Measurement of Pressure Distribution and Forces Acting on an Airfoil S. Ghosh, M. Muste, S. Breczinski, J. Johnson, S. Cook, and F.

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1 57:00 Mechancs of Fluds and Transfer Processes Laboratory Experment #3 Measurement of Pressure Dstrbuton and Forces Actng on an Arfol S. Ghosh, M. Muste, S. Brecznsk, J. Johnson, S. Cook, and F. Stern 1. Purpose The purpose of ths nvestgaton s to measure the surface pressure dstrbuton, wake axal velocty profle, and lft and drag forces on a Clark-Y arfol set at two angles of attack (0 and 16 degrees), and to compare the results, ncludng ther uncertantes, wth benchmark data. The experment wll also ntroduce students to concepts related to dgtal acquston systems: calbraton, nose, settlng tme, and samplng tme. Addtonally, ths laboratory wll provde students wth further analyss usng an mage-based system (epiv/flowcoach) wth two Clark-Y arfol models at angles of attack 0 and 16 degrees.. Experment Desgn.1. Part 1: Wnd Tunnel The geometry of and forces actng on a generc arfol n a constant flow feld (U ) are shown n Fgures 1a and 1b. These experments are conducted usng a Clark-Y arfol mounted n the test secton of a closed crcut, open test secton, vertcal return wnd tunnel (Fgure ). The tunnel enables measurements for turbulent flows up to Re = 300,000. (Re = U c/ ν, where U s the free-stream velocty n the tunnel, c s the arfol chord length, and ν s the knematc vscosty of ar). It has four 90 o corners equpped wth turnng vanes, two dffusers, a contracton secton, test secton and fan. The vanes, settlng chamber and contracton secton help n achevng a unform flow n the test secton. (a) Geometry (b) Hydrodynamcs Fgure 1. (a)-(b): Arfol characterstcs (a) Layout of the open test secton wnd tunnel (b) Arfol schematc showng measurement system components Fgure (a)-(b): Wnd tunnel layout The tunnel s closed crcut s approxmately 18.3 m long. The test secton s a 0.76 m by 0.76 m square, 1.5 m long. A resstance temperature detector and a Ptot tube are placed upstream n the upper half of the test secton to 1

2 8 U montor and control the temperature and free stream velocty, respectvely. The Ptot tube s connected to a pressure transducer along wth a dgtal dsplay for vsualzaton of expermental condtons. A Clark-Y arfol was selected for the experment because t exhbts good aerodynamc performance over a wde range of Reynolds numbers and also because there s abundant benchmark data avalable for comparson. The geometry of the Clark-Y arfol and the postonng of the pressure taps used n the experment are llustrated n Fgure 3b. Postonng of the arfol at varous angles of attack s made wth a hand wheel connected to a dgtal dsplay. The arfol s set on a par of load cells that measure the overall forces (lft and drag) actng on the arfol (see Fgure 3a and 3c). An overall vew of the system s provded n Fgure 3a. Data acquston s conducted wth an Automated Data Acquston System (DA), as shown n Fgure 3c. DA s controlled and nterfaced by LabVew software, descrbed n Appendx B. DA contans several measurement modules: tunnel controls, pressure measurements, velocty measurements, and force measurements. The pressure dstrbuton around the arfol s obtaned from 9 pressure taps, connected, usng tygon tubes, to the ports of a scannng valve that sequentally cycles through each pressure tap. Pressures selected by the scannng valve are measured by a dfferental pressure transducer that has one port connected at all tmes to the pressure measured n the free stream (p ), wth the other port connected to the scannng valve output port. The wake velocty profle s measured wth a traverse-mounted Ptot tube wth stagnaton pressure routed through one of the scannng valve nput ports. The automated traverse allows for consstent and effcent velocty measurements at specfed vertcal postons wth the use of the DA. The load cell measures forces drectly appled to the arfol. It s calbrated durng the experment to obtan a relatonshp between forces actng on the arfol and voltage output from the load cell. (a) Chord-wse Pressure Taps Tygon Tubng L To Load Cell Scanvalve Load Cell D (b) P Tangent to surface at P Camber Lne Arfol chord (angle of attack) , x/c (c) Fgure 3. Expermental layout: a) photograph of test secton and nstrumentaton; b) Clark-Y arfol geometry; c) DA components

