1. .
.
Investigation of the limitations of XFLR5 for
aerodynamic predictions at low Reynolds numbers
3Philip Chan, 2Francisco Gomez, 1Hugo Villafana
Advisors: 1*Wilson Chan, 1Tyler Davis, 1Joseph Tank, 1Geoff Spedding, 1Denise Galindo
1Department of Aerospace and Mechanical Engineering, University of
Southern California, Los Angeles, CA 90089
2Department of Mechanical and Aerospace Engineering, University of
California, Irvine, Irvine, CA 92697
3Department of Mechanical Engineering, University of California, Riverside,
Riverside, CA 92521
Abstract
Over the past decades, Unmanned Air Vehicles (UAVs) have become
popular within the industrial, military, and consumer community. The
ability to deliver packages to any location in the world by remote
access has created a number of significant benefits to these
communities. Typically, larger air vehicles have been used for
accomplishing these autonomous tasks due to the familiarity with its
aerodynamic characteristics: lift and drag. However, these
communities wish to make the vehicles more compact, while still
maintaining its aerodynamic performance. Creating smaller air
vehicles becomes advantageous to these communities due to its
increase in stealth and maneuverability. With smaller vehicles the
Reynolds numbers are smaller. Programs like XFLR5 have been
shown to give accurate estimates of aerodynamic characteristics, at
Reynolds numbers above 200,000. The objective of the project is to
investigate if XFLR5 can accurately predict aerodynamic
characteristics of a standard airfoil (NACA0010) at Reynolds numbers
lower than 200,000. This investigation will be supported with airfoil
testing in the Biegler Hall of Engineering wind tunnel. If the results in
the wind tunnel are similar to the results in XFLR5, then XFLR5 can
be used as a resourceful technique in designing and manufacturing
efficient airfoils and Micro Air Vehicles (MAV). If this were not the case,
then adjustments on XFLR5’s parameters would have to be made in
order to obtain similar results to those of the wind tunnel.
Characterization of the Test Flow
Boundary Layer Thickness for 30m/s
T: Laminar = 0.412cm, Turbulent = 2.62cm
Boundary Layer Thickness for 5m/s
T: Laminar = 1.01cm, Turbulent = 3.38cm
Momentum Deficit
Results
Re = 40k Re = 180kRe = 100k
Re = 40k Re = 180kRe = 100k
Laminar Separation Bubbles (LSB)
-4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10
,
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
CL
Wind Tunnel
XFLR5
Conclusions
Ø XFLR5 can effectively predict:
• Aerodynamic trends
• Demonstrates development of LSB
• Ability to locate stall angle
Ø The aerodynamic characteristics for lift are not
accurately calculated by XFLR5, so a correction factor
of 0.75 must be applied to match experimental results.
-4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10
,
-0.5
-0.4
-0.3
-0.2
-0.1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
CL
XFLR5
Wind Tunnel
-4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10 11
,
-0.3
-0.2
-0.1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
CL
Wind Tunnel
XFLR5
Re = 40k Re = 100k
Re = 180k
Ø Therefore, XFLR5 can be
used to predict
aerodynamic
characteristics of the
NACA0010 airfoil for Re
between 40k to 180k.
XFLR5
XFLR5 is a computer program created by M. Drela, designed to
calculate the different aerodynamic characteristics of an airfoil, such
as lift and drag for different angles of attack and Re. To do this, XFLR5
divides the airfoil into a preset number of panels (e.g. 100) and solves
for the pressure for every individual panel. From the pressure, XFLR5
can extrapolate lift and drag forces, lift and drag coefficients, and
generate plots, such as CL vs α, CD vs α, or CL/CD vs α.
z
y
Hu H, Yang Z. An Experimental Study of the Laminar Flow Separation on
a Low-Reynolds-Number Airfoil. ASME. J. Fluids Eng. 2008;130(5):
051101-051101-11. doi:10.1115/1.2907416.
"2D Boundary Layer Modelling | Aerodynamics for Students."
Aerodynamics for Students. N.p., n.d. Web.