University of Michigan Department of Aerospace Engineering 5ft 7ft Wind Tunnel Data Acquisition Bible

Transcription

1 University of Michigan Department of Aerospace Engineering 5ft 7ft Wind Tunnel Data Acquisition Bible Richard B. Choroszucha 16.V.2010

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3 Contents List of Figures vi I Gathering Data Step Program 2 2 Getting Started Preliminaries Running the GUI Start Panel Updating Atmospheric Conditions Updating Test Parameters Notes On Run Acquisition Properties Obtaining a Calibration Calibration Load Calibration Calibrating From Scatch Calibrating a Force or Moment Channel Polynomials of Different Degree Data Acquisition 13 i

4 4.1 Zeroing Forces and Moments Options Other (User Defined) Variable Counter Manometer Sensor Acquiring Data Plot Vs Notes On Test Take Next Data Point Plotting Previous Data Points Possible Uses Saving Data Saving All Data Saving Plotted Data II Analysing and Viewing Data 18 5 MAT Calibration Files 19 6 MAT Data Files 20 7 Comma Separated Value Files (CSV) 21 8 TEXFiles (TEX) 22 9 Excel Files (XLS) Text Files (TXT) Binary Files (BIN) 25 ii

5 III The GUI GUI Panels Start Manometer Properties Acquisition Properties Test Parameters Atmospheric Conditions Notes On Run Load Calibration Calibrate Balance Start Visible Options Use Zero Input Erase Last Set Reset Data Options Visible User Inputs Other Manometers Counter Sensor Notes On Current Test Current Values of Plotted Parameters Current States Menus Save Data iii

6 Save All Data to MAT Save All Data to BIN Save All Data to CSV Save All Data to TXT Save Plotted Data to CSV Save Plotted Data to TEX Save Plotted Data to XLS Calibration Calibrate Load Calibration Parameters Display Calibration Parameters Acquisition Acquisition Properties Display All Data Points Plot Last Test Plot Vs Start Stop Data Update Atmospheric Conditions Update Test Parameters Notes On Run Plotting Y-Options Units Erase Last Data Set iv

7 IV Appendix 41 A Free and Open Source Alternatives 42 v

8 List of Figures 2.1 Welcome Screen Main Acquisition Window Main Plotting Window Main Calibration Window Calibration Viewer Start Panel An Example of a Manometer Bank Manometer Properties Window Acquisition Properties Window Test Parameters Window Atmospheric Properties Window Notes On Run Window Load Calibration Dialogue Box Result of Pressing the Start Visible Button Options Panel Zero Input Window Erase Last Data Set Window Reset All Data Window Result of Pressing the Options Visible Button User Inputs Panel for Other vi

9 12.16User Inputs Panel for Manometer User Inputs Panel for Counter User Inputs Panel for Sensor Notes On Current Test Panel Current Values Panel Current States Panel

10 A Note To the User Write everything down in your logbook. The importance of this document cannot be stressed enough. If you have a thought, write it down; use the logbook to write out your methodology or anything that could be pertinent to your test. Finally, write down all observations, you never know when this may come in handy.

11 A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams

12 Part I Gathering Data 1

13 Chapter 1 12-Step Program If you would like to use this program in a plug and play fashion, if not then see 2. For a quick start of the acquisition follow these steps: 1. Start MATLAB. 2. Find the folder containing Choroszucha.m and run. 3. Press the Test Parameter button. (a) Enter the name of the test. (b) Enter the wetted surface area. 4. Press the Atmospheric Conditions button to update the atmospheric conditions. (a) Find one of the barometers, calibrate, read and enter. (b) Plug in the temperature in F. 5. Put in any notes about the current test by pressing the Notes On Run button. 6. Either calibrate the load balance or load previous calibration parameters. To calibrate balance press the Calibrate Balance and either follow screen prompts or refer to Select what you would like to plot against using the Use... radio button panel. 8. Press the Zero Input button to zero out the inputs. 9. If you have chosen Manometer or Other from the radio buttons, enter your current settings in the User Inputs panel. 10. Press the Take Next Data Point. 11. Change wind tunnel settings, update U ser Inputs panel if necessary, press the Take Next Data Point and repeat. 2

14 Choroszucha When finished with the current test, Save Data, Reset Data, go through the Start panel and begin next test. The default acquisition properties are samples per second for 1 second, and taking three data points per one press of the Take Next Data Point button.

15 Chapter 2 Getting Started 2.1 Preliminaries Before you begin make sure you have the following: 1. A computer with MATLAB. 2. The Data Acquisition Toolbox. 3. A copy of Choroszucha.m. 2.2 Running the GUI Open MATLAB and locate the directory that Choroszucha.m is located. You may either use MATLAB s interface or you may take the UNIX approach and use cd. Using the UNIX approach you will need to type something like this: >> cd../education/ My Homework /Aero/5-by-7/ Then you will need to run the GUI by typing in: >> Choroszucha Upon running the program you will be confronted by a welcoming screen like Figure 2.1. Figure 2.2 will appear after you have reliquished your soul, this is the main acquisition window, this is also accompanied by an empty plotting window which can be seen in Figure 2.3. For a further explanation of what each button and menu does please see Part III. 4

16 2.2. RUNNING THE GUI Choroszucha 5 Figure 2.1: Welcome Screen

17 2.2. RUNNING THE GUI Choroszucha 6 Figure 2.2: Main Acquisition Window

18 2.2. RUNNING THE GUI Choroszucha 7 Figure 2.3: Main Plotting Window

19 2.3. START PANEL Choroszucha Start Panel Updating Atmospheric Conditions One of the first things that should always be done, and done periodically throughout long tests, is to record the atmospheric conditions. This includes the wind tunnel temperature and the atmospheric pressure. To update the atmospheric conditions locate and press Atmospheric Conditions in the Start panel. This will open a window allowing you to enter the data. Be sure to write this down in your logbook. More on updating the atmospheric conditions can be found in Updating Test Parameters A useful, but not required, thing to do is input a test name, this could be either a reminder of what the test is, the team/project name, etc. If you intend on plotting force coefficients you will need to input the wetted surface area. To update the test parameters locate and press the Atmospheric Conditions in the Start panel. This will open a window allowing you to enter the specified parameters. More on updating the test parameters can be found in Notes On Run As an added reminder of what should be in your logbook you may enter notes on this run of the wind tunnel. Say you would like to note that in this test you are changing the angle of attack at a specific wind velocity, this is one spot you may enter it. To add notes on the run, press the Notes On Run button, type in notes and close the window, it will automatically save. More on the run notes can be found in Acquisition Properties If you wish to change the default parameters on the acquisition, although not recommended, you may by pressing the Acquisition Properties button. More on the acquisition properties can be found in

20 2.3. START PANEL Choroszucha Obtaining a Calibration This can be done in one of two ways, you may either load a previous calibration by pressing the Load Calibration button or you may perform a calibration by pressing the Calibrate Balance button. More on this can be found in the next chapter, 3.

21 Chapter 3 Calibration 3.1 Load Calibration Pressing the load calibration window will open a dialogue box asking you to select a mat file containing the calibration. Typically this will have calibration in the file name. 3.2 Calibrating From Scatch To create a new calibration you have one of two options. You may either press the Calibrate Balance button or you may find the menu Calibration and select Calibrate. Both will take you to main calibration window, displayed in Figure

22 3.2. CALIBRATING FROM SCATCH Choroszucha 11 Figure 3.1: Main Calibration Window Calibrating a Force or Moment Channel To calibrate a force or moment, select that force or moment by pressing the button of the main calibration window, as seen in Figure 3.1. This will open the Calibration Viewer, Figure 3.2.

23 3.2. CALIBRATING FROM SCATCH Choroszucha 12 Figure 3.2: Calibration Viewer To obtain a calibration curve attach the weight to the load pan and input the weight (in pounds) into the Weight edit box of the calibration viewer. When the weight has settled, press Take Next Data Point. Continue adding weights until you are satisfied. Once finished press Done in the calibration viewer. Do this for the remaining forces and moments. Once all forces and moments have been calibrated press Done in the main calibration window and you will return to the main acquisition window. To begin acquiring data. Note: The moment calibrations are multiplied by a moment arm dictated by the program. When calibrating, enter the weight of the mass used Polynomials of Different Degree The GUI is capable of polynomial calibrations. It is not recommended to use this, but if there are issues with the response this may be useful.