3 .1.1. Data reducton (DR) equatons The measured varables are the test secton ar temperature, free stream velocty, pressure dstrbuton around the arfol, axal velocty profle behnd the arfol, and lft and drag forces actng on the arfol. Usng these measurements, the pressure coeffcent at each pressure tap, C P, and the lft coeffcent for the arfol, C L, are obtaned. The data reducton equaton for the pressure coeffcent, C P, s gven by: p p p, p,, U (1) U where p s the statc pressure at any pressure tap on the arfol surface, p s the free stream pressure (measured on the Ptot statc port), s ar densty, and U s the free-stream velocty, gven by: pstagn p U () where p stagn s the stagnaton pressure measured at the tp of the Ptot tube placed at the upper half of the test secton. The data reducton equaton for the lft coeffcent, C L, s gven by: L C L L,, U, b, c U (3) bc where L s the lft force actng on the arfol surface, b s the arfol span, and c s the arfol chord (as shown n Fgure 1a). The data reducton equaton for the drag coeffcent C D s gven by D C D D,, U, b, c U (4) bc where D s the drag force actng on the arfol surface. The lft force, L, can be obtaned n two ways. The frst method s by ntegratng the measured pressure dstrbuton over the arfol: L p p sn ds (5) s where θ s the angle of the surface normal to free-stream flow at each of the pressure taps (Fgure 3b), as specfed n Appendx A. The drag force, D, can also be obtaned n two ways. The frst method s by measurng the velocty dstrbuton upstream and downstream of the arfol body. Drag s then found by ntegratng the change n momentum: yu D u U u dy (6) yl where u s the velocty measured at each pre-determned elevaton n the wake of the arfol, y L s the lower most elevaton of the measurements, and y U s the upper most elevaton of the measurements. Refer to Method n Appendx C for the dervaton of equaton (6). Alternatvely, both the drag and lft forces can be drectly measured wth the load cell usng the followng calbraton equatons: D AD ( V V0) (7) L AL V V ) (8) ( 0 where A D and A L are coeffcents for drag and lft, respectvely, determned from the load cell calbratons, V and V 0 are the load cell voltage output when U 0 and U = 0, respectvely. 3

4 .. Part : epiv/flowcoach As n EFD Lab, Partcle Image Velocmetry (PIV) wll be used to track flud moton and calculate velocty magntudes and vectors around a Clark-Y arfol at angles of attack of 0º and 16º. Data wll be gathered usng an epiv (Educatonal PIV) system or a FlowCoach system, dependng on the lab secton. In epiv/flowcoach analyss, a seeded flud s llumnated by a laser sheet, and a camera takes rapd photographs of the flud flow, at a rate of 30 Hz. Four parameters are used to control the camera settngs: Brghtness Ths controls the overall brghtness of the mage. For the best PIV results, brghtness should be set to a medum-low value. Exposure Ths controls how long the camera sensors are exposed per mage frame taken. Hgher values correspond to shorter exposure tmes, and lower values correspond to longer exposure tmes. PIV analyss benefts from hgh exposure values (short exposure tmes), to facltate software trackng of patterns of partcles. Gan Ths controls the senstvty of the sensors per unt tme. Usng hgher gan wll amplfy the sgnal obtaned by the sensors, so typcally hgher gan values are needed for mages taken wth short exposure tmes, whch would otherwse be very dark. However, ncreasng the gan has a sde effect: usng hgher gan ncreases the nose n the mage. Frames Ths specfes how many mages the camera wll take, for PIV analyss. At least two mages are needed to process vectors, and takng more wll allow the software to average results and reduce precson error. After mages are captured, they are processed to determne velocty vectors and magntudes. The software takes a par of consecutve mages and breaks t nto many small regons, called nterrogaton wndows. In each nterrogaton wndow, the PIV software compares the two mages, determnes how far the pattern of partcles has moved n the amount of tme between the two mages, and calculates a sngle velocty vector for that wndow. Ths s repeated across the entre measurement area, generatng a vector feld. Wth the epiv system, three PIV parameters can be adjusted. Wndow Sze Ths sets the sze (n pxels) of the nterrogaton wndow. Ideally, smaller wndows are desred, because they show more flow detal, averagng over a smaller regon of the flow. However, f values are too small, fewer partcles pass through the nterrogaton wndow, whch can result n unstable vector computaton. Shft Sze Ths determnes the dstance (n pxels) that the software moves to start a new nterrogaton wndow. For example, f a wndow sze of 80 and a shft sze of 40 were used, the software would compute a vector n the frst 80x80 nterrogaton wndow, and then shft 40 pxels, computng a second vector n a new 80x80 wndow. The two wndows would overlap by 50%. A smaller shft sze results n more vectors beng computed, but the ncreased overlap means that some of the data reported s repeated between the vectors. PIV Pars Ths specfes how many pars of mages are used for PIV calculatons. PIV analyss compares any two consecutve mages, f 10 mages are captured, up to 9 PIV pars can be specfed for computaton. Results computed for each ndvdual par are averaged together, reducng precson error. 4

5 3. Experment Process 3.1. Part 1: Wnd Tunnel Test Set - up Data Acquston Data Reducton Uncertanty Analyss Data Analyss Faclty & condtons Clark-Y arfol Prepare expermental procedures Set AOA Statstcal analyss Remove outlers Estmate bas lmts Compare results wth benchmark data, CFD, and /or AFD Install model Calbraton Set up arfol n the test secton Set tunnel speed D ata reducton equatons Evaluate Eq. 1 E valuate Eq. Evaluate Eq. 3 Data reducton sheet Estmate precson lmts Use Fg. 7a as reference for pressure Use Fg. 7b as reference for lft coeffcent Prepare measurement systems Calbrate load cell for lft and drag Intalze data acquston software Open Labvew program Evaluate Eq. 4 Evaluate Eq. 5 Evaluate Eq.6 Evaluate Eq. 8 Evaluate Eq. 1 Use Fg. 7c as reference for drag coeffcent Report dfference between expermental and reference data Ptot tube Pressure transducer Scan valve Enter hardware settngs and reference pressure Run tes ts & acqure data Estmate total uncertanty Evaluate Eq. 6 Evaluate f lud physcs, EFD process and UA Pressure taps Load cell Measure arfol pressure dstrbuton Evaluate Eq. 9 Answer questons n secton 4 Measure lft force Prepare report Measure drag force Store data Wrte results to output fle Fgure 4. EFD Process for Wnd Tunnel Measurements Test Setup The experment measurement system s comprsed of the wnd tunnel, the arfol, and the DA (see Fgure 3). The DA acqures measurements veloctes and temperature n the test secton, pressures on the surface of the arfol, forces on the arfol, and the angle of attack. Before takng the measurements there are several preparatory operatons: Load cell calbraton Install the model n the test secton and set t to zero angle of attack. Wth wnd tunnel velocty set to zero, calbrate the load cell. The load cell measures three force components,.e., Fx (the drag force), Fy and Fz (the lft force). Calbratons are only conducted for lft and drag forces. For ths purpose, a seres of fve loads (from 0 to kg) wll be successvely appled to a specal calbraton frame, as demonstrated by the TA. Open the calbraton software and follow the nstructons specfed n Step 1, Appendx B. Usng the software, plot the measurements. Calbraton coeffcents wll later be calculated by applyng a lnear regresson to the measured data. Tunnel flow condtons Set the target flow condtons n the tunnel test secton, as per Step, Appendx B. A Reynolds number of 300,000 (15 m/s free stream velocty) wll be used n ths experment to compare results wth the avalable benchmark data. 5

