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
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.
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|
|Flow Solution Rate||22.618 sec/time-step||8.996 sec/time-step|
|Post-Processing (end of job)||74.445||38.495|
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|
|Flow Solution Rate||161.172 sec/time-step||15.751 sec/time-step|
|Post-Processing (every 10 iteration)||811.118||433.838|