AERO 307

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AERO 307 Reflection

Most memorable moment of AERO 307 was when we actually got something that was quantifiable and when all of our results reflected the effort and time we put into the project and labs, especially the mini-project in which we only had two weeks to work on. Designing and actually making the parts for the jagged trailing edge took three full lab times and 3 or so hours before we started testing. Then the set up was very tedious and time-consuming, taking about 2/3 hours to mount the vehicle and the rake and setting them up. Fortunately, we were able to get some data that reflected all of the time we put in for it. At times, you don’t get any data, such as the initial flow viz experiment we tried to conduct on the NACA 4412. That was such a disappointment since we used two lab times to try to conduct the experiment. We eventually went with our backup plan and it worked, so I was relieved but that week was very stressful. 

However, I do feel better prepared for senior year in which there is no single answer. Like data collection and analysis, the results you get will vary from other groups and there is no correct answer. What matters is the analysis and what you think went wrong to produce such results and what can be done to improve the results and for future experimentation . The course has helped me better understand about myself and what I am capable of and what I had to and have to improve on. As I cooperated in the setup and the data collection, now I know what I have to do in order to increase the efficiency and the rate at which we get our work done. What I still have to work on is joining a discussion and sharing my ideas, as I sometimes tend to stay quiet. But to makeup for that, I helped out more in the manufacturing and/or the experimental set up and also in the report writing, in which I tried to start it up for them so that it’s easier for my teammates. 

Full aircraft configuration for stability testing sounds like an interesting experiment that I’d really liked to have done in the lab. I think cylinder lab could be pushed to an earlier course that aero students have to take or to like AERO 304. It took us a while to get used to setting up and using the wind tunnel, so getting some kind of experience beforehand would be helpful so that we could get more experimentation done once we start taking AERO 307. If we have basic knowledge of how to use the wind tunnel and the basic concepts using something like a cylinder, we would be able to better handle a full aircraft configuration and efficiently set up and analyze it. 

Furthermore, through the lab, I now know what it actually looks like when an airfoil stalls and when the transition point occurs. In addition, I now know what values are shown in the rake as vortices are produced and sizes are changed with various angles of attack and velocities. In other classes I have taken, they don’t physically show us what it looks like. They do show us images and graphs of what it looks like when it stalls and they do introduce the concepts and they do teach us how to calculate. AERO 307 helped me get a hands-on experience and helped me see physically what I have learned. This course has made me more interested in aerodynamics and testing. I am excited for the summer as I will get to continue to help out on the solar car. I heard that there are a lot of things to get done so I would like to contribute as much time as I can.

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Jagged Trailing Edge (cont.)

After a whole day of manufacturing on Tuesday (5/31) and partially on Wednesday (6/1), we were finally able to create a sawtooth trailing edge and the jig. We went a little over our testing time trying to finish this since we ran into problems, such as the screw not being long enough to connect to the vehicle or the sawtooth not having enough span to cover the whole trailing edged of the vehicle. However, we succeeded and we were able to place it onto the vehicle as you can see here:

The jig, which essentially is just three plates sandwiched together, was placed on using brackets which were bolted onto the side of the vehicle. The jagged trailing edge was slid in between and bolted at three points. A control trailing edge (no jaggedness) was also made so we had something to compare the jagged trailing edge with. Aluminum tape was used to cover up the gaps for a more smoother transition. With this completed, we mounted the vehicle into the wind tunnel. This took a decent amount of time since we had to take out the other force balance first which took a while since the cable kept on getting on stuck. Then, we had to carry the vehicle inside the wind tunnel and balance the vehicle on a bucket. 

We then had to make sure the tubes went through the top of the tunnel and the vehicle was bolted on correctly. After that we took off the tape on the side and mounted the bear claw rake from the side. Since we were running out of time and we determined that the wake would be small, we adjusted the vehicle height so that the trailing edge would be about in the middle of the rake and 1.5 times behind the width of the trailing edge. 

