You are asked by your college crew to estimate the skin friction drag in their eight-seat racing shell. The hull of the shell ma
y be approximated as half a circular cylinder with 450 mm diameter and 7.32 m length. The speed of the shell through the water is 6.71 m/s. Estimate the location of the transition from laminar to turbulent flow in the boundary layer on the hull of the shell. Calculate the thickness of the turbulent boundary layer at the rear of the hull. Determine the total skin friction drag on the hull under the given conditions
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Answer:
Re=100,000⇒Q=275.25
Re=500,000⇒Q=1,757.77
Re=1,000,000⇒Q=3060.36
Explanation:
Given:
For air =25°C ,V=8 m/s
For surface =179°C
L=2.75 m ,b=3 m
We know that for flat plate
⇒Laminar flow
⇒Turbulent flow
<u> Take Re=100,000:</u>
So this is case of laminar flow
From standard air property table at 25°C
Pr= is 0.71 ,K=26.24
So
Nu=187.32 ()
187.32=
⇒h=1.78
heat transfer rate =h
=275.25
<u> Take Re=500,000:</u>
So this is case of turbulent flow
Nu=1196.18 ⇒h=11.14
heat transfer rate =h
=11.14(179-25)
= 1,757.77
<u> Take Re=1,000,000:</u>
So this is case of turbulent flow
Nu=2082.6 ⇒h=19.87
heat transfer rate =h
=19.87(179-25)
= 3060.36