Chapter 6 Cascades

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Cascade Nomenclature

Prepared by Dr. S. Ramamurthy, [email protected]


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Effect of velocity distribution on profile drag coeff.

Common camber line shapes

Suction & Pressure Surface

Zero Lift Direction

Weinigs Lattice coefficient

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Aerofoil representation

British Practice:

Aerofoil built around basic circular or parabolic camber line

12C4/35 P30 Denotes an aerofoil for which the maximum thickness to chord ratio(t/c) is 12%, C4 denotes

the base profile, 35 is the camber angle in degrees, P denotes a parabolic arc camber line and 30 is the

percentage of the chord from the leading edge where maximum camber occurs.

American Practice:

Series of aerofoils developed by NACA

A series of camber lines used, each associated with design lift coefficient (CLO) of a single aerofoil.

NACA 65-(12)10

Camber line corresponding to CLO=12/10=1.2 and a profile shape 65 with approximate 10% thickness.

Ordinates for other camber are obtained by direct scaling in proportion to the camber CLO



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Section of profiles in use in axial machines

Characteristics of the Clark Y profile (t/c=10%, Rec=8*105)Prepared by Dr. S. Ramamurthy, [email protected]


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Lift and Drag Characteristics of flat and cambered

Plates (t/c=0.02, Rec=3*105) adopted from Wallis

Eckerts results for axial fan(Rec=3*105, same Camber

and rotational speed) showing comparison between

the performance of cambered plate and profiled blade



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NACA 6510

C4

3-Different airfoils used in

Turbo machines



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NACA 65 series of cascade aerofoils

(L.J. Herring ,J.C. Emery and J.R. Erwin.

Courtesy NACA)



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Blades in cascade and the effectof proximity on blade performance

Data for an NACA 65(27) 10 aerofoil in cascade

(b1=450,s/c=1.0)

Note: 65(27) 10 means 65 series foil,

CLO=2.7,t/c=10%;CLO is design lift

Coefficient, related to camber angle

q as sketched



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Blade setting variables

Flow & pressure distributionover symmetrical aerofoil

Flow & pressure distributionover an inclined aerofoil

Root and tip sections of a typical

Compressor rotor blade illustratingThe degree of twist



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: = Prepared by Dr. S. Ramamurthy, [email protected]


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Layout of a conventional low speed cascade tunnel (Lieblen) (Courtesy of NASA)

A sample plot of inlet and outlet stagnation pressures

and fluid outlet angle (adopted from Todd) Compressor cascade characteristicsDiagrammatic representationOf fluid deviation

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Fig. 1 Space chord ratio correction

For nominal deflection

Fig. 2 Reynolds number correction

For nominal deflection

Fig. 3 Nominal deflection as a

Function of nominal outlet angle

Fig. 4 Off-design performance of

cascade



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Effect of staggerPrepared by Dr. S. Ramamurthy, [email protected]


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Chapter 6 Cascades

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