Full-scale Flight Conditions Research Articles

Numerical analysis of high-lift configurations with oscillating flaps

This study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport k-omega turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of 0.5 times 10^{6} the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of 20 times 10^6, reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

Numerical Simulations of the F-16XL at Flight-Test Conditions Using Delayed Detached-Eddy Simulation

The F-16XL flight-test data have been used for many years in the Cranked-Arrow Wing Aerodynamics Program International series as a challenging test case for numerical prediction of military aircraft at full-scale flight conditions. The complexity of the configuration and the variety of flight-test conditions available challenge most computational fluid dynamics codes and turbulence models. This study documents the use of the Kestrel flow solver with its solution-based mesh refinement capability and delayed detached-eddy simulation turbulence models for F-16XL flight condition 25, which is a subsonic high-angle-of-attack flight condition that has proven particularly challenging for computational researchers. The spectral content of the pressure data and the integrated lift, drag, and pitching moment coefficients are also presented. The more advanced turbulence models, coupled with the more refined meshes, show very good agreement with flight-test data and reasonable resolution of the unsteady frequency content.

Microphone Array Measurement in European Transonic Wind Tunnel at Flight Reynolds Numbers

This paper presents an experimental investigation of small-scale model airframe noise at various Reynolds numbers up to the real flight case. The study consists of data acquired with a microphone array in the European Transonic Wind Tunnel. The advantage of this wind tunnel is to enable testing simultaneously at cryogenic temperatures and increased pressure levels, which extends the range of achievable Reynolds numbers up to those pertaining to full-scale flight conditions. At the DLR, German Aerospace Center, the microphone array measurement technique has been further developed to perform measurements under combined cryogenic and pressurized conditions. For this purpose, a microphone array consisting of 96 microphones was designed and constructed. In this paper, aeroacoustic results are presented for various Reynolds numbers up to the real flight case on an Airbus K3DY half-model of scale . The results showed significant Reynolds number and Mach number dependency for various sources. Of particular note are various dominant sources appearing on the flap at real flight Reynolds numbers. To the author’s knowledge, this is the first time that airframe noise data for a small-scale model have been acquired at real flight Reynolds numbers.

Distinctive features of the flow past high-speed flight vehicles with air-breathing engines on subsonic, transonic, and low supersonic velocity ranges

The aerodynamic characteristics and distinctive features of the flow past hypersonic integral-layout flight vehicles with air-breathing engines intended for cruise flight in the atmosphere are experimentally investigated. The experiments were conducted on a simplified model designed with regard for the general principles of integration of vehicles of the class considered. The tests were performed in a wind tunnel over the Mach and Reynolds number ranges 0.6 ≤ M ≤ 4 and 6.3 × 106 ≤ Re ≤ 16 × 106, respectively. Balance testing was carried out, the pressure distributions over the vehicle surface were measured, and the flowfields on the model surface were photographed. The effects of mounting a nacelle and contouring the internal duct are considered. The effect of the corrections on the duct flow in the absence of jet modeling is estimated. The results obtained can be used as a basis for developing the aerodynamic configurations of integral-layout flight vehicles, for forming their thrust and aerodynamic parameters under full-scale flight conditions, and for testing computation methods.

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

Despite the proven capability of synthetic-jet actuators in delaying boundary-layer separation in laboratory experiments, a capability that allows the geometry and operating conditions of these devices to be designed and selected for maximum flow-control effectiveness in full-scale flight conditions has yet to be developed. In this two-part paper, the key results obtained during a 3-year research programme aiming at establishing such a capability based on a better understanding of the fluid mechanics of synthetic jets and an improved modelling capacity are reported. In Part 1 of this paper, the experimental studies of the behaviour of synthetic jets in both quiescent flow and a boundary layer are described. The work has led to an improved understanding of the dimensionless parameters that determine the formation and development of vortex rollup and how the strength of rollup can be enhanced by optimizing the geometry and operating condition. Based on the study of the nature of vortical structures produced as the result of the interaction with a boundary layer and their impact in the near-wall region where flow control is desired, the conditions for producing effective vortical structures for delaying flow separation were established. The finding from this work forms the basis of a number of criteria used for designing synthetic jet actuators for full-scale flight condition to be presented in Part 2.

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.

Introduction to the Abrupt Wing Stall Program

The Abrupt Wing Stall (AWS) Program has addressed the problem of uncommanded, transonic lateral motions, such as wing drop, with experimental, computational, and simulation tools. Background to the establishment of the AWS program is given as well as program objectives. In order to understand the fundamental flow mechanisms that caused the undesirable motions for a pre-production version of the F/A-18E, steady and unsteady flow field details were gathered from dedicated transonic wind-tunnel testing and computational studies. The AWS program has also adapted a free-toroll (FTR) wind-tunnel testing technique traditionally used for low-speed studies of lateral dynamic stability to the transonic flow regime. This FTR capability was demonstrated first in a proof-of-concept study and then applied to an assessment of four different aircraft configurations. Figures of merit for static testing and for FTR testing have been evaluated for two configurations that demonstrated wing drop susceptibility during full-scale flight conditions (the pre-production F/A-18E and the AV-8B at the extremes of its flight envelope) and two configurations that do not exhibit wing drop (the F/A-18C and the F-16C). Design insights have been obtained from aerodynamic computational studies of the four aircraft configurations and from computations quantifying the impact of the various geometric wing differences between the F/A-18C and the F/A-18E wings. Finally, the AWS program provides guidance for assessing, in the simulator, the impact of experimentally determined lateral activity on flight characteristics before going to flight. SYMBOLS AND ABBREVIATIONS

Hypersonic flow in an MHD-acceleration facility and under full-scale conditions

A formulation of the problem, a method of solution, and calculated results are considered for flow past the windward side of a sphere under conditions of an aerodynamic facility (a wind tunnel) with magnetohydrodynamic (MHD) acceleration of the air flow and the corresponding full-scale flight conditions in the Earth's atmosphere. Calculations were performed on the basis of numerical solution of Navier-Stokes equations taking into account thermochemical nonequilibrium of air and catalytic properties of the body surface. Results of the mathematical simulation of flow around a sphere in an MHD-acceleration wind tunnel are compared with experimental data obtained at the Central Aerohydrodynamic Institute (TsAGI). The problem of recalculation of experimental data for full-scale conditions is analyzed.

Effect of Reynolds number on upper cowl flow separation

This paper describes testing on subsonic inlet cowlings for high-bypass-ratio turbofan engines, conducted in a low-speed pressurized wind tunnel. These new data bridge the gap between earlier low Reynolds number model data for cowl flow separation and full-scale flight conditions. Innovative model test approaches were employed and are described. New cowl flow separation data matched previously obtained data at comparable Reynolds numbers. Higher Reynolds number data, up to flight value levels, behaved in an orderly fashion and were suitable for improving currently available theroretical descriptions of the phenomena governing engine inoperative cowl flow separation.