THEORY OF PROPULSION 13' Boundary Layer Effects

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THEORY OF PROPULSION 13. Boundary Layer Effects

• P. M. SFORZA
• University of Florida

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Gap leakage losses
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Curved streamline effects
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Curved flow losses
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Cross-flows in the blade passage
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Boundary layer regions
Separation region
Turbulent boundary layer
Transition
Laminar boundary layer
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Blade loading
Blade element theory for axial machines gives the
blade loading
deflection coefficient mass flow coefficient

Separation limits the amount of turn allowable, so
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Correlation for thin blades
For (t/l)max10 experiments suggest
Which, in turn, leads to
Dbb2 - b3 from experiment show this correlation
is conservative for values of s O(1) Thus there
should be a basis in the physics of the flow
field.
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Blade pressure distributions
b2
Sp
Ss
-3.1(1-x/l)
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Lift on the blade
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The blade lift coefficient
Lower surface
Upper surface
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Modeled lift coefficient
Neglecting the drag (eltlt1) yields
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Comparing flow turning predictions
Modeled flow
Empirical correlation
Experimental result
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Experimental drag profile
operating point Db.8(Db)stall
Db18.6o
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Turbine expansion process
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Heat transfer in the blade passage
T(y)
S
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Thermal boundary layer
Heat transfer to the wall
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Adiabatic wall temperature
pe, Te, and Tw not x-dependent and Prandtl number
Prmcp/k1
Stagnation enthalpy is constant
Temperature distribution
Wall heat transfer is zero
Adiabatic wall temperature
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Non-unity Prandtl number
Momentum diffusivity Thermal diffusivity