Axial-centrifugal contra-rotating light weight, compact compression system

1 . A method for providing efficient axial-centrifugal compressor systems including compressing of fluid based thrust generation for downstream combustion including aero engines comprising:

involving a combination of a contra rotating assembly-based compressor stages which is free of any stator blades in a twin spool configuration comprising of a first low pressure [LP] rotor blade assembly which is rotated in a direction opposite to a second high pressure [HP] rotor blade assembly,

the first low pressure [LP] rotor blade assembly including:

at least one axial compressor rotor and is free of any stator, which is rotated at a lower speed, and

the second high pressure [HP] rotor blade assembly including:

at least two rotors, comprising:

one axial compressor rotor, and

one backend centrifugal compressor rotor and is also free of any stator,

the axial compressor rotor of the first low pressure [LP] rotor blade assembly and the axial compressor rotor of the second high pressure [HP] rotor blade assembly provided with low-aspect ratio blades with a ratio of the height of the blade to the chord length of the blade maintained in the range of 0.7 to 1.5 and together operating as contra-rotating axial compressor stage free of any stator and operatively connected to the backend centrifugal compressor rotor of the second high pressure [HP] rotor blade assembly as a backend centrifugal compressor stage which is also free of any stator,

wherein the first low pressure [LP] rotor blade assembly which is rotated at a lower speed on a front rotor-shaft/LP turbine spool rotating with a rotational speed (N1) and the second high pressure [HP] rotor blade assembly used comprising of the one axial compressor rotor and the one centrifugal compressor rotor on a common rear rotor-shaft/HP turbine spool and hence, rotating at equal speed (N2)

and with the speed ratios

N 2 /N 1

being maintained of a magnitude greater than 1 in the range of 1.1 to 1.4 whereby the contra-rotating two rotor blade compressor assemblies free of any stator blades favour stator free weight reduction and together with the higher rotational speed of HP turbine spool with respect to the front rotor-shaft/LP turbine spool enable stall free operations with efficient thrust to weight ratio involving both the contra rotating and the centrifugal compressor free of any stator operations;

furthermore, operatively connecting the contra rotating axial compressor stage and the backend centrifugal compressor stage through an inter-stage connecting duct comprising an annular duct of S-shape maintaining its inlet radii along with the compressor system hub and shroud radii greater than its exit radii;

and providing for a curved shaped discharge diffuser of the centrifugal compressor rotor for a radial to axial turning annular passage at the exit of the centrifugal compressor rotor stage such as to minimize the overall outer dimension whereby after the passage is directed to either a purely axial direction or an inclined to axial direction by a small angle in the range of up to 100 to 15° as the curved shaped discharge diffuser for a uniform pressure distribution for entry to a downstream combustor, thereby providing for the efficient axial-centrifugal compressor systems eliminating stator with weight reduction and thereby efficient thrust to weight ratio.

2 . The method as claimed in claim 1 , comprising: maintaining stated desired speed variation combination of the two spools to maintain the first low-pressure [LP] rotor blading assembly comprising of the axial rotor rotating at low speed and the high-pressure [HP] rotor blading assembly comprising of the one axial rotor and the one centrifugal rotor rotating at higher speed enabling improvement of overall performance with increase in the speed variation combinations such as to achieve overall pressure rise, wider operating range and higher efficiency with stable operating characteristics of the front rotor.

3 . The method as claimed in claim 1 , wherein

the axial compressor rotor blades of the first low pressure [LP] rotor blade assembly and the second high pressure [HP] rotor blade assembly used have an aerofoil shaped profile of its blade sections.

4 . The method as claimed in claim 1 , further comprising controlling operational parameters for maximizing pressure ratio and thrust development involving:

selective speed combination of the two spools wherein the low-pressure (LP) rotor blading assembly comprising the axial compressor rotor and the high-pressure (HP) rotor blading assembly comprising the one axial compressor rotor and the one centrifugal compressor rotor and the rotational speed ratio thereof; and

mass flow range maintained is in the range of stall to choke limit.

5 . The method as claimed in claim 1 , wherein the speed ratios N2/N1 is selected:

N 2 d /N 1 d =1.25

and

the contra-rotating axial blade of the first low pressure [LP] rotor blade assembly and the second high pressure [HP] rotor blade assembly used have the low-aspect ratio blades with a ratio of the height of the blade to the chord length of the blade maintained as 0.8.

6 . The method as claimed in claim 1 , wherein the axial compressor rotor of the first low pressure [LP] rotor blade assembly is highly loaded as compared to the axial compressor rotor of the second high pressure [HP] rotor blade assembly for a stall-free operation of the axial compressor rotor of the first low pressure [LP] rotor blade assembly over a wide range of mass flow rates, facilitating a broader operating range for the contra-rotating stage and increased pressure rise with higher rotational speed of HP spool providing improved flow configurations within the centrifugal compressor flow passage.