Applied Computational Fluid Dynamics
Farhad Ghaffari, Principal Investigator
Co-investigators: Brent L. Bates and James M. Luckring
NASA Langley Research Center/ViGYAN, Inc.
Research Objective
To assess the vortical-flow prediction capability
of the state-of-the-art unstructured-grid methodology for a complex generic
fighter wind tunnel model over a wide range of flow conditions.
Approach
The analytical description of a generic fighter wind
tunnel model, known as modular transonic vortex interaction (MTVI), was used
to generate the geometrical database from which the computational surface
grid definition was derived for the entire geometry. The MTVI configuration
incorporated a 60-degree sharp-edged cropped delta wing with segmented leading-edge
flaps, chine-shaped fuselage, and twin vertical tails positioned on the aft-inboard
region of the wings. The complete geometry was represented by about 28,000
surface triangles. The flow-field grid, generated using an advancing front
method, consisted of about 825,000 tetrahedral cells. The grid spacing, distribution,
and the extent of the far-field boundaries were consistent with an earlier
calibration study performed on the isolated MTVI fuselage configuration.
Since the subject vortical flow (emanating from sharp edges) is presumed
to be mostly governed by inviscid flow phenomena, the present computational
effort was performed based on an Euler formulation.
Accomplishment Description
Computational results were obtained
for the MTVI configuration for a wide range of flow conditions using the
flow solver USM3D. A typical solution obtained at 22 degrees angle of attack
and a Mach number of 0.4 and superimposed over the computational surface
grid is shown in the figure. The figure illustrates the total-pressure contours
at several cross-flow planes along with the particle tracings within the
core region for both primary vortex systems (one emanating from the chine
forebody and the other from the wing leading-edge flaps). The figure clearly
shows the geometric complexity, in particular the deflected wing leading-edge
flaps (two inboard segments deflected at 30 degrees), and the predicted vortical-flow
structures. This solution, initiated from the free-stream flow conditions,
was advanced for 2,000 iterations during which the total residuals dropped
about 1.5 orders of magnitude. The solution required approximately 150 megawords
of memory and used about 10 hours of computational time on Cray Y-MP. Additional
analysis has shown that the computed surface pressure coefficients, forces,
and moments agree reasonably well with the measured experimental wind tunnel
data.
Significance
The present unstructured-grid methodology provides
reasonable flow predictions. The versatility of the methodology in grid generation
for complex geometries makes it an efficient technique for routine analysis
applications.
Future Plans
Computations will be extended to parametrically
investigate the aerodynamic effects for various geometrical modifications
such as the fuselage chine shapes, tail arrangements, and wing leading-edge
flap deflections.
Keywords
Euler computations, Fighter configuration, High angle of attack, Vortex flows
Publication
Ghaffari, F.: On the Vortical-Flow Prediction Capability of an Unstructured-Grid Euler Solver. AIAA Paper 94-0163, Jan. 1994.
Total-pressure contours in various cross-flow planes and vortex core
particle traces; alpha = 22 degrees and free-stream Mach number = 0.4.
