Numerical and experimental investigations have been performed to determine the effect of a variation of the inter blade row axial gap on turbine efficiency. The geometry used in this study is the 1.5 stage axial flow turbine rig of the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen University. The influence of the blade row spacing on aerodynamics has been analyzed by conducting steady and unsteady RANS simulations as well as measurements in the cold air turbine test rig of the Institute. Both potential and viscous flow interactions including secondary flow were investigated. The results show an aero-dynamic improvement of efficiency and favorable spatial distribution of secondary kinetic energy by reduction of the axial gap. It is shown that this relation tends to become less pronounced for multistage turbines.

Numerical and experimental investigations have been performed to determine the effect of a variation of the interblade row axial gap on turbine efficiency. The geometry used in this study is the 1.5-stage axial flow turbine rig of the Institute of Jet Propulsion and Turbomachinery at Rhejnisch Westfalische Technische Hochshule (RWTH) Aachen University. The influence of the blade row spacing on aerodynamics has been analyzed by conducting steady and unsteady Reynolds-averaged Navier-Stokes (RANS) simulations as well as measurements in the cold air turbine test rig of the Institute. Both potential and viscous flow interactions, including secondary flow, were investigated. The results show an aerodynamic improvement of efficiency and favorable spatial distribution of secondary kinetic energy by reduction of the axial gap.

The leading technology of the Siemens SGT5-4000F heavy duty gas turbine is demonstrated through recent engine measurements at customer sites. The 4000F fleet comprises more than 240 engines that exceed performance targets because of well established, non-heuristic design processes that are continuously enhanced. On-site measurements of pressure, temperature and flow were performed at various locations in the flow path of the 4-stage turbine to support validation of Siemens’s proprietary 3D Computational Fluid Dynamics (CFD) analysis suite. Despite inherent but well understood modeling deficiencies, these advanced CFD prediction capabilities surpassed other tools and increased the accuracy of the overall turbine design process. The performance of each turbine stage and flow features related to the exhaust diffuser were captured by the calculations. Overall performance characteristic shapes coincided with heat balances based on measurements. Radial traverses at the turbine exit, static pressure along the engine axis, and temperature sensors were matched well. The level of accuracy in delta predictions exceeded industry standards. The design suite was able to predict performance parameters prior to measurement within respective confidence levels. Therefore, this advanced 3D CFD design suite, validated with the test data, will form the basis for future turbine development programs.

Numerical investigations of a 1.5 stage axial flow turbine geometry were performed to determine the effects of a variation of the inter-blade row axial gap on turbine efficiency. In order to study the influence of blade row spacing, both steady and unsteady RANS simulations were conducted. State of the art meshing including fillet radii and high grid density was used. In addition to an overall improvement of the aerodynamic efficiency with a decreasing axial distance between the rows, the numerical results showed differences in radial distribution of efficiency downstream of the trailing edges. Furthermore, transition on the blades’ suction side was investigated and compared to former fully turbulent numerical results [1]. The intermittency distributions showed that the laminar fraction of the boundary layer on the rotor, as well as on the second stator suction side, decreases with increasing gap.