After this, we were finally able to run the wind tunnel. We started out slow in the beginning and gradually increased it to 25 m/s. The control was tested first and data was taken on the rake and force balance. After calzing the Scanivalve and zeroing the force balance, we recorded a wind-off measurement and two or three sets of data after starting the wind tunnel. Wind off measurements was taken after the wind tunnel was turned off. The control trailing edge was switched out with a jagged trailing edge and the similar procedure was taken. Results will be provided in the report and analyzed, but we calculated that there was about a 5% difference in the Coefficient of Lift between the Control and the jagged trailing edge. After that, at a slower speed, we did some flow viz using smoke and lasers.   

Top image shows the vortices from the control and the bottom image displays the vortices from the jagged trailing edge. Better images will be provided in the report but majority of what is seen here are vortices created from the pod and force balance. Wing tip vortices, which are hard to see in these images, were observable and it was pretty interesting to see. Majority of our analysis will be coming from the graphs but it was just really exciting to watch the vortices forming and the jagged trailing edge showing some kind of result. 

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Jagged Trailing Edge (cont.)

The sawtooth trailing edge was manufactured:

It was cut in Mustang 60 after hours, and this will be used as the jagged trailing edge. Minor changes were made for the jig that will hold and connect the sawtooth to the trailing edge of the vehicle:

The picture shows the side view of the trailing edge of the vehicle and the attachment. Instead of making two triangular shapes, we will use three wooden boards and we will have the one in the middle have enough space so that the sawtooth can fit right in. The first and last boards will be tapered off so that there will be an easier transition. In addition to the double sided tape that will be used to connect the attachment, Panels will be bolted onto both sides of the vehicle and the attachment, so that they are secured on. Holes will be drilled into them next week after the first Prove group is finished. Also, for the rake, we will be using the bear claw rake: 

This will give us higher resolution vortices that occur at the trailing edge and we will be able to see the small changes that occur from adding the jagged trailing edge. We will have to do it two times though, one above and once below, and we still have to see how and where we are going to mount it. 

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Prove Lab - Jagged Trailing Edge

For our mini project, we will be working on the Prove Lab Vehicle and adding a jagged trailing edge to it. In order to accomplish this, we are first thinking of adding a jig to the trailing edge of the vehicle. 

The jig will be built using basswood, which will be cut using a laser cutter. The jig will have two triangular shaped ones and a small piece in the front, as you can see in the image, that will span the whole trailing edge. It will be sanded into a smooth curve so that it will sit flush against the curvature of the trailing edge of the vehicle. The jagged trailing edge, which will look like a sawtooth, will be attached to the jig and secured with three bolts. Through our research, we figured out that the sawtooth can’t exceed 45 degrees, thus we have chosen 40 degrees for one of our designs, which means it will have a length of about .7 inches and they will go across the trailing edge of the vehicle. If we have time, we are thinking of changing the density and frequency of them. After the first group with the other Prove Lab project is done, the jagged trailing edge will be added to the vehicle, and tested with the force balance and the rake. We have to make sure that the rake is safely secured since we may have to run it at higher Reynolds Numbers. We have also figured out that the boundary layer thickness will be about 1.03 inches if we run it at 25 m/s, thus a 1 inch sawtooth height. We are thinking of using velocities of 5 and 25 m/s and at 5 m/s, we will use the force balance and flow viz with the laser and for 25 m/s, we will use the force balance,flow viz with the laser, and the rake. 

We still have to do a little more research about the jagged trailing edge and figure out where to obtain the materials we need. After getting those materials, we should be good to get going next week in cutting and manufacturing the parts. We won’t be able to do the actual wind tunnel testing until dead week, but we would like to get ready for it as much as we can. 

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Flow Viz (cont.)

