An Experimental Investigation on Surface Water Transport and Ice Accreting Process Pertinent to Wind Turbine Icing Phenomena

Transcription

1 An Experimental Investigation on Surface Water Transport and Ice Accreting Process Pertinent to Wind Turbine Icing Phenomena Dr. Hui HU Advanced Flow Diagnostics and Experimental Aerodynamics Laboratory ry Department of Aerospace Engineering, Iowa State University 2251 Howe Hall, Ames, IA

2 Wind Turbine Icing and Anti-/De /De- Icing Wind turbine icing represents the most significant threat to the integrity of wind turbines in cold weather. Change airfoil shapes of turbine blades. Cause imbalance to the rotating system. Shedding of large chuck of ice can be dangerous to public safety. Cause errors to anemometers to estimate wind resource. Some thermal de icing systems could consume up to 7% of the total power generated by the wind turbine on cold days.

3 Rime Ice and Glaze Ice Glaze ice formation a) Rime ice formation Oncoming air flow with supercooled water droplets b) Glaze ice is the most dangerous type of ice. Glaze ice form much more complicated shapes and are difficult to accurately predict. Glaze ice is much more difficult to remove once built up on aircraft wings or wind turbine blades.

4 Surface Tension Induced Flow - Maragoni Flow inside Water Droplets Incoming flow with super- cooled water droplets a) Incoming flow with super- cooled water droplets b) Temperature of Plate, T Wall =21.9 O C Video was taken at f=.5hz; Re-play speed is f=5hz (Hu and Jin, Int. J. of Multiphase Flow, Vol. 36, No.8, pp ,, 21)

5 Molecular Tagging Thermometry Technique (MTT) to Quantify the Time Evolution of the Droplet Cooling and Evaporation Process Test plate, T=5. O C ~28 m a). The first phosphorescence image acquired at.5ms after excitation laser pulse Temperature ( O C) Curve fit Experimental data Temperature ( O C) Time (s) 4 2tan V R 3 Test plate, T=5. O C 1 H ( ) R 2 ( 1 cos ) (2 cos ) 3 3sin m b). The second phosphorescence image acquired at 3.5ms after the same excitation laser pulse 2 H R V Water droplet Test Plate (T=5. O C) Solid surface (Hu and Huang, AIAA Journal, Vol. 47, No.4, pp813-82, 82, 29 ) m V/V o, h/h o Droplet volume, V Droplet heigth, h Contact angle Time (second) Contact angle (degrees)

6 Phase Change Process within An Icing Water Droplet t =.5 s ~25 m t = 5. s t = 2. s Liquid t = 35. s Solid water ice Test Plate, Tw = -2. O C Test Plate, Tw = -2. O C Test Plate, Tw = -2. O C Test Plate, Tw = -2. O C Instantaneous phosphorescence images 4 Temperature ( O C) t=.5s Temperature ( O C) t=5.s Temperature ( O C) t = 2. s Temperature ( O C) t = 35. s Y ( m ) 2 Y ( m ) 2 Y ( m ) 2 Y ( m ) 2 Test Plate (T W =-2. O C) X ( m) Test Plate (T W =-2. O C) X ( m) Test Plate (T W =-2. O C) X ( m) Test Plate (T W =-2. O C) X ( m) Unsteady heat transfer and phase changing process inside small icing i water droplets (Hu and Jin, International Journal of Multiphase Flow, 36(8): , 21)

7 Surface Water Transport in Glaze Ice Accretion Process Collaborating with Dr. Alric Iowa State University Numerical simulation results of surface water transport (Wang & Rothmayer,, Computers and Fluids 29). Videos of ice accretion V α 5. deg. Flow direction Glaze ice accreting process over a NACA12 airfoil (Waldman and Hu,, 214)

8 ISU Icing Research Tunnel The ISU Icing Research Tunnel (ISU-IRT), IRT), originally donated by UTC Aerospace System ( formerly Goodrich Corp.), is a research- grade multi-functional icing wind tunnel. The working parameters of the ISU-IRT IRT include: Test section: 16 inches by 16 inches by 6 ft Velocity: up to 6m/s; Temperature: down to -3 C; Droplet Size: 1 to 1 micrometers; Liquid Water Content (LWC):.5 ~ 2 grams/cubic meter. The large LWC range allows ISU-IRT IRT tunnel to be run over a range of conditions from rime ice to extremely wet glaze ice. ISU-Icing Icing Research Tunnel (ISU-IRT) IRT)

9 Digital Image Projection (DIP) technique (USA Patent Pending) 6 Projector Camera Linear curve fitting measurement data Z( x, y) BD s CA KCA d height (mm) Height (mm) 4 2 K=1.266 mm/pixel Z Host computer Target plate Displacement (pixel) Phase difference, (radians) X Y Vertical Translation Stage Reference image Deformed image due to the existence of a semi-sphere sphere on the reference plane Height distribution

10 Transient Behavior of Wind Driven Water Film/Rivulet Flows for Icing Physics Study (Funded by NASA and NSF) (Hu et al. 211, Experiments in Fluids)