24 Chapter 4 Data Acquisition This chapter will address how to acquire data from the wind tunnel. 4.1 Zeroing Forces and Moments After calibration you may need to Zero the forces and moments. Zeroing is the addition of an extra constant to make the force or moment zero. 4.2 Options Before you can begin acquiring data you must select what to plot against. Your independent variable can be either a user defined variable, counter, manometer input or sensor input. These will be highlighted in the coming subsections Other (User Defined) Variable Using this GUI you are allowed to plot the acquired data against a variable of your choice. But it should be noted that you need to adjust the User Inputs above Take Next Data Point. You can delete the last data set, but this is strongly discouraged. Using a user defined input, you can take several data points at one setting and begin to get statistics. 13

25 4.3. ACQUIRING DATA Choroszucha Counter In selecting Counter, all forces and moments will be plotted against the data point number Manometer You can directly enter the heights of the manometer taps associated with the total and stagnation pressure Sensor Using a separate channel you can obtain the velocity directly from the wind tunnel. 4.3 Acquiring Data Plot Vs. In the Acquisition menu there is an option entitled Plot Vs. that will open the main plotting window. By default this will start with the GUI, but may need to be re-initialised if you have deleted data points Notes On Test Again, this is not a logbook replacement. If you have observations, or would like to make a note about this test, you should do it here Take Next Data Point Pressing this button you will acquire the specified number of points per test, as selected under the Acquisition Properties button. It will acquire however many samples per second for the time you have selected. It will then take an arithmetic mean and display that number. No filtering is occurring. and filter the data yourself. When you are finished, you will have to go back

26 4.4. SAVING DATA Choroszucha Plotting Previous Data Points After you have acquired the desired samples from pressing Take Next Data Point, you have the option of plotting the most recent acquired forces and moments as a function of time Possible Uses Some extra features that may not be readily apparent are listed below. Error Statistics After the wind tunnel has settled, you can take as many data points as you like. If you increase the number of Points Per Test in the Acquisition Properties button, you can automatically acquire that many points. This can be useful for getting error bars. Temporal Data If you save all the data, you have access to the time histories of all the force and moment data points. If you are interested in investigating specific events, you can change the Force Time To Sample in the Acquisition Properties button to plot the event versus time. 4.4 Saving Data There are many options when saving data. You may save all the data, and/or save the plotted data in various formats Saving All Data With the exception of the MAT file, a little progress window will appear to show the state of the save. MAT File If you have MATLAB readily available, then this is a nice option because you only need take it to another computer with MATLAB, or alternative, and read the file. This will give

27 4.4. SAVING DATA Choroszucha 16 you all the raw and calculated data in one file. Be careful, MATLAB changes the standard often, meaning that you may have compatibility issues. There are some other options which may work in reading in the mat files, these can be found in Appendix A. Universal Binary File By far the best, and most conservative option. These universal files are populated by ones and zeros that can be read by any machine running any operating system. This creates many folders and files. To transfer the files it is recommended to compress the main folder. Comma Separated Value Comma separated values are a clear text format that is delimited by commas. This can be useful in reading into another language because you always know the separator. This creates many folders and files. To transfer the files it is recommended to compress the main folder. Text File Another clear text format that is delimited by \t or the tab delimeter. This can be useful in reading into another language because you always know the separator. This creates many folders and files. To transfer the files it is recommended to compress the main folder Saving Plotted Data Comma Separated Value This will save the plotted data in a specified format separated by commas. TEX A very neat option, this will output a table and figure in a pdf format.

28 4.4. SAVING DATA Choroszucha 17 Excel For quick manipulation you may save the plotted data as an Excel file. This option is not available for saving all the data because of the limitations on the size of an Excel spreadsheet.

29 Part II Analysing and Viewing Data 18

30 Chapter 5 MAT Calibration Files 19

31 Chapter 6 MAT Data Files 20

32 Chapter 7 Comma Separated Value Files (CSV) 21

33 Chapter 8 TEXFiles (TEX) 22

34 Chapter 9 Excel Files (XLS) 23

35 Chapter 10 Text Files (TXT) 24

36 Chapter 11 Binary Files (BIN) 25

37 Part III The GUI 26

38 Chapter 12 GUI Panels This chapter will cover the functions of the various GUI panels, what they do, what they may lead to, etc Start Figure 12.1: Start Panel As suggested by the title, this panel is where you should start, but you may not need all the buttons. Figure 12.1 displays the Start Panel. This can be found in the upper left corner of the Choroszucha window Manometer Properties Pressing the Manometer Properties button will allow you to change the multiplier and the noted specific gravity of the liquid you are using in the manometer. 27

