Carlo Cravero

COMPUTATIONAL ANALYSIS OF FLOW SEPARATION CONTROL FOR THE FLOW OVER A WALL-MOUNTED HUMP USING A SYNTHETIC JET

Flow control and MEMS are currently receiving great attention from the applied aerodynamics community. The application of current CFD techniques (routinely used in the industrial practice for standard aerodynamic design) to the flow control simulation constitutes a challenging field for existing modelling approaches. In the paper the use of CFD software, commercially available, has been investigated for the prediction of flow control strategies in a wall-mounted hump. This configuration, deeply investigated with several experimental techniques, has been selected as test-case. Both steady and unsteady flow (induced by a syntethic jet actuator) have been computed and the comparison with experimental data highlights the difficulties of current CFD in modelling the separation bubble extension.

A Design Methodology for Radial Turbomachinery: Application to Turbines and Compressors

Different design/analysis tools are combined in an automatic procedure for the design of radial turbomachinery. The algorithms developed have different complexity levels ranging from the meanline one-dimensional design tool to the fully three-dimensional Navier-Stokes based analysis. Each code gives complementary information to the designer. The codes have been written and developed by the author at DIMSET. The design procedure is developed for both radial compressors and turbines and it is proposed for the dimensioning of rotating machinery for microgasturbine power plants.Copyright

An Educational Software Suite for Teaching Design Strategies for Multistage Axial Flow Compressors

The T-AXI turbomachinery design system, an axisymmetric methodology recently developed with an educational purpose, has shown great capabilities in the redesign of existing axial flow gas turbine components. Different turbomachines, single or multistage configurations, have been already reproduced with excellent overall performance results: examples are the NASA/GE E3 HP compressor and LP turbine. In this paper, the authors present a detailed analysis of the results of a “case-study” application of the code as a complementary tool to be used during a turbomachinery design course. The NASA/GE E3 HP compressor has been chosen as the test case. Starting from the data available in open literature the different steps of the redesign have been reported: from the flowpath generation through the thermodynamic properties distributions to the overall turbomachine performance analysis. Particular attention has been given to some critical aero design parameters. The links to some interesting and useful literature sources are reported. The free-vortex, the only vortex law included in the first version of the code has been used for a first EEE compressor redesign. Different design vortex methodologies have been implemented in the new release of the code and their effects on the angular momentum are reported. The corresponding geometries can also be interfaced to a mesh generator and then the turbomachinery configurations analyzed by a 3D Navier-Stokes solver. In this way the flow field can be carefully analyzed and the fluid-dynamic physics better understood. With the above software structure the student has the opportunity to test the effects of different design strategies on the turbomachinery performance and to understand the need of a hierarchy of tools that give complete information for the multistage turbomachinery design. Finally, in the last section of the paper, the authors present how a project such as T-AXI, developed from their research activity in turbomachinery, numerical methods and CFD, can be included in the education tool CompEdu.

A NURBS-Based Optimization Tool for Axial Compressor Cascades at Design and Off-Design Conditions

Optimization techniques based on evolutionary strategies have become a general procedure in the industrial and academic worlds for the aero-mechanical design of turbomachinery blades. The airfoil geometry, parameterized using NURBS curve model, has been optimized minimizing the loss at both design and off-design working conditions, guaranteeing also the mechanical requirements. In the present work the authors, using a genetic algorithm (GA)-based tool, have explored the design space of modern axial flow compressor profiles reaching the target of better performance. The outlet flow angle and the mechanical-related quantities have been taken into account as design constraints. A fully integrated software procedure has been developed and applied to the redesign of existing airfoils in two different ways. The first redesign has been performed only at design condition while a further redesign has been implemented taking into account also two reference off-design conditions in order to increase the useful operating range. These reference off-design conditions are automatically obtained by using a loss curve model recently presented by the authors for prescribed velocity distribution airfoils. The computational tool has been applied for the optimization of the UKS-31 stator midspan section showing improved aerodynamic performance for both single and multi-point analysis.Copyright

Three-Dimensional Design Optimization of Multistage Axial Flow Turbines Using a RSM Based Approach

The problem of the automatic design optimization for multistage axial flow turbines is considered and a design strategy based on a 3D Navier-Stokes solver and a RSM (Response Surface Method) approach is described. A multi-objective optimization code based on non-dominated sorting genetic algorithm (NSGA-2) is used to drive the optimization process in order to maximize the specific power while keeping the massflow rate constrained. In the present work the meridional channel is kept unchanged while for each blade the spanwise distribution of the profile restaggering is considered together with the inclusion of compound lean. The performance from the multistage turbine for the optimization loop are obtained from surrogate models built through a set of artificial neural networks. The neural networks are trained and tested using large DoEs and are not updated during the optimization process. This aspect is considered important to guarantee that the optimization converges to an optimum. The use of the 3D flow solver with coarse meshes in order to validate large DoEs in short times is discussed in some details. The above strategy has been applied to a four stage axial turbine from the open literature.Copyright

Comparison of Semi-Empirical Correlations and a Navier-Stokes Method for the Overall Performance Assessment of Turbine Cascades

Turbomachinery flows can nowadays be investigated using several numerical techniques to solve the full set of Navier-Stokes equations : nevertheless the accuracy in the computation of losses is still a challenging topic. We describe a time-marching method developed by the authors for the integration of the Reynolds averaged Navier-Stokes equations in turbomachinery cascades. The attention is focused on turbine sections and the computed aerodynamic performances (outlet flow angle profile loss, etc.) are compared to experimental data and/or correlations. The need for this kind of CFD analysis tools is stressed for the substitution of standard correlations when a new blade is designed

Throughflow Design Using an Automatic Optimisation Strategy

A procedure has been developed to optimise the design of an axial turbine stage. A standard, streamline curvature throughflow code, with standard loss correlations, was combined with a simple parameterisation of the geometry and a standard, constrained minimisation routine. An analytic differentiation of the loss correlations was also carried out to provide insight into the influence of each of the flow variables on the stage performance. The complete procedure has been demonstrated on a single high pressure axial steam turbine stage. The initial and optimised configurations for the stage were then analysed using a 3D Navier-Stokes solver. The results confirm the improved performance and give some additional insight into the origin of the benefits.Copyright

The Development of an Aerodynamic Performance Prediction Tool for Modern Axial Flow Compressor Profiles

The development of a computational tool (MP-LOS) for the aerodynamic loss modeling and prediction for axial-flow compressor blade sections is presented in this paper. A state-of-the-art quasi 3-D flow solver, MISES, has been used for the flow analysis on existing airfoil geometries in many working conditions. Different values of inlet flow angle, inlet Mach number, AVDR, Reynolds number and solidity have been chosen to investigate a possible working range. The target is a loss prediction formulation that will be introduced into throughflow or axisymmetric Navier-Stokes codes for the performance prediction of multistage axial flow compressors. The loss coefficient has been correlated to the flow parameters that have shown an influence on the profile loss for the blades under study. The proposed correlation, using the described computational approach, can be extended to any profile family with the aid of any code for the parametric design of blade profiles.Copyright