#naca4412

These are some of the graphs that I produced from the XFOIL data that I collected.  According to these plots, it appears that max L/D for a NACA4412 at 30 m/s occurs at roughly at an angle of attack around ~7 degrees. 

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.

Continuing on with our current theme of examining sources of error in the lab, one significant subject of interest is that of flow through the tunnel itself. This is important because we make one crucial assumption in order to conduct any of our data analysis: that the flow is steady. Is it really though? Let’s find out.

The trouble with a wind tunnel is that it uses a practically invisible substance we call “air”, and without some form of flow visualization (i.e. smoke), it is difficult to determine the state of the flow through the tunnel. Therefore, the best we can hope for is to minimize the chances of disrupting the flow so that we can make our assumption of steady flow. While there may be some disturbances to the flow that are naturally occurring in the lab, I think it is useful to discuss those that we can actually account for with careful consideration. Keep in mind that it would be very difficult to correct our data for any significant disruptions to the assumed steady nature of the flow. Rather, we want to ensure that our data can be accepted as valid.

Upon preparing to start collecting data, we always allow for a “warm-up” period of a few minutes, in which the tunnel gets up to speed and steadies out. Now here is the important step: after we set the angle of attack for the next round of data collection, we wait approximately 10 seconds from the time the airfoil is clamped in place to the time we hit “collect” in LabView. The reason for this is that when we rotate the airfoil when the tunnel is on, the motion “perturbs” the flow (thus the title of this post). Basically, the flow over the wing is “pushed” in a direction other than downstream, causing a sort of wave in the wake of the wing. This can affect the flow properties such as pressure both downstream and upstream. Therefore, we wait. Ideally, the longer the time in between this perturbation and data collection, the better. However, our time is limited in the lab, and we want to make sure to get all of the data we need. Regardless of this ideal, 10 seconds has proven to be enough time, since we collect data for approximately 15 seconds, and no significant anomalies or differences are observed from when we start collecting to when we stop. 

Hello again, it’s weird to think that this spring quarter is now 40% complete but with each passing week comes new and exciting errors in our Matlab calculations. This week we continued to test the infinite wing with a NACA 4412 airfoil. This week we recorded and attempted to process the recorded pressure data across the upper and lower surfaces of the wing. My team decided to examine the wing in the same orientations but at different Reynolds Numbers. Reynolds Numbers are used to compare and estimate the characteristics of flow around similar objects. The number itself is calculated using the geometry of the object, the density of the fluid, the viscosity of the fluid, and the velocity of the fluid. 

Our tests were similar to the previous week in testing the properties of the airfoil at post-stall angles of attack. We recorded data from 0-degrees up to 25-degrees. Throughout the testing one of the group members was analyzing the data recorded and comparing it to a fairly accurate computer program called Xfoil. All of the pressure data recorded matched up really well to the Xfoil approximations. 

The photos above show the NACA 4412 at 0 degrees and 15 degrees angle of attack. It is clear that the pitched up airfoil effectively blocks an appreciable portion of the test section. 

The test section is 3′ x 4′ x 12′. The chord of our fullspan airfoil is 9 7/8″ (200mm). When pitched up at 15 degrees, it blocks approximately 5.5% of our test section area. This can be calculated by assuming it is a flat plate, and the sin of the angle of attack is the area presented to the flow.