We conducted a flow viz using the IR camera today. We were ultimately looking for the transition points from laminar to turbulent flow. Procedure was a lot more simpler than using the lotion or the dish soap. We just placed a wet towel over the airfoil and placed ice over it to cool down the airfoil. After 10 min or so, we took it off, one person climbed on the wind tunnel, and recorded using the IR camera while the wind tunnel was running. We ran it for about 30 seconds or so from 0 to 20 degrees angle of attack at about 15 m/s. We obtained some interesting results: 

By using the IR camera, it enabled us to observe something more meaningful than the lotion or the dish soap.

In order to identify where the transition points were we first did some research and found out that:

Skin Friction Coefficient increases in transition region and it is much higher in turbulent than laminar. Local Skin Friction Coefficient approaches zero when laminar separation bubble occurs. Thus, significant changes in temperature corresponds to the turbulent flow, lower temperature indicates the laminar flow/separation bubble, and sudden change in temperature indicates that it has hit the transition point. 

Looking back at the gif, at 0 degrees AoA, we can observe a few things. High Cf has increased the temperature at the Leading Edge. Coldest temperature can be observed in the center, which displays the laminar flow and separation bubble. Then there is a sudden increase in temperature, indicating the transition. After that, turbulence and wakes that occur at the trailing edge are displayed with increase in temperature. At 5 degrees AoA, everything looks similar except the transition point has moved further up the airfoil. The increase in temperature displayed after the transition point shows turbulence and wakes that occur. At 10 degrees AoA, there is a temperature rise, decrease in temperature, and sudden increase near the leading edge. Thus, transition point has jumped forward and is observable closer to the leading edge.

No heat exchange seems to occur after transition point, indicating that the flow has started to separate. At 15 degrees AoA, the transition point near the leading edge has disappeared and little heat transfer occurs at the LE showing that little flow is going over upper surface. Also, the lowest, uniform temperature is observable for most of the airfoil since not much heat transfer is happening, and therefore we can say that the airfoil has stalled and flow has separated. Finally, at 20 degrees AoA, majority of the airfoil is dark blue, which indicates that heat transfer is not occurring at all. Therefore, the flow has completely separated. From this flow viz, we were able to observe the transition point travel up the airfoil closer toward the leading edge as the AoA was increased. It was a good method to observe where the laminar flow, transition point, and turbulent flow occurred. 

The highlight moment of my flow viz challenged was when we actually got some results using the IR camera. I was pretty disappointed after all of the testing using the lotion and the soap failed, so when we got some actual observable results, I was fascinated. We got some clear transition points from the camera and it went up the airfoil as the AoA increased, and that were some agreeable results. Lowlight moment was when we couldn’t observe a lot of things from the lotion and soap. We spent about two lab times trying to experiment with it and we got nothing from it, so that was disappointing. Once again, we learned that experiments take longer than we expected and planning things from the beginning is challenging. We have to make sure that our experiment will actually work by testing it beforehand so we don’t waste time at the wind tunnel.

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Flow Viz

For our flow viz, we attempted to use lotion to observe the flow on the surface of the airfoil and ultimately find the stall point. We spent about an hour and half setting up the box, installing the airfoil and the paper inside the wind tunnel, and testing the wind tunnel out to make sure that the paper didn’t fly away. Unfortunately though, after all of that, the paper ripped away from the ground and walls and we also figured out that the lotion turned out to be too viscous even after we diluted it. We even tested it out behind the wind tunnel at around 200 and 400 RPM and nothing was very observable. 

Since lotion was too viscous, on Thursday, we tried out dish soap, which is a lot less viscous and a lot easier apply to the airfoil than the lotion. We tested it out beforehand this time out of the car on a frisbee and the soap did flow and it was observable at that time. I even attempted to find the right concentration so that it wasn’t too viscous nor too runny, figuring only at the end that the best was 1:1. However, when we took it to the wind tunnel and experimented with it, nothing was really observable except for maybe the edges of where majority of the soap had gathered, as seen here:

Since it took about an hour or so to set up the airfoil and the paper again--which didn’t fly away this time, we only had the chance to run it twice. First time with just the dish soap as mentioned before and the second time with red dye since we were advised that it might be able easier to see something if it was colored. The red dye did make it easier to see the mixture, but again, we failed since the mixture was too concentrated and viscous even though the concentration was the same to the plain dish soap. We were unable to get any recordings of that since we ran out of space on the camera, but nothing was actually observable before and after running the wind tunnel. If we diluted more, then we could have seen something. Unfortunately though, we ran out of time, and we came to the conclusion that its going to take more than just soap or lotion in order for this kind of experimentation to work; its more difficult than we initially thought. 