6 Pressure transducer operaton Wth tunnel settngs at the target condtons (Re=300,000), software wll be used by the TA to demonstrate the effect of the nose of DA. Ths nose takes the form of a resdual sgnal n the DA recordngs that collectvely represents the electronc nose, dgtzaton effects, other uncontrolled envronmental parameters, and the effect of the dgtzaton levels: the resoluton wth whch the DA converts the analog to dgtal sgnal. Two mportant data acquston parameters wll be establshed, usng another set of software nterfaces. The settlng tme (tme needed for the DA to recover after changng ts settng from one pressure tap to the next) and the samplng tme (the length of tme needed for a measurement to capture the actual mean value of a turbulent, fluctuatng quantty) wll be explaned and demonstrated by the TA Data Acquston The data acquston steps are lsted below: 1. Install the arfol, and calbrate the load cell for both lft and drag forces, followng Step 1, n Appendx B.. Set the arfol angle of attack to 0, and adjust the wnd tunnel motor speed to acheve a Reynolds number of 300,000 (15 m/s free stream velocty). Detals are specfed n Step, Appendx B. 3. Wth the flow and angle of attack set to the desred values, measure the lft and drag forces on the arfol, usng the load cells. Open the Labvew program for load cell data acquston and follow the procedure n Step 4, Appendx B. The software records the voltage output from the load cells. These voltage values wll be converted to forces usng the calbraton equaton (equaton (7) and (8)) and the establshed calbraton coeffcents. 4. Mantanng the same flow condtons as above, measure the pressure dstrbuton around the arfol. Open the Labvew program for the pressure transducer, and follow the procedure n Step 3 of Appendx B. Enter the values of the settlng and samplng determned above n the software nterface. The DA software wll measure the pressure dstrbuton around the arfol, as well as the free-stream velocty. Pressure s measured n reference to the statc pressure tap on the traverse-mounted Ptot tube. For ths reason, ensure the Ptot tube s postoned well below the arfol wth the use of the traverse. The TA wll demonstrate the proper use of the traverse controller. The software outputs the average pressure measured at each tap and graphcally dsplays the measurements as they are collected. The nput connectons to the scannng valve are as follows: a. Ports 0 to 8 are connected to the correspondng pressure taps located on the arfol (see Fgure 3.b). b. Port 40 s connected to the statc pressure tap on the traverse mounted Ptot tube (whch s connected to the reference sde of the pressure transducer, and s therefore redundant). c. Port 4 s connected to the stagnaton pressure tap on the traverse-mounted Ptot (for velocty measurement, step 6 below). 5. Repeat Steps through 4 for an angle of attack of For angle of attack of 16 wth the same flow condtons as above, measure the velocty profle downstream of the arfol. Before acqurng data t s mportant to establsh a datum for whch to reference the elevaton of traverse-mounted Ptot tube. Use the traverse controller to poston the tp of the Ptot at the same elevaton as the tralng edge of the arfol. It s mportant to consult the TA for proper traverse controller operaton. Open the Labvew program for velocty profle measurement, and follow the procedure n Step 5 of Appendx B. The DA software wll measure the pressure dfference sensed by the Ptot tube and wll nternally convert ths pressure dfference to a velocty. Velocty s graphcally dsplayed at each pre-determned elevaton (defned n DA) allowng the velocty profle to be vsualzed Data Reducton A spreadsheet wll be provded for the data reducton. Data reducton ncludes calculaton of the followng quanttes: 1. Calculate C p for all 8 pressure taps.. Calculate the lft force L and the correspondng lft coeffcent C L on the arfol by ntegratng the measured pressure dstrbuton over the arfol surface. 3. Calculate the lft force L and the correspondng lft coeffcent C L on the arfol usng data obtaned from the load cell. 4. Calculate the drag force D and the correspondng drag coeffcent C D on the arfol usng data obtaned from the load cell. 5. Repeat Steps 1 through 4 for an angle of attack of For angle of attack of 16, calculate the drag force D and the correspondng drag coeffcent C D on the arfol by ntegratng the change n momentum from the measured velocty profle downstream of the arfol. 6

7 Uncertanty Assessment Uncertantes for the expermentally measured pressure and lft coeffcents wll be evaluated. The methodology for estmatng uncertantes follows the AIAA S-071 Standard (AIAA, 1995) as summarzed n Stern et al. (1999) for multple tests (sectons 6.1 and 6.3). The block dagram for error propagaton to the fnal results s provded n Fgure 5. Based on prevous experments, t was found that bas and precson lmts for, U,, s, and c are neglgble, so for the present analyss, we wll only nclude the bas lmt for p p. The spreadsheet provded for calculatng expermental uncertantes contans estmates of bas and precson lmts for the ndvdual measured varables, based on prevous experments. The data reducton equaton for the pressure coeffcents (equaton (1)) s of the form C p f ( p p,, U). For EXPERIMENTAL ERROR SOURCES ths analyss, we wll only consder bas and precson lmts for p p (see uncertanty analyss spreadsheet). Note that ths uncertanty assessment does not nclude error sources such as pressure lag exceedng the data acquston delay tme, undetected leaks n the pressure tubng, model orfce effects, vbraton effects on the probes, unsteady flow effects, and undetected leaks n the scannng valve. The total uncertanty for the pressure coeffcent measured at each pressure tap s gven by equaton (4) n Stern et al. (1999): U B P (8) The bas lmt n Equaton (8) s the same for all taps and s gven by equaton (14) n Stern et al. (1999). Neglectng correlated bas lmts and dscardng the terms wth neglgble bas lmts: B j B ( p p) B( p p) (9) 1 where B s the bas lmt for the ndvdual varable and p ANGLE OF ATTACK C X B, P TEMPERATURE T B, P T T = f ( ) = (T) = f (T) ar ar FREE-STREAM VELOCITY U B, P U U U = (p - p ) stagn (p -p ) C [(p - p ), (T), U ] = p U L C [L,, U, c] = L U bc C p B, P C p T L B, P C L SURFACE PRESSURE p B, P p p INDIVIDUAL MEASUREMENT SYSTEMS MEASUREMENT OF INDIVIDUAL VARIABLES DATA REDUCTION EQUATIONS EXPERIMENTAL RESULTS Fgure 5. Block dagram showng propagaton of error through data reducton equatons s the senstvty coeffcent. Ths senstvty coeffcent,, s evaluated usng the average values for the ndvdual varables, and s gven by: p p C _ p p p p p U (10) The precson lmt for each pressure tap n Equaton (8) was estmated usng equaton (3) n Stern et al. (1999): P S M (11) where S s the standard devaton of the pressure coeffcents at each pressure tap, evaluated usng equaton () n Stern et al. (1999) for M = 10 repeated tests. Precson lmts wll have dfferent values at each of the 8 taps. However, for ths experment, the precson lmt wll be calculated only at tap 0, where pressure measurements wll be repeated 10 tmes. The data reducton equaton for the lft coeffcent, equaton (3), s of the form f ( p p,, s,, U, c). For ths analyss, we wll only consder bas and precson lmts for p p (see data reducton spreadsheet). The total uncertanty for the measurement of the lft coeffcent s gven by (equaton 4 n Stern et al., 1999) U B P (1) The bas lmt n equaton (1) s gven by equaton (14) n Stern et al. (1999). Neglectng correlated bas lmts and dscardng the terms wth neglgble bas lmts: B j 1 B ( p p) B( p p) (13) 7

8 Gven the above assumptons and usng the lft force determned by ntegraton (equaton (5)), the expresson for the bas lmt of the lft coeffcent s: B B k p p p p 1 C L B 0.5U p p sn ds Notatons used n equaton (14) are defned n Table 1 and Appendx A (k = 9). The precson lmt n Equaton (1) was estmated usng equaton (3) n Stern et al. (1999): P S M (15) where S s the standard devaton of the lft coeffcents evaluated usng equaton () n Stern et al. (1999) for M = 10 repeated tests. An average value for the precson lmt wll be provded n the uncertanty analyss spreadsheet, based on prevous measurements. c k 1 (14) 3.. Part : epiv/flowcoach Test Setup Pror to the experment, your TA wll prepare the epiv/flowcoach system Data Acquston The epiv/flowcoach expermental procedure follows the steps lsted below: 1. Wth TA assstance, nstall the Clark-Y arfol model wth 0º angle of attack n the epiv/flowcoach test secton. Flush all bubbles from the test nsert module, and reassemble the devce.. Detach the reservor from the epiv devce, unscrew the ld, and nsert a thermometer to measure the temperature of the water. Ths wll be used to determne ts vscosty later. Close the reservor and reattach t to the system. For FlowCoach use, the reservor s a large tub located at the bottom of the test stand. 3. Turn on the epiv system by flppng the swtch on the back of the devce. For FlowCoach use, the power swtch s located on the attached power strp. 4. Adjust the knob on the front of the epiv system to approxmately ¾ of the maxmum flow rate. Rotate the knob fully clockwse, then turn t two revolutons counterclockwse. Consult TA for proper flow rate wth the FlowCoach system. 5. On the computer desktop, open the FLOWEX software. Clck on the Acqure button, on the left sde of the screen. 6. Specfy camera parameters for PIV mage acquston. Recommended values are 55, 100, 100, and 10, for brghtness, exposure, gan, and frames, respectvely. 7. Clck on the Capture button to acqure 10 mages. When FLOWEX returns to the Acqure dalogue, press F5 to refresh the screen and vew your mages, whch should appear smlar to the example n Fgure 10, below. If your mages look sgnfcantly dfferent, modfy your camera settngs and re-capture the mages. 8. Once you have satsfactory results, clck on the Analyze button on the left sde of the FLOWEX screen. 9. Specfy parameters for PIV processng. Values of 0, 10, and 9 should be used for wndow sze, shft sze, and PIV pars, respectvely. 10. Clck on the Process button to begn PIV processng. Ths computaton wll take a few mnutes to complete. When FLOWEX returns to the Analyze dalogue, press F5 to refresh the screen to vew your results. You should be able to see mages of a velocty vector feld and velocty magntude contours. 11. Scroll the screen down below the two mages under the Results secton. Rght-clck on Velocty vector feld data and save the fle to a workng drectory on the computer. Rename the fle to nclude your group number and the angle of attack tested. 1. Turn off the epiv/flowcoach system by flppng the approprate swtch. 13. Repeat steps 1 through 11 usng the 16º angle-of-attack model. 8

9 Mass (kg) Data Reducton Calculate the Reynolds number around the arfol for each angle of attack, usng equaton (16), below. U av c Re (16) If usng the epiv system, use a value of 0 mm for the chord length c. If usng the FlowCoach system, use a value of 50 m for the chord length c. The knematc vscosty of water, ν, should be determned from the reservor temperature that you recorded durng data acquston. To obtan the average velocty n the test secton, U av, open the text fle contanng your velocty vector data for 0-degrees angle of attack (renamed from velocty_vec.txt ) and copy the entre contents of the fle. If usng the epiv system, open the fle Lab3 Data Reducton Sheet (epiv-0deg.), avalable on the class webste, and paste the coped data nto the green cells on the frst tab, labeled Raw Velocty Vector Data. If usng the FlowCoach system, use the fle Lab3 Data Reducton Sheet (FlowCoach-0deg.). Repeat ths process for your 16- degree-angle-of-attack data. Usng the TecPlot software, generate mages of the velocty vector feld, streamlnes around the arfol, and velocty magntude contours for both 0º and 16º angles of attack. Instructons for usng TecPlot, E-PIV/FlowCoach Data Post-Processng Instructons, are downloadable from the class webste, at 4. Data Analyss 4.1. Part 1: Wnd Tunnel Data analyss ncludes the followng steps, shown below. Use the data reducton sheet for all calculatons, and attach t along wth your lab reports. The data analyss secton of the lab report must nclude the answers to all 6 questons gven below. 