Blade Design Procedure - Turbomachinery Aerodynamics - Lecture Slides, Slides of Turbomachinery

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1

Aerodynamic Design of Axial Compressor

---------------- Blade design Procedure

2 2

C1-r = Ca,1r + Cw,1r

1,r =^

-1 (^) w.1r -1^ a,1r

1,r 1,r

C C

α sin = cos

C C

1 1,r 1,m m

r

U = U.

r

1,r =^

-1^ 1,r^ w,1r

a,1r

U - C

β tan

C

INDIVIUAL STAGE DESIGN METHOD

Absolute Vel

Absolute Angle

Blade Speed

Relative Angle

     

1,a 1,r 1,r

C V = cos β

     

2 2,r 2,m 2,m

r U = U. r

If, d m = constant, U 1,m =U 2,m

     

2m w,2r w,2m

r C = C. r

     

w,rm m

C DR = 1 - 2.U.r

Check

Relative Vel

Degree of Reaction, Rx should never be zero anywhere on the rotor blade

C a,2r = Ca,m = const

or assume a value for

AVDR = C (^) a1. ρ 1 /C (^) a2. ρ 2

-1 w,2r 2,r a,2r

C

α = tan

C

 (^) ( )

   

-1 2,r^ w,2r 2,r a,2r

U - C β = tan C

Δβ = β 2,r (^) - β 1,r

≈ 1 0.

V 2 <V 1 →

V 2 =V 1 →

V 2 >V 1 →

Generally accepted

Rarely Used

transonic fan design – possibility

INDIVIUAL STAGE DESIGN METHOD

       

2,r

a,2r

2,r

C V = cos β

Δβ = β 2,r (^) - β 1,r -> Flow Turning Angle

Provide angle of incidence, ir at design point

Usually, itip = -(1o^ to 2o^ ) and

i root =+(1o^ to 2o^ )

Need to choose solidity of the blade section

M (^) u = U/a

INDIVIUAL STAGE DESIGN METHOD

β 1,r^ ′ = β 1,r + i r

β 2,r^ ′^ = β 2,r - δ r•

r• 2,r^ ′ 2,r r

s δ = β - β = m .θ. c

(Carter’s deviation – valid at design point)

At any radius

Deviation,

18

1.Degree of reaction vary along the radius

depending on the law of profile and its values change from 0 to 0.2 at the root to 0.8 to 1 at the tip.

2. There are certain other parameters that affect the dynamics of flow. These geometrical parameters are:- Degree of divergence, θD Flow turning angle, ∆β Blade solidity, c/s

( 1 ) D

1 c

cos Δ + - cos = 180 × c π (^) h s

c^ β^ β^ β θ

These three are connected by

19

Transonic Compressor Basic Characteristics

3-D Blade Shapes

Follow similar step-by-step procedure for STATOR blade design by building up airfoil sections from hub to tip to match with the ROTOR blade design.

Stage design is completed after the rotor-matched stator design is completed.

Modern Blade designers have started using 3-D airfoils which are set on cylindrical coordinates, even as they are radially stacked.