Cordoli. Bump in macchina

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Design of a High-Lift System for a Laminar Wing

The design of high-lift (HL) systems represents a challenging task within the aerospace community, due to its multidisciplinary, multi-objective and multi-point nature. Within the paper an additional difficulty is considered, consisting in the design a HL system for a High Aspect Ratio Low Sweep (HARLS) wing, featuring Natural Laminar Flow (NLF) at transonic cruise conditions. In a first “analysis” phase a realistic optimization problem is defined and solved by adopting different approaches in terms of employed flow model, meshing strategies, geometry parameterization and optimization strategies. In a second “application” phase, the design of an optimal feasible HL system is developed for the HARLS-NLF wing, by considering a close coupling between 3D CFD-based optimization, kinematical layout studies and mechanical integration studies

Induced Drag and Vorticity in Viscous and Inviscid Flows

An overview of the different methods to compute lift-induced drag and on latest Research efforts on the assessment of drag definitions is provided during this workshop

AERODYNAMIC FORCE BY LAMB VECTOR INTEGRALS IN UNSTEADY COMPRESSIBLE FLOWS

The new aerodynamic force theory based on Lamb vector field integration, valid in general for unsteady and compressible flow regimes, provides an exact expression of the whole aerodynamic force. Different flavours of the steady formula have been developed in the last decades, with identification of lift-induced and parasite drag contributions subject of recent studies focusing on steady applications. To transfer the maturity achieved on compressible steady vortical methods to unsteady flows, different Lamb vector-based force formulas and decompositions are here extended to the unsteady regime and compared through numerical applications on twodimensional compressible flows with moving bodies

On the spurious effects in Lamb-vector-based force decomposition methods

Recent methods based on Lamb vector integration allow for a far-field formulation and decomposition of the whole aerodynamic force, with identification of local flow structures associated with the force generation. Different exact Lamb-vector-based force formulations were proposed in the past and the decomposition of total drag into lift-induced and parasite contributions was subject of very recent studies. However, inconsistencies were also reported, raising questions on the physical role of a non-zero induced drag found in two-dimensional flows. Moreover, the effect of the arbitrary pole (appearing in Lamb-vector-based formulas) on the numerical accuracy of such methods was never investigated. Additionally, the separation of parasite drag into viscous and wave drag contributions by Lamb vector field analysis is still questioned. In this paper, the accuracy of different force formulas and of the drag decomposition in lift-induced and parasite contributions is first analyzed, for steady flows. Two-dimensional numerical solutions around RAE2822 and NACA0012 airfoils are considered, the latter in both inviscid and viscous flows (at low and high Reynolds number), to analyze consistency between lift-induced/parasite drag definitions and the drag generated in isentropic flow conditions (reversible drag) or due to entropy production (irreversible drag). A spurious induced drag contribution (related to the streamwise momentum perturbation) is identified, resulting in negative induced drag values in two-dimensional flows. The effect of a shift in the pole location is also analysed, with reference to its impact on the total force and on drag decomposition accuracy, then a new approach to parasite drag breakdown into physical constituents (viscous and wave contributions) is proposed and results are compared against predictions obtained using consolidated thermodynamic-based methods and against available results from recent literature

A unified thermodynamic/Lamb-vector-based analysis of the aerodynamic force

The Lamb vector, cross-product of flow vorticity and velocity, is at the basis of different far-field methods developed in the last decades for the aerodynamic force analysis and decomposition, as an alternative to the nowadays well-assessed thermodynamic methods. We here propose a mixed approach, where exact Lamb-vector-based force formulas are used in combination with a thermodynamic-based calculation of the Lamb vector through Crocco’s equation. In computational fluid dynamics, this way of calculating the Lamb vector, therefore, inherits from the numerical form of the flow momentum equation and discretely satisfies the local (and integral) momentum balance on which farfield methods rely. The resulting hybrid method, which does not require an explicit vorticity calculation, provides results in far better agreement with regard to near-field force data when compared to standard vorticity-based approaches, especially in the presence of shock waves, where inaccuracies of domain integrals involving the Lamb vector were systematically reported by different authors. In addition, it overcomes the limitations of previous thermodynamic methods, which only compute the drag force

Wave Drag and Vorticity in Two-Dimensional Viscous and Inviscid Flows

Recent methods based on flow vorticity and Lamb vector integration allow for a far-field formulation and decomposition of the whole aerodynamic force with identification of local flow structures associated with the force generation. Different exact and theoretically equivalent Lamb vector-based force formulations were proposed in the past and the decomposition of total drag into lift-induced and parasite contributions was subject of very recent papers. However, different results can be obtained in the practise when applying a selected force formula to numerically computed flow-fields, with sensitivity of the computed total force to additional degrees of freedom, such as the choice of the control volume or the location of the arbitrary pole appearing in Lamb vector-based formulations. Moreover, the separation of irreversible drag into viscous and wave drag contributions by Lamb vector field analysis is still questioned. In this paper, the accuracy of the total force formula and of the drag decomposition in lift-induced and parasite contributions is first analyzed, for a steady flow regime. Then, to verify the possibility to relate wave drag to Lamb vector integrals, the effectively inviscid flow around an airfoil in transonic flow is first studied, being, in this case, wave drag the only drag contribution. Finally, the study is completed by a viscous high Reynolds number analysis, where an approach to drag decomposition into physical constituents (viscous and wave contributions) is illustrated and results are compared against predictions obtained using consolidated thermodynamic-based methods

Analysis and Application of Suitable CFD-Based Optimization Strategies for High-Lift System Design

The design of high-lift (HL) systems represents a challenging task within the aerospace community, due to its multidisciplinary, multi-objective and multi-point nature. Within the paper an additional difficulty is considered, consisting in the design a HL system for a High Aspect Ratio Low Sweep (HARLS) wing, featuring Natural Laminar Flow (NLF) at transonic cruise conditions. In a first “analysis” phase a realistic optimization problem is defined and solved by adopting different approaches in terms of employed flow model, meshing strategies, geometry parameterization and optimization strategies. In a second “application” phase, the design of an optimal feasible HL system is developed for the HARLS-NLF wing, by considering a close coupling between 3D CFD-based optimization, kinematical layout studies and mechanical integration studies