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Slide 2 AXIAL FLOW COMPRESSORS P M V Subbarao Professor Mechanical Engineering Department An Efficient Way to Ingest Life in Large amount of Fluids !!! Slide 3 An Option for High Specific Speed In aero applications, the specific speed is defined as: and the flow coefficient as Slide 4 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 Slide 5 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. Slide 6 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: 1,600K Thrust-to-weight ratio: Approx 5.7:1 Slide 7 Slide 8 Stages of an Axial-flow Compressor Slide 9 Selection of Pressure Ratio per Stage Slide 10 The first step in a design of Axial Flow Compressor.... The Aerofoil A Cascade of Aerofoils.. Invention of high population element Slide 11 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 Slide 12 Geometrical Description of NACA 65 Slide 13 Slide 14 NACA 65 Series of Aerofoils Slide 15 Cascade of Aerofoils Slide 16 Viscous flow through Cascade Slide 17 Cascade Geometry = stagger angle ( positive for a compressor cascade) = blade inlet angle = blade outlet angle Slide 18 Lift & Drag of a cascade Slide 19 Selection of Inlet flow angle Slide 20 Cycling of Kinetic Energy in Axial Flow Compressor Slide 21 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), Slide 22 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. Slide 23 V a1 2 /c p p1p1 T1T1 p 01 T 01 p 03 = p 02 T 03 = T 02 V a2 2 /c p p2p2 V a3 2 /c p p3p3 s T Thermodynamics of An Axial flow Compressor Stage Slide 24 Kinematics of An Axial Flow Compressor Stage Inlet Velocity Triangle Outlet Velocity Triangle Slide 25 Kinetics of An Axial Flow Compressor Stage Rate of Change of Momentum: Inlet Velocity Triangle Outlet Velocity Triangle Power Consumed by an Ideal Moving Blade Slide 26 Energy Analysis of An Axial Flow Compressor Stage Inlet Velocity Triangle Outlet Velocity Triangle Change in Enthalpy of fluid in moving blades : Slide 27 Isentropic compression in Rotor Blade Degree of Reaction of A Stage, R : Slide 28 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. Slide 29 Power input to the compressor : Current Practice : Theoretical Power input to the compressor: Inlet Velocity Triangle Outlet Velocity Triangle Slide 30 For an isentropic compressor: Slide 31