OS-V: 1305 Flutter Analysis of a Generic Transport Aircraft Model

Flutter analysis of a Generic Transport Aircraft (GTA) model is performed using the KE method.

The results are validated against a publication from the AIAA Journal1.

Model Files

Before you begin, copy the file(s) used in this problem to your working directory.

Benchmark Model



Figure 1. GTA Model
Dimension details of the model:
Dimension
Value (mm)
Wing Span
19000
Uniform Chord Length
2200
Length of Aircraft
22000
Height of Aircraft
6000
The model is symmetric about the X-Z plane and the structural domain consists of a stick model with CBAR and CELAS2 elements. Flutter analysis is performed for a Mach number of 0.3, density ratio of 1.0, and equally spaced reduced frequencies in the range [0.50, 1.50] Hz. Unit of output velocity is defined in knots using PARAM, VREF.

Results

From the .flt file, the flutter point (where damping changes sign) corresponding to the lowest mode is identified as the 7th mode (flutter point A) with a velocity between 308.698 knots to 343.006 knots.
Note: By definition, instability (flutter or divergence) occurs when the damping values are zero. At this point, if the frequency is zero, then the instability is due to divergence. Otherwise, the instability is due to flutter.


Figure 2. Flutter Analysis Summary from the .flt File
Plotting the v-g curve, the velocity at this flutter point is 327.668 knots. This is the most critical flutter point that needs to be avoided.


Figure 3. Identify Flutter Points. The flutter point corresponding to the lowest velocity is also visually identified.


Figure 4. Identify Frequency Value at the Critical Flutter Point from the v-f Curve.
Plotting the v-f plot for the 7th mode (corresponding to the critical flutter point), the frequency value for 7th mode at a velocity of 327.668 knots is determined as 13.334 Hz.
Flutter Speed
Value
Reference1
Approximately 300 knots
OptiStruct
327.668 knots
The results from the OptiStruct flutter analysis are verified.
Note: The slight difference in flutter speed may be attributed to:
  • Uncertainties in the model. The precise geometry, damping, and other data used in the reference are not known and may differ from what was used in OptiStruct1.
  • The order approximation for the DLM kernel. The order used in the reference is not known and may differ from what was used in OptiStruct1.

Reference

1 M. Karpel, A. Shousterman, C. Maderuelo, and H. Climent,“Dynamic Aeroservoelastic Response with Nonlinear Structural Elements,” in AIAA Journal, 2015, vol. 52, no. 11, pp. 3233–3239. doi: 10.2514/1.J053550.