Renato Tognaccini

Computational fluid dynamics-based drag prediction and decomposition

A method for the computation and breakdown of the aerodynamic drag into viscous and wave components is proposed. Given a numerical solution of the Reynolds averaged Navier-Stokes equations, the method, based on a Taylors series expansion of the far-field drag expression, allows for the determination of the drag related to entropy variations in the flow. The identification of a spurious contribution, due to the numerical dissipation and discretization error of the flow solver algorithm, allows for drag computations weakly dependent on mesh size. Therefore, accurate drag evaluations are possible even on moderately sized grids. Results are presented for transonic flows around an airfoil and a wing-body configuration

Lift and Lift-Induced Drag Computation by Lamb Vector Integration

Calculations of the lift and lift-induced drag in steady incompressible high-Reynolds-number flows are proposed in terms of volume integration of the Lamb vector (cross product of the vorticity and the velocity vector). Although conventional far-field methods can compute the profile drag by the volume integral, induced drag is usually obtained by Maskell’s method, which requires a two-dimensional plane cut from three-dimensional data. Using the Lamb vector integration, plane data reconstruction is not necessary, and a definition of the lift-induced drag in viscous flows is obtained. Furthermore, an insight of the drag production is provided by the analysis of the Lamb vector field. Numerical solutions of the flow around arbitrary-shaped bodies can be analyzed by the present method. In particular, the analysis of an elliptic wing is here proposed. The acquired aerodynamic forces are evaluated in comparison with the results of classical methods.

Aerodynamic force by Lamb vector integrals in compressible flow

A new exact expression of the aerodynamic force acting on a body in steady high Reynolds number (laminar and turbulent) compressible flow is proposed. The aerodynamic force is obtained by integration of the Lamb vector field given by the cross product of vorticity times velocity. The result is obtained extending a theory developed for the incompressible case. A decomposition in lift and drag contribution is obtained in the two-dimensional case. The theory links the force generation to local flow properties, in particular to the Lamb vector field and to the kinetic energy. The theoretical results are confirmed analyzing numerical solutions obtained by a standard Reynolds Averaged Navier-Stokes solver. Results are discussed for the case of a two-dimensional airfoil in subsonic, transonic, and supersonic free stream conditions.

Drag computation and breakdown in power-on conditions

A thrust‐drag accounting system is proposed that makes it possible to calculate installation drag from computational fluid dynamics calculations. Given a numerical solution of the viscous subsonic or transonic flow around an aircraft configuration in power-on conditions, an entropy drag expression is derived. Therefore, a method for the computation and breakdown of the entropy drag in viscous and wave components can be extended and applied to powered configurations. The possibility of identifying spurious contributions improves the accuracy of the drag calculation for a given grid. Two applications are presented: a simple two-dimensional model problem and a transonic flow around an isolated nacelle with core and fan jets.

Far-Field Drag Analysis of NASA Common Research Model Simulation

A far-field drag analysis was performed on the computational fluid dynamics simulation results of the NASA Common Research Model produced by Japan Aerospace Exploration Agency for the Drag Prediction Workshop 4. Three levels of grid resolution were employed in that simulation, and the far-field analysis successfully obtained values close to the converged drag values estimated by near-field analysis of the convergence study for all levels of grid. Drag decomposition by the far-field analysis also revealed which parts of the flow and which components of the drag varied with angle of attack. Visualized images of drag production were obtained from the far-field analysis and gave good insight into drag production.

The start-up vortex issuing from a semi-infinite flat plate

The subject of the present work is the start-up vortex issuing from a sharp trailing edge accelerated from rest in still air. A numerical simulation of the flow has been performed in the case of a semi-infinite at plate by solving the Navier–Stokes equations in the ψ_ω formulation. The numerical algorithm is based on a fast multigrid implicit integration of the difference equations in an unstructured mesh that is dynamically built to minimize the computational costs. A local refinement of the mesh near the edge of the plate increases the accuracy of the simulation. The results show that the asymptotic stage of the vortex evolution is self-similar in the mean, but the appearance of instabilities produces a time-dependent flow which is not instantaneously self-similar.

Vorticity Based Breakdown of the Aerodynamic Force in Three-Dimensional Compressible Flows

Recently, a definition of the lift-induced drag in terms of a field integral of the Lamb vector has been proposed in case of incompressible high-Reynolds-number flow and verified by postprocessing computational-fluid-dynamics solutions around wings. The possibility to extend this definition also to the case of compressible flows is investigated in this paper. An exact expression of the aerodynamic force in three-dimensional flows is discussed; it allows for a breakdown of the aerodynamic force (both drag and lift) in its physical contributions. Its applicability is analyzed in case of Reynolds-averaged Navier–Stokes numerical solutions around an elliptic wing in subsonic and transonic conditions. A rigorous and unambiguous definition of lift-induced drag is obtained. It still depends on the vortex force of the flow (the volume integral of the Lamb vector field), but a compressibility correction term is also to be taken into account. Both viscous and wave drag components can be computed by a surface integr...

Aircraft Lift and Drag Decomposition in Transonic Flows

A vorticity-based exact theory for the analysis of the aerodynamic force is here applied to three-dimensional aircraft configurations in steady transonic flow by postprocessing numerical solutions....

Advances in Aerodynamic Drag Extraction by Far-Field Methods

Far-field methods for aerodynamic drag calculation and breakdown around aircraft configurations by Computational Fluid Dynamics are widely adopted. Recent improvements and advances of one of these algorithms are discussed. Because these methods rely for breakdown purposes on the detection of the boundary-layer region around the body, an analysis of possible alternatives to the currently adopted boundary-layer sensor is proposed. Furthermore, a recently published study in the case of inviscid flow on the influence of the accuracy of the numerical solution at far field has been repeated in viscous flow. It shows how a far-field solution influences the computation of near-field drag, in particular, in high-lift conditions. Finally, an application to a complex high-lift three-dimensional configuration of an alternative method for the computation of the lift-induced drag is discussed. The method is based on the integration of the Lamb-vector field.

Time singularities in conjugated thermo-fluid-dynamic phenomena

The thermo-fluid-dynamic field that arises when an infinite thick plate is impulsively accelerated to a constant speed in a laminar regime is studied, taking into account the coupling of the convection and conduction in the fluid with the conduction in the solid. Two significant cases are discussed depending on the boundary condition imposed on the unwetted side of the plate: constant temperature or adiabatic wall. The work is particularly focused on analysing the singularities arising in the field at the initial time. For this purpose an exact analytical solution of the problem governed by the Navier-Stokes equations with constant properties and by the energy equations in the fluid and in the solid is proposed and discussed