A CFD investigation of synthetic jets

MacPherson, Iain (2003) A CFD investigation of synthetic jets. PhD thesis, University of Glasgow.

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Abstract

On current helicopter designs, the rotor blades are commonly articulated at their root. This system is employed to ensure that the resultant force of the rotor disc acts through its hub, preventing a rolling moment from being produced in forward flight. The movement which the blades are allowed however, restricts control of the blade angle of attack and allows potential lifting capability to be lost. To address this problem, on-blade flow control using synthetic jets is suggested. Miniature synthetic jets show promise for the alleviation of a number of flow control problems. These may be especially suitable for helicopter application since proposed actuator designs are remotely activated and do not require a secondary jet fluid. These features mean that actuators may be located at large spanwise distances from the rotor hub. An investigation of the operation of synthetic jets and their ability to effect flow control is begun with a CFD study of a single synthetic jet actuator issuing into an otherwise still atmosphere. A jet flow is developed from a rapidly deforming cavity. Velocity profiles are compared with previously published data. Simulations are next extended to crossflow conditions. An alternative synthetic jet model is developed to improve computational efficiency. For this, the deforming cavity is removed and the flow to and from the actuator is simulated by means of an imposed sinusoidally varying velocity. Both approaches for the production of a synthetic jet flow are compared and the same essential features are found. Depending on conditions, different flow behaviours are observed. The actuator produces vortices on its blowing schedule which are either convected with the freestream, or become part of a recirculating system which becomes permanently established a short distance downstream of the actuator exit. When varying freestream and jet operating conditions, optimal mean reduction of surface pressures is found to coincide with the first occurrence of the latter flow behaviour. Using the simpler actuator model, a parameter study is performed to determine optimum jet operation across a range of conditions. The operation of a single synthetic jet on an aerofoil section is finally considered. The same flow behaviours are once again produced. On the aerofoil, the large velocity variation means that achieving the maximum pressure reduction requires operation at high values of reduced frequency. A single actuator makes only a small difference to the overall lift, but the improvement is encouraging and suggests that a number of actuators may make a more significant difference.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Ken Badcock
Keywords: Aerospace engineering
Date of Award: 2003
Depositing User: Enlighten Team
Unique ID: glathesis:2003-71212
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 May 2019 10:49
Last Modified: 10 May 2019 10:49
URI: http://theses.gla.ac.uk/id/eprint/71212

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