1. If the lft L s a functon of the free-stream velocty U, densty, chord c, angle of attack, and vscosty, what are the dmensonless groups ( parameters) that characterze ths problem?. How do the expermental measurements of the pressure dstrbuton apply to a full-scale arcraft wth a smlar arfol secton? 3. Include the calbraton plots for both lft and drag along wth your lab report. The plots should have Voltage on the x-axs and Mass on the y-axs, and should nclude the calbraton equaton. Fgure 6, below, shows an example plot for lft calbraton. The drag calbraton plot should be made n the same way. Mass [kg] Lft [V] Lft calbraton y = x R = Volts Fgure 6. Load cell calbraton curve 4. Plot versus x/c for each angle of attack. Plot the benchmark data (Fgure 7a) correspondng to the same angle of attack on the same graph. Show the calculated uncertanty for at the tap number where precson lmts were performed, usng an uncertanty band. Indcate the percentage of uncertanty on the graph. Example plots are gven n the data reducton spreadsheet. Also nclude a plot of the normalzed velocty profle measurement taken at 16º angle-of-attack. 5. Plot the results for C L, obtaned from both pressure dstrbuton and load cell, wth the benchmark data. Fgure 7b shows the benchmark data for C L, and the coordnates are gven n data reducton sheet. 6. Plot the results for C D, obtaned from both velocty profle and load cell, wth the benchmark data. Fgure 7c shows the benchmark data for C D, and the coordnates are gven n the data reducton sheet. 9

10 (a) Dstrbuton of pressure coeffcents for = 0, 4, 8, and 16 (b) Varaton of C L wth angle of attack (c) Varaton of C D wth angle of attack Fgure 7. (a)-(c): Arfol reference data at Re=300, Part : epiv/flowcoach Your lab report should nclude the plots that you generated of the velocty vector feld, streamlnes around the arfol, and velocty magntude contours for both 0º and 16º angles of attack. Answer the followng questons, and nclude them as well: 1. Include your Reynolds number calculatons for the Clark-Y arfol model. Compare your streamlne plots for each angle of attack. Do you observe any flow separaton on the top surface of the arfol? Do you expect to see any separaton? Why or why not?. On each streamlne plot, mark the flow stagnaton pont. How should the pressure at ths pont compare to the pressure at other locatons on the arfol? 10

11 5. References AIAA (1995). AIAA- 071 Standard, Amercan Insttute of Aeronautcs and Astronautcs, Washngton, DC. Granger, R.A. (1988). Experments n Flud Mechancs, Holt, Rnehart and Wnston, Inc. New York, N.Y. Marchman III, J.F. and Werme, T.D. (1984). Clark-Y Performance at Low Reynolds Numbers, Proceedngs AIAA nd Aerospace Scence Meetng, Reno, NE. Robertson, J.A. and Crowe, C.T. (1993). Engneerng Flud Mechancs, 5th edton, Houghton Mffln, Boston, MA. Stern, F., Muste, M., Bennat, L-M., Echnger, B. (1999). Summary of Expermental Uncertanty Assessment Methodology wth Example, IIHR Report, Iowa Insttute of Hydraulc Research, The Unversty of Iowa, Iowa Cty, IA. Whte, F.M. (1994). Flud Mechancs, 3rd edton, McGraw-Hll, Inc., New York, N.Y. APPENDIX A SPECIFICATIONS FOR THE EXPERIMENTAL FACILITY COMPONENTS Relevant geometrcal notatons are provded n Fgure 3b. The postonng of the pressure taps on the arfol surface s also specfed n Fgure 3b. Arfol Geometry: - maxmum thckness, t = m; - arfol wng span, b = 0.76 m; - chord length, c = m Angle notatons: - surface to chord lne angle, ; - angle of surface normal to free- stream flow, ; - angle of attack,. The numercal values for the arfol relevant geometrcal characterstcs are provded n the table to the rght. These values are also provded n the data reducton sheet. Lft force can be computed usng the trapezodal scheme for the numercal ntegraton L s 1 p p sn ds p p p 1 p sn 1, s 1, N Tap Number () x/c s Surface Element Length (mm) Surface (-1) - () to Chord Lne Angle (degrees) Tralng Edge

