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Fluid Dynamic Modelling<img alt="" src="" style="BORDER:0px solid;" /> Dynamic Modelling<div><strong></strong></div><div><div><p style="text-align:justify;"></p></div><div><h3>Mission:</h3><p style="text-align:justify;">The laboratory deals with the physical-mathematical models used for the numerical resolution of the Navier-Stokes equations. Most of the efforts are devoted to the simulation of the turbulent flows, the laminar-turbulent transition, the flow control, the reduction of the aerodynamic drag, and the flow around rotary-wing configurations.</p><h3>Goals:</h3><p style="text-align:justify;">The main goal of the laboratory is the development, implementation and validation of physical-mathematical models employed in the simulation of flow field around a body moving in a fluid. The aim is the modelling of particularly relevant subjects such as:</p><ul style="list-style-type:disc;"><li><p>Turbulent flows;</p></li><li><p>Laminar-turbulent transition;</p></li><li><p>Rotary-wing aerodynamics;</p></li><li><p>Drag reduction;</p></li><li><p>Flow control.</p></li></ul><p style="text-align:justify;">The laboratory contributes to the development of several CIRA in-house developed flow solvers with the aim to enhance and improve their simulation capabilities:</p><ul style="list-style-type:disc;"><li><p>UZEN – URANS solver for structured multi-block grids;</p></li><li><p> SPARK-LES – a "large eddy simulation" code for reacting flows on structured multi-block grids;</p></li><li><p> NOLLI – a code for the non-local linear stability analysis of the boundary layer;</p></li><li><p>RAMSYS – a Boundary Element Method (BEM) code for the "preliminary" design of unsteady potential flows around rotary-wing configurations.</p></li></ul><h3>Research Topics:</h3><h4>Simulation of turbulent flows</h4><p style="text-align:justify;">In the field of the simulation of turbulent flows, the focus is placed on the hybrid RANS-LES methods, numerical techniques that make use of a RANS model in the zone of attached boundary layer and of eddy-resolving models in the zone of the field where the flow is detached. The eXtra Large Eddy Simulation (XLES) and the methods based on the pioneering work of Spalart on Detached Eddy Simulation (DES) are the techniques currently under investigation.   </p><p style="text-align:center;"><strong><img src="" alt="" style="margin:5px;width:600px;height:262px;" /> </strong></p><p style="text-align:center;">XLES of a "mixing layer"; Kelvin-Helmholtz instability calculation by using UZEN<br></p><h4>Laminar-turbulent transition</h4><p style="text-align:justify;">The issue of the laminar-turbulent transition is being faced by the methods based on the intermittency function. These methods allow to reproduce the natural transition of a flow and to simulate important phenomena, such as the laminar separation bubbles, where the transition plays a primary role.</p><p style="text-align:center;"><img src="" alt="" style="margin:5px;width:600px;height:272px;" /><br></p><p style="text-align:center;">Transition on wing DLR-F5. Experimental visualization (left). Skin firction lines and transition line by UZEN code  (right)<br></p><h4>Rotary-wing aerodynamics</h4><p style="text-align:justify;">The laboratory is putting efforts in the modelling and numerical simulation of the aerodynamics of a rotary-wing configuration. The dynamic stall, a phenomenon particularly important for the performances of a rotary-wing, is under investigation.</p><p style="text-align:center;"><img src="" alt="" style="margin:5px;width:600px;height:233px;" /><br></p><p style="text-align:center;"> BEM simulation of "tilt-rotor".  RAMSYS code (left). Dynamic stall of an airfoil. UZEN code (right)</p><p style="text-align:justify;">Moreover, some other particular and more specific aspects are modelled by BEM methods. These are the interaction between obstacles and the wake of a rotor, and between the wake of a wind turbine and a helicopter flying at low altitude.</p><p style="text-align:center;"> <img src="" alt="" style="margin:5px;" /></p><p style="text-align:center;">Interaction between the wake of a helicopter in hover conditions and a building. RAMSYS code<br></p><h4><br></h4><h4>Drag reduction and flow control</h4><p style="text-align:justify;">Another line of research regards the "riblets", particular devices for the reduction of the aerodynamic drag.  The goal is modelling of the effect of these devices. This allows the simulation of the flow around complex geometries in realistic flight conditions.</p><p style="text-align:center;"><img src="" alt="" style="margin:5px;width:600px;height:258px;" /><br></p><p style="text-align:center;">Example of riblet (left). Effect of the riblets on the friction coefficient of the NASA CRM configuration. UZEN code (right)<br></p><p style="text-align:justify;">The laboratory is also investing resources in the modelling of the synthetic jets, fluidic actuator used for the active control of the flow, and in particular to mitigate or suppress the separation of the flow.</p><p style="text-align:center;"><img src="" alt="" style="margin:5px;width:600px;height:332px;" /><br></p><p style="text-align:center;">Control by synthetic jet of the flow around a circular cylinder <br></p></div></div>