AAE 33301 Lab 5 Post-Lab Assignment

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Purdue University *

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Mechanical Engineering

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Feb 20, 2024

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Lab 5 Post-Lab Assignment AAE 333 01 Lab 5 : Wakes and Drag Measurement II Post-Lab Assignment 1. Lab Objectives (5) 1.1 Lab Objectives In this lab our objective was to understand and be able to learn about pressure and skin friction drag. Also be able to study the effect of body shape and geometry on the drag force and drag coefficient. We will also get to know the wind tunnel and hand-on experiment about the software to take drag measurements. 1.2 Goals and Expectation Met In this experiment, the goals of the lab group are to be able to see how different shape and frequency will produce different drag. Using the wind tunnel. We will need to measure 6 different objects and 3 types of stands. The frequency of the experiment will be set for 10, 15, 20, 25, and 30hz. The drag value will be saved on the computer after each run. Using the value we have, we will have to calculate the Cd for the post-lab assignment. All expectations were met for the experiment. 2. Data Presentation and Analysis (25 points) (1) Drag Coefficient vs. Reynolds Number (10 points) Use the drag measurements and geometry/measurements to calculate the drag coefficient vs. Reynolds number for each model. Show all C d vs. Re data on a single plot.
Lab 5 Post-Lab Assignment (2) Discussion of Results (15 points) (a) (8 points) Briefly compare your results with the drag coefficients presented in Figure 3 in the Lab 5 Background document. If there are significant differences, can you explain why? The values are very different, I think we have a human error somewhere in our calculations. But the trend is very much similar. For figure 3, the drag coefficient is about 1 and it drops to 0.3 as the flow becomes turbulent. (b) (7 points) For each test model, briefly discuss the results and include an explanation about which type of drag (form or skin friction) would most likely be dominant. 1. Vertical Plate Form drag dominates. The skin friction will only act across the small thickness of the plate. 2. Horizontal Plate Skin friction dominates. The form drag is only acts on the thickness at the front edge. 3. Small Cylinder At low frequencies, the flow would likely to attached to the surface of the cylinder and there for skin friction will dominates. However at higher frequencies, it will create wake at the back of the cylinder, resulting in form drag dominates. 4. Smooth Cylinder Will be similar to Small Cylinder, skin friction will dominant at lower frequencies and at higher frequencies form drag will be dominant. 5. Rough Cylinder Opposite of smooth cylinder, at low frequency, skin friction will be the dominant and it is higher than smooth cylinder. And at high frequency, form drag will dominant. The detachment will also occur much earlier due to the geometry of the cylinder.
Lab 5 Post-Lab Assignment 6. Airfoil Front Skin friction will likely to dominant. The flow will be detached much later in the flow direction so there will be very small form drag. 7. Airfoil Back Form drag will be dominant due to the flow detached and cause form drag.
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