12 APPENDIX B THE AUTOMATED DATA ACQUISITION SYSTEM (ADAS) Step 1: Calbraton of Load Cell a. Gettng started wth the calbraton of load cell. Double clck on the program Lft_Force_Xducer_Calbraton.v from the ADAS shortcut and open the calbraton program. b. From the man menu select Calbraton. A table shown n the rght cell wll pop up showng the mass (kg) versus lft and drag forces (Volts). Ht Run to start the program and clck on Acqure Sgnal. Keep ncreasng the weghts on the Load cell as drected by the TA and keep acqurng data to obtan the lnear regresson. The data recorded can be seen on the table. Fgure B.1 c. Select and clck on the Plot tab from the man menu. The lnear calbraton curve between the loadng mass and the output voltage can be observed once you ht the Plot button on the Load cell Sgnal as shown n Fgure B.3. Fgure B. d. Clck on Wrte Results from the Load cell Sgnal box and the recorded data wll be wrtten to an output text fle that wll be used later to convert the sgnal from Volts to Newtons. Fgure B.3 Fgure B.4 Step : Settng up Wnd Tunnel Condtons a. Once the calbraton s complete, the next step s to swtch on the wnd tunnel. The wnd tunnel desred speed s controlled usng the program shown n Fgure B.5. Open the program VWT_Set_Motor_Speed.v from the ADAS. Clck Run button on the program. b. Open program VWT_Tunnel_Velocty.v and ht Run after nputtng the atmospherc pressure n mm of Hg n the Ambent Pressure box. The wnd tunnel velocty s dsplayed on the lower left hand corner of the man page. Adjust the speed on the tunnel by adjustng the Desred Voltage as shown n Fgure B.5. Once the wnd tunnel velocty s set at the desred level proceed to step 3. Fgure B.5 Fgure B.6 1

13 Step 3: Measurement of pressure dstrbuton a. Open program VWT_Scanvalve_Data_Acquston.v. Select the Ref Cond tab from the man menu. Enter the values of manometer flud densty and the ambent absolute pressure n the two boxes as shown n Fgure B.7. b. After enterng the densty and pressure values, select Port Lst tab from the man menu. Enter the pressure tap numbers n the order they are requred to be scanned as shown n Fgure B.8. Clck on the Run button to start scannng the pressure taps. Fgure B.7 Fgure B.8 Step 4: Lft and drag force measurement c. Open program ATMI_Load_Cell_Test.v and clck Run. The nstantaneous lft force wll be dsplayed on the Lft graph. The dsplay shows the force n terms of volts, whch can be converted to Newtons usng the calbraton curve. Once the force s noted clck on the STOP button. Step 5: Measurement of velocty profle a. Open program VWT_Wake_Survey.v. Select the Input tab from the man menu. Enter the values of settlng tme, angle of attack, and the ambent absolute pressure n the three boxes as shown n Fgure B.10. Then specfy the output fle path and fle name by clckng on the folder button as shown n Fgure B.10. Fgure B.9 b. Next select the A/D tab and specfy the nput channel the pressure transducer s connected to. Specfy samplng tme and data rate. Refer to Fgure B.11 Fgure B.10 Fgure B.11 13

14 c. Open the nput fle VHIL_Staton_Lst.txt. Verfy all the Ptot tube elevaton postons are correct n mm. See Fgure B.1. d. Ensure Ptot tube datum has been establshed by frst locatng the tp of the traverse-mounted Ptot tube at the elevaton of the arfol tralng edge. Clck Run and the DA wll move the Ptot tube to the specfed elevatons to record velocty. The velocty profle wll be dsplayed n the plot. See Fgure B.13. Fgure B.1 Fgure B.13 14