ZEUS Information

• ZEUS is an ZONA’s Euler Unsteady aerodynamic solver to provide aeroelastic solutions for complex configurations.
• It uses Cartesian grid and employs boundary layer coupling.
• Cell-centered finite volume method using Jameson’s artificial dissipation scheme.
• Dual-time stepping algorithm for unsteady solution.
• Automated mesh generation scheme that requires only the surface mesh for input.
• Overset grid capability for complex configuration.
• Includes ZAERO's 3D spline module and Nastran modal solution importer.
• Multi-grid acceleration for fast solution convergence.
• Generates either time-domain aeroelastic responses or frequency-domain generalized aerodynamic forces for flutter, LCO, and static/trim aeroelastic analysis.

• Because ZEUS solves the Euler’s equation with a small disturbance boundary condition, all required geometric information existing in ZAERO is sufficient for ZEUS input.
• ZEUS mesh is generated by an automated mesh generation scheme.
• Fuselage, wing, horizontal tail, vertical tail, launcher and pylons can be fitted into a single block of mesh.
• Tip missile with fins and under wing stores can be fitted into other blocks of mesh, respectively.
• Communication between blocks of mesh is accomplished through the overset grid scheme.
• Each block of mesh is automatically generated by a Y-Zone technique.
• 95% of the input for ZEUS is identical to that of ZAERO.
  

All components within each block are projected on an X-Y plane. On this X-Y plane, all components are divided into several spanwise zones, called the Y-Zones. The Y-Zone technique can automatically generate the mesh by a line-tracing method that spans across all Y-Zones. An example of division of an aircraft model into spanwise zones is shown at right with descriptions of each zone listed below.

ZONE 1: Left launcher
ZONE 2: Outboard left wing
ZONE 3: Inboard left wing and outboard left horizontal tail
ZONE 4: Outboard left strake and inboard left horizontal tail
ZONE 5: Inboard left strake
ZONE 6: Fuselage
ZONE 7: Inboard right strake
ZONE 8: Outboard right strake and inboard right horizontal tail
ZONE 9: Inboard right wing and outboard right horizontal tail
ZONE 10: Outboard right wing
ZONE 11: Right launcher

• Complex configurations can be modeled by multiple blocks of mesh with over-lapping regions; the overset mesh.
• Communication of flow solutions among blocks is through the interpolation of solutions in the overlapping regions.
• Solution convergence is acheived by sub-iterations.

• Thin Plate Spline
• Infinite Plate Spline
• Beam Spline
• Rigid Body Attachment methods

Displacement of ZEUS Panel Model Splined to FEM Model

• Nine blocks of overset meshes to model the missile body and eight wrap-around fins
• Block 1: Missile Body
• Blocks 2-9: Eight wrap-around fins
• CPU time for each angle of attack case is approximately 10 minutes with one CPU

• M=0.822, α=0.6°
• Aspect Ratio: 7.92
• Taper Ratio: 0.4
• Swept Angle: 25°
• Twist from root to tip: 2.6° ~ -2.0°
• Supercritical Airfoil with max t/c = 12%
• Pitch mode at reduced frequency = 0.102

5 Blocks

• Block 1: Aircraft, 133x78x69
• Block 2: Trail, 55x26x50
• Block 3: Canard, 75x21x61
• Block 4: Inbord Engine, 73x24x36
• Block 5: Outboard Engine, 69x23x41

• Interactive process for solving the trim variables such as α, β, p, q, and r as well as aircraft accelerations.
• Capable of dealing with dertermined trim system as well as over-determined trim system
  (more unknown trim variables than trim equations).
• Generation of flight loadsand output of NASTRAN FORCE and MOMENT bulk data cards for subsequent detailed stress analysis.

• Capable of generating frequency-domain generalized aerodynamic forces and computing flutter boundaries using the g-method.
• Transient response analysis for LCO predictions.

• Flutter model was tested in NASA Langley Transonic Dynamic Tunnel (TDT) with heavy gas.
• Between M=0.77 to 0.82, two flutter modes were found; the Wing/Nacelle mode (17Hz) and the wing tip (22Hz).
• The Wing/Nacelle mode has low unstable damping (hump mode).
• Dynamic pressure can be continuosly increased without damaging the model until encountering the wing tip flutter mode.
• Beyond M=0.82, the unstable damping of the Wing/Nacelle becomes high which can lead to the destruction of the wing due to flutter. For this reason, the wing-tip flutter mode condition cannot be reached.

• 12 natural modes are included in the flutter analysis.
• The infinite plate spline method (for the wing and pylon) and thin plate spline method (for the fuselage and Nacelle) are used to transfer the modes from the structural grid to the aerodynamic grid.

• The 17Hz hump mode predicted by ZEUS correlates with the low unstable damping of the Wing/Nacelle mode observed in the TDT.
• The flutter boundary of wing-tip mode predicted by ZEUS agrees well with TDT data while ZAERO linear aerodynamics largely
  over-predict the flutter boundary.