Bio-Inspired Airfoil for Turbulent Flow

A nine-step flowchart of the planned CFD process, from generating the airfoil CAD and meshing it, through boundary conditions and running ANSYS Fluent with the Transition SST model, to exporting lift and drag coefficients and flow contours. — The planned CFD workflow, from CAD and meshing to lift and drag results in ANSYS Fluent.

The idea

Humpback whales have rows of bumps, called tubercles, along the front edge of their flippers. Studies have shown that similar bumps on a wing can create small vortices that keep air attached to the surface for longer, which can raise lift and delay stall. That makes them interesting as a passive flow control device: no moving parts and no power needed.

The gap

Almost all of that research was done in smooth, steady, low-speed flow. Real aircraft fly through turbulence, and the published results disagree on how much tubercles help with drag and efficiency. Very few studies check computer simulations against wind tunnel measurements under turbulent conditions.

What we proposed

The proposal compares a smooth NACA 0012 wing with versions that have sinusoidal leading-edge tubercles, varying the bump size and spacing, the angle of attack and the flow conditions, and measuring lift, drag and stall angle.

CFD first. The wings would be modelled in SolidWorks and simulated in ANSYS Fluent, with a mesh independence study and the baseline wing checked against published data before any tubercle results are trusted.
Wind tunnel second. 3D-printed wings would be tested in a low-speed wind tunnel with a six-component force balance and pressure measurements, first in smooth flow to validate the CFD, then with screens added to create turbulence.
Statistics. Repeated runs at each angle, uncertainty estimates, and significance testing with confidence intervals, so any improvement can be told apart from noise.

Why it matters

If tubercles hold up in turbulent air, they could make aircraft and drones more efficient and more forgiving near stall, with the same idea carrying over to wind turbine blades and propellers.

Status

This is a research proposal. The study has not been run, so there are no measured results yet. The lift and drag charts below are the trends we expect, predicted from earlier published work: a stall delayed from about 12° to 15°, and more lift and less drag after stall.

An eight-step flowchart of the planned wind tunnel test, from activating the tunnel and installing and calibrating instrumentation, through mounting the wing and collecting data, to comparing results with the baseline and the CFD model. — The planned wind tunnel procedure, used to check the CFD results against measurements.

Chart titled Anticipated Lift Coefficient vs. Angle of Attack. The smooth baseline wing (solid blue) peaks near 1.45 at about 12 degrees and then drops sharply; the tubercle wing (dashed red) peaks near 1.6 at about 15 degrees and then falls off gradually, keeping more lift at high angles. — Predicted lift: the tubercle wing is expected to stall later, near 15° instead of 12°, and keep more lift after stall. A predicted trend from the proposal, not a measurement.

Chart titled Anticipated Drag Coefficient vs. Angle of Attack. Both wings have similar low drag up to about 15 degrees; beyond that, drag for the smooth wing (solid blue) rises steeply to about 1.5 at 30 degrees, while the tubercle wing (dashed red) rises to about 0.65. — Predicted drag: about the same before stall, and much lower for the tubercle wing past stall. A predicted trend from the proposal, not a measurement.

Chart titled Lift Coefficient, CFD Prediction vs. Wind Tunnel, for the tubercle wing. A solid blue CFD curve and red wind-tunnel points with error bars follow the same shape, with the points slightly lower and dropping off faster above 20 degrees. — The expected agreement between CFD and wind tunnel lift for the tubercle wing. Both curves are predictions; the wind tunnel test has not been run.

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