## Abstract

Coanda wall jets are obtained by tangential blowing over convex surfaces. For sufficiently large jet velocities, the flow quickly transitions to turbulence. Turbulent Coanda wall jets remain attached to the surface for relatively large distances downstream of the nozzle. This can be exploited for technical applications, such as the tail rotor less NOTAR helicopter or for circulation control (augmentation) of airfoils. The dynamics of the turbulent flow structures are oi interest since they are likely to influence the jet properties (jet spreading and associated jet velocity decay and ultimately jet separation location). Of particular interest here are the energetic large scale coherent structures that significantly contribute to the wall normal mixing and hence the jet spreading. These structures appear to be the consequence of instabilities of the turbulent mean flow. The turbulent mean velocity profile of the wall jet has an inflection point, thus giving rise to a shear layer instability, and as a consequence spanwise coherent structures develop that travel in the downstream direction. The outer layer of the wall jet is unstable with respect to a Gortler-type centrifugal instability mechanism leading to streamwise coherent structures. In the present paper results from steady Reynolds Averaged Navier-Stokes (RANS) calculations and unsteady simulations based on our Flow Simulation Methodology (FSM) of a turbulent Coanda wall jet are presented. The k-uj turbulence model and an Explicit Algebraic Stress Model (EASM) were employed. Using steady RANS calculations, the amplification of streamwise coherent structures was investigated. The streamwise structures were forced at both linear and non-linear amplitudes. At small, linear disturbance amplitudes the disturbance amplitude growth rates were consistent with Linear Stability Theory (LST) results. Resonance mechanisms appeared to play a role when the streamwise structures were forced with larger, non-linear amplitudes. The dynamics of the unsteady flow structures were explored in time accurate FSM simulations. When the spanwise extent of the computational domain was made deliberately very narrow the streamwise structures could be suppressed. As a consequence of this, the spanwise structures gained in strength, leading to an earlier separation of the wall jet.

Original language | English (US) |
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Title of host publication | 34th AIAA Fluid Dynamics Conference and Exhibit |

Publisher | American Institute of Aeronautics and Astronautics Inc. |

ISBN (Print) | 9781624100314 |

DOIs | |

State | Published - 2004 |

Event | 34th AIAA Fluid Dynamics Conference and Exhibit 2004 - Portland, OR, United States Duration: Jun 28 2004 → Jul 1 2004 |

### Publication series

Name | 34th AIAA Fluid Dynamics Conference and Exhibit |
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### Other

Other | 34th AIAA Fluid Dynamics Conference and Exhibit 2004 |
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Country | United States |

City | Portland, OR |

Period | 6/28/04 → 7/1/04 |

## ASJC Scopus subject areas

- Engineering (miscellaneous)
- Aerospace Engineering