Flow Induced Noise Generation By Partial Cavities

Transcription

1 Flow Induced Noise Generation By Partial Cavities Harish Ganesh, Juliana Wu and Steven L. Ceccio University of Michigan, Ann Arbor USA 2nd FLINOVIA Symposium Penn-State University, State College, PA Sponsor: Office of Naval Research Program Manager: Dr. Ki-Han Kim

2 Motivation Partial/Cloud cavitation: Significant source of noise, performance deterioration, and erosion Mechanisms of transition, shedding, and their relationship to underlying flow Void fraction flow field measurements for CFD code validations

3 Cavitation Dynamics on NACA0015 Hydrofoil Cavitation type depends upon attack angle ( ) and cavitation number ( ) TYPE 2 Shedding L/c < 2/3 L/c = 2/3 ( ) Physical mechanisms and associated acoustics Sheet Cavitation TYPE 1 Shedding L/c > 2/3 SuperCavitation ( ) NACA 0015 Cavitation Map Arndt et al. (2000)

4 Arndt et. al.- Cavitation Dynamics on NACA0015 Hydrofoil Type 1 Type 2 Suction side surface pressure transducer data from Kjeldsen, Arndt & Effertz (2000) α = 7 degrees What causes the abrupt change in dynamics?

5 Present Study Flow loop: Michigan 9 water tunnel with reduced area test section NACA0015 Hydrofoil: AR = 1.5 and Chord = 50 mm Flow conditions: U 0 = 8 m/s, p o = kpa, = 0.4-4, Dissolved Oxygen ~ 50% Sat Measurements: Inflow quantities, acoustic pressure using hydrophone (B- K) Cavitation visualization: High-speed videos Void fraction measurements: Time resolved X-ray densitometry

6 X-ray Densitometry 21 cm square test section Mäkiharju, S.A., The Dynamics of Ventilated Partical Cavities Over a Wide Range of Reynolds Numbers and Quantitative 2D X-ray Densitometry for Multiphase Flow, 2012, Ph.D. Thesis, University of Michigan, Ann Arbor, USA Test section area reduced to achieve lower attenuation through water

7 Cavitation Observation Top High speed videos from Top and side synchronized with hydrophone Filmed at 7500 fps and played back at 15 fps Side

8 Time Shock Collapse? Shock Collapse Reducing /2

9 Incipient Cavitation Filmed at 7500 fps and played back at 15 fps X-ray measurements of incipient cavity (0-50%) Side Filmed at 1000 fps and played back at 15 fps

10 Type 2 Shedding: HS Video ( =10 ) High speed videos from Top and side synchronized with hydrophone Re-entrant liquid flow induced shedding Top Top Side Side Filmed at 7500 fps and played back at 15 fps Shedding is not spanwise uniform Length is nearly constant

11 Type 2 Shedding: X-ray ( =10 ) X-ray measurements synchronized with hydrophone (0-100%) 10, 5.8 Side Filmed at 1000 fps and played back at 15 fps

12 Type 2 Shedding: Spectral Content σ 0 / 2 = 5.8 = 10 degrees Morse-Wavelet-transform

13 Type 1 Shedding: HS Video ( =7 ) Top 7, 4.2 High speed videos from Top and side synchronized with hydrophone LE Cycle Collapse Roll-up pinch Cavity Begins off and fills Max growth length arrest (L (L 1 ) 2 ) Side Side Filmed at 7500 fps and played back at 15 fps Length oscillates between cycles Can lead to lift and drag changes Multi-modal

14 Type 1 Shedding: HS Video ( =10 ) Top 10, 4.1 High speed videos from Top and side synchronized with hydrophone Growth L 2 Growth L 1 Cycle Rollup Begins and growth Collapse and arrest Side Filmed at 7500 fps and played back at 15 fps Length oscillates thrice between cycles # of steps can change Multi-modal

