1. AXIAL FLOW COMPRESSORS
P M V Subbarao
Professor
Mechanical Engineering Department
An Efficient Way to Ingest Life in Large amount of Fluids !!!

2. An Option for High Specific Speed
In aero applications, the specific speed is defined as:
and the flow coefficient as

3. Schematic representation of an axial flow compressor
It is easy to design a turbine that will work…. It requires a considerable skill to design a compressor that will work…

4. Antonov An-225 Mriya
The Antonov An-225 Mriya is a strategic airlift cargo aircraft, designed by the Antonov Design Bureau in the 1980s.
Payload: 250,000 kg (550,000 lb) !!!
Cruise speed: 800 km/h.
Altitude: 11,000 m (36,100 ft).
Thrust Required: 1350 kN
Power plant: 6 × ZMKB Progress D-18 turbofans.

5. The Progress D-18T ( Lotarev D-18T)
General characteristics
Type: Three-spool high bypass turbofan engine with a single-stage fan.
Fan diameter: 2.33 m (91.73 in)
Dry weight: 4,100 kg (9,039 lb)
Components
Compressor: Seven-stage IP compressor, seven-stage axial HP compressor
Combustors: Annular combustion system
Turbine: Single-stage HP turbine, single-stage IP turbine, four‑stage LP turbine
Performance
Maximum thrust:  kN
Overall pressure ratio: 27.5
Bypass ratio: 5.7
Turbine inlet temperature: 1,600°K
Thrust-to-weight ratio: Approx 5.7:1

7. Stages of an Axial-flow Compressor

8. Selection of Pressure Ratio per Stage

9. The first step in a design of Axial Flow Compressor…..…..
Invention of high population element ……
The Aerofoil…
A Cascade of Aerofoils…..

10. Aerofoil Geometry 1: zero lift line 2: leading edge 3: nose circle
4: camber
5: thickness
6: upper surface
7: trailing edge
8: main camber line
9: lower surface

11. Geometrical Description of NACA 65

13. NACA 65 Series of Aerofoils

14. Cascade of Aerofoils

15. Viscous flow through Cascade

16. Cascade Geometry
λ = stagger angle ( positive for a compressor cascade)
a’1 = blade inlet angle
a’1 = blade outlet angle

17. Lift & Drag of a cascade

18. Selection of Inlet flow angle

19. Cycling of Kinetic Energy in Axial Flow Compressor

20. Macro Geometric Specification of An Axial Compressor
The geometry of a compressor can be categorised into 3 main designs types,
A Constant Outer Diameter (COD),
A Constant Mean Diameter (CMD) or
A Constant Hub Diameter (CID),

21. Specifications of An Axial Compressor
There are several different parameters that can specify a particular compressor.
The first set of input parameters are based on the running conditions for the machine.
These involve mass flow, pressure ratio , rotational speed and the number of stages.
Stage degree of reaction : For controlling the distribution of the load between the rotor and the stator.
If this is not of importance, the outlet flow angle for the each stage must be set instead.

22. Thermodynamics of An Axial flow Compressor Stage
p03 = p02
T03 = T02
Va32/cp p3
Va22/cp p2 T
p01
T01
Va12/cp p1 T1 s

23. Kinematics of An Axial Flow Compressor Stage
Inlet Velocity Triangle
Outlet Velocity Triangle

24. Kinetics of An Axial Flow Compressor Stage
Rate of Change of Momentum:
Inlet Velocity Triangle
Power Consumed by an Ideal Moving Blade
Outlet Velocity Triangle

25. Energy Analysis of An Axial Flow Compressor Stage
Change in Enthalpy of fluid in moving blades :
Inlet Velocity Triangle
Outlet Velocity Triangle

26. Isentropic compression in Rotor Blade
Degree of Reaction of A Stage, R :

27. Compressible Flow Machines
Owing to compressibility of gas in a compressor
The degree of reaction for equal pressure rise in stator and rotor will be greater than 0.5.
The stage total pressure rise will be higher in order to get equal static pressure rise in stator and rotor.

28. Power input to the compressor :
Inlet Velocity Triangle
Outlet Velocity Triangle
Current Practice:
Theoretical Power input to the compressor:

29. For an isentropic compressor: