02propeller_test

# 02propeller_test - Propeller Testing Screw propeller...

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Propeller Testing Screw propeller replaced paddle wheel ~1845 in Great Britain (vessel) - Brunel In test; independent variables are velocity of advance V A shaft rotation speed n (rev/sec), N (rev/min) dependent variables are: torque Q thrust T i.e. we build a propeller, rotate it a a given speed in a given flow and measure thrust and torque (at this point - conceptually - not practical at full scale) are considering propeller in general, no ship present, => open water velocities relative to blade: V A V R V A 2* π *n*r *n*d π *n*d test at given n, vary V A , measure thrust (T), torque (Q) and calculate efficiency ( η ο ) Q T V A Q T η o typical performance curve at given rotaion speed, note zero efficiency at V A = 0 and T = 0 η o Obviously, testing at full scale impractical, hence use model scale and apply to geopmetrically similar propeller. Expect performance to depend on: VA velocity of advance D diameter of propeller n rotational speed ρ fluid density μ dynamic viscosity ( ν = μ / ρ = kinematic viscosity p - p v pressure of fluid (upstream static pressure) compared to vapor pressure 9/8/2006 1

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First non-dimensionalize: using n and D T Thrust K T := 2 4 ρ⋅ n D Torque K Q := Q 2 5 n D V A J := advance_velocity nD D V A Reynold's number based on diameter: Re D := μ p p v nominal cavitation index (presure) σ N := 1 2 ⋅ρ⋅ V A 2 dimensional analysis would show: fJ Re D , = D , = , , K T ( σ N )
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02propeller_test - Propeller Testing Screw propeller...

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