Numerical Simulation of Nacelle Flowfield for Counter-Rotating Open Rotor Propellers

This paper summarizes the development of a tool for designing axisymmetric nacelles for counter-rotating open rotor (CROR) engines, based on predefined geometries, global input relations and one-dimensional perfect gas equations. A nacelle geometry was generated to match the flight conditions and base dimensions of the Airbus AI-PX7 CROR propeller. Furthermore, the 3D turbulent flowfield around the nacelle was evaluated via Computational Fluid Dynamics (CFD) for four different angles of attack: 0\ub0, 4\ub0, 6\ub0 and 8\ub0. The computations were performed for the nacelle without the propellers as a first analysis. The formation of shock waves, boundary layer separation and inlet flow distortion were the main parameters of the CFD study. The nacelle design was considered to be successful as a preliminary approach, since, even for the highest angle of attack, no critical conditions for the engine performance were detected

Influence of Variable Geometry Compressor on Transient Performance of Counter-Rotating Open Rotor Engines

This work describes a methodology used for counter-rotating (CR) propellers performance estimation. The method is implemented in an in-house program for gas turbine performance prediction, making possible the simulation of the counter-rotating open rotor (CROR) architecture. The methodology is used together with a variable geometry compressor control strategy to avoid surge conditions. Two cases are simulated under transient operation for both fixed and variable geometry compressor. The influence of the variable geometry control on the transient performance of CROR engines is evaluated and a comprehensive understanding on the transient behavior of this type of engine could be obtained. It is shown that the use of the variable geometry compressor control does not significantly affect the overall engine performance, while avoiding the surge conditions, thus ensuring the engine operation safety

Numerical investigation of film and impingement cooling schemes for gas turbine application

In modern gas turbine engines, many sophisticated cooling schemes are used to maintain the turbine blade temperature in acceptable levels. These schemes, such as convective cooling, film cooling, impingement cooling and the use of pin fins, can be combined to increase the cooling effectiveness. Jet impingement cooling, pin fins and convective cooling are internal cooling techniques, in which the cooling is achieved based on coolant flow through internal blade channels decreasing the blade metal temperature. Film cooling is an external cooling technique, in which the cold fluid (air) is injected into the hot gas flow through discrete holes providing a coolant film at blade surface, protecting the blade metal. In this way, the present work refers to the numerical investigation of internal and external cooling strategies applied in gas turbines. The methodology developed to analyze such strategies is based on the flat-plate approach with laboratory length scales and Computational Fluid Dynamics (CFD) techniques, being the flow, in the study domain, considered viscous, turbulent and compressible. A commercial CFD program is used to solve the general equations of fluid mechanics with Reynolds Average Navier-Stokes (RANS) technique for steady state regime and Shear Stress Transport (SST) turbulence model to determine the flow eddy viscosity. The combined effects of internal and external cooling is studied through a highly sophisticated scheme, called louver, which combines the effects of impingement and film cooling. Pin fins and ribs turbulator geometries applied in the channel between the impingement and the film cooling have the purpose of evaluating the impact of these geometries on the film cooling effectiveness over the flat surface in comparison to the louver scheme without turbulator. This study concluded that, pin fins proved to be the most promise solution because they increased in 7% the film cooling effectiveness. Ribs also have a good potential to increase the effectiveness, because an increase of 4% in film cooling effectiveness was observed. In addition, the effects of the turbulator are dependent on their location, since the turbulator positioned near the film cooling hole exit showed improvements in the film cooling effectiveness in relation to the turbulator near of the impingement cooling jet

A Propeller Model for Steady-State and Transient Performance Prediction of Turboprop and Counter-Rotating Open Rotor Engines

This paper describes a methodology used for propeller performance estimation, which was implemented in an in-house modular program for gas turbine performance prediction. A model based on subsonic generic propeller maps and corrected for compressibility effects, under high subsonic speeds, was proposed and implemented. Considering this methodology, it is possible to simulate conventional turboprop architectures and counter-rotating open rotor (CROR) engines in both steady-state and transient operating conditions. Two simulation scenarios are available: variable pitch angle propeller with constant speed; or variable speed propeller with constant pitch angle. The simulations results were compared with test bench data and two gas turbine performance commercial software packages were used to fulfill the model validation for conventional turboprop configurations. Furthermore, a direct drive CROR engine was simulated using a variable inlet guide vanes (VIGV) control strategy during transient operation. The model has shown to be able to provide several information about propeller-based engine performance using few input data, and a comprehensive understanding on steady-state and transient performance behavior was achieved in the obtained results

Aerodynamic Analysis of Conventional and Boundary Layer Ingesting Propellers

The boundary layer ingestion (BLI) concept has emerged as a novel technology for reducing aircraft fuel consumption. Several studies designed BLI-fans for aircraft. BLI-propellers, although, have still received little attention, and the choice of open-rotors or ducted propellers is still an open question regarding the best performance. The blade design is also challenging because the BLI-propulsors ingest a nonuniform flow. These aspects emphasize further investigation of unducted and ducted BLI-propulsors and the use of optimization frameworks, coupled with computational fluid dynamics simulations, to design the propeller to adapt to the incoming flow. This paper uses a multi-objective NSGA-II optimization framework, coupled with three-dimensional RANS simulations and radial basis function (RBF) metamodeling, used for the design and optimization of three propeller configurations at cruise conditions: (a) conventional propeller operating in the freestream, (b) unducted BLI-propeller, and (c) ducted BLI-propeller, both ingesting the airframe boundary layer. The optimization results showed a significant increase in chord and a decrease in the blade angles in the BLI configurations, emphasizing that these geometric parameters optimization highly affects the BLI-blade design. The unducted BLI-propeller needs approximately 40% less shaft power than the conventional propeller to generate the same amount of propeller force. The ducted BLI-propeller needs even less power, 47%. The duct contributes to the tip vortex weakening, recovering the swirl, and turning into propeller force, as noticed from 80% of the blade span to the tip. However, the unducted and ducted BLI-configurations presented a higher backward force, 26% and 46%, respectively, compared to the conventional propeller, which can be detrimental and narrow the use of these configurations