![]() ![]() "Airfoil lift coefficient" is by far not the "wing lift coefficient". They were also used for the detection of compression shocks.By far more important for the highspeed behaviour and at least as important for the lift coefficient is the wingshape(aspect ratio, trapezium or squary, the form of the wingtips, swept wings etc). Aerodynamic forces and moments were calculated by a chordwise integration of the pressure distribution, obtained by 60 unsteady, temperature-compensated differential pressure sensors (Kulite XCQ-093D) mounted into the model (see Fig. The accuracy was less than \(0.02^\circ\). The pitch motion \(\varDelta \alpha (t)\) of the wind tunnel model was measured by four laser triangulators (Micro-Epsilon optoNCDT 1605 with LD 1605-20) pointing at target bars attached to the model. So also LCOs or flutter with high growth rates in amplitude could be observed and recorded directly. Safety systems such as brakes and a flutter control system, both attached to the flutter test rig, enable investigations of aeroelastic systems at the stability limit and even beyond. A sketch of the test setup is depicted in Fig. During the flutter tests, the mean angle of attack was preset to \(\alpha \approx 0^\circ\), so that flutter measurements were performed directly within the characteristic laminar drag bucket of the airfoil model (see Fig. In this way, the mean angle of attack \(\alpha\) was adjusted and kept constant during the measurements, hence changes of the angle of attack due to the elastic suspension and varying aerodynamic pitching moments under changed flow conditions could be compensated as well. The flutter test rig was integrated into the 2D support of the DNW–TWG, which enables rotation of the entire test rig including the wind tunnel model. The wind off eigenfrequency was 47.7 Hz, the corresponding damping coefficient was \(D_\alpha \approx 0.39\) %. The relevant mass moment of inertia of all oscillating components including the wind tunnel model was \(I_\alpha \approx 0.065\) m \(\times\) s \(^2\), related to c/4. The model was thus able to perform self-excited pitching oscillations around c/4. In the present results, the heave springs were mechanically locked so that an aeroelastic system with a single experimentally specified degree of freedom was provided. This allows the airfoil model to perform motions with the two degrees of freedom heave and pitch. The test rig consists of two spring systems (each built up from two plate springs and a torsion spring), one on each side of the wind tunnel walls. The model was made of carbon fiber composites in shell construction and connected to the experimental test rig via two aluminium bases at \(x/c=0.25\). 2.1 Flutter experimentĪ CAST 10-2 laminar airfoil model with a chord length of \(c=0.3\) m and a span of \(s=0.997\) m was elastically mounted into a flutter test rig, which was previously used by Dietz et al. The measurements were performed in a Mach number range of 0.5 \(\le\) Ma \(\le\) 0.8 and a variable total pressure \(p_0\) between 40 and 75 kPa, resulting in a chord-based Reynolds number of \(1.15\times 10^6 \le\) Re \(\le 2.83\times 10^6\). By means of a two-dimensional adaptation of the upper and lower tunnel walls to the steady flow field, wall-induced perturbations were minimized. The measurements were performed in the adaptive test section of the DNW–TWG. The presented results were obtained by a 2D flutter experiment on a CAST 10-2 supercritical laminar airfoil model, carried out in the Transonic Wind Tunnel Goettingen (DNW–TWG). In addition, a relation between the motion of the model and that of the boundary layer transition for transonic flow conditions is quantified here for the first time. The laminar airfoil model was elastically mounted with a single degree of freedom in pitch and performed self-excited limit cycle oscillations at a Mach number of \(\approx 2\times 10^6\). The data basis is a 2D flutter experiment under transonic flow conditions. The unsteady boundary layer behavior of a supercritical laminar airfoil model, which undergoes limit cycle oscillations in pitch, is investigated by the application of hot-film anemometry. ![]()
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