Multi-element High-lift System Research Articles

High-Lift Computational Strategy for Slotted, Natural-Laminar-Flow Airfoils

This work uses a computational fluid dynamics approach to evaluate the ability of the aft element of a slotted, natural-laminar-flow airfoil, designed for transonic applications, to function as a high-lift device. The analysis is based on the Reynolds-averaged Navier–Stokes equations with a laminar–turbulent transition model for subsonic flow at representative flight conditions and a fully turbulent model for the aft-element optimization. Results obtained at angles of attack near maximum lift contribute to the understanding of stall characteristics and show that maximum aerodynamic efficiency is obtained with a constant slot width between the flap and main element. Results indicate that the microflap can augment the effectiveness of the aft element. Drag calculations when compared with angle of attack and lift show insight on the aerodynamic efficiency of the microflap system in landing as a lift effector, as well as a drag device. Pitching-moment data are also presented for completeness. Results obtained with Fowler flaps are consistent with other studies of extended-flap configurations; more specifically, the aforementioned velocity ratio decreases toward the aft-element trailing edge, indicating that the multi-element high-lift system is operating as intended.

Microjet Configuration Sensitivities for Active Flow Control on Multi-Element High-Lift Systems

Various characteristics of small surface-normal jets (microjets) located on a flap’s pressure-side near the trailing edge are investigated as an active aerodynamic load control technology for multi-element high-lift systems. Two-dimensional computational studies are carried out to investigate the sensitivity of microjet aerodynamic effectiveness to configuration. Initially, the effects of microjet location and width are explored. The study shows that lift enhancement decreases as the microjet is moved forward from the trailing edge, and that wider microjets are more effective in lift enhancement and drag reduction, whereas thinner microjets are more efficient. Microjet exit velocity profile effect on the integrated forces is also studied, and the effects are shown to be insignificant. To gain preliminary insight of the microjet system requirements, several plenum configurations are studied, and a preliminary analysis of the power requirements to supply the air mass flow is presented. Next, the study is extended to a geometry with moderate trailing edge separation to demonstrate microjet’s separation mitigation capability. To gain better understanding of the system requirements, pulsed versus continuous microjets are examined, and it is found that pulsed blowing causes a breakdown of the favorable effect of the microjet on the trailing edge flow and therefore reduces the circulation control effectiveness of the microjet.

Towards the Design of Synthetic-jet Actuators for Full-scale Flight Conditions

Due to the large parameter space that is involved in the design of synthetic-jet actuators used for flow separation control, it is essential to develop low-dimensional models for actuator-performance prediction and establish the conditions for design optimisation so that candidate actuators can be identified at the initial design stage. In Part 2 of this paper, three low-dimensional models that are capable of predicting actuator performance for synthetic jet actuators of different scales are described. Using these models the parametric relationships required for optimising the actuator performance are established. Finally, based on a better understanding of the fluid mechanics of synthetic jets (described in Part 1) and the improved modelling capacity, a methodology for designing synthetic-jet actuators used for flow separation control at full-scale flight conditions is developed. This methodology is illustrated in the design of actuators for delaying flow separation on the leading and trailing edge devices of a multi-element high-lift system of a typical commercial-aircraft wing at take-off conditions.

In-Flight Boundary-Layer State Measurements on a High-Lift System: Main Element and Flap

Flight experiments on NASA Langley Research Center’ s B737-100 airplane were conducted to document e ow characteristics for further understanding of the e ow physics on multielement high-lift systems. The measurements presented in this paper show that signie cant regions of laminar e ow exist on the main element and the foree ap of the airplane. Flow mechanisms that affect the extent of laminar e ow include relaminarization of the e ow in the leading-edge region of the main element and contamination of the laminar e ow on the e ap by turbulent shear layers emanating from upstream elements. This information should be valuable in the development and assessment of high-Reynolds-number wind-tunnel experiments and numerical models for predicting the e ows around multielement wings at full-scale high-lift conditions.

High-lift design optimization using Navier-Stokes equations

This article presents a design optimization method for maximizing lift without increasing the drag of multielement airfoils at takeoff and landing configurations. It uses an incompressible Navier-Stokes flow solver (INS2D), a chimera overlaid grid system (PEGSUS), and a constrained numerical optimizer (DOT). Aerodynamic sensitivity derivatives are obtained using finite differencing. The method is first validated with single-element airfoil designs and then applied to three-element airfoil designs. Reliable design results are obtained at reasonable costs. Results demonstrate that numerical optimization can be an attractive design tool for the development of multielement high-lift systems.

The NASA B737-100 high-lift flight research programme — measurements and computations

AbstractThe aerodynamic performance of a multi-element high-lift system has a critical influence on the direct operating cost of a subsonic civil transport aircraft. A thorough understanding of the aerodynamic characteristics of these multi-element aerofoils and wings allows aircraft companies to design and build more competitive aircraft with high-lift systems that are less complex and lighter for given high-lift performance or that have improved lift and drag characteristics for given system complexity and weight. Flight experiments on NASA Langley's B737-100 aircraft have been conducted to further enhance the understanding of the complex flows about multi-element high-lift systems at full-scale flight conditions. In this paper, an overview of the flight program is provided, followed by highlights of experimental results and computational analysis. Measurements included surface pressures on the slats, main element and flap elements using flush pressure ports and pressure belts, surface shear stresses using Preston tubes, off-surface velocity distributions using boundary layer/wake rakes, aeroelastic deformations of the flap elements using an optical positioning system, and boundary layer transition detection using hot-film anemometers and an infrared imaging system. Boundary layer transition measurements on the slat using hot-film sensors are correlated with the flow visualisation results from an infrared imaging technique. Extensive application of several computational techniques and comparisons with flight measurements are shown for a limited number of cases. This program has generated an extensive set of data, much of which are still being analysed.