Fig 10 - uploaded by Juergen Rauleder
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Quadrant map showing the four types of turbulent motion (turbulence events) belonging to the quadrants and their contribution to the Reynolds shear stress, u 0 v 0 .
Source publication
Measurements were made of the vortically dominated flow produced by a rotor hovering in ground effect over a mobile sediment bed. Time-resolved particle image velocimetry and particle tracking velocimetry were used to measure the two-phase flow as the rotor wake interacted with the bed. Mobilized sediment particles were tracked, with the objective...
Context in source publication
Context 1
... interactions. These four types of turbulent motion are classified by the signs of the fluctuation velocities. The signs of u 0 and v 0 , as well as the magnitude and recurrence of each of these four discrete turbulence events, determine their respective contributions to the Reynolds stresses. The measurements are plotted on a quadrant map (see Fig. 10), which essentially shows the main directions of the turbulent momentum transfer relative to the bulk movement of the fluid ...
Citations
... In addition, recent studies (Ref. 19) have also shown that the vortical structures present in the outwash region are responsible for the erosion and entrainment of the dust particles into the rotor wake which leads to brownout phenomena. Thus, the characterization of the instantaneous nature of the rotor wake flowfield is very important to understand and minimize these effects. ...
... Such high velocities are know to pose a serious threat on the safety of the personnel operating on the ground and can also be detrimental to the environment and structures around (Ref.18). In addition, the vortical wake can also lead to the brownout phenomenon during helicopter landing which is the formation of the dust cloud around the vehicle (Ref.19). Brownout can have disastrous effects as it lowers the visibility of the pilot resulting in sudden loss of situational awareness which can lead to accidents (Ref.20). ...
An experimental investigation of the rotorwash generated by a counter-rotating coaxial rotor system was conducted by using a modular and thrust scaled experimental rig. The studies were carried out for in-ground-effect condition by varying the height of the rotor system above the ground for two axial separations of the coaxial rotor system. Comparisons were made between isolated single rotor and torque matched coaxial rotor configurations to study the effects of rotor interactions on the downwash and outwash for in-ground conditions. High-speed Particle Image Velocimetry (PIV) was used to measure the temporally resolved velocity field of the rotor wake and its interaction with the ground. Both time averaged and instantaneous characterization of the transition and outwash region of the coaxial rotor wake for in-ground conditions is investigated. The self-similar characteristics of the time-averaged outwash velocity across all operating conditions is explored. The effects of the time-averaged outwash velocity on the PAXman model and the spatio-temporal interactions of tip vortex structures in the transition and outwash region for coaxial rotors are discussed.
