Welcome back to Sports & Building Aerodynamics, in the week on the 100 meter sprint aerodynamics. In this fifth module we're going to focus on stadium aerodynamics and its relation to sprint records. And we start again with a module question. What is the effect of the stadium geometry on the 100 meter sprint? Is it A) The stadium geometry affects the sprint and will yield more records. B) The stadium geometry does not affect the sprint. C) The stadium geometry affects the sprint and will yield less records. Or D) The stadium geometry does affect the sprint, but it can yield more as well as less records. Please hang on to your answer and we'll come back to this question later in this module. At the end of this module you will understand the complexity of wind-flow patterns inside the stadium. You will understand how these wind-flow patterns can influence sprint times. And you will understand how the IAAF should actually adjust its wind speed measurement in stadiums. The research in this module actually has been performed in 2014 and it actually just was completed last week. So just eight days before the launch of the first session of this MOOC. So it's very, very fresh and we hope that you will like it. So, let's first start with the problem statement. Well building aerodynamics and sports aerodynamics are actually two different worlds. But they can have quite a substantial effect, and that is the effect of building aerodynamics on sports performances. So, actually what we want to do in this module is to bridge the gap between those two worlds, and to see how they are actually connected. And how this can be translated into a better measurement or a better evaluation of performances of top athletes. So we start with aerodynamics of sports stadiums. And for this we performed wind-tunnel measurements in the closed-circuit wind tunnel at the Von Karman Institute. And here I would really like to acknowledge the excellent support of our colleagues and friends at the Von Karman Institute; Professor Jeroen van Beeck, Gertjan Glabeke, and Emre Barlas, who really did a fantastic job in these very complex PIV measurements in this wind tunnel. So it's a wind tunnel with a cross section of three by two square meters, a test section length of 15 meters. Here, you have an inside view of the wind tunnel with the turntable at the front of the image. And in the back you see actually the corner vanes. It's kind of difficult to see, but actually that's the direction from which the wind is coming. So, what was done here is Particle Image Velocimetry measurements in different types of stadium models. You can see the stadium models here. So, we had a model with two openings at the ends of one of the stands. Then we had a model with four stands, then a model with just one stand. And then actually a completely closed stadium circumference model. This is another view of the four models. And in this module we're going to focus on the first measurement results, which are the ones for this particular case, with the stadium with the two openings. Which is also the case of the stadium in Brussels, the Koning Boudewijn Stadium, where the Diamond League meeting is held every year, it's the Memorial Ivo Van Damme. So this is the stadium geometry, well the geometry of the generic stadium model. You see the dimensions indicated here in meters. So the height of the roof of the stand is 35 meters. What was done then is the PIV measurements with the double cavity Quantel laser with the laser sheet actually parallel and very close to the ground surface to represent measurements at the height of athletes running in the stadium. You see some other characteristics of the PIV measurements listed here. I'm not going to read them all in detail, you can go through them if you want. Then the camera actually was placed below the turntable, so below the model and there is a transparent part of the turntable. And then these are some other characteristics of the measurements. And the error of the measurements is about 0.05 meters per second, which is quite a high accuracy for these rather complex flow patterns that have been measured here. These are the characteristics, actually, of the roughness fetch. So actually it was a rather smooth fetch that was used with a shear coefficient of 0.14. So no roughness elements, but the natural boundary layer generation over this rather long fetch in this atmospheric boundary layer wind tunnel. This is the top view of the generic stadium geometry, where you also see the track indicated here, with this point indicating the measurement position, so where the wind speed is measured during the race. And you also see the start and the finish line indicated here and the running direction with this arrow. And the results will be presented in two different ways. We'll show the time-averaged velocity vector fields and an example is given here. Where also the colors, the contours indicate the dimensionless wind speed, so the wind speed ratio. That is the wind speed divided by the wind speed at the stadium height. And we'll also show streamlines, and these are indicated here with again on the background the contours of the magnitude of the wind velocity. So these are at the height of the athletes in the stadium. And this is then the running direction. Also CFD simulations were performed. And these CFD simulations that are shown here give you an impression of how complex these flow patterns actually are, and how transient they are, how turbulent they are. What you see here is the wind speed ratio. In this case, wind speed divided by a reference wind speed at the same height in the free field, not for the generic stadium configuration, but this is for the actual configuration of the Koning Boudewijn Stadium in Brussels. And you can see with the yellow and the red colors the higher wind speed areas, and with the blue colors the low wind speed areas. You also see how wind speed and wind direction actually change continuously over the 100 meter track. And if you see this complexity and you compare that to the very simple single measurement, at one position in the stadium, it's clear that this measurement for many occasions, and many, many times will not be representative of the actual much more complex wind conditions. And this is only for one wind direction. The situation gets even much more complex with different wind directions. And this we can see by the wind tunnel measurements. So let's have a look at some of the wind tunnel measurements. We focus now again on the generic stadium configuration. So not the Koning Boudewijn Stadium but a configuration that is very similar, also with these two openings. This is for a given wind direction parallel to the short sides of the stadium. And here you see that if you look at the measurement point, that actually there's not a substantial along-track component of the wind velocity. And if you look at the track of the 100 meter, this is actually the same. So, in this case, the measured wind velocity is about the same as the one that is experienced by the athletes. However, this does not hold if we look at this wind direction. Here you see that actually we measure quite a high wind speed. While actually for a very large part of the 100 meter track, the wind speed is much lower. So this could mean that based on this wind speed measurement, a valid record would be disapproved. It would not be ratified while actually it should have been. Let's look at yet another wind direction. Here, you see a jet of air coming into one of the corners of the stadium. And, what you also see is that at the measurement point, that there is not a real strong component along the track. But that actually, if you look closer at the wind velocities over the track that there is a substantial head wind. But the measurement indicates almost no along-wind component. And if you look at this wind direction it's actually the other way around. The measurement indicates almost no along-wind component, but the athletes at the 100 meter track, in fact, experience quite a substantial tail wind. So also here the single measurement is not representative of the actual wind that the athletes experience. So given this complexity, as mentioned already a few times, it's certainly very clear that this measurement at one point is insufficient. And that, considering the importance of these races and all the efforts that athletes do to give their best and establish new records, it is really important that the IAAF gives a bit more attention to measurement accuracy and measurement representativity. So actually what should be done is more measurements, more measurements along the track to get a more representative value and we would like to suggest that measurement equipment, an anemometer, should be installed every ten meters. So, let's go back to the module question now. What is the effect of the stadium geometry on the 100 meter sprint? And the right answer is answer D. Depending on the wind direction, depending on the stadium geometry, it can yield more records, but it could also yield less records. And this actually has to do indeed with representativeness or the lack of representativeness of this single measurement position. In this module we've learned about the complexity of the wind-flow patterns in a stadium. How these wind-flow patterns can influence sprint times and how the IAAF should adjust its wind speed measurement in stadiums. This almost concludes the week on the 100 meter sprint aerodynamics, and in this week we have learned about the importance of form drag in running. The effects of wind on running performance. The effects of altitude on running performance. The importance of representative wind speed measurements during races. And how the geometry of the stadium can influence running performance. Before concluding this week, we'll first present now our final module of this week. In which you can see an interview with a professional athletics coach. And then after that, we will move on to the sixth week and in the sixth week we're going to focus on cycling aerodynamics. And not only cycling aerodynamics, we'll also include some car aerodynamics there. So thank you very much for watching and we hope to see you again in the next module and then in the next week.