Оценка надежности высоконадежных систем с учетом ЗИП

Предложены приближенные верхние и нижние оценки коэффициента готовности высоконадежной восстанавливаемой системы со структурной избыточностью. Полученные расчетные соотношения могут использоваться для оценки надежности высоконадежных систем с учетом различных стратегий пополнения ЗИП

Time Resolved Flow Field Investigations of Low Reynolds number Transient Maneuvers

Transient pitch and plunge maneuvers of low aspect ratio wings in a special low Reynolds number wind tunnel have been investigated by means of high speed Particle Image Velocimetry to analyze the leading edge vortex dynamics quantitatively. A specific requirement of the measurement was to design and apply an optical arrangement for the laser light sheet which moves with the wing so as to keep the light sheet in fixed position on the upper side of the model. This became necessary because of the low pulse energy of high speed lasers and the large amplitudes of motion. This paper shows the principle and the implementation of this particular set-up. The evaluation procedure shows some specific steps concerning the preprocessing, for example, mask generation and disparity correction. The temporally-resolved data sets enable a tracking of vortices and a detailed analysis of the leading edge vortex dynamics in terms of circulation build-up and convection velocity

Ermittlung der Massenkräfte periodisch bewegter Tragflügelmodelle unter Anwendung von optischer Messtechnik

Im Rahmen eines DFG-Projektes zur instationären Aerodynamik von Tragflügeln bei kleinen Reynolds-Zahlen werden Messungen der aerodynamischen Kräfte von im Windkanal periodisch bewegten Tragflächen verschiedener Geometrien und Bewegungsparameter durchgeführt. Die Massenträgheitskräfte, welche durch die Schlagbewegung hervorgerufen werden, sind mit 80 − 90 % der Gesamtkräfte deutlich größer als die aerodynamischen Kräfte der kleinen Tragflügelmodelle. Somit ist eine Kompensation der mittelsWindkanalwaage gemessenen Kräfte erfahrungsgemäß mit größeren Unsicherheiten behaftet. Diese Arbeit soll einen neuen Ansatz zur Bestimmung der Massenträgheitskräfte während eines Windkanalversuchs aufzeigen. Eine optische Positionserfassungs-Messtechnik wird zur Rekonstruktion der 3D-Verschiebungen des Tragflügels verwendet. Diese werden weiterhin zum Berechnen der Tragflächen-Beschleunigungen herangezogen. Mit der bekannten Masse, der Schwerpunktlage sowie dem Massenträgheitsmoment des Modells, können nun die exakten Massenkräfte und -momente des Tragflügels bestimmt werden

Transition Prediction in Low Reynolds Airfoil Flows using Finite Element/Difference Solvers Coupled with the en Method: A Comparative Study

Peer reviewed: YesNRC publication: Ye

LES/RANS Simulation of Airfoil Flows near Combined Leading-Edge Trailing-Edge Stall

Peer reviewed: YesNRC publication: Ye

Simultaneous Measurements of Unsteady Aerodynamic Loads, Flow Velocity Fields, Position and Wing Deformations of MAVs in Plunging Motion

Micro Aircraft Vehicles (MAVs) normally operate at very low Reynolds numbers for which existing design methods developed for conventional aircraft are usually not adequate. The performance of airfoils deteriorates rapidly as the Reynolds number decreases below 105. Additionally, the wings of MAVs usually have low aspect ratios of ≤ 2 so that the wing tip vortices influence the overall wing behavior significantly which may result in non-linear characteristics. Because MAVs must be highly maneuverable and are usually very sensitive to gusts, their dynamics and unsteady aerodynamics are of much interest

Three-Dimensional Flow Field Investigations on Pitching Low Aspect Ratio Wings at Low Reynolds Numbers

Three-dimensional, unsteady flow fields of a pitching low aspect ratio wing were measured by tomographic PIV [6] in air. The analysis of the vortex dominated flow field provides a deeper understanding of vortex interaction and three-dimensionality of the low Reynolds number (Re ? 10,000) flow. In order to recover the complete flow field the measurement set-up was designed to be traversable. A high spatial resolution and a large volume thickness could be achieved by a set of high sensitive sCMOS cameras. A specific feature of this campaign was to locate the measurement domain directly above the flat-plate-wing surface. Evaluation of the measurement data is performed by DLR in-house software. A selection of measurement results of this highly complex flow is presented in this paper

Airfoil Stall Simulations with Algebraic Delayed DES and Physically Based Synthetic Turbulence for RANS-LES Transition

For accurate computations of massively separated flows, a variety of Detached Eddy Simulation (DES) approaches have been recently developed. The Algebraic Delayed Detached Eddy Simulation (ADDES) proved to be an efficient approach in performing a reliable switch between RANS and LES regions, thus avoiding Modeled Stress Depletion (MSD). Nevertheless, as with other embedded LES approaches, it requires a large adaptation distance until LES regenerates the physically expected turbulence content, downstream of the RANS-LES interface. In order to shorten this grey area of the embedded LES approaches, a flexible synthetic turbulence generator that can provide a physically realistic velocity field of fluctuations is further developed and applied. The implementation is first tested in a flat plate boundary layer and then for the HGR-01 airfoil at high angles of attack where is validated against experimental data. Results have shown that, applying synthetic turbulence, the generation of turbulent content is effectively accelerated and the resolved turbulence shows good agreement with PIV data. In addition, visualizations and spectral analysis display the physical behavior of turbulence in the LES region

Detached-Eddy Simulation of Aerodynamic Flows Using a Reynolds-Stress Background Model and Algebraic RANS/LES Sensors

A new variant of delayed detached-eddy simulation (DDES) based on the Low-Re epsilon-h-RSM as RANS background model is presented which is optionally combined with novel algebraic sensors for the RANS/LES switch. The RSM is aimed to improve RANS-mode predictions of pressure-induced separations on smooth surfaces, while the new sensors eval- uate boundary-layer properties to distinguish between attached and detached flow regions and place the RANS/LES interface at separation onset. After calibration and basic validation for decaying isotropic turbulence, the epsilon-h-based DDES is applied to a backward-facing step flow with massive separation and compared to experiments. The results are well in line with original DDES and can be further improved by applying stochastic forcing of the turbulent subgrid stresses. For the HGR-01 airfoil at stall, both the RSM-based approach and the algebraic sensors are found essential in capturing separation onset at the trailing edge and ensuring LES mode in the separated flow. However, the actual DES computations still suffer from under-resolved turbulence in the separated LES region when compared to PIV measurements, which can neither be compensated by stochastic forcing, nor by a different RANS model or a local grid refinement. Thus, the need to extend the present method by a more sophisticated forcing becomes evident