Investigation Of Turbine Pressure Controlled Vortex Design Technology

Turbine aerodynamic design is an important research direction of turbomachinery,playing a significant role in high performance aeroengine and gas turbine. With the rapiddevelopment of computational fluid dynamics (CFD) and blade modeling method, turbineblade design technique has been developed speedily. Nevertheless, turbine aerodynamicdesign is still a challenge reaseach topic. A series of research about turbine design have beenconducted in this thesis. These studies mainly consist of the following aspects:Firstly, a turbine design method based on Pressure Controlled Vortex Design (PCVD) ispresented to design a small size turbine stage. Contrary to conventional CVD method withdirect assumptions of tangential circulation cur and axial velocity czdistributions, the mainobjective of PCVD is to control the axial velocity and radial pressure in the stator-rotor gap.Through controlling axial velocity cz, the PCVD establishes a direct tie to meridional streamsurface. Thus stream surface variation is induced, resulting in a large secondary flow vortexcovering the full blade passage in respective stator and rotor. This secondary flow vortexcould be dedicated to control passage vortex generation and development. Through radialpressure p, the PCVD is also associated with macroscopic driving force of fluid motion. Sothe stream surface variation and pressure are organically unified in order to achieve betterbenefit of CVD. The emphasis of this design method is secondary flow mitigation andmigration. Core concept behind PCVD is to mainly control the spanwise pressure gradient byaltering profile loading at various spanwise locations. Therefore not only the local profile liftis affected, but also the resulting throat widths, stage reaction degree and massflow rate arealtered or redistributed respectively. With the PCVD method, the global stage efficiency isincreased successfully while mass flow rate keeps constant. Additionally there is no endwallshape optimization, stacking optimization or pitch/chord variations, concentrating solely onvarying blade profile deflections and stagger.Secondly, based on the radial pressure control, a3D PCVD method incorporating3Dpressure control approach into PCVD technique is proposed and a high performance turbinedesign framework including advanced blading,3D geometry features as well as endwallprofiling is formed. Via stream surface thickness variation and stream surface deflection induced by PCVD, the secondary flow vortex in cascade is rationally utilized and dominated.A well-posed boundary layer flow pattern is presented, so the relevant secondary flow lossesare reduced largely. Through further control of spanwise, streamwise and azimuthal pressure,favorable pressure gradients are achieved in the above three directions. Not only canboundary layer separation and thickening be effectively controlled, but also profile loss canprofit. The3D PCVD results of the first stage in a low pressure turbine demonstrate that thenew design turbine isentropic efficiency increases by0.76%and the power rises by0.6%withthe massflow unchanged. The3D PCVD also greatly increases the turbine root reaction andsignificantly improves the matching characteristics between stator and rotor in a largemeridional expansion turbine.Finally a multi-stage3D PCVD method is developed and demonstrated with amulti-stage low pressure turbine in this thesis. The design process has been carried out basedon stage-by-stage design approach and the stage matching is also interpreted for effectivedesign. A systematic investigation has been carried out to evaluate the3D PCVD effects in amulti-stage turbine environment. An optimal design over the entire operating range isachieved relative to the baseline turbine and the3D PCVD turbine has fine off-designperformance. Numerical results fully demonstrate the advantage of this design method.Although3D PCVD is executed at design condition, the multi-stage turbine performance atoff-design condition has improved greatly simultaneously.