The pollutant and noise emissions as well as the fuel consumption of jet engines for the civil aviation have to be significantly reduced in the future. The following concepts are being pursued:
1- Increasing the thermal efficiency of the process by increasing the pressure ratio and the turbine inlet temperature
2- Increasing the propulsion efficiency by a higher by-pass ratio
3- Lean combustion concept
In this context, the short helical combustor (SHC) has been proposed.
The SHC is an innovative concept for a gas turbine combustor. The idea is to utilize the angular momentum of the flow from the compressor in the combustor and subsequently in the turbine. Hence, the axes of the burners of the SHC are not parallel to the rotational axis of the machine. They are tilted in the circumferential direction and arranged in a helical and staggered configuration. The SHC concept allows a reduction of the axial length, and therefore enables a better integration of the combustion chamber in to the engine. This is advantageous regarding the rotor dynamics as well as the engine weight. Furthermore, the Outlet Guide Vanes (OGV) and the Nozzle ... mehr Guide Vanes (NGV) can be designed with a lower deflection angle so that the number of vanes may be reduced. Accordingly, a reduction of the aerodynamic losses and the cooling air requirements is possible.
In a preliminary study at RRD, the SHC concept was numerically analyzed.
Within this FVV project, the concept is further investigated. In the first step, a generic geometry is found by means of a parametric study. This geometry is then used as a basis for further investigations. As design parameters the tilting angle of the burner axis and the number of the burners are varied. A single and a double annular configuration with a burner tilting angle of 45° is identified to be suitable to maintain the relevant scaling rules. These configurations are chosen for further investigations using CFD.
Subsequently, the non-reacting flow fields of selected generic SHC models are investigated by transient numerical simulations. The major focus is on the influence of the tilting angle of the burner axis. Furthermore, the interactions of the adjacent swirling flows and their effects on the combustor exit flow angle are analyzed. The double annular configurations exhibit better performance regarding to the compact recirculation zones of the swirling flows as well as high flow angle at the combustor exit. Moreover, it is shown that the structure and homogeneity of the flow is highly sensitive to the swirl direction of circumferentially adjacent burners.
A circumferentially co-rotating configuration is found to be suitable regarding to a homogeneous and symmetric flow pattern in the combustion primary zone.
Finally, for the double annular configurations calculations are carried out with chemical reaction.
It is shown that in the reacting case, the swirl direction of the radially adjacent burners has a major influence on the flow field. The radially counter-rotating configuration is found to be optimal regarding the symmetry of the flow field and maximum flow angle at the combustor exit.
In summary, it is shown that a double annular SHC configuration with a burner tilting angle of 45°, circumferentially co-rotating and radially counter-rotating swirlers has the potential to reduce the axial length of the combustor as well as the deflection angle of the NGV by approx. 30%.
Accordingly, the weight of the machine as well as the required number of OGV and NGV may be reduced, which might lead to a reduction of the turbine cooling air.