Pressure Measurements Laboratory

Transcription

1 Lab # Pressure Measurements Laboratory Objectves:. To get hands-on experences on how to make pressure (surface pressure, statc pressure and total pressure nsde flow) measurements usng conventonal pressuremeasurng nstrumentatons.. To learn how to determne the aerodynamc characterstcs of an arfol based on the arfol surface pressure dstrbuton measurements. 3. To know how to do raw data acquston, expermental data reducton and processng, measurement error estmaton, and fnal result analyss and dscusson of an expermental study. Techncal Background:. The pressure-measurng nstrumentatons: a. Mechanca pressure gauge: to measure the atmosphere pressure to calculate the ar densty. b. Ptot-statc pressure probe: to measure the statc pressure and total pressure nsde wnd tunnel to determne the dynamc pressure and flow velocty. c. Electrcal pressure transducer: DSA37 pressure acquston system. The DSA37 dgtal sensor arrays ncorporate temperature compensated pezoresstve pressure sensors wth a pneumatc calbraton valve, RAM, 6 bt A/D converter, and a mcroprocessor n a compact self-contaned module.. The precson of the pressure acquston system s ±0.% of the full scale (± 0 nch H O).. See manual for further detaled nformaton.. The test arfol: The arfol used n the present experment s a GA(W)- arfol (also labeled as ASA LS()-047). The GA (W)- has the maxmum thckness of 7% of the chord length. Compared wth standard ACA arfols, the GA (W)- arfol was specally desgned for low-speed general avaton applcatons wth a large leadng-edge radus n

2 order to flatten the peak n pressure coeffcent near the arfol nose to dscourage flow separaton. The arfol s qupped wth 43 pressure taps at ts medan span, and the locatons of the pressure taps are ndcated n Fg.. Y/C X/C Fgure. GA(W)- arfol and pressure tap locatons. Table : The coordnate of the pressure taps on the GA(W)- arfol. Lower Surface Upper Surface tap x/c y/c tap x/c y/c

3 TAP s at the arfol leadng edge (LE) and TAP s at the arfol tralng edge (TE) TAP -0 are along the lower surface, TAP -43 are along the upper surface The chord length of the arfol s 0mm,. e., C 0mm. 3. Calculatng arfol lft coeffcent ( C l ), drag coeffcent ( C d ), and moment (coeffcent) ( C m, LE ) by numercally ntegratng the surface pressure dstrbuton around the arfol: Fgure. Pressure tap numberng conventon Frst, recall that the surface pressure taps are numbered n the counterclockwse drecton as shown n Fg.. Although t may seem somewhat unntutve at frst, ths numberng conventon allows us to formulate relevant equatons n a very generc way. A total of 43 pressure tap locatons are gven by ther Cartesan gven n table. 43, Total umber of Pressure Taps x, y, as,..., lower surface, from LE to TE x, y, as,...,43 upper surface, from TE to LE

4 Wth the conventon, the arfol surface s broken nto panels. The -th panel s bounded x y respectvely. The excepton s that the by the -th and +-th taps at ( ) y -th panel s defned by ( ) y x, and (, + + ) x, and ( x, ) y, but n your spreadsheet or program, you can treat ths by addng a fcttous +-th tap whch smply takes on the value from the frst tap. Consder the -th panel shown n Fg., where p+/ represents pressure (assume to be) actng on the -th panel. Let p p + / + / ( p + p ) + ( p + p ) If we assume the pressure varaton on the -th panel to be constant at p +/ as defned by Eq., ths s equvalent to trapezodal true ntegraton. Furthermore, defne x x x x x, x, y y + + y y y y () () Fgure 3. Dscrete representaton of arfol surface element ote that x and y can be negatve because x and y are not monotonc n the ndex. Usng Eqs. and, the normal and axal components of the pressure force actng on the -th panel can be wrtten as

5 δ x (3) p + / p+ / δ A y (4) where the prme ndcates a two-dmensonal quantty (force per unt span). Smlarly, the moment contrbuton from the -th panel to the total moment about the leadng edge can be wrtten as δm LE, or where r δf ( x + y k) ( δ A + δ k) + / + / ( x + y k) ( p z + p x k) + / + / + / + / [( x ) x + ( p y ) y ]j p (5) + / + / + / + / δ M x ( p+ / x ) x+ / ( p + / y ) y / LE, + ( x + x ), y ( y y ) + / + + / + + ote that aerodynamc moment s defned to be postve n the ptch-up drecton. ow that we have derved the expressons for the dfferental force and moment from each panel, we can ntegrate them over the arfol surface. A M LE δ δa δm LE ( p x ) x ( p y ) + / p + / p + / x y + / + / y + / Fnally, the lft and drag per unt span can be obtaned as follows. L cosα Asnα D snα + A cosα (6) (7) (8)

6 Requrements for the Lab Report You are requred to prepare a formal lab report wth followng results ncluded:. Usng your data: a. A table showng all the data you obtaned. P P b. A plot of pressure coeffcent ( C p ) dstrbuton for upper and lower V ρ surface of the arfol for the angles of attack (α) you used. c. Comments on the characterstcs of the pressure dstrbuton d. Calculate lft coeffcent ( moment (coeffcent) ( C m, LE L ), drag coeffcent ( ρ V c M LE ). ρv c C L e. The velocty at the test secton and Reynolds number of the flow.. Usng the entre group data to plot the curves of Cl vs α, 3. Report requrement: a. Calculatons for all the steps leadng up to the fnal answer b. Raw data shown as spreadsheet D ), and ρ V c C D Cd vs α and C, vs α. m LE c. A bref dscusson about the measurement error estmaton of your results Some helpful nformaton related to ths lab can be found from:. About the arfol aerodynamcs for the textbook of John Anderson, Fundamentals of Aerodynamcs 3 rd or 4 th Edton, McGraw-Hll. About the GA(W)- arfol and experment from the paper of Z. Yang, H. Ma, F. Haan, and H. Hu, "An Expermental Investgaton on the Flow Separaton on a Low-Reynolds-umber Arfol", AIAA at ( 3. About the DSA37 pressure transducer at

7 The Expermental Data eeded for the Lab # Atmosphere pressure n the lab, P? atm The temperature n the wnd tunnel, T? The densty of ar n the wnd tunnel, ρ? The statc pressure of the n comng flow P? The total pressure of the ncomng flow P? The velocty of the ncomng flow, V? The angle of attack of the arfol α? The surface pressure data from the 43 pressure taps around the arfol P M M P 43?? total ote: For the arfol surface pressure dstrbuton measurements, t s recommended to run the DSA 37 unt wth the data acquston of 300 ~ 400Hz for about 0 seconds n order to calculate the averaged pressure for each pressure tap.

8 The expermental parameter settngs for the Lab#: Frst ame Last ame angle of attack motor speed Sunl Arolla AOA5,0,5 5Hz Danel Dvorak AOA6,,6 5Hz Danel Garrck AOA7,,8 5Hz Xuan Ge AOA8,3,9 5Hz Chrstopher Karstens AOA9,4,0 5Hz Meng Lo AOA5,0,5 0Hz John Meyer AOA6,,6 0Hz Katrne lsen AOA7,,8 0Hz Ahmet Ozbay AOA8,3,9 0Hz Suganth Selvaraj AOA6,,6 0Hz Jason Ryon AOA5,0,5 5Hz Spencer Pack AOA9,4,0 5Hz Le Sh AOA7,,8 5Hz Hephzbah Thamp AOA8,3,9 5Hz Ka Zhang AOA9,4,0 5Hz