Aerodynamic

The validation of the overall drag balance of winglet designs is not trivial. While the induced drag obeys the potential theory without restriction, the strongly three-dimensional viscous flow, especially in the transition region, is difficult to capture with simple means such as two-dimensional airfoil calculations (e.g. XFOIL). In an experimental investigation in the wind tunnel, a scaled-down model leads to very small (subcritical) Reynolds numbers in the interesting area of the wing tip; on the other hand, a restriction to the outer area on a large scale is problematic due to the changed effect on the total span. It will therefore be investigated to what extent the latter approach represents a feasible approach.

In a first step, a wing of large aspect ratio without and with winglet is to be calculated by means of a multiple hydrofoil method. Subsequently, a half-model approach is to be used to determine a version that is greatly shortened from the inside and has a lift distribution over the remaining span that is as equal as possible. In the second step, a model of the shortened configuration is to be built and measured in the wind tunnel, whereby mainly the viscous drag is to be determined by means of wake measurement and compared with the above-mentioned profile calculations in level flow. Finally, the overall drag balance of the complete wing without and with winglets is to be determined.

Contact person

© M. Kretschmar

Research Assistant

Name

Dipl.-Ing. Jürgen Frey

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Contact Information

Organization Name

Chair of Flight Mechanics and Control

Chair of Flight Mechanics and Control

Address work

Visiting address:

WIK Windkanal, Room 10 Marschnerstraße 28

01307 Dresden

work Tel.

fax Fax

+49 351 463-38187

In modern spinning machines, the yarns reach speeds at which they are exposed to gas-dynamic effects. Nevertheless, thin fibers move at very low, subcritical Reynolds numbers. In addition, the surface exhibits significant roughness, so that the contour can deviate greatly from an idealized cylindrical shape. As the strength of the yarns during spinning is still very limited, the aerodynamic forces are still of interest.

Preliminary tests on cylinders and ropes from 1 mm in diameter at low speed show that their resistance can be determined relatively reliably on the basis of the wake dent. In the case of yarns, the diameter is an order of magnitude smaller. In addition to measuring the wake on the original with the finest possible resolution, it is also conceivable to examine an enlarged model with increased kinematic viscosity. The flow channel for diluted gases provides a suitable test facility for this purpose.

The tasks include:

• Trailing measurement with fish mouth probe or hot wire
• Correction of Barker effect and compressibility
• Comparative measurements with reduced density
• Simulation of the surface on an enlarged model
• Comparison of wake and force measurement