11 Time Evolution of a Wind-Driven Droplet/Rivulet Flow over a Flat Surface 2 Droplet/Rivulet Thickness (mm) Droplet/Rivulet Thickness (mm) Downstream Distance (mm) Measured Droplet/Rivulet Thickness y= t = t Downstream Distance (mm) Measured Droplet/Rivulet Thickness y= t = t +1.s Droplet/Rivulet Thickness (mm) Measured Droplet/Rivulet Thickness t = t +5.s Downstream Distance (mm) Moving speed of the contact line (mm/s) Contact line moving speed vs. time rear end of the droplet/rivulet front end of the droplet/rivulet Time (s) Wet Surface Area (S/S o ), Droplet/Rivulet Volume (V/V o ) V/V o S/S o Wet area on the test plate & droplet /rivulet volume (mass) vs. time Time (s) Hu et al., AIAA , 261, 212

12 Transient Behavior of Wind Driven Water Film/Rivulet Flows (Dry Surface Condition) Effects of various important parameters: Temperature of the surface Thermal conductivity of the subtracts Roughness of the test surfaces Surface hydrophobicity Coatings or nano-structures on the test surfaces. Boundary layer airflow Boundary layer airflow Boundary layer airflow Water flow rate: Q= 1 ml/min Free stream airflow: V =1m/s Water flow rate: Q= 1 ml/min Free stream airflow: V =15m/s Water flow rate: Q= 1 ml/min Free stream airflow: V =2m/s

13 Wind-driven driven Water Runback Flow over a NACA 12 Airfoil Digital image projector Digital camera incoming airflow Incoming flow Water droplets NACA12 airfoil Picture of the test section in the icing wind tunnel Spray nozzles Experimental conditions: Incoming flow velocity: Water flow rate: Spray droplet size: (Zhang K. and Hu H., AIAA , 741, 214) V 1 ~ 2 m / s Q 1.ml / min D 1 ~ 5um

14 Micro-sized Water Droplets Impinging onto a NACA-12 Airfoil Test Conditions Angle of attack of the airfoil: α. deg. Temperature of the wind tunnel : T 2 C. The liquid water content (LWC) : LWC =5. g/m 3 Frame rate for Image acquisition: f = 3 Hz Airflow velocity V=2m/s Airflow velocity V =15m/s Airflow velocity V =2m/s Airflow velocity V =25m/s V =15m/s V =2m/s V =25m/s

15 Water Runback Flow over a NACA 12 Airfoil V = 1m/s V = 15m/s V = 2m/s V = 25m/s V = 1m/s V = 2m/s Velocity of the oncoming airflow (m/s) Transition location from film flows to rivulet flows (% airfoil chord length) Averaged width of the rivulet flows (% airfoil chord length) Averaged gap between the rivulet flows (% airfoil chord length) >

16 Water Runback Flow over a NACA 12 Airfoil Water Runback Scaling Laws: Feo (21) and Rothmayer (23) all suggested that wind- driven water film thickness would follow a x 1/4 law : S x=.13c Hu et al., AIAA Journal (215), submitted

17 Glaze Ice Accreting Process over a NACA12 Airfoil Test Conditions Oncoming airflow velocity : V 2 m/s Angle of attack of the airfoil: α 5 deg. Temperature of the wind tunnel : T 8 C. The liquid water content (LWC) : LWC =3. g/m 3 Total recording time : t = 11 seconds Frame rate for Image acquisition, f = 15Hz, 1X replay Videos of ice accretion V α 5. deg. Upper surface Lower surface (Waldman R. and Hu H., 215, Journal of Aerocraft, submitted)

18 Glaze Ice Accreting Process over a NACA12 Airfoil V = 2 m/s T = - 8. C; = 5 ; LWC = 1.1 g/m 3 V = 4 m/s V = 6 m/s (Waldman R. and Hu H., 215, Journal of Aircraft, submitted)

19 IR Thermometry to Quantify the Unsteady Heat Transfer Process Experimental Conditions: V = 35 m/s; T = - 8. C; AOA = 5 ; LWC =.3 g/m 3 Rime ice accretion E D C B A Incoming airflow Experimental Conditions: V = 35 m/s; T = - 8. C; AoA= 5 ; LWC = 3. g/m 3 Glaze ice accretion E D C B A (Liu Y. and Hu H., 215, AIAA Journal, submitted)

20 Hydrophilic, Hydrophobic and Superhydrophobic a). drop on a smooth surface; b). Wenzel state; c). Cassie Baxter state; d). combined state. Lotus leaves Measured θ = 14 [deg] Measured θ = 17 [deg] Measured θ = 67 [deg] Hydrophilic; < 9 o Hydrophobic; 9 o < < 15 o Superhydrophobic; > 15 o

21 Effects of Surface Hydrophobicity on Surface Water Transport and Ice Accretion Process Surface engineering to change the surface hydrophobicity of the airfoils/wings for wind turbine anti-/de /de-icing applications Anti-icing of superhydrophobic surface in freezing rain reported by Cao et al. (29) Anti- icing coating test on wind turbines

22 Surface Chemistry: Effects of Hydrophobicity of the Airfoil Surface on the Impingement of Water Droplets ( Weber number ~ 8 ) Acquired at 12K FPS, replay at 4X slower Without Super-hydrophobic Surface coating Without Super-hydrophobic Surface coating With Super-hydrophobic Surface coating With Super-hydrophobic Surface coating Normal impact 45 degree slope

23 Surface Chemistry: Effects of Hydrophobicity of the Airfoil Surface on the Impingement of Water Droplets With Super-hydrophobic Surface coating Without Super-hydrophobic Surface coating With Super-hydrophobic Surface coating Without Super-hydrophobic Surface coating

24 Thank you Very Much for Your Time! Questions? Upper surface Lower surface Wind-driven driven water film flow over a NACA12 airfoil pertinent to aircraft raft icing (Zhang and Hu,, 214)