Question

4.( 10 pts) Chapter 9 External Flows The fixed keel of the sailboat is about 38 in deep. The boat moves at a speed of 3 knots (i.e. 5.1 ft/s) in a lake with water temperature of 40°F. The keel can be approximated as a rectangular flat plate with an average length in flow direction /=(34+15)/2 = 24.5 in, and a depth of 38 inches. (Considering a laminar BL to turbulent BL transition happens at Red - 2x10° in this situation.) 1) (3 pts) What is the Reynolds number Re, for flow over the plate? 2) (3 pts) What is the coefficient of drag for the plate, Cor? 3) (3 pts) What is the friction drag force on the keel? (notice there are two sides) 4) (1 pt) If the downstream keel flow BL transitions into turbulent BL, what is the effect of this on the overall skin friction drag? 34 in 38 in 15 in

Answer 1

(W sec. 6:531810" Parsec = 1.3575X105 IS @yoc , rerater dt? 0 15 L = 62.428 $73. [A=(24.5*38 )=932 zh Tw boat &L Re 24.540 SE Rec 62.428% 5.1*(2405) 1:3575 XIoT 5.1.14 sec Rei 47884460.41 = 47.88444106->2*106 so How is turbulent. 2) 1% = 2.0955 xlo Drag coeficient (CD) for forbulent flow, 0.072 0.072 Co= (Res's (47.88448200 (3) Drag force for force is emented the tone. keel, so The dosag by both side of 2 Fo= 2x G x btw A Nboat 2.0955 x103 x 62.428 * • (131) (s. 1² zel fo=22 lbf

५) The Cp for lamelor flow is given by. 1.46 c parabolic rebuity profile) G= Rew If Ra=2x106. 146 ६. LCD lensland =10323710 = rzx10° fonbulant Sh pub Co Laminar Rew) Сртов Ren Turb Honce Collamenco L Coltorb follamena fo so turbulent.