Prediction of Clearance in Industrial Gas Turbine Validated by Field Operation Data

Abstract

During load operations the gas turbine is characterized by cyclic transients and long dwell times, resulting clearance variation occurs. Tight clearances in both the compressor and the turbine section is one key to high component efficiencies. However, under any operating condition, some clearance must be maintained in order to avoid contact between rotating and stationary parts. The optimization of the clearances during the running is one of the most relevant key to improve the engine performance, a Hydraulic Clearance Optimization (HCO) system is installed on the Ansaldo Energia gas-turbine models fleet in order to control turbine blade-tip clearances by appropriate shifting of the rotor against the flow direction and consequently reducing the radial gaps above the turbine blade tips. In particular the proposed procedure takes into account the HCO effect on the blade clearances and their optimizing during the operation conditions. The proposed procedure is based on a combination of 2D/3D FEM model of complete rotor-casing assembly and field operation data. The computational approach is based on a 2D axi-symmetric finite element model of the engine rotor, including the stacked rotor discs and the connecting tie-rod. Particular care has been put in the definition of the boundary conditions which are: the centrifugal loads, the tierod pre-tightening, the thermal transient conditions. To take into account 3D effect of airfoil twisting and bending, the 3D models of the assembly blade-disk are built. The 3D FE displacements of the tip blades are combined with the 2D FE displacements of the complete rotor in the evaluation process. 3D casing FEM model are built to calculate the casing distortion due to temperature difference between cylindrical shell and horizontal flange. The procedure evaluates the axial and radial clearance combining the rotor/stator displacements. The clearance and temperature values are measured and filed thanks to tip timing capacitive sensors and thermocouples sensors installed on same stages. The proposed procedure gives results in good agreement with the measured clearances in all the transient operation conditions.

An Introduction Into the Clearance Management of Ansaldo GT36 From Development to Validation

“…As early as the conceptual design phase a whole engine model (WEM) for transient clearance analyses was set-up. It follows the well-established design principals as outlined in [3] and [4].…”

“…(3) Vanes: u total = u thermal + u gas (4) The centrifugal part of the deformation is scaled with the rotational speed, the gas load part with inlet and outlet gas pressure and the thermal part with cooling and hot gas temperature assuming a constant cooling effectiveness factor. The material properties at the different operating temperatures are considered in the process.…”

Whole Engine Thermal Analysis for Calculation of Clearances in a Heavy-Duty Gas Turbine

“…Simulation of whole engine thermo-mechanical behaviour can be achieved in several ways. As demonstrated throughout the literature (Bozzi et al, 2012) and (Bordo et al, 2012), the accurate prediction of clearances has a considerable impact on engines reliability and efficiency. (Visser et al, 2015) investigated the thermal network model functionality in a gas turbine system simulation environment.…”