gauges. Questions which are addressed in the chapter, are among others: which principle for the measurement of the collected driving rain water works best in practice, what is the influence of the shape, size and surface finish of the driving rain gauge on the readings, in which direction should further development of the designing and testing of driving rain gauges go.

The full-scale measurement set-up functioned for twenty-four months. Chapter 5 presents the measured data. The presentation and analysis include statistics (average and variation) of wind, rain and driving rain, correlations between intermediate reference wind and rain data and driving rain data, correlations between weather station wind data and intermediate reference wind data, parameterisations of the empirical driving rain model with the measured data. An improved driving rain model is also presented.

In chapter 6 we describe the model for the CFD calculations of wind and raindrop trajectories at the site of the Main Building. Results of the calculations are compared to the full-scale measurements. The main goal in the chapter is the investigation of the suitability of CFD for driving rain calculations, especially the aspects which should be dealt with to obtain reliable results.

Chapter 7 reports the main conclusions and suggestions for further research.