39 12.1. START Choroszucha 28 If you intend on plotting your forces as a function of air speed there are two built-in settings that will allow you to do so, these are the Manometer and Sensor setting in the Options Panel, see for further reference. The manometer, the bank of tubes filled with liquid (see Figure 12.2), has tubes attached to a static pressure orifice and a total pressure pitot tube in the wind tunnel. We may use Bernoulli s Law and temperature and density equivalences to arrive at the equation for the air speed in feet per second qoil T R V = α, (12.1) P atm where V is air speed in feet per second [ft/sec], α is the multiplier, for the red gauge oil α = , q oil is the height difference in inches of oil [in. red gauge oil] of the static pressure and total pressure ports, T R is the temperature in degrees Rankine [ R] and P atm is the atmospheric pressure in inches Mercury [inhg]. (12.1) is specifically for the red gauge oil used in the 5ft 7ft wind tunnel. Figure 12.2: An Example of a Manometer Bank Figure 12.3 below is the window that will appear if you press the Manometer Prop-

40 12.1. START Choroszucha 29 erties button allowing you to change the multiplier α and the specific gravity of the liquid you are using, it is strongly discouraged that you modify these parameters unless you are using a different liquid. Figure 12.3: Manometer Properties Window In the event that you do need to modify these parameters, enter the values into the respective edit box and press Update. The defaults are a multiplier value of and a specific gravity of Acquisition Properties The acquisition properties determine your sample time, frequency and number of times to perform a sample per press of the Take Next Data Point button. Sample rate is the number of samples per second, time to sample is the length of time to sample. To calculate the number of data points you will use the following equation: N = S t, (12.2) where N is the number of data points, S is the sample rate and t is the time to sample. There are two options currently, one for sampling pressure, which will be used for determining the velocity; and the second for the forces and moments. Finally, there is Points Per Test edit box. This box allows you to set the number of data points to take per press of the Take Next Data Point button Figure 12.4 below is the window that will appear if you press the Acquisition Properties button. The window will allow you to change all the previously discussed acquisition parameters. Figure 12.4: Acquisition Properties Window

41 12.1. START Choroszucha 30 To change the acquisition properties select the edit box of the desired parameter and enter the preferred value. Then press the Update button Test Parameters The Test Parameters contain the name of the test or team running and the wetted surface area of the test section. Figure 12.5 shows the window that will appear if you press the Test Parameters button. Figure 12.5: Test Parameters Window To change the test parameters select the edit box of the desired parameter and enter the preferred value. Then press the Update button. The defaults are nil and 1 [ft 2 ] for the Test Name and Surface Area, respectively Atmospheric Conditions The atmospheric conditions are used in some calculations so it is imperative that these be updated. Figure 12.6 shows the window that will appear if you press the Atmospheric Conditions button. It should be noted that these must be given in the units of inched Mercury [inhg] and degrees Fahrenheit [ F ] for atmospheric pressure and temperature, respectively. Figure 12.6: Atmospheric Properties Window To change the atmospheric conditions select the edit box of the desired parameter and enter the preferred value. Then press the Update button. The defaults should not be used.

42 12.1. START Choroszucha Notes On Run Note: THIS IS NOT A LOGBOOK REPLACEMENT! You should write down everything in your own logbook. The notes on the run are meant for comments on the current run, e.g. what this test is supposed to accomplish. A window like Figure 12.7 will appear if you press the Notes On Run button. Figure 12.7: Notes On Run Window To update notes on the run, press the Notes On Run button, enter the text and simply close the window. It will automatically save Load Calibration The load calibration allows one to load previous calibrations. By pressing the Load Calibration button a window like Figure 12.8 will appear allowing you to select what calibration file to use.

43 12.1. START Choroszucha 32 Figure 12.8: Load Calibration Dialogue Box Unless modified by the user, the calibration file should contain calibration in the name Calibrate Balance This will open the Calibration Window, see Start Visible Once you are finished with this panel you may choose to make it invisible by pressing the Start Visible button. The result of pressing this button can be seen in Figure 12.9.

44 12.2. OPTIONS Choroszucha 33 (a) Start Visible (b) Start Invisible Figure 12.9: Result of Pressing the Start Visible Button This feature is meant to make it harder to accidentally change settings Options The options panel contains buttons that will allow you to choose what you wish to plot your forces against, whether or not to zero input and whether or not to erase the last or all data sets. Figure shows the Options panel which is located in the top centre of the main Choroszucha window. Figure 12.10: Options Panel Use... These radio buttons allow you to choose what parameter your forces will be plotted against.

