Development goals for next generation aircraft engines are mainly determined by the need to reduce fuel consumption and environmental impact. To reduce NOx emissions lean combustion technologies will be applied in future development projects. The more compact design and the absence of dilution holes in this type of engines shortens residence times in the combustion chamber and reduces mixing which results in higher levels of swirl, turbulence and temperature distortions at the exit of the combustion chamber. For these engines interactions between components are more important, so that the traditional engine design approach of component-wise optimization will have to be adapted. To study new lean burn architectures the European FACTOR project investigates the transport of hot streaks produced by a non-reactive combustor simulator through a single stage high-pressure turbine. In this work high-fidelity Large Eddy Simulation (LES) of combustor and complete high-pressure turbine are discussed and validated against experimental data. Measurement data is available on P40 (exit of the combustion chamber), P41 (exit of the stator) and P42 (exit of the rotor) and generally shows a good agreement to LES data.
With the goal of increasing the thermodynamic efficiency of aircraft engines, the temperature in the combustion chamber has risen to the point where the gas temperature is above the melting point of materials used in the chamber and cooling systems are mandatory. Today, most of the existing lean burn combustors rely on multiperforated liners to keep hot gases away from the walls. However, resolving all holes of the combustor in the CFD design phase remains beyond currently available computational resources, so the effusion cooling system is often modeled by homogeneously injecting air on the whole surface of the liner, especially in the context of Large Eddy Simulation (LES) based CFD. This paper investigates a novel approach to simulate the effect of jets emitted from discrete holes on the flow inside a combustion chamber. In this new modeling approach, jet diameters are treated to be resolvable by the grid while conserving the correct mass and momentum flow rate. LES are performed on the combustion simulator of the engine representative FACTOR test rig at two different operating points and compared to measurement data as well as previous simulations obtained using a homogeneous air injection modeling on liners. The new approach shows globally similar results as the well validated homogeneous injection model and is applicable on realistic industrial geometries at a negligible level of additional cost (+0.3%).
The next generation of lean combustion engines promises to further decrease environmental impact and cost of air traffic. Compared to the currently employed Rich Quench Lean (RQL) concept, the flow field at the exit of a lean combustion chamber is characterized by stronger variations of velocity as well as temperature and higher levels of turbulence. These specific features may have a substantial impact on the aerothermal performance of the high-pressure turbine and thereby on the efficiency of the entire engine. Indeed, high levels of turbulence in the Nozzle Guide Vane (NGV) passages locally impact the heat flux and result in globally over dimensioned cooling systems of the NGV. In this study, Large Eddy Simulations (LES) are performed on an engine representative lean combustion simulator geometry to investigate the evolution of turbulence and the migration of hot streaks through the high-pressure turbine. To investigate the impact of non-uniform stator inlet conditions on the estimated thermal stress on the NGVs, adiabatic LES predictions of the lean combustor NGV FACTOR configuration are analyzed through the use of high statistical moments of temperature and two point statistics for the assessment of turbulent quantities. Relations between temperature statistical features and turbulence are evidenced on planes through the NGV passage pointing to the role of mixing and large scale features along with marked wall temperatures that locally can largely differ from obtained mean values.
Erosion of compressor and turbine blades operating in extreme environment fouled with sand particles, ash or soot is a serious problem for gas turbine manufacturers and users. Indeed, operation of a gas turbine engine in such hostile conditions leads to drastic degradation of the aerodynamic performance of the components, mostly through surface roughness modification, tip clearance height increase or blunting of blade leading edges. To evaluate associated risks, the computation of particle trajectories and impacts through multiple turbomachinery stages by Computational Fluid Dynamics (CFD) seems a decent path but remains a challenge. The numerical prediction of complex turbulent flows in compressors and turbines is however necessary in such a context and validations are still required. Recently, Large-Eddy Simulation (LES) has shown promising results for compressor and turbine configurations for a wide range of operating conditions at an acceptable cost. With this in mind, this article presents the assessment of a LES solver able to treat turbomachine configurations to predict solid particle motion. To do so, the governing equations of particle dynamics are introduced using the Lagrangian formalism and are solved to compute locations and conditions of impact, namely particle velocity, angle and radius. The fully unsteady and coupled strategy is applied to blade geometries for studying the main areas and conditions of impacts obtained with LES. For comparison, a one-way coupling computation based on a mean steady flow field where only the Lagrangian particles are advanced in time is performed to evaluate the gain and drawbacks of both methods.
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