After discussing with my teammates, we have decided to do something more promising: using the IR camera to observe surface effects on the airfoil. We still have to discuss what we are looking for specifically but we can definitely get more out of it than what we tried to use initially for our flow viz. 

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NACA 4412 Reflection

Dealing with all this data is overwhelming but once we organized it and gathered our thoughts in what we were ultimately looking for, we were able to manage it. The most interesting aspect was seeing the graphs being plotted out and seeing the trend from the data points we obtained; plotting out things that we can’t really see in the wind tunnel was interesting for me. Since we had our code ready during test day, we were able to plot the Cp and Cl graphs as we tested, making sure that the data we obtained looked reasonable. Looking at that and seeing it getting plot out for every change in AoA and Reynolds Number was a great experience for me. When we saw a non-sensical data, if we were still experimenting when this happened, we took the data again to make sure it wasn’t some mistake from the pressure readings. If we got the same data again, then we tried to talk it out and thought of what may have caused this error. Being on clamp duty, on the other side, was not a very good experience. You just have to be strong and take one for the team. 

AERO 304 was like following a recipe step by step and it wasn’t as enjoyable and interesting like AERO 307. In AERO 307, instead of following the recipe step by step, we have gradually transitioned to eyeballing it and maybe trying something else new to obtain a different and favorable flavor that nowhere else has thought of so that we can awe our customers. I am finding this more interesting so far than AERO 304 and I think I am learning more since we get to plan out most aspects and if we fail, we learn something new and we get to plan out something else, which is just a great experience.

For the next few weeks, I would like to continue to bring my positive attitude and willingness to learn. One thing I should do better is communicating with my teammates and voicing my opinions. I did try to do that more often this time but it can be improved. As expected, the material I am learning here in AERO 307 is very valuable and is going to be helpful for my future careers since they require teamwork, communication skills, adaptability, and much more. 

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NACA 4412 Graphs, Results, and Reflection

In our experiment, we tried to examine the NACA 4412 airfoil in three different aspect ratios - “infinite” span and two finite spans. Only one of the finite wings were tested due to technical issues. We took measurements using pressure ports along the chord, the rake to measure the wake of the infinite span wing, and a force balance. Since there was so much that can be analyzed from the data we obtained, for our report, we decided to analyze the stall points at each Reynolds Number and found the error between the data we obtained and ones plotted on Xfoil.

Plotting some Cp datas we get this: 

There are some differences between the xfoil data and experimental data, but they are mostly the same with small errors. Thus, since these Cp graphs match up with the xfoil graph, the following graphs will be valid since all the calculations are based on the Cp calculation. 

Plotting Cl vs. alpha for the data obtained from Day 1, we got this:  

Re1 indicates Reynolds Number of 185,000, Re2 indicates Reynolds Number of 250,000, and Re3 indicates Reynolds Number of 500,000. We chose these Reynolds Numbers because we wanted to match Reynolds numbers in order to take repeatable measurements over several days of testing. Re1 allowed all three airfoils to match the Reynolds number, Re2 allowed the two larger wings to match Reynolds numbers, and Re3 was added only to see if it changed the data at all for the infinite wing. Also, we decided that the focus of our data collection should be on determining the positive and negative stall for the airfoil and determining if our data matched previous experiments within a given uncertainty.

Looking at the graph, the wing stalls at 10° for all Reynolds numbers and within a range of -5°, -6°, and -8° for Re1, Re2, and Re3 respectively. At the stall points, we see that the coefficient of lifts are 1.15, -.35, -.5, and -.75 respectively.

