Fluid Dynamics

Research activities in the area of basic and applied fluid dynamics are carried out at the Department of Aerospace Engineering using both experimental and numerical techniques. The investigations have been and are supported through both institutional funds (Italian Ministry of University, CNR, European Commission) and research contracts with several industries and research institutions. In the following a brief description of the main resarch areas is given

Aerodynamics of lifting surfaces An extensive research activity has been devoted to the study of non-conventional lifting systems, such as forward-swept wings and canard configurations. Experiments have been conducted both in the subsonic wind tunnel of the Department and in the medium speed wind tunnel of CSIR (South Africa), within an extensive research cooperation. The obtained data are compared with the results of CFD computations, using both codes developed within the Department (such as potential panel methods and non-linear vortex-lattice methods) and commercial codes for the solution of the RANS equations. A significant activity is being carried out to validate the numerical procedures and to develop new codes for the optimization of lifting configurations.

Lombardi G. – Canard Tip Vortex Splitting in a Canard-Wing Configuration: Experimental Observation. Journal of Aircraft, Vol. 32, No.4, July/Aug. 1995, pp. 875-877.
Lombardi G., Salvetti M.V., Pinelli D.- Numerical Evaluation of Airfoil Friction Drag. Journal of Aircraft, Vol. 37, No. 2, March-April 2000, pp. 354-356.

Wall-interference effects in wind tunnels Experimental and numerical techniques are being used to develop new procedures for the correction of wall-interference effects in subsonic and transonic wind tunnels. This activity is also part of the research agreement with CSIR (Council for Scientific and Industrial Research, South Africa).

Lombardi G., Salvetti M.V. – Effect of a Splitter Plate on Transonic Wing Flow: a Numerical Study. Journal of Aircraft, Vol. 36, No. 4, July-Aug. 1999, pp. 718-720.

Bluff Body Aerodynamics Research activities have been carried out for many years at the Department in the field of bluff body aerodynamics, regarding both basic aspects and engineering applications, and this research area remains one of the most important within the Fluid Dynamics research group. The main topics of interest, which are currently being analysed using both experimental and numerical techniques, are:
- Characterization of vortex shedding from two-dimensional and three-dimensional cylindrical and prismatic bodies, and of the related unsteady loads.
- Analysis of the influence of afterbody rounding on the base drag of axisymmetrical bodies.

Buresti G., Fedeli R, Ferraresi A. - Influence of afterbody rounding on the pressure drag of an axisymmetrical bluff body. J. Wind Engineering and Industrial Aerodynamics, Vol. 69-71, 1997, pp. 179-188.
Buresti G., Lombardi G., Talamelli A. - Low aspect-ratio triangular prisms in cross-flow: measurements of the wake fluctuating velocity field. J. Wind Engineering and Industrial Aerodynamics, Vol. 74-76, 1998, pp. 463-473.
Buresti G. - Vortex shedding from bluff bodies. In “Wind Effects on Buildings and Structures” (Riera J.D., Davenport A.G., Eds.), Balkema, Rotterdam, 1998, pp. 61-95.
Buresti G., Lombardi G. - Experimental evaluation of the mean and fluctuating forces on finite-length triangular prisms in cross-flow. “International Symposium on Bluff Bodies Aerodynamic Applications”, Sept. 2000, Bochum, Germany.

Aerodynamics of high-performance cars Since 1992 the Department has carried out activities connected with the aerodynamic design of high-performance cars, and a research agreement has been established with Ferrari Auto envisaging a continuous cooperation in basic and applied investigations of mutual interest. In particular, a new numerical optimization procedure was developed, which allows desired aerodynamic characteristics to be obtained taking into account the geometrical constraints imposed by style requirements. As a result of the research agreement, the Department has been and is still involved in the aerodynamic design of the new Ferrari production cars.

