Velocimetry Techniques and Instrumentation

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1 AeE 344 Lectue Notes Lectue # 05: elocimety Techniques and Instumentation D. Hui Hu Depatment of Aeospace Engineeing Iowa State Univesity Ames, Iowa 500, U.S.A

2 Methods to Measue Local Flow elocity - Mechanical methods: Taking advantage of foce and moments that a moving steam applies on immesed objects. ane anemometes Popelle anemometes

3 Methods to Measue Local Flow elocity - Pessue diffeence methods: Utilize analytical elationship between the local velocity and the static and total pessues The tubes sensing static and stagnation pessues ae usually combined into one instument known as Pitotstatic tube. Pessue taps sensing static pessue (also the efeence pessue fo this measuement) ae placed adially on the pobe stem and then combined into one tube leading to the diffeential manomete (p stat ). The pessue tap located at the pobe tip senses the stagnation pessue (p 0 ). Use of the two measued pessues in the Benoulli equation allows to detemine one component of the flow velocity at the pobe location. Special aangements of the pessue taps (Theehole, Five-hole, seven-hole Pitot) in conjunction with special calibations ae used two measue all velocity components. It is difficult to measue stagnation pessue in eal, due to fiction. The measued stagnation pessue is always less than the actual one. This is taken cae of by an empiical facto C. p 0 p C a. steamlined aifoil sta t ( p b. Flat plate ( p 0 0 p sta t p,( Benoulli ) / sta t ) / )

4 Methods to Measue Local Flow elocity -3 Themal methods: Compute flow velocity fom its elationship between local flow velocity and the convective heat tansfe fom heated elements. Hot wie anemometes Hot film anemometes

5 Paticle-based Flow Diagnostic Techniques Seeded the flow with small paticles (~ µm in size) Assumption: the paticle taces move with the same velocity as local flow velocity! Flow velocity f = Paticle velocity p Measuement of paticle velocity

6 Methods to Measue Local Flow elocity - 4 Fequency-shift methods: Based on the Dopple phenomenon, namely the shift of the fequency of waves scatteed by moving paticles. Lase Dopple elocimety(ld) o Lase Dopple Anemomety (LD) Plana Dopple elocimety (PD) o Plana Dopple Anemomety (PDA) Intefeence finges

Dopple Shift The Dopple effect, named afte Chistian Dopple (an Austian mathematician and physicist

7 Dopple Shift The Dopple effect, named afte Chistian Dopple (an Austian mathematician and physicist ), is the change in fequency and wavelength of a wave that is peceived by an obseve moving elative to the souce of the waves. Light fom moving objects will appea to have diffeent wavelengths depending on the elative motion of the souce and the obseve. Obseves looking at an object that is moving away fom them see light that has a longe wavelength than it had when it was emitted (a ed shift), while obseves looking at an appoaching souce see light that is shifted to shote wavelength (a blue shift).

8 Dopple Shift a. Stationay Sound Souce b. Souce moving with souce < sound c. Souce moving with souce = sound ( Mach - beaking the sound baie ) d. Souce moving with souce > sound (Mach.4 - supesonic)

9 Fundamentals of LD Take the coodinate system to be at est with espect to the medium, whose speed of light wave is c. Thee is a souce s moving with velocity s and emitting light waves with a fequency f s. Thee is a detecto moving with velocity, and the unit vecto fom s to is n i.e.. Then the fequency f at the detecto is found fom If c>> s, then the change in fequency depends mostly on the elative velocity of the souce and detecto. ) sin( ) sin( ) sin( ) ˆ ( ˆ 0 ˆ ˆ ˆ ˆ f f f c c e e f f e e n c n f f f f f i s s i s s s s

10 Dual-Beam LD Fingspacing : sin( / ) Fingnumbe : 4 DT N ; de D f sin( / ) T T Fequency of the scatteing sin( / ) f light : T Fequency shift accodingto sin( / ) f Dopple shift theoy:

11 -component LD systems Dual-beam lase setup only can measue one component of the velocity with its diection nomal to the finge planes. Two-colo LD system can be used fo - components of flow velocity measuements. A-ion Lase beams Blue (488nm) Yellow (54.5 nm) T -component LD

A eceiving lens at an off-axis collection angle pojects pat of this finge patten onto detectos, which poduce a Dopple

12 Phase Dopple Paticle Analyzes/PDPA Systems As paticles pass though the pobe volume, they scatte light fom the beams and ceate an intefeence finge patten. A eceiving lens at an off-axis collection angle pojects pat of this finge patten onto detectos, which poduce a Dopple bust signal with a fequency popotional to the paticle velocity. The phase shift between the Dopple bust signals fom the diffeent detectos is popotional to the size of the spheical paticles. PDPA system

The local velocity of fluid flow is calculated by U= L/t. L t= t 0 +t t=t 0 U L t 00 80 spanwise voticity (/s) -0.9-0.7-0.5-0.3-0. 0. 0.3 0.5 0.

13 Y (mm) Paticle-based techniques: Paticle Image elocimety (PI) To seed fluid flows with small tace paticles (~µm), and assume the tace paticles moving with the same velocity as the low fluid flows. To measue the displacements (L) of the tace paticles between known time inteval (t). The local velocity of fluid flow is calculated by U= L/t. L t= t 0 +t t=t 0 U L t spanwise voticity (/s) m/s GA(W)- aifoil shadow egion -60 A. t=t 0 B. t=t 0 +0 s Classic -D PI measuement X (mm) C. Deived elocity field

14 Methods to Measue Local Flow elocity - 5 Make tacing methods: Tace the motion of suitable flow makes, optically o by othe means to deive local flow velocity. Paticle Imaging elocimety (PI) Paticle Tacking elocimety (PT) Molecula Tagging elocimety (MT) t=t 0 PI image pai t=t 0 +4 ms t=t 0 t=t 0 +5ms MT&T image pai Coesponding flow velocity field

15 Steeoscopic PI Measuements of a Wing-Tip otex (Funded by AFOSR) Y pixel X Lase Sheet Z Camea Camea Steeo PI technique X/C= Re C 5,000; 5.0deg Y pixel X/C = X pixel Displacement vectos in left camea X pixel Displacement vectos in ight camea X/C=.0 CFD simulation esults

16 Lab#04 Measuements of Pessue Distibutions aound a Cicula Cylinde Flow Aound a Cicula Cylinde unifom flow + a -D doublet = flow aound a cicula cylinde Stagnation points Pessue coefficient on the suface of cylinde R sin ( ) R cos ( ) R cos ( ) R sin ( )

17 Lab#04 Measuements of Pessue Distibutions aound a Cicula Cylinde At the suface of the cylinde, Accoding to Benoulli s equation Pessue coefficient distibution on the suface of the cicula cylinde will be: sin 0 a P P P P 4sin ) sin ( P P C p R P Incoming flow X Y Angle, Deg. Cp

18 Pessue Distibution aound a Cicula Cylinde Numeical esults fo the velocity magnitude and pessue distibutions ove a cicula cylinde using FlowLab (h=35.8 m/s, Re=.89E+05)

19 Lab#04 Measuements of Pessue Distibutions aound a Cicula Cylinde Y P Incoming flow R X

20 cp --> Lab#04 Measuements of Pessue Distibutions aound a Cicula Cylinde Cp distibution aound a cylinde EFD CFD AFD theta (ad ) --> Cp distibutions ove a cicula cylinde

21 Requied Results fo the Lab Repot To make a table showing all the time-aveaged data you obtained fo all the cases you tested. To show all the calculation steps leading up to the final answe. To plot pessue coefficient (C p ) distibutions on the cylinde fom fo all the cases you tested. To make comments on the chaacteistics of the pessue distibution compaed with the theoetic pedictions. To calculate the dag coefficients (C d ) of the cicula cylinde fo all the cases you tested. To plot the dag coefficients (C d ) of the cicula cylinde as a function of at the Reynolds numbes.

Instrumentation. Dr. Hui Hu Dr. Rye Waldman. Department of Aerospace Engineering Iowa State University Ames, Iowa 50011, U.S.A

Instrumentation. Dr. Hui Hu Dr. Rye Waldman. Department of Aerospace Engineering Iowa State University Ames, Iowa 50011, U.S.A AerE 344 Lecture Notes Lecture # 05: elocimetry Techniques and Instrumentation Dr. Hui Hu Dr. Rye Waldman Department of Aerospace Engineering Iowa State University Ames, Iowa 500, U.S.A Sources/ Further