Microjet Angle Sensitivity for Active Flow Control on Multi-Element High-Lift Systems

This paper concerns the modeling and analysis of angled active flow control microjets using Computational Fluid Dynamics (CFD). Two geometries are considered: a 2D NLR7301 two-element airfoil with 20 flap deflection, and a 3D Common Research Model in a high lift configuration (CRM-HL) with inboard and outboard flaps deflected 40 and 37, respectively. An overset grid system representing the NLR7301 is generated and microjets with a width of 0.5% of the wing chord are placed on the pressure and suction sides of the NLR flap at 95% of the flap chord. A code-to-code comparison against published CFD solutions is presented for a normal-blowing pressure-side jet for momentum coecient range of 0.0004 < Cµ < 0.04. A case matrix is then run for the same range of Cµ values over a range of jet angles ✓ (30 o↵ the flap surface upstream of the microjet to 30 o↵ the downstream flap surface), and the trends are discussed. Subsequently, a jet trade-o↵ study is then performed for the NLR7301 in which pressure-side normal and suction-side tangent jets are compared individually and in tandem. The overset grid system representing the CRM-HL geometry is borrowed from the LAVA entry of the 4th AIAA High Lift Prediction Workshop (HLPW4). Microjets with a width of 0.5% of the mean aerodynamic chord are implemented on the inboard flap at 95% and 4.75% of the flap chord on the pressure and suction sides, respectively. Jet-o↵ solutions are shown to match those reported in the HLPW4, after which two studies are performed: a single pressure-side jet angle sweep is performed for a Cµ of 0.00278, and a pressure-suction jet trade-o↵ study similar to that performed for the NLR7301. Findings indicate that for system analysis-relevant Cµ values, there exists a range of microjet angles local to normal-blowing for which optimal induced aerodynamic coecient deltas remain e↵ectively constant. For the 2D NLR7301 drag is significantly influenced by jet momentum, while for the 3D CRM-HL pressure drag changes overshadows it. When comparing pressure-side normal-blowing and suction-side tangentblowing jets, both normal, tangent, and tandem blowing increases lift as long as the tandem jets are strong enough. Drag is reduced for all NLR7301 jet configurations of the trade-o↵ study, while for the CRM-HL it is increased by normal blowing. All NLR7301 simulations presented were computed using the Unsteady Reynolds-averaged Navier-Stokes (URANS) equations, while the CRM-HL cases were computed using RANS.