Measurements of Biofouling Drag Using a 2-D Channel Flow Apparatus with Models of Bio-fouled Panels

Transcription

1 International Congress on Marine Corrosion and Fouling 2018 Measurements of Biofouling Drag Using a 2-D Channel Flow Apparatus with Models of Bio-fouled Panels Scott Gowing (1) presenting Peter Chang (2), Scott Storms (3) (1) CSRA (2) NSWC Carderock (3) NSWC Philadelphia Sponsored by the Naval Innovative Science and Engineering (NISE) program 1 Distribution Statement A: Approved for Public Release

2 Goal Provide Equivalent Roughness of Biofouling for Numerical Drag Predictions Measure drag on model biofouled panels Determine size of uniform sandgrain roughness that causes same drag as model biofouling Use sandgrain sizes as input to CFD codes to predict hull drag caused by biofouling modeled in panels Provide quantitative assessments for: - Hull maintenance decisions - Evaluations of biofouling mitigation schemes Hydraulically Smooth Heavy Slime (Vargas 2018) 2

3 Channel Flow Facility View of basin end Bulk velocity from flowmeter Pressure gradient along channel yields friction factor Vary speed with pump 3

4 Channel Flow Facility Turbine Flow Meter Channel Pressure Transducers (4 ranges) Constant area transition Variable Speed Pump Pressure Control Data Acquisition 4

5 Channel Cross Section Model Biofouler Plates Smooth Calibration Plates 1 8 5

6 Sample Plates Smooth plastic or polished metal plates for calibration Metal backplate with dovetails Printed biofouler plates with dovetails Backplate and printed panel mesh to create biofouler plate assembly (assembly insures constant channel height) 6

7 Model Fouler Plates 7

8 Smooth Plates Channel overview mirror plates - top view mirror plates - end view Polished metal or acrylic plates provide smooth surface 8

9 Pressure drop re tap #1 (psid) Channel Flow Friction C f = dp dx Measured Skin Friction Friction based on streamwise pressure gradient, channel height, and bulk flow rate Pressure gradient measured over multiple taps 0.70 h ρ u E E E E E x/h 9

10 Channel Flow Friction Prandtl s Equation for Smooth Channel Friction Integrate log-law with modified B relation for channel flow Integration yields analytic equation (some rounding involved) 1 1 4C f log Re h 4C f C f log Re h ( 4C f k h)re h 4C f Equation for Smooth or Rough Channel Friction Equation can be solved (implicitly with Excel Goal Seek) to relate C f and relative roughness (k/h) 10

11 Smooth Plate Data all smooth data Prandtl Schultz & Flack 2013 Lee & Moser 2015 smooth mirror smooth plastic C f E E E E E E+05 Re channel Smooth plastic and mirror plates Smooth plastic and mirror plate data match Prandtl predictions Schultz & Flack data a little higher Lee & Moser data are in-between 11

12 Roughness Effects DB=7.63 u u = log u y υ ΔB Add Roughness Effects Roughness shifts velocities lower by constant value in log layer Adjust DB constant in log law to represent roughness (typical approach) 12

13 DB CFD Roughness Calculations 20 Uniform sandgrain roughness (Nikuradse) u k υ = k s log log k_s^+ s CFD calculations use uniform sandgrain to model roughness effects Derive equivalent sandgrain roughness for coated or biofouled surfaces from channel flow experiments measuring friction via pressure drop Allows CFD calculations for biofouled surfaces 13

14 CFD Roughness Calculations (uniform roughness) Schultz CFD calculations use uniform sandgrain roughness (Vargas) Derive equivalent sandgrain roughness for biofouled surfaces from channel flow experiments Enables CFD calculations for fouled surfaces Experiments validate CFD predictions 14

15 Biofouler Plate Data C f E E E E E E+05 Re channel all smooth data 5 pts panel 8 panel 7 panel 9 panel 1 panel 1X0.5 panel 1X3 panel HPX0.5 panel HPX1.0 panel oyster panel half oyster Drag values up to 2X or more of smooth values Some panels show fully rough drag behavior - friction no longer dependent on Re channel 15

