Ralf Gerd Hörnschemeyer

Influence of Off-Design Performance on the Design of Aircraft with Laminar Flow Technology

Laminar ow is among the most discussed technologies towards satisfying the ambitious goals for more fuel e cient aviation. Both passive as well as active laminar ow control systems are sensitive to external in uences and system failures. A sudden degradation of laminar ow immediately results in loss of ight performance. Such o -design cases have to be considered already in preliminary design synthesis for correct sizing of the aircraft. In the scope of this paper, an approach is presented that incorporates o -design cases of laminar aircraft into preliminary design synthesis. The authors chose to use the extended-range twin-engine performance standards (ETOPS) as framework for deriving operational standards for aircraft with laminar technology. Di erent requirements for minimum o -design performance are derived that directly impact overall aircraft design synthesis. In a case study, the sensitivities of the overall design synthesis towards these o design requirements are discussed. Design parameters such as maximum take-o weight, block fuel, as well as the aircraft economics are used for evaluation of the di erent concepts.

Life Cycle Engineering in Preliminary Aircraft Design

In preliminary aircraft design, the assessment of aircraft life cycle is mainly focused either on life cycle costs, or on economic and environmental analysis of certain life cycle phases. This paper presents an interdisciplinary approach for life cycle engineering during preliminary aircraft design enabling the evaluation of costs and environmental impact of the entire aircraft life cycle. The developed sustainability analysis modules are integrated in a platform together with an aircraft design suite. This allows for feeding back economic, ecological and social impact into the aircraft design synthesis, hence enabling future optimization of aircraft designs for sustainability.

Gains in Fuel Efficiency: Mulit-Stop Missions vs. Laminar Aircraft

Improvements in aircraft operations as well as application of innovative technologies are amongst the most discussed paths towards greener and more fuel ecient aviation. Especially on long-haul routes the payload factor is low due to large fuel weights; this decreases the aircraft eciency signicantly. Intermediate stops for refueling is one possible solution for increasing eciency on long-haul routes. This paper presents a comparison between multi-stop refueling operations with current aircraft technology, and an innovative aircraft concept that features laminar ow technology for decreasing drag. The presented results are based on preliminary aircraft designs and analysis with detailed ight performance simulations of the associated missions. The potential of gains in fuel eciency for the two dierent approaches is compared. Additionally, the impact on transport productivity and direct operating costs for the two concepts is presented in the scope of this paper.

Vortex Creation and Wing-Tip Geometry Dependencies

This study presents experimental 3C-PIV investigations of the vortex topology at the wing-tip. The aim is to identify geometrical aspects of the wing-tip, which exert dominant influence on the production of the axial velocity component. Different wing-tip shapes are considered. Typical rectangular round and flat shapes as well as shapes, which feature a rounding of the layout are used. Special focus is placed upon vortex creation at the wing-tip, where vorticity is accumulated by primary and also to some extent by secondary vortices. The evolution and gradual enhancement of the radial circulation profile is displayed. A rounding of the side of the tip results in a more intensive vortex. An increasing rounding of the layout has the opposite effect. Correlation of vortex topology and therefore wing-tip shaping are shown. In a second step a calculation and analysis of the real, inviscid, as well as the viscid axial velocity component at the center of the vortex is performed. Therefore the geometrical features of the tip can be related to the production and suppression of the axial velocity component during the vortex creation phase at the wing-tip.

Investigation on Turbulence Structures in the Wake of a Generic Rocket Configuration

A generic, blunt-based rocket model has been investigated experimentally in a subsonic wind tunnel