Project COMROTAG

 Development and Testing
of Computational Methods to Simulate
Helicopter Rotors with Active Gurney Flap

 

 

Research  Background

 

            Active Rotor Technology is a dynamically developing sub-domain of Rotorcraft Engineering, which is focused on the improvement of performance of modern helicopters and their environmental impact by active control of operation of main rotors. The active control of helicopter rotor may concern several different aspects, but the project COMROTAG focuses on one of them – the active control of air-flow on helicopter-rotor blades by Active Gurney Flap.

            According to the definition: the Active Gurney Flap (AGF) is a fully retractable structure protruding perpendicularly to chord line on the lower blade surface at the trailing edge. The kinematics of the flap consists of continuous, prescribed, vertical motion achieved through a mechanism mounted inside the rotor blade. Possible applications in helicopter rotors include: lower frequencies of deployment (one deployment per revolution) applied for performance enhancement and higher frequencies of deployment applied for vibration control. It is expected that application of the Active Gurney Flap will enable helicopters to operate with reduced power consumption or reduced main rotor tip speed whilst preserving current flight performance capabilities, especially in terms of retreating blade stall.

            Project COMROTAG focuses on numerical simulations of flow around rotor blades equipped with Active Gurney Flaps by solution of Unsteady Reynolds-Averaged Navier-Stokes equations. The simulations are conducted using original, developed in the Institute of Aviation methodology concerning modelling of kinematics of rotor blades equipped with Active Gurney Flap in rotating and deformable mesh zones. An algorithm implemented as User-Defined Function in the ANSYS FLUENT solver ensures reversible deformation of computational mesh in the zone encompassing Active Gurney Flap maintaining at the same time high quality of mesh cells.

 

The flow around the helicopter rotor of blades equipped with AGFs is considered fully unsteady, taking into account following phenomena:

         forward flight of the rotor

         rotation of the rotor around the rotation axis

         time-variable pitch of rotor blades – the movement resulting from given collective and cyclic pitch controls as well as from pitch-flap coupling

         flapping of rotor blades around a flapping hinge

         lead-lag motion of rotor blades around a lead-lag hinge (if any)

         cyclic deployment and retreat of the Active Gurney Flaps mounted on the rotor blades

 

Flow of information during the simulation of operation of a rotor equipped with an Active Gurney Flap is presented in the diagram below:

     

General scheme of the proposed methodology of computational simulation of flight

 of helicopter rotor with blades equipped with the Active Gurney Flaps

 

 

 

 

 

 

Division of computational mesh into blocks enabling modelling of kinematics of rotor blades and arrangement of mesh blocks in the computational domain is presented in the pictures below

 

(c)

 

(b)

 

(a)

 
 


 

 

Structure of computational mesh: (a) cylinder-cone zones surrounding each blade, (b) cylinder-shape zone, (c) far-field zone

 

 

 

 

 

 

Segment of the rotor blade equipped with the Active Gurney Flap. (a) AGF fully retracted , (b) AGF fully deployed.

 

 

  

Stages of 3D-mesh deformations during deployment of the AGF

 

 

CFD Simulations of Flow around the Blades Equipped with the AGF

 

Example: 2.5D simulation of flow around the oscillating blade segment equipped with the AGF. Flow conditions: M=0.1, Re=1164800. Blade-segment pitching amplitude = 5 deg, average pitch = 5 deg, reduced frequency k=0.231. Harmonic movement of the AGF - consistent in phase with pitching of the blade. Maximal deployment of the AGF = 1.5% of blade chord. Flow simulations: conducted using the ANSYS FLUENT solver. Flow model: 3D, unsteady, compressible, viscous, turbulence model: k-w SST.

Assumed oscillations of angle of attack (a) and relative height of AGF (Hagf/C).

Comparison of dependencies CL vs. a for active and inactive AGF.

 

 

Comparison of dependencies CD vs. a
for active and inactive AGF.

 

Comparison of dependencies Cm vs. a
for active and inactive AGF.

 

 

 

Contours of velocity magnitude and vorticity magnitude in a plane of symmetry
of the rotor-blade segment, for selected angles of attack (a).

 

Acknowledgements

 

The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) for the Clean Sky Joint Technology Initiative under grant agreement no CSJ-GA-2013-619627, within the project COMROTAG.

Computational research presented in the paper was conducted in University of Warsaw Interdisciplinary Centre for Mathematical and Computational Modelling, based on the Computational Grant No. G55-4.

Project is being conducted in the Computational Aerodynamics and Flight Dynamics Group in the Department of Aerodynamics of the Institute of Aviation.

The author of the concept of modelling of kinematics of rotor blades equipped with Active Gurney Flap is dr Wieńczysław Stalewski.