16 sqrt(2/c f ) DB Derivation for DB shift Results all plastic plates panel #8 panel #9 panel #1 panel # ln (Re*sqrt(C f )) y = 2.745x y = x y = x y = x y = x Plot Re*sqrt(C f ) product vs sqrt (2/C f ) Fit data with linear fits For each plate, calculate DB at each data point - difference of sqrt(2/c f ) rough - sqrt(2/c f ) smooth (from linear fit) Determine equivalent sand grain size that yields measured DB 16

17 DB Roughness Forms Roughness Functions Granville Different roughness functions (sandgrain-type, Colebrook-type) possible for fitting if panels are not characterized by single size scale Adjust size scale to force conformity with selected function (DB determined by DC f ) Schultz

18 DB delta B DB delta B Sandgrain Type Fits Sandgrain Roughness Function Sizes Colebrook sizes (tested at scale) Colebrook 16 panel #8 14 panel HPX panel #9 10 panel HPX k+ k s Sandgrain sizes (tested at scale) Colebrook sandgrain panel #8 panel HPX0.5 panel #9 panel HPX k+ + k s Data slopes match Colebrook sizes better than sandgrain sizes but CFD uses sandgrain sizes in roughness function -> sizes must be defined using sandgrain scales 18

19 delta B DB Comparisons Comparison to Other Biofouler Data Colebrook type panel #7 panel #1 Schultz ks+ Panels #1 and #7 (barnacle data) have similar form to barnacle fouling measured by Schultz

20 D B Roughness Scaling Some Panels are Scaled (l = scale ratio) Colebrook type 14 panel # scaled values scaled DB value X k s + Modeled roughness scale = 1/l * actual roughness scale Correct DB using Colebrook function DB FS = DB MS + ddb/dk s+ * dk s+ and dks + = (l * k s+ ) Works well if fully rough 20

21 Comparisons EQUIVALENT SANDGRAIN SIZES (mm) Heavy Calcareous Fouling* Barnacle 2 (13%, 8.7 mm) Barnacle 1 (19%, 6.6 mm) Medium Calcareous Fouling* Barnacle 1 (6%, 6.6 mm) Barnacle 1 (4%, 6.6 mm) Small Calcareous Fouling/Weed* Tubeworm (18%, 0.9 mm) Tubeworm# Heavy Slime* Tubeworm (7%, 0.9 mm) Incipient Fouling 2 (3%, 0.7 mm) Incipient Fouling 1 (3%, 0.6 mm) Deteriorated Coating/Light Slime* Present data Other data Channel data show fouler ranking similar to other data: slime tubeworms small calcareous heavy calcareous fouling increasing sandgrain sizes 21

22 Comparisons Heavy Calcareous Fouling* Barnacle 2 (13%, 8.7 mm) Barnacle 1 (19%, 6.6 mm) Medium Calcareous Fouling* Barnacle 1 (6%, 6.6 mm) Barnacle 1 (4%, 6.6 mm) Small Calcareous Fouling/Weed* Tubeworm (18%, 0.9 mm) Tubeworm# Heavy Slime* Tubeworm (7%, 0.9 mm) Incipient Fouling 2 (3%, 0.7 mm) Incipient Fouling 1 (3%, 0.6 mm) Deteriorated Coating/Light Slime* EQUIVALENT SANDGRAIN SIZES (MM) 1.5X coverage 2.5X coverage 4.5X coverage Present data Other data Variations in spatial density show increases in relative sandgrain sizes Sandgrain size increase not proportional to increased coverage 22

23 Credits Project sponsored by the NSWCCD 219 program Jack Price, Krista Michalis - Program managers Eric Holm - Project manager Abel Vargas - Fluid dynamic modeling Christina Dehn - Panel preparation 23

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