15 Type 1 Shedding: X-ray ( =7 ) X-ray measurements synchronized with hydrophone (0-100%) 7, 4.2 Filmed at 1000 fps and played back at 15 fps Side Growth arrest due to cloud collapse observed

16 Type 1 Shedding: X-ray ( =10 ) X-ray measurements synchronized with hydrophone (0-100%) 10, 4.1 Filmed at 1000 fps and played back at 15 fps Side Cavitation at trailing edge can have an effect on spectral content

17 Type 1 Shedding: Spectral Content σ 0 / 2 = 4.1 = 10 degrees Morse-Wavelet-transform

18 Type 1 with Shocks: X-ray ( =10 ) X-ray measurements synchronized with hydrophone (0-50%) 10, 3.0 Bubbly Shock Side Filmed at 1000 fps and played back at 15 fps

19 Type 1 Shedding: Void Fraction Top ~0.6 10, , 3.0 ~0.3 Side

20 Type 1 with Shocks: Spectral Content σ 0 / 2 = 3.0 = 10 degrees Morse-Wavelet-transform

21 Shedding Dynamics: Flow Processes X-ray measurements synchronized with hydrophone (0-50%) 10, 3.0 Side Filmed at 1000 fps and played back at 15 fps

22 Shedding Dynamics: Flow Processes Wavelet transform of Acoustic Signal 10, 3.0 Side

23 Shedding Dynamics: Flow Processes X-ray measurements (0-50%) 10, step with shocks 1 step with shocks Side Does cloud collapse cause cavitation near trailing edge? Filmed at 1000 fps and played back at 15 fps

24 Shedding Dynamics: Hydrophone ( =7 ) St C = 0.14 Top Side St C = 0.42 TS Organ Pipe Mode St C = 6.7 St C = 0.28 = 7 degrees

25 Shedding Dynamics: Hydrophone ( =10 ) St C = 0.12 Top St C = 0.36 St C = 0.48 Side St C = 0.24 TS Organ Pipe Mode St C = 6.7 = 10 degrees

26 Shedding Dynamics: Void Fraction Averaged void fraction L 4 L 3 L 2 L 1 = 7 degrees St C = 0.14 Side St C = 0.42 St C = 0.28

27 Shedding Dynamics: Void Fraction Averaged void fraction L 4 L 3 L 2 L 1 = 10 degrees St C = 0.12 Side St C = 0.48 St C = 0.24

28 Conclusions Goal: To address the source of transition in cavity dynamics 1. Shed cloud collapse influences cavity growth and hence the cycle duration 2. Cavity can attain different lengths in a given cycle depending upon the nature of the shed cloud 3. At lower cavitation numbers, Side propagating bubbly shocks are observed 4. Secondary cavitation at the trailing edge is also observed The line of demarcation between the processes can be thin, thus making the flow multi-modal.

29 Thanks for your attention

30 Cavitation Occurs in liquids, when local pressure in close to vapor pressure 1 2 Partial cavitation: Occurs in separated flows attached to the object with stable cavity lengths Cloud Cavitation: Characterized by cavity volumetric oscillations accompanied by shedding

31 Arndt et al.- Cavitation Dynamics on NACA0015 Hydrofoil Cavitation type depends upon attack angle ( ) and cavitation number ( ) f frequency C- Chord (also L C ) V- Velocity NACA 0015 Cavitation Map Arndt et al. (2000) L/c = 2/3 TYPE 2 Shedding L/c < 2/3 Type 1: St ~ 0.15 independent of σ Type 2: Re-entrant jet induced shedding Frequency is ~ linear with σ Cavity length based St ~ 0.3 Sheet Cavitation SuperCavitation TYPE 1 Shedding L/c > 2/3

32 Propagating Bubbly Shocks Ganesh et al. Bubbly shock propagation as a mechanism for sheet-tocloud transition of partial cavities, JFM, Vol. 802, 2016 Shedding cavities can exhibit both re-entrant and bubbly shock induced shedding What are the mechanisms involved in NACA0015 hydrofoil cavitation?

