Dynamic testing in wind tunnels is aimed at collecting unsteady
aerodynamic values like forces, surface pressures, velocities, and flow
field data. The reasons might be split into four categories:
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Moving models (e.g. maneuvering aircraft) and vehicle components (e.g. propellers, rotors, flaps)
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Structural deformations due to aerodynamic loads (e.g. flutter or limit cycle oscillation)
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Unsteady incoming flow (e.g. gusts)
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Unsteady flow phenomena even at rigid and fixed models (e.g. flow separation, vortex bursting)
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DNW operates a number of tunnel-specific dynamic test beds and the
corresponding common measurement techniques and data acquisition
systems. Based on these experiences dynamic experiments are performed
in several DNW tunnels.
The NWB operates two different dynamic model support systems:
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The
rotary motion support enables the model to perform a continuous rolling
and spinning motion about the wind axis. The angle of attack and the
angle of sideslip can be adjusted independently up to very high values.
The maximum rotation speed is 300 RPM (= 5 Hz). Typical applications
are force and moment measurements on fighter aircraft configurations to
obtain lateral dynamic derivatives.
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The Model Positioning System ( MPM)
was developed by DNW and utilizes a six-degree-of-freedom test rig that
can oscillate a model around its body axis or create combined motions
to simulate realistic flight maneuvers. Typical applications of dynamic
tests incorporating the MPM are force measurements on transport
aircraft for determination of dynamic derivatives, as well as transient
maneuvers with or without ground effect. |
For dynamic trans- and supersonic tests at the TWG two categories of supports are frequently used:
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Different
dynamic rear sting supports for 3D models are available for the TWG.
They are used for fast forced and free roll motions (continuous,
oscillating, and controlled transition). The test set up is used for
the analysis of flow phenomena, validation, and data sets of generic
configurations and advanced missiles at moderate to high angles of
attack. A forced pitch support is under development.
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The
DLR operates dynamic pitch and heave rigs for 2D and half models,
specially designed for the TWG. The unsteady tests include flutter and
limit cycle oscillation as well as structure to flow interaction.
Models might rigid or dynamically scaled; integration of flexible and
actively controlled components (e.g. flaps or nacelles) is state of the
art. The experiments cover fundamental research, including validation,
as well as development tests for industrial projects (e.g. helicopter
blades or wing to nacelle interference).
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In addition to the classical dynamic measurement techniques
(pressure, forces) advanced optical surface and flow field methods
(e.g.
PSP or
PIV)
for dynamic measurement are in development and on their way to regular
application. Dynamic derivative balances have been used in the past and
can be reactivated on demand. All these are complemented by the
available dynamic data acquisition capabilities.