David Cleaver

Full Name:

Dr David Cleaver

Department:

Dept of Mechanical Engineering

Job Title:

Lecturer

Telephone:

+44 1225 384771

E-mail Address:

D.J.Cleaver@bath.ac.uk

Postal Address:

Dr David Cleaver
4E 2.42
Dept of Mechanical Engineering
University of Bath
Bath
BA2 7AY
United Kingdom

Research Topic:

I am working as part of the Aerospace Engineering Research Centre within the field of experimental fluid dynamics, in conjunction with Prof. I. Gursul , Dr. Z. Wang and D. E. Calderon, on a range of topics broadly focused around unsteady aerodynamics, active flow control, and micro air vehicles. A brief overview of my PhD research topic (dated 2009 in the form of a poster (~2Mb)) can be found here, with animations of the vortex modes are shown below. More recent information can be found in the journal articles and conference papers at the bottom of this page (or via PURE at bath.ac.uk). Generally we are investigating the possibility of increasing the lift and reducing the drag of MAVs through small-amplitude high-frequency motion. So far the results have shown very significant improvements (up to 305% increase in lift!). The next step is to produce these improvements more efficiently through wing flexibility. In addition, I have also worked on a grant for the Office of Naval Research Global investigating the possibility of hydrofoil drag reduction using the unsteadiness inherent in waves, and I am starting work on a grant in conjunction with Prof. Gursul and Airbus to investigate the possibility of high frequency active flow control for load reduction on aircraft. 
 
RIGID AIRFOIL ANIMATIONS

 

 

Mode 1: Convected LEV

 
Description: Description: 1,00 = St - 090 - PL - Vorticity - small scale

 

 

Mode 1: Convected LEV (interesting wake)

 
Description: Description: 2,00 = St - 090 - PL - Vorticity - small scale

 

 

Mixed: Convected but Weak LEV

 
Description: Description: 2,50 = St - 090 - PL - Vorticity - small scale

 

 

Mode 2: Attached LEV

 
Description: Description: 3,00 = St - 090 - PL - Vorticity - small scale
 

 

 

LEV DIPOLE: for flat plate geometry, leads to low lift and high drag

 
 
 
 
FLEXIBLE WING ANIMATION
 

Rigid (left) vs Highly Flexible Wing (right)

 

This animation is large (4.6MB) so may take some time to load. The wings are derived from DIC data, the flow fields are derived from DDPIV and PIV data. The isosurfaces are vorticity magnitude:

Rigid isosurfaces: ωc/U = 8, 16, 24

Flexible isosurfaces: ωc/U = 12, 18, 24

 

 
 
 
 

Journal Articles (for copies see PURE database on bath.ac.uk):

Cleaver, D.J., Wang, Z.J., Gursul I., and Visbal M.R. "Lift Enhancement by means of Small Amplitude Airfoil Oscillations,” AIAA Journal, Vol. 49, No. 9, 2011, pp. 2018 - 2033.
A combination of the first two conference papers in a finalised format. Focuses on lift augmentation due to small-amplitude oscillations, up to 305% increase with local optima around the natural shedding frequency, its subharmonic and higher harmonics. Also, shows the LEV dissipation typical of a mode 2 flow field (animation above)
 
Cleaver, D.J., Wang, Z.J., and Gursul I. "Bifurcating Flows of Plunging Airfoils at High Strouhal Numbers,” Journal of Fluid Mechanics, Vol. 708, pp. 349 - 376.
Very detailed measurements for bifurcating wakes behind a NACA 0012 airfoil demonstrating forces and flowfields together for the first time. Bifurcation due to deflected jets. Deflected jets form due to TEV dipoles which create asymmetric results (high lift) from symmetric situations. The direction of the jet depends on the initial conditions (alpha, starting position, acceleration rate), and will only form at high plunge velocities due to a minimum TEV dipole strength criteria.
 
Cleaver, D.J., Wang, Z.J., and Gursul I. "Investigations of Mechanisms of High Lift for a Flat Plate Airfoil Undergoing Small-Amplitude Oscillations,” AIAA Journal, in press.
Comparison of the forces and flow fields for NACA 0012 and flat plate airfoil for two angles of attack 0 and 15. For 0 the flat plate experiences jet switching due to an instability driven by the LEV. For 15 the flat plate experiences low lift and high drag at high Strouhal numbers due to LEV dipole formation. Airfoil geometry therefore has a very significant effect!
 
 

Conference Papers:

Cleaver, D.J., Wang, Z.J., and Gursul, I. "Delay of Stall by Small Amplitude Airfoil Oscillation at Low Reynolds Numbers," 47th AIAA Aerospace Sciences Meeting, AIAA 2009-392, 2009.
First paper presenting the difference modes associated with the destruction of the LEV and the effect this has on drag / thrust.
 
Cleaver, D.J., Wang, Z.J., and Gursul, I. "Lift Enhancement on Oscillating Airfoils," 39th AIAA Fluid Dynamics Conference, AIAA-2009-4028, AIAA, 2009.
Presents detailed lift measurements along with accompanying PIV for a single fixed mean angle of attack of 15deg.
 
Cleaver, D.J., Wang, Z.J., and Gursul, I. "Vortex Mode Bifurcation and Lift Force of a Plunging Airfoil at Low Reynolds Numbers," 48th AIAA Aerospace Sciences Meeting, AIAA 2010-390, 2010
Presents detailed lift and PIV measurements for 5, 10 and 15deg fixed mean angle of attack showing significant bifurcations at high Strouhal numbers.
 
Cleaver, D.J., Wang, Z.J., and Gursul, I. "Rigid and Flexible Foils Oscillating Near a Free Surface," 50th AIAA Aerospace Sciences Meeting, AIAA-2012-1195, 2012.
Studies the effect of amplitude, depth and flexible trailing edge devices through drag and PIV measurements for an oscillating NACA 0012 airfoil.
 
Cleaver, D.J., Wang, Z.J., and Gursul, I. " Effect of Airfoil Shape on Flow Control by Small-Amplitude Oscillations," 50th AIAA Aerospace Sciences Meeting, AIAA-2012-756, 2012.
Studies the effect of airfoil geometry for 0 and 15deg angle of attack and wide range of parameters. Very interesting jet switching phenomenon.
 
Cleaver, D.J., Wang, Z.J., and Gursul, I. "Oscillating Flexible Wings at Low Reynolds Numbers," 51st AIAA Aerospace Sciences Meeting, AIAA-2012-756, 2012.
Studies the effect of airfoil geometry for 0 and 15deg angle of attack and wide range of parameters. Very interesting jet switching phenomenon.