Plotting Cl vs alpha for Re = 185,000 from Day 1, 2, and 3, we got this:

Here, the repeatability of our results was tested. Day 1,2, and 3 were spent testing the infinite wing; the finite wing and force balance were used on day 4. As you can see, days 1-3 provide stall angles within 1% of each other, and Cl values at stall within 2% of each other. Thus, our plots are reliable and accurately represent the stall point for the NACA 4412 wing. Our data is slightly off from xfoil data because  xfoil is based purely on potential flow, with fudge factors to try to account for things like 3D effects and the boundary layer.

Plotting Re = 250,000, we get something similar to the Re = 185,000 with better force balance results. 

Taking the average for each Reynolds Number, we get this: 

By taking the average, the variations in data points from different days were balanced out and we obtained a more accurate and appropriate curve for each of the different Reynolds Number, displayed in one single graph. Looking at the graph, you can see that there’s not much difference between the average and graph from the Day 1 data. Thus, here, we have further validated the small errors of the data obtained for each of the days. 

Looking at the rake: 

You can see boundary Layers near the bottom and top of the pressure port with its slight increase in velocity from 9 to 10 m/s. Vortices occur at the edge of the separated boundary layer, where the velocities change the direction, which you can see around .35 m. Stall may have occurred at these locations if the separation occurred at the trailing edge and the flow may not have reattached. You can also see that the velocity gradually decreases and reaches the minimum velocity at around 0.4. 

One problem though was the Location of Probe vs. Cp. Since we took it at different velocities, we were unable to compare and observe the wall effects. 

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NACA 4412 Lab - Test Day 4

The force balance was used today to directly measure the aerodynamic forces and moments on the airfoil. The experiment was conducted with velocities of 17.75 m/s and 24 m/s to match the Reynolds Number. Data was recorded in increments of 2 from -12 to 22 degrees. Since we were told that the balance was linearly bias, we took times of how long it took to take data for each angle so we can calculate the error later. 

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NACA 4412 Lab - Test Day 3

Since the force balance wasn’t ready to be used this week, we did something similar to Test Day 2, in which we used the same NACA 4412 airfoil and the rake was placed closer to the wall. Wall effects were observed with the rake this time, as seen in the figure.

Again, angles of -16 to 16 in increments of two were measured for the two velocities and plotted. Also, for the higher velocity, we used the smoke machine for flow viz. Thus, when analyzing the graph for the second velocity for this particular data set, we have to keep in mind that the inlet was blocked by someone who was holding the smoke machine. It still has to be analyzed but this may have affected the readings and caused errors. Also, since we wanted to get a flow viz for multiple angles of attack, data was recorded at more angles of attack, thus getting more resolution on the graphs. 

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NACA 4412 Lab - Test Day 2

For our second test day, we obtained repeat test data for the Reynolds Number and angles tested last week to be able to determine the repeatability of the experiment. A rake was added and we obtained total pressure readings in the wake that will allow us to calculate the estimated total drag of the wing

shown is the rake:

The rake was .406 m from the trailing edge of the wing and there were 29 ports total. Starting with y=0 at the tunnel floor and going up:

1-3: Floor Boundary Layer Probes

4-8: Lower resolution ports below the central probe

9-14: Higher resolution ports below

15: Central Probe

16-21: Higher resolution ports above the central probe

22-26: Lower resolution port below 

27-29: Ceiling Boundary Layer Probes

30: Tunnel total pressure

The wind tunnel was run at 11.4 m/s and 15.4 m/s. This was to match the 195,000 and 250,000 Reynolds Number from last week’s experiment. The angles were set from -16 to 16 in increments of 2. Similar procedures were followed as last week to determine repeatability. 

When we were obtaining the data, for the higher Reynolds Number at port 4 of the rake, we obtained a number above 1, which isn’t supposed to occur at that location. This may have been due to the fact that somehow the airfoil was sending a freestream flow at that location or may been due to the fact that when it was set up, the tube was pinched, which offsets the data. Also, people were coming in and out of the door, and it still has to be determined but that may have caused the data to be thrown off. 

