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The work presented in this paper is a culmination of a multiyear joint experimental and computational effort to explore the feasibility of using active flow control (AFC) on a simple hinged flap system for recovering lift comparable to a conventional high-lift system consisting of Fowler flaps. The baseline configuration chosen for this work is the high-lift version of the NASA Common Research Model (CRM), which is a representative modern aircraft consisting of wing, fuselage, nacelle/pylon, slats, Fowler flaps, and slat and flap brackets. A simplified high-lift (SHL) system was created by replacing the Fowler flaps and flap brackets with a simple hinged flap system equipped with integrated modular AFC cartridges on the suction surface of the flap shoulder, and the resulting geometry is known as the CRM-SHL-AFC configuration. Parametric studies were conducted in the earlier phases of this effort to numerically evaluate and downselect the more efficient AFC designs for wind-tunnel tests. These simulations were performed with the PowerFLOW® code, which is a lattice-Boltzmann-based computational fluid dynamics code. Good agreement was reported in a previous paper between the numerical results and the experimental data for the lift characteristics of the CRM-SHL-AFC configuration as a function of actuation levels at the nominal landing conditions. The current effort is focused on demonstrating the applicability of the PowerFLOW code for predicting the aerodynamic performance of the conventional and the AFC-enabled simplified high-lift CRM configurations for a broad angle of attack range, including maximum lift conditions. [ABSTRACT FROM AUTHOR]

This survey paper consists of a review of flow-control applications using numerical simulations, where the goal is to provide guidance to the developers of flow-control approaches. The computational methods are described with the focus on practical simulations of flow control for flight vehicles. One approach uses the unsteady Reynolds-averaged Navier-Stokes formulation, and the other method is based on the lattice Boltzmann method. Special boundary conditions used to model a set of flow-control techniques and to guide the development of new actuation methods are highlighted. Results of studies aimed at solving a broad set of aerodynamic and propulsion flow problems through computational simulations are presented. The flow-control techniques are used for the control of flow separation as well as manipulating vortical flow structures for achieving a desired objective. The results include flow-control implementations for aircraft and rotorcraft targeting commercial and military applications. In cases where experimental data are available, selected flow-control scenarios are used to illustrate the validity of the computational methods in predicting realistic flows. [ABSTRACT FROM AUTHOR]

Numerical simulations have been performed for a vertical tail configuration with deflected rudder. The suction surface of the main element of this configuration is embedded with an array of 32 fluidic actuators that produce oscillating sweeping jets. Such oscillating jets have been found to be very effective for flow control applications in the past. In the current paper, a high-fidelity computational fluid dynamics (CFD) code known as the PowerFLOW® code is used to simulate the entire flow field associated with this configuration, including the flow inside the actuators. The computed results for the surface pressure and integrated forces compare favorably with measured data. In addition, numerical solutions predict the correct trends in forces with active flow control compared to the no control case. Effect of varying yaw and rudder deflection angles are also presented. In addition, computations have been performed at a higher Reynolds number to assess the performance of fluidic actuators at flight conditions. Unsteady characteristics of oscillatory micro-jets issued from these actuators are also analyzed in this paper. [ABSTRACT FROM AUTHOR]

An unsteady Reynolds-averaged Navier-Stokes solver is applied for the simulation of a synthetic (zero net mass flow) jet created by a single diaphragm piezoelectric actuator in quiescent air. This configuration was designated as case I for the Computational Fluid Dynamics Validation 2004 (CFDVAL2004) workshop held at Williamsburg, Virginia, in March 2004. Time-averaged and instantaneous (phase-averaged) data for this case were obtained at NASA Langley Research Center, using multiple measurement techniques. Computational results from two-dimensional simulations with one-equation Spalart-Allmaras and two-equation Menter's turbulence models are presented along with the experimental data. The effect of grid refinement, preconditioning, and time-step variation are also examined. [ABSTRACT FROM AUTHOR]

Presents a study that proposed a boundary condition for simulating the flow over passively porous surfaces of aircrafts. Description of the model used; Application of two structured-grid flow solvers in evaluating the model; Discussion of results.

The accuracy and efficiency of several lower and higher order time integration schemes are investigated for engineering solution of the discretized unsteady compressible Navier–Stokes equations. Fully implicit methods tested are either the backward differentiation formulas (BDF) or stage-order two, explicit, singly diagonally implicit Runge–Kutta (ESDIRK) methods. For this comparison an unsteady two-dimensional laminar flow problem is chosen: flow around a circular cylinder at Re=1200. At temporal error tolerances consistent with engineering simulation, ∊≈10−1–10−2, first-order implicit Euler (BDF1) is uncompetitive. While BDF3 is quite efficient, its lack of A-stability may be problematic in the presence of convection. At these same error tolerances, the fourth-order ESDIRK scheme is 2.5 times more efficient than BDF2. It is concluded that reliable integration is most efficiently provided by fourth-order Runge–Kutta methods for this problem where order reduction is not observed. Efficiency gains are more dramatic at smaller tolerances. [Copyright &y& Elsevier]

A 10%-scale high-lift version of the Common Research Model (CRM-HL) was tested in the NASA Langley Research Center's 14 by 22 ft subsonic tunnel. The focus of the wind-tunnel tests was to investigate the vortices generated at the nacelle/pylon region and their effect on the aerodynamic performance. The wind-tunnel measurements included the acquisition of force and moment data, steady pressure data, as well as surface flow visualization using minitufts. For some select cases, numerical simulations were performed to aid in understanding the wind-tunnel data. Wind-tunnel tests, with and without the nacelle/pylon, indicated a lift degradation of the conventional CRM-HL at high angles of attack. The surface flow visualization with fluorescent minitufts revealed that the lift degradation is due to flow separation caused by the nacelle/pylon vortex system on the inboard wing. The consequent flow separation was successfully mitigated using a nacelle chine installed on the inboard side of the engine nacelle. [ABSTRACT FROM AUTHOR]

A 10%-scale high-lift version of the Common Research Model and an active flow control (AFC) version of the model equipped with a simple-hinged flap were successfully tested. The main objective of the test was to develop an AFC system that can provide the necessary lift recovery on a simple-hinged flap high-lift system while minimizing its pneumatic power requirement. The tests were performed in the 14- by 22-Foot Subsonic Tunnel at the NASA Langley Research Center. Three types of AFC devices were examined: the double-row sweeping jets (DRSWJ), the alternating pulsed jets (APJ), and the high-efficiency low-power (HELP) actuators. The DRSWJ and the APJ actuators used two rows of unsteady jets, whereas the HELP actuators used a combination of unsteady and steady jets, to overcome strong adverse pressure gradients while minimizing the mass flow usage. Nozzle pressure ratio, mass flow consumption, and the power coefficient were used for judging the performance efficiency of the AFC devices. The current data are presented with the Transonic Wall Interference Correction System method applied. The HELP actuation concept was effective in controlling flow separation in the linear region of the curves comparing lift coefficient to mass flow rate. The HELP actuation achieved a targeted lift coefficient increment of 0.5, thus meeting the lift performance goal of the NASA Advanced Air Transport Technology project. [ABSTRACT FROM AUTHOR]