# Assignment: Lab report measurement II

## Assignment: Lab report measurement II

Assignment: Lab report measurement II ORDER NOW FOR CUSTOMIZED AND ORIGINAL ESSAY PAPERS ON Assignment: Lab report measurement II Hello there I need help writing my lap report for the experiment WIND TUNNEL Assignment: Lab report measurement II I am attaching all the information that should be included in the lab report (full report) please follow the same sample report in order I get better grade in the sample report you will see some comments in red, it is the professor comments that should be followed. the file 1 is the sample report excel sheet (data) lap experiment procedure please check the spelling once you write attachment_1 attachment_2 attachment_3 attachment_4 Experiment 6: Drag Forces Acting on Objects in a Wind Tunnel Introduction and Theory Wind Tunnel is a duct with carefully controlled and monitored air flow, in which an object can be positioned and the forces and/or pressures acting on the object can be measured. Since the resultant forces a essentially the same, whether air is blown over a stationary object, or the object is moving through the air, the wind tunnel can be used to study aerodynamics of airplanes, airplane wings, or vehicles. Pitot Tube Wind speed can be measured with a simple device called a Pitot tube. The illustration below (taken from NASA GRC website) explains the probes operation. Aerodynamic Drag Drag is the force exerted by the moving air on an object in the direction of the air velocity. It is commonly broken into two components: friction drag and form drag. The friction drag, sometimes called the skin friction drag, is the force created by boundary layer phenomena. To minimize friction drag on an aircraft all the sheets of metal on the wing join smoothly, and even the rivets are rounded over and as flush with the surface as possible. The form drag, also called pressure drag, is affected by the shape of the body. A streamlined shape will generate less form drag than a blunt or flat body. Drag force Fd can be normalized to yield so called coefficient of drag: Eq. 1 where ? is the air density, V is the air velocity and A is the projected area, that is the area that you see when looking at the object from the wind direction. Experimentally determined values for Cd are available in literature for a wide range of shapes. In particular, graphs presenting Cd as a function of Re can be found in most Fluid Mechanics books (see Figure 1 below). Recently, a single closed-form expression has been developed for flow around a sphere [3], which covers a wide range of Re from creeping flow (Re<2) all the way to Re = 106. The equation is presented below as Eq. 2: (Eq. 2) Note that for creeping flows around a sphere (Re<2) Eq. 2 reduces to . Figure The effects of Reynolds number (Re) and surface roughness on the drag coefficients of a sphere (Cd). Experimental Goals (1) Using wind tunnel reading as a standard, demonstrate that Pitot tube can be used to accurately measure the wind speed. (2) Determine drag coefficient Cd(Re) in as large a range of Reynolds number as possible, for smooth spheres and spheres with bumps created by rubber bands. Note: If writing an Abstract report ignore Goals 1 and 3 and only write about Goal 2. (3) Estimate random uncertainty of wind speed, including the standard deviation and the 95% confidence interval using up to 120 measurements. Experimental Procedures Part 1: Confirming tunnel wind speed with Pitot tube Measure the pressure using Pitot tube using the following procedure: ? Make sure wind tunnel is not running ? Remove any test objects from the wind tunnel ? Connect the Pitot tube to the differential pressure transducer ? Insert the Pitot tube through the opening in the tunnel floor and position it near the center of the test area ? Set the tunnel wind speed to desired magnitude in your range and measure the corresponding pressure difference (in millibars) Part 2: Measuring drag of objects The wind tunnel test will be performed on three objects: (1) 3.0 diameter sphere, (2) 3.75 diameter sphere, (3) 3.75 diameter sphere with a rubber band bump. Perform the following for each of the objects: ? Mount test object in the wind tunnel ? Confirm that the pitch angle is zero ? Zero all readings ? Set the wind tunnel at the lowest wind speed in the range you decided to measure ? Record five sets of data using software (recorded data includes normal force, axial force, air speed and pitch angle). ? Repeat Step 5 for all other speeds in your range ? Reduce wind speed to zero ? Save the data file. Use informative file name. Part 3: Random uncertainty estimation Take 120 measurements (no more than 2 points per second) for a single condition: Sphere 2 at 80 mph. Save the data to a file. Presentation of Results Note: Include all three parts in Results but only write about Part 2 in the Abstract. Part 1 Calculate the wind speed determined from the Pitot tube pressure and plot it against the wind speeds set in the wind tunnel. Use consistent units! Add a straight line with the slope of 1 for comparison. Discuss briefly right after the results are presented (not in the Abstract). Part 2 This is the main part of the laboratory. If writing Abstract Report only write about this part. ? For each data file, discard all columns except the wind speed and the axial force (drag) ? For each wind speed and drag force, calculate the Reynolds number Re and the coefficient of drag Cd. Note that sphere diameter is the characteristic length used in calculating Reynolds number. ? Create a single Cd vs Re plot that include data from all configurations. Plot each set of data as points (no lines) with added trendlines (least square fits). Also add the Cd vs. Re relation of Eq. 2 with a solid line. Include all important observations in the Abstract. Try to explain the big change in Cd caused by the rubber band. Part 3 Estimate standard deviation and the 95% confidence interval on the measured wind speed based on first N = 6 recorded measurements. Repeat for first N = 11, 21, 41, and all 120 measurements. Graph std. deviation and 95% confidence interval as a function of N. References ? J.P. Holman, Experimental Methods for Engineers, 7th Edition, McGraw Hill, New York, 2001 ? Operating Instructions for Aerolab Educational Wind Tunnel, 9580 Washington Blvd Laurel MD 20723 ? F. A. Morrison, An Introduction to Fluid Mechanics, Cambridge University Press, New York, 2013. This correlation appears in Figure8.13 on page 625. Appendix (related to Part 3) Repeatability is a measure of random uncertainty the closeness of agreement between independent results obtained with the same method on identical test material, under the same conditions (same operator, same apparatus, same laboratory and after short intervals of time). The measure of repeatability is the standard deviation qualified with the term: `repeatability as repeatability standard deviation. Estimation of random uncertainty Random component of uncertainty can be estimated by repeating same measurements several times. The resulting data set (sample population) can then be analyzed to yield its statistics that can be used to estimate the corresponding statistics of the entire population: ? Mean of the sample population xm is used to estimate the mean of entire population ? Precision Index (a.k.a. Standard Deviation of the sample population) Sx is used to estimate the standard deviation ? of entire population The most common statistic used to express random uncertainty in engineering is so called 95% confidence interval. This interval can be estimated based on the mean and the precision index: using +/-t95 Sx, where t95 is tabulated and depends on the size of the sample population. For large samples it approaches 1.96. Mean value: Precision Index: There is about 95% probability that a single measurement falls between and . The random uncertainty of a mean (average) of N measurements is smaller than the random uncertainty of a single measurement it shrinks by factor of . Therefore, there is about 95% probability that a mean of N repeated measurement falls between and , where . Assignment: Lab report measurement II Get a 10 % discount on an order above $ 100 Use the following coupon code : NURSING10

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