Designing Active Flow Control Actuators for High-Lift Wing Configurations

Overview

NASA’s Advanced Air Transportation Technology (AATT) Project is examining various approaches to reduce the cruise drag and fuel burn associated with modern high-lift aircraft designs without sacrificing aerodynamic performance during takeoff and landing. One possible approach to solving this problem is to use an active flow control (AFC) system that could provide the required lift when needed, while reducing the possible cruise drag associated with external mechanisms used to deploy a conventional slotted (Fowler) wing flap during high-lift flight. A system integration study conducted by Boeing¹ indicated that a fuel burn reduction of up to 2.25% is possible if an AFC-enabled simple hinged flap system could provide the necessary lift recovery during the landing approach. The AFC-related performance gains are due to drag reduction from the removal of the external fairings needed for the Fowler flap mechanism. The main challenge of this work is to develop an AFC system that can provide the necessary lift recovery for a simple hinged flap while using minimal pneumatic power.

Project Details

A joint multi-year computational and experimental study at NASA’s Langley Research Center was conducted to design and test two high-lift configurations of the Common Research Model (CRM). An AFC-enabled simple-hinged flap configuration (CRM-SHL-AFC) was developed to produce a lift coefficient comparable to a conventional high-lift configuration (CRM-HL). Using numerical solutions generated by the Lattice-Boltzmann-based flow solver PowerFlow, the team examined the effect of geometric size and placement of rows of sweeping jet and steady blowing jet actuators in order to assess the lift augmentation potential of different actuator arrangements. These parametric studies were used to identify the most promising AFC configurations for physical wind tunnel testing.

Results and Impact

"High fidelity time-accurate simulations for complex aircraft wing configurations consisting of hundreds of tiny actuators require substantial computing resources available only on high-performance computing systems, such as the ones at the NASA Advanced Supercomputing (NAS) facility at NASA’s Ames Research Center."

Numerical solutions were obtained for both the conventional and AFC-enabled CRM high-lift configurations over a broad angle of attack range, including maximum lift conditions. The predictions for lift augmentation with variation in actuation levels were verified by the wind tunnel test data. A combination of sweeping jets and steady blowing jets on the CRM-SHL-AFC configuration was shown to match or exceed the lift coefficient of the conventional CRM-HL configuration over a broad angle of attack range, using actuation with a nozzle pressure ratio (NPR) of 2.41. Examination of surface and off-surface flow fields demonstrated that AFC enhances lift by reducing the reverse flow regions on highly deflected simple-hinged flaps. While the entire upper surface of the flap was separated in the absence of actuation at a 16-degree angle of attack, using an AFC with an NPR of 2.41 significantly reduced the reversed flow regions, resulting in higher lift. The results of this work clearly demonstrate the usefulness of the current computational fluid dynamics tools and methodology for conducting parametric studies on complex, high-lift aircraft wing configurations using embedded AFC actuators, as well as helping the design process of future aircraft configurations prior to conducting expensive experimental work.

Why HPC Matters

High fidelity time-accurate simulations for complex aircraft wing configurations consisting of hundreds of tiny actuators require substantial computing resources available only on high-performance computing systems, such as the ones at the NASA Advanced Supercomputing (NAS) facility at NASA’s Ames Research Center. A large number of simulations were required to conduct the parametric studies completed for this project. For example, a typical medium resolution grid case running on 2,520 Intel Xeon Skylake cores of the Electra supercomputer required approximately 240 hours of wallclock time, or 600,000 processor-hours to complete.

What's Next

As work continues, the team plans to repeat some of the CRM-SHL-AFC configuration simulations at finer grids, which will require a much larger amount of compute hours for each given case. These simulations are required to quantitatively assess any numerical errors in in the computational model. In addition, several new configurations are under consideration during the next year as part of the overall project, and substantial compute resources will be required to meet these project goals.

Related Links

• CFD and Experimental Data Comparisons for Conventional and AFC-Enabled CRM High-Lift Configurations
• Wind Tunnel Testing of High Efficiency Low Pressure (HELP) Actuation for Active Flow Control
• [1] System-Level Trade Studies for Transonic Transports with Active Flow Control (AFC) Enhanced High-Lift Systems