45 12.2. OPTIONS Choroszucha 34 Other Selecting the Other radio button changes the User Inputs panel to a user defined x-axis, see Manometers Selecting the Other radio button changes the User Inputs panel to a velocity defined x-axis, where the velocities are obtained by the difference of two selected manometer tubes, see Counter Selecting the Other radio button changes the User Inputs panel to a x-axis defined by the number of times the Take Next Data Point button has been pressed, see Sensor Selecting the Other radio button changes the User Inputs panel to a velocity defined x-axis, where the velocities are obtained by differences of pressure transducers, see Zero Input Zeroing the inputs allows for you to calibrate the balance at any point, assuming a linear fit is chosen. It works by acquiring data at that instant, meaning and subtracting the respective voltage from each force channel. Figure shows the warning window that will appear if you press the Zero Inputs button. By pressing Yes the program will perform the zero, but by pressing No or closing the window, nothing will happen. Figure 12.11: Zero Input Window

46 12.2. OPTIONS Choroszucha Erase Last Set Erasing the last set will remove the data that was taken by the last press of the Take Next Data Point button. Figure is the window that will appear upon pressing the Erase Last Set button. By pressing Yes the program will perform the deletion, but by pressing No or closing the window, nothing will happen. Figure 12.12: Erase Last Data Set Window Reset Data Resetting the data will clear all raw data, calculated data and notes. It does leave the calibration. Figure is the window that will appear if you press the Reset Data button. By pressing Yes the program will perform the reset, but by pressing No or closing the window, nothing will happen. Figure 12.13: Reset All Data Window Options Visible Once you are finished with this panel you may choose to make it invisible by pressing the Options Visible button. The result of pressing this button can be seen in Figure

47 12.3. USER INPUTS Choroszucha 36 (a) Options Visible (b) Options Invisible Figure 12.14: Result of Pressing the Options Visible Button This feature is meant to make it harder to accidentally change or erase anything User Inputs Other Figure 12.15: User Inputs Panel for Other Manometers Figure 12.16: User Inputs Panel for Manometer

48 12.4. NOTES ON CURRENT TEST Choroszucha Counter Figure 12.17: User Inputs Panel for Counter Sensor Figure 12.18: User Inputs Panel for Sensor 12.4 Notes On Current Test Note: THIS IS NOT A LOGBOOK REPLACEMENT! You should write down everything in your own logbook. Figure 12.19: Notes On Current Test Panel

49 12.5. CURRENT VALUES OF PLOTTED PARAMETERS Choroszucha Current Values of Plotted Parameters Figure 12.20: Current Values Panel 12.6 Current States Figure 12.21: Current States Panel

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51 13.1. SAVE DATA Choroszucha 40 Chapter 13 Menus 13.1 Save Data Save All Data to MAT Save All Data to BIN Save All Data to CSV Save All Data to TXT Save Plotted Data to CSV Save Plotted Data to TEX Save Plotted Data to XLS 13.2 Calibration Calibrate Load Calibration Parameters Display Calibration Parameters 13.3 Acquisition Acquisition Properties

52 Part IV Appendix 41

53 Appendix A Free and Open Source Alternatives The world of Open Source and Freeware is vast and the quality is often outstanding. There are several Computer Algebra Systems, some of my favourite Open Source alternatives to MATLAB are: 1. Octave Octave is readily available on any UNIX environment, coupled with GNUplot, this is an amazingly powerful tool with a great deal of compatibility to MATLAB. For users of Cygwin, all you need to do is type octave at the terminal command prompt and then it is the same interface as MATLAB. For Windows users I strongly recommend downloading and using Cygwin or creating another partition on your hard drive for dual booting a Linux distro. For those new to Linux I would recommend Ubuntu as it is about as simple to install as putting the CD into the tray and following the directions. 2. FreeMAT FreeMAT is meant as a MATLAB clone, it grows bigger and better every day. 3. SciLab/SciCos SciLab is close to a clone, again it has a great deal of compatibility, has a Simulink front end available. It also has a LabVIEW toolbox which is quite useful. The only issue is the file extensions and some annoying UI features. 4. SAGE SAGE is a very different language from the rest listed, but it is based in python and can even be accessed via the internet. All these are available across all major platforms, Linux, Mac and Windows. 42