Overset Module

Cobalt's Overset module allows the use of multiple grids in the same simulation.  The grids are assembled (hole-cuts calculated and donor/receptor pairs determined) automatically within the Overset module so that the grids act as a grid system.  Each grid can move independently to create relative motion between the grids to simulate cases such as store separation, aircraft take-off and landing, and control surface movement. The Overset module requires additional licensing. A new Overset module was introduced in Cobalt v7.0

Improved Hole-Cut

In Cobalt v7.0, the hole-cut interface is calculated to lie midway between non-cuttable boundaries of overset grids or all the way to the fringe boundary - whichever is closer.   This creates a fairly smooth hole-cut boundary.  This methodology can handle tiny gaps, such as those between control surfaces, well.  Since the user can estimate where the hole-cut boundary is going to be, matching grid resolution between the overset grids is easier than the previous Overset module.

Improved Efficiency

The improved efficiency provides a reduction in the overall solution time using the new versus previous Overset module. For the wing/aileron/flap configuration with an oscillating aileron, the overall time to set-up the flow (500 iterations) was reduced by 58% on 512 processors. This is one particular case.  Other cases have shown similar speed-up. Timing depends on individual case specifics and will vary.

Wing/Aileron/Flap Set-Up Cobalt v6.0 Cobalt v7.0
Iterations 500 500
Grid Assembly 71.9 13.686
Flow Solution Rate 22.618 sec/time-step 8.996 sec/time-step
Post-Processing (end of job) 74.445 38.495
Total 12047.6 5078.15

For the aileron oscillating portion, time per iteration (flow solution + grid assembly + aileron movement) was reduced 90%.  This time will vary according to how many grids are in motion, g number of cells in the grids, etc. Post-processing time was also reduced – an important time-savings when requesting flow visualization during a  time-accurate run.

Wing/Aileron/Flap (Aileron Oscillating) Cobalt v6.0 Cobalt v7.0
Iterations 100 100
Grid Assembly 73.92 8.417
Flow Solution Rate 161.172 sec/time-step 15.751 sec/time-step
Post-Processing (every 10 iteration) 811.118 433.838
Total 17610.7 2612.9