33 Cavity Length Cavity Length vs / 2a 7 degrees ( ) 10 degrees ( ) Open symbols = X-ray Filled symbols =HSV FSL theory for thin cavity negative compliance not observed

34 Cavity Behavior Four Modes of Cavity Shedding Identified 1. Incipient shedding 2. Re-entrant flow, rear pinch off (Type 2) 3. Multi-step shedding with shocks (Type 1) 4. Shock induced shedding (Intermittent Type 1) It is important to note that the flow is multi-modal

35 Incipient Cavitation: Void Fraction Top 10, 6.3 ~ , 6.3 ~0.04Side

36 Type 2 Shedding: HS Video ( =7 ) Top 7 High speed videos from Top and side synchronized with hydrophone Re-entrant liquid flow induced shedding Side 5.8 Filmed at 7500 fps and played back at 15 fps Shedding is not spanwise uniform Length is nearly constant

37 Type 2 Shedding: X-ray ( =7 ) X-ray measurements synchronized with hydrophone (0-100%) 7, 5.8 Side Filmed at 1000 fps and played back at 15 fps

38 Type 2 Shedding: Mean Void Fraction Top 7, 5.8 ~0.3 10, 5.8 ~0.3 Side

39 Type 2 Shedding: RMS Void Fraction Top 7, 5.8 ~ , 5.8 ~0.10Side

40 Type 2 Shedding: Spectral Content σ 0 / 2 = 5.8 = 10 degrees

41 Type 1 Shedding: Mean Void Fraction Top ~0.4 7, 4.1 ~0.5 Side 10, 4.1

42 Type 1 Shedding: RMS Void Fraction Top 7, 4.2 ~ , 4.1 ~0.20Side

43 Type 1 Shedding: Spectral Content σ 0 / 2 = 4.1 = 10 degrees

44 Type 2 with Shocks: Spectral Content σ 0 / 2 = 3.0 = 10 degrees

45 Shedding Dynamics: Flow Processes L σ 0 / 2 = 3.54 = 10 degrees

46 Next Steps Goal: To address the source of transition in cavity dynamics 1. Measure unsteady pressures beneath cavity (Shock speed and Mach number) 2. High resolution void fraction measurements 3. Examine NACA and Side plano-convex hydrofoil? 4. Measure unsteady boundary conditions Larger Hydrofoil with 8.25 inch span.

47 Bubbly Shock Speeds: t-s Diagrams

48 Bubbly Shock Speeds U S /U O 7 degrees ( ) 10 degrees ( ) / 2

49 Void Fractions Pre- and Post-shock / 2 ~3 kpa U 2 S (p 2 p 1 ) (1 2 ) L (1 1 )( 1 2 ) / 2 7 degrees ( ) 10 degrees ( )

50 St C From the Void Fraction at L1 Top St C = 0.14 σ 0 / 2 = 5.85 σ 0 / 2 = 4.83 St C = 0.42 σ 0 / 2 = 3.19Side St C = 0.28 = 7 degrees

51 St C From the Void Fraction at L2 Top St C = 0.14 σ 0 / 2 = 5.85 σ 0 / 2 = 4.83 St C = 0.42 σ 0 / 2 = 3.19Side St C = 0.28 = 7 degrees

52 St C From the Void Fraction at L3 Top St C = 0.14 σ 0 / 2 = L 2 σ 0 / 2 = 4.83 St C = 0.42 σ 0 / 2 = 3.19Side St C = 0.28 = 7 degrees

53 St C From the Void Fraction at L4 Top St C = 0.14 σ 0 / 2 = L 2 σ 0 / 2 = 4.83 St C = 0.42 σ 0 / 2 = 3.19Side St C = 0.28 = 7 degrees

54 Acoustic Pressure From Hydrophone Top σ 0 = 0.78 U 0 =8 m/s = 7 degrees Side Time Expanded