Paolo Adami

Three-Dimensional Investigations for Axial Turbines by an Implicit Unstructured Multi-Block Flow Solver

An unstructured 3D implicit approach (HybFlow) is briefly described for gas turbine applications. The numerical approach is based in an upwind finite volume scheme with an implicit time marching algorithm. The linear solver is GMRES with right preconditioning obtained by the ILU(0) incomplete factorization. A two k-w turbulence model is considered for viscous flows. The new multiblock extension of the code is here considered for improving the computational efficiency of the basic procedure in view of the application to complex 3D geometries. Particular concern has been placed in the new approach for memory saving while keeping at the same time a great geometrical flexibility and grid transparency. The strategy developed is therefore described considering the whole process and all phases required in the solution of internal flows.Both memory and CPU time costs are addressed to verify the performances of the multiblock scheme as also computational accuracy for 2D tests. The flow conditions investigated range from the low speed regime up to the transonic one to prove the accuracy of the approach using hybrid unstructured configurations. Finally the application to the transonic cooled annular IGV blade row is considered to assess the multiblock strategy for a 3D case.Copyright

A finite-volume method for the conjugate heat transfer in film cooling devices

Abstract The present work concerns the activity performed to upgrade an in-house finite-volume computational fluid dynamics solver for computing heat transfer in gas turbine cooling devices. The ‘conjugate simulation’ of fluid heat transfer and metal heat conduction has been considered. To this aim the original code has been coupled to a new one solving the Fourier equation in the solid domain. This modification allows the ‘conjugate heat transfer’ investigation in the fluid and solid domains at the same time. Moreover an external radiation source can be modelled having included an extra term for the energy balance at solid—fluid interface. The approach has been validated through two different test-cases. The first one is a two-dimensional laminar flow over a flat plate, the second one is a film-cooled plate. The code uses conformal meshes, without using interpolation functions at the interfaces. This allows the study of configurations more complex than those in the open literature, such as the complete film-cooled stage shown in this work. In this example the complete cooling system of the nozzle has been modelled, including the two plenums and six rows of cooling channels as well. The conjugate heat transfer (CHT) has been evaluated on rotor blades as well.

Numerical Investigation of Internal Crossflow Film Cooling

A full-3D unstructured solver is applied for the investigation of the physics involved in the flow of modern film cooling devices. The numerical simulation is based on a TVD upwind finite volume method that exploits the implicit time-marching approach. A conventional two equations eddy viscosity closure is considered for the turbulent flow field without wall-functions. The present application aims to investigate and discuss the flow field physics as obtained from a numerical RANS (Reynolds Averaged Navier-Stokes) simulation comparing different cooling duct systems devices. The CFD outcome is discussed against experiments considering the discharge coefficient as a means to quantify the accuracy of the numerical simulation. Particular attention is focused on the geometrical discretization, on the grid characteristics and on the capabilities of CFD for an efficient and realistic modelling of the flow field. The basic features of the film cooling technique are addressed considering the experimental test configurations investigated by Karlsruhe University for cylindrical, fanshaped and laid back fan shaped configurations with cross/parallel flows arrangement.Copyright

Analysis of the shroud leakage flow and mainflow interactions in high-pressure turbines using an unsteady computational fluid dynamics approach

Abstract Endwall leakage flows interaction in shrouded high-pressure steam turbines is investigated to provide insights about loss and performances. The prediction of flow through the seal and the understanding of the leakage jet interaction with the main flow is performed using computational fluid dynamics (CFD). A modern research solver is used coupling the labyrinth and the main vane flows including most of the relevant geometric and aerodynamic features. Two similar shroud configurations are here analysed for two high-pressure turbine configurations. Each configuration refers to a different blade technology commonly used by Ansaldo Energia. The computational algorithm is based on a numerical solver developed and applied to solve the compressible Navier-Stokes equations in a multi-rows unsteady environment. The problem has been approached modelling the unsteady 1.5-stage interaction. The CFD results are commented addressing the potential source of losses.

