Question

As shown in Video V9.2 a kayak is a relatively streamlined object. As a first approximation in calculating the drag on a kayak, assume that the kayak acts as if it were a smooth, flat plate 17.0 ft long and 1.8 ft wide. Determine the drag as a function of speed. Round the values to 3 significant digits. Speed, ft/s Drag, lb

Answer 1

The drag force for a flat plate is given by fp = 5 SUS CREA - (0) A= Area & that plate = 1T x 108= 30.6ft? The coefficien of drag force, Cog is a fan of Reynald's Numbers (ke). Welve, Rood Ux17 l'Atlá U —27 1.21x105 Assuming a velocity The range of ke will be from the Fig. the Re transitional stage sange, Isu=8ftle, 14X106 <re < 112x10² range lier in the flow condition, the flat plate For transitional dray to efficient is given by 1100 -0.455 " log (Re) 2:58 Re 30.6 17.&2) 4 (3) >> Fo x1-94% 02 _0.455 11002 I log (1-4X10" ujas8 (14xidu to - 29.682 U2 50.455 Too E log(1-4X10°c)2.5$ (1-4xl0u) 5 Sub: U= 2, 4, 6, 8 in 4 we get toas,

o (ft/) F, (146) о. 364 1, А2 3:08 5. 32

400 200 Ср Smooth cylinder 0.6 0.4 Smooth sphere 0.2 0.1 0.06 10-1 100 101 102 104 105 106 10/ 103 Re = PUD

Turbulent boundary layer, narrow turbulent wake (E)

Figure reference: Young, D.F., Munson, B.R., Okiishi, T.H. and Huebsch, W.W., 2010. A brief introduction to fluid mechanics. John Wiley & Sons.