Lombardi G., Manacorda G., Paap H.G., Vicerè A. – Optimized Aerodynamic Design for High Performance Cars. AIAA Paper 98-4789. Presentato al 7th AIAA/USAF/NASA/ISSMO Symposium on Multidisciplinary Analysis and Optimization, St. Louis, Sept. 1998.

Measurement and analysis procedures for characterization of turbulent flows
New hot-wire measurement procedures were developed for the characterization up to second-order moments of highly turbulent flow fields using X-wire probes. Pressure probes for the direct measurement of the streamwise vorticity component were also designed.
More recently, new techniques for the analysis of fluctuating signals are being developed for the characterization of turbulent and transitional flows, and, more generally, of unsteady flow fields, such as bluff body wakes. These procedures are based on the continuous complex wavelet transform, which permits to obtain the time variation of the contribution of the different frequencies present in a signal to various physical quantities, such as its energy or its correlation with another signal. Futhermore, intermittent fluctuations that are slowly-modulated in frequency and amplitude may be extracted to facilitate the study of their connection with different physical mechanisms.

Buresti G.; Lombardi G. - Application of continuous wavelet transforms to the analysis of experimental turbulent velocity signals. In: “Turbulence and Shear Flow Phenomena – 1” (S. Banerjee, J.K. Eaton Eds.), Begell House Inc., 1999, pp. 767-772.
M.V. Salvetti, G. Lombardi, F. Beux, ``Application of a wavelet cross-correlation technique to the analysis of mixing'', AIAA Journal, Vol. 37, No. 8, August 1999.

Coaxial Jets The study of the aerodynamics of coaxial jets is of great interest both for engineering applications (as the design of new generation industrial burners) and for basic research in developing turbulent flows. The Department started the experimental activity in this field within research contracts with ENEL, and investigations are presently being carried out using both numerical analysis and the new coaxial jet facility of the laboratory, which allows different and highly controlled flow configurations to be studied.

Buresti G., Petagna P., Talamelli A. - Experimental investigation on the turbulent near- field of coaxial jets. Experimental Thermal and Fluid Science, Vol. 17, 1998, pp.18-26.
Salvetti M.V., Orlandi P., Verzicco R., "Numerical Simulations of Transitional Axisymmetric Coaxial Jets", AIAA Journal, Vol. 34, No. 4, pp. 736-743, Aprile 1996.

Numerical models The department has a significant experience in the development of potential-flow codes for aeronautical applications, and in the use of codes for the solution of the Navier Stokes equations (Direct Numerical Simulation and RANS). Presently, the main research activity in computational fluid dynamics concerns the development of reduced-order models for the simulation of turbulent flows. In particular, significant contributions have been given in the field of Large Eddy Simulation (LES), with the introduction of a new subgrid scale model. The potential of methods based on Proper Orthogal Decomposition (POD) are also being deeply investigated. The different numerical codes are used in conjunction with experiments in the investigations regarding coaxial jets, turbulence development, and bluff body aerodynamics. The capabilities of the LES approach for industrial applications on unstructured grids are also being investigated in collaboration with INRIA (Institut National de Recherche en Informatique et Automatique, France).

L. Polito, “Note sui potenziali di Liénard-Wiechert nell’Aerodinamica e nella Teoria della Relatività”, Atti del Dipartimento di Ingegneria Aerospaziale, Università degli Studi di Pisa, A.D.I.A. 95-1, Gennaio 1995.
M.V. Salvetti, Y. Zang, R.L. Street, S. Banerjee, "Large-eddy simulation of free-surface decaying turbulence with dynamic subgrid-scale models", Physics of Fluis, Vol. 9, No. 8, pp. 2405-2419, 1997.
M.V. Salvetti, F. Beux, "The effect of the numerical scheme on the subgrid scale term in large-eddy simulation", Physics of Fluids, Vol. 10, No. 11, pp. 3020-3023, 1998.
M.V. Salvetti, R. Damiani, F. Beux, ``3D coarse large-eddy simulations of the flow above two-dimensional sinusoidal waves'', International Journal for Numerical Methods in Fluids, vol. 34, 2001.