3. Summary of CFD Workshop
In recent days, CFD is one of the powerful tool for the prediction of the aerodynamic characteristics. Especially, due to the effort of the enhanced computing power, CFD works for the aircraft design takes larger proportion than the past.
In this chapter, I want to review series of the papers related to the CFD workshops predicting exact aerodynamic value of the generic airliner aircraft, minimum drag and high lift. Those workshops showed edge of the CFD technology because 'Top-end' of the CFD's like NASA, Boeing, DLR, JAXA, and other academic contributors participated.
Purpose of the drag work shop is enhancement of the CFD prediction capability for the airliners which is very sensitive for the drag due to the fuel economy. Quality of the CFD can be varied by mesh, turbulence model, solver, and others. After few drag-prediction-workshops, workshops for high-lift prediction was held which represents complex geometry of slat and flap in high AoA. Additional mesh work shop was also held for both geometries of drag and high-lift ones.
3.1. Drag Work shop
3.1.1. Case & Geometry
Among the three workshops, drag, high-lift, and mesh, it is the oldest and longest workshop. Drag prediction is one of the most important task to determine economy of the aircraft. Indeed, the target of the CFD condition is narrower than others (only considering cruise condition) however, accuracy requirement is much severe than the others.
Progress of the workshop took long time to generate full-model of the aircraft as shown in the Fig. 1; 1st case only describe the body and the main-wing while the 2nd had added effect of engine and its pylon. The 3rd workshop combine the effect of bump between wing and fuselage; most of the airliner has that kind of fairings for the purpose of landing gear integration, structural bulkhead, and aerodynamic continuity. 4th, 5th, and 6th workshops fully described the airliner OML via addition of horizontal tails. Fig. 2 shows summary of the workshops from 1st to 5th briefly, and I re-organized case-summary in Table 1.
Fig. 1. Generic airliner model progress during the workshop
Fig. 2. Case expansion during Drag-prediction workshops
Table 1. Re-summary of Drag-prediction workshop cases
Below table 1 summarizes cases of the workshops through 1st to 6th ones. The first workshop attempted estimate drag of the simple body in cruise condition of M 0.75 w/ CL = 0.5 while AoA variation and Mach number changes occurs as optional cases. As described in the previous paragraph, Engine nacelle is added to depict the aircraft in more realistic manner while boundary layer trip effect is investigated in the second workshop. The third workshop now regard the effect of the body-fairing in between wing and fuselage while grid convergence of the same cases are studied to show effect of the grid size.
The fourth workshop had considered the effect of the downwash generated by the main-wing on the horizontal tail. Also, Mach sweep and impact of Reynolds number effect are shown for better precision which is important for the skin-friction and transition of the laminar-turbulent flow. The fifth one compare the turbulence model performance via validation cases of flat plate, bump, and standard NACA0012 airfoil in the low Mach number. Buffet phenomena is also studied in M 0.85 condition. The sixth workshop remarkably conducted aero-elastic for both static and coupled method in M 0.85 condition, and effectiveness of the grid adaption technique is shown.
From now on, I will review the workshops to edge of the CFD technique for aircraft drag.