Interaction Between Wake and Film Cooling Jets: Numerical Analysis

The present work presents the results obtained from the numerical investigation of the 3D unsteady flow field in a film-cooled turbine vane. The blade under research is the AGTB-B1 investigated in the cascade of the High Speed Cascade Wind Tunnel of the University of Armed Forces Munich. The unsteady flow consists of a wake which periodically interacts with the shower-head film cooling system of the blade nose. The paper discusses the aerodynamical interaction between the film-cooled blade and the periodic wake produced by a moving row of bars placed in a plane upstream the cascade. The predictive approach is based on a U-RANS CFD solver using a conventional two-equation closure. The unsteady CFD results are discussed against the experimental data available. Special emphasis is devoted to the unsteady interaction of the wake with the shower-head film-cooling system of the blade.Copyright

Numerical Predictions of Film Cooled NGV Blades

Film-cooling is commonly used in modern gas turbines to increase inlet temperatures without compromising the mechanical strength of the hot components. The main objective of the study reported here is the critical evaluation of the capability of CFD, to predict film-cooling on three-dimensional engine realistic turbine aerofoil geometries. To achieve this aim two different film-cooling systems for NGV aerofoils are predicted and compared against experiments. The application concerns the following turbine vanes: • the AGTB-B1 blade investigated by the “Institut fur Strahlantriebe of the Universitat der Bundeswehr Munchen (Germany)”; • the MT1 HP NGV investigated by QinetiQ (ex DERA, UK). In the first test case the application mainly focuses on the interaction between the main flow and the coolant jets on the leading edge of the cooled aerofoil. In the second case, vane heat transfer rate is predicted with the film-cooling system made of six rows of cylindrical holes in single and staggered configuration.Copyright

An Implicit Algorithm for Stator-Rotor Interaction Analysis

A simple time-accurate algorithm is presented for the computation of the unsteady stator-rotor interaction. The algorithm is based on the scalar approximate factorization method originally developed for the computation of complex three-dimensional steady flows. The method introduces a physical time step, used to march in time, and a numerical time step to iterate in between physical time steps. The method is formulated so as to take full advantage of the implicit formulation and provide an implicit treatment of the unsteady terms. A set of preliminary tests on a turbine stage, still in the experimental testing phase, proved the speed and accuracy of the method which was able to capture the essential features of a transonic stage.Copyright

Fault Detection and Identification by Gas Path Analysis Approach in Heavy Duty Gas Turbine

The possibility to get information about gas turbine “health” state is largely based on availability and reliability of operational data and on-line acquisition systems. However, further instruments are needed in order to deduce useful information in maintenance scheduling from actually measured data. In Gas Path Analysis approaches, a model to simulate the engine behavior is required. Furthermore, in order to individuate, locate and evaluate faulty conditions, a diagnostic approach needs to be developed and introduced. This paper presents a critical discussion of the problem to highlight the main requirements of a diagnostic approach. Furthermore, some procedures to verify the ability of a diagnostic tool can be obtained directly from the theoretical background of GPA. To demonstrate how these procedures work, an application case has been examined. An engine model has been specifically developed for the monitored heavy-duty gas turbine. It allows to calculate thermodynamics data and to identify performance parameters through a mathematical modeling process. The suitability of this model to be introduced in a diagnostic system has been investigated. An exhaustive description of the procedures and discussion of results are reported.Copyright

Three-dimensional unsteady investigation of HP turbine stages

Abstract This article deals with a three-dimensional unsteady numerical simulation of the unsteady rotor—stator interaction in a HP turbine stage. The numerical approach consists of a computational fluid dynamics (CFD) parallel code, based on an upwind total variation diminishing finite volume approach. The computation has been carried out using a sliding plane approach with hybrid unstructured meshes and a two-equation turbulent closure. The turbine rig under investigation is representative of the first stage of aeronautic gas turbine engines. A brief description of the cascade, the experimental setup, and the measuring technique is provided. Time accurate CFD computations of pressure fluctuations and Nusselt number are discussed against the experimental data.

Unsteady Heat Transfer Topics in Gas Turbine Stages Simulations

High pressure gas turbine stages are nowadays working under very challenging conditions. An usual HP stage design is based on transonic highly loaded blades cooled through impingement and film cooling techniques. An important research field for such type of turbine stages is presently represented by the investigation of unsteady performances for loss reduction and heat transfer optimization. Two special issues related to the unsteady stage interaction are addressed in the present work: the first concerns the casing/tip leakage flow, the second the effect and redistribution of inlet temperature hot-spots. The investigation of both requires unsteady modeling since these phenomena are mostly driven by the rotor-stator interaction. High temperature spots, for example, travel through the stator vane as a “hot streaks” of fluid that is mainly redistributed and steered: a simple model of this process is known as Kerrebrock and Mikolajczak’s “segregation effect”. A series of steady and unsteady simulations have been made on the HP MT1 turbine stage test rig of QinetiQ. Given an inlet uniform total pressure field, three different total temperature distributions have been simulated. The first is a uniform reference distribution of total temperature, while the other two non-uniform distributions have been obtained from experimental data with a different alignment with respect to the NGV leading edge. The numerical results have been compared with the experimental values provided by QinetiQ. The comparisons have been discussed focusing on the rotor blade and casing unsteady pressure and heat transfer rate.Copyright