The following are the Cl vs alpha graphs of Reynolds Number of 195,000 and 250,000, respectively. The blue asterisks show the ideal data points and the red line indicates our trend we obtained. Overall, it follows the trend closely though at the end, it diverges from around 10 degrees. For 195,000 Reynolds Number, it has more error than the 250,000, and this may because of the lower velocity, which is harder to obtain pressure measurements from, thus causing this divergence. 

Though the third experiment still has to be done, I obtained more experience on using the Scanivalve and recording the data. I have a better understanding of how it works now and I feel pretty comfortable using it. The most challenging part of the experiment was actually deciding how many points we were going to record at how many angle of attacks and what kind of results we were trying to obtain. Our team had to actually meet outside of class to come up with a plan for our second experimentation. Our meeting went smoothly and we were able to agree on what we were going to record. Also, during our experimentation, I believe we are getting better at communicating effectively so that the whole procedure gets done smoothly and accurately. Because of that, we are left with extra time and we were able to use that time to record extra data points. 

We still have to organize our other graphs and analyze our results, but we should be able to obtain graphs that are similar to what was shown in the lab and that is agreeable. There may be some outliers, but those we should be able to brainstorm some potential contributors that lead to that kind of an error. 

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NACA 4412 Lab - Test Day 1

We started the Wind Tunnel Testing on the NACA 4412 airfoil.

The wind tunnel was run at 11.2 m/s and 15.1 m/s. The angle of attack was changed from -16 to 16 degrees in increments of 2. After enzing, we first started at 0 degrees then decreased angle of attack. After -16 degrees, it was placed back to 0 degrees and we increased angle of attack at increments of 2. 

I took part in recording the data on the Scanivalve and placing the clamps onto the side of the airfoil. There was some miscommunication in which angles we recorded and haven’t recorded, but that was resolved afterwards. 

We were able to obtain some interesting data and it looked similar to the example graph given in the lab. Some of the plotted lines that seemed to be weird or off was tested again, and made sure that it was correct. Since we had time at the end, we ran the wind tunnel at a higher Reynolds Number and observe the change in pressure. Setting the airfoil at the correct angle was difficult since every time we tried to change the angle, it was pushed up or down by the strong wind, displacing the airfoil further than we wanted.

The data has to be plotted and further analyzed, but the graph should display something similar to this, as shown in the lab:

Error bars will be included for analysis and we will have a figure for each AoA we measured. In the report, we will include the ones that display significance and analyze those. 

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NACA 4412 Lab

In this lab, we will be testing a NACA 4412 wing section and we will be able to:

- develop a testing plan to maximize the results and information for the given timeframes

- determine the aerodynamic force and coefficient of moment of finite and infinite NACA 4412 wing, using the force balance and pressure moments

- determine the stall characteristics and relationship to Reynolds Number

-perform more detailed error and uncertainty analysis

For the first test, we will be able to obtain pressure measurements and graph Cp plots at different angles of attack and Reynolds Numbers. Also, we will be able to calculate lift and pressure drag based on the measured Cp. 

Upon measuring the span and chord of the infinite and finite wings, we obtained:

Red wing: 26.5 in span, 4  5/8 in chord

Blue wing: 18 in span and 6.25 in chord

Infinite: 4 ft span and 10 in chord

Upon consideration of the max velocity it can be run at for the finite wings, we determined one of the Reynolds Number to be 193,000. In addition, It will be run at angles of -10 to 16 in increments of 2. 

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Cylinder Lab Reflection

The cylinder lab was pretty easy to understand and simple: we went in, got a brief introduction to the equipment, started it up, took some measurements, and used the Matlab code to make sure the data made sense. This hands-on experience is quite interesting and different from our other classes. Forming into four or five person groups, we plan and conduct an experiment ourselves, which is definitely more hands on, proactive, and easier to communicate. Previous classes and their labs have been about coding or overly crowded experimentations, and AERO 304 was like that and only three or four people out of eight were actually doing the experimentation. I don’t think I learned much from that. 

The most interesting part of this lab was using the Scanivalve interface in which we were able to obtain interesting pressure measurements from the cylinder. In this lab, I think we weren’t getting things done efficiently and fast enough, thus I would like to work on planning the procedure better beforehand and also, on my communication skills with the team so that things will get done as fast and efficiently I would like it to be. I have obtained a better knowledge about the Wind Tunnel and how most of the interface works in the control room. I would like to obtain sufficient knowledge on all of the things that the wind tunnel has to offer. 

In addition to that, I understand that the following labs aren’t going to be as simple as this initial lab. As a team, we are going to have to think of how we are going to conduct the experiment, and we are going to have to set up the apparatus, collect the data efficiently, make sure that they make sense, analyze the data, and look for potential error.  I believe this is a great opportunity for me to improve on my teamwork and communication skills. Also, I believe I should work on my coding skills since it has been a while. 

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Cylinder Lab

In this experiment, we measured the pressure on the cylinder using the Scanivalves and the drag coefficient of a circular cylinder was determined using discrete pressure measurements. We also evaluated the effects of Reynolds Number and surface roughness, and we thought of sources of uncertainty and error in the wind tunnel test. 

After the pressure readings were taken, Cp was calculated using Cp = (p-p_inf)/(1/2*rho*v^2) with p being the static pressure, p_inf being the freestream pressure, rho being the density of the fluid, and v being the mean velocity. 

Plotting Coefficient of Pressure vs theta for each velocity, I obtained this:

The graph with the lower Reynolds Number follows closely to the graph that was shown in the lab manual-- with the pressures at the rough surface of the cylinder having a less Cp value than the smooth surface. The graph with the higher Reynolds Number, however, does not look anywhere close to the lab manual graph, and this was most likely due to wall effects, which caused the wall to divert the air flow toward the cylinder, leading to a lower coefficient of pressure. However, from both of the graphs (ignoring the “smooth line” on the second graph), I can see that the data from the rough surface of the cylinder is a lot closer to the ideal line and separation occurs a lot later than the data obtained from the smooth surface. This shows that the roughness has generated turbulence in the boundary layer, causing the flow to get energized and stay close the surface as long as possible. This can be visually seen in the video I posted earlier in the week. 

After doing some research online, Cd could be done by taking the integral from 0 to 2pi of Cp*cos(theta) dtheta, which can be done on matlab by multiplying each Cp value by cos(theta) with theta being its corresponding radian value and then using Simpson’s Rule to find the area under the curve (integrate). 

Note: Small errors may have been made during the experimentation when one of the lab members accidentally pressed the wrong button, causing the system to crash. This lead to having to reset the whole interface and calzing the Scanivalves, and this may have caused some slight changes in the pressure. 

There were some unexpected pressure readings, and this could most likely been due to wall effects and/or due to the fact that the cylinder was at a contracted section, which lead to flows that were not straight. This could be avoided by placing the cylinder not so close to the wall and mounting them in the middle of the wind tunnel section towards the back, in which we will be able to obtain better pressure readings at higher Reynolds Numbers. 

For the next experimentation, I could use different velocities in the wind tunnel and I could take more data points for more accuracy by recording data in smaller increments. Also, dimples act similarly to a sandpaper, tripping the boundary layer and making the flow turbulent. Thus, in the next experimentation, dimples could be added to the cylinder and see how that differs with sandpaper on the cylinder.

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At one point of the lab, we ran the smoke through the wind tunnel so that it went over the rough part of the cylinder, and as expected, it tripped the boundary layer and it stayed attached. After analyzing the data, I will be able to observe the effects of the sandpaper more clearly and numerically.

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At a higher velocity, the wake is a lot more disorganized and the vortices are almost not visible; you can barely see their alternative shedding from the cylinder.