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

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

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…

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.

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: 229.77 kN Overall pressure ratio: 27.5 Bypass ratio: 5.7 Turbine inlet temperature: 1,600°K Thrust-to-weight ratio: Approx 5.7:1

Stages of an Axial-flow Compressor

Selection of Pressure Ratio per Stage

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

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

Geometrical Description of NACA 65

NACA 65 Series of Aerofoils

Cascade of Aerofoils

Viscous flow through Cascade

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

Lift & Drag of a cascade

Selection of Inlet flow angle

Cycling of Kinetic Energy in Axial Flow Compressor

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),

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.

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

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

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

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

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

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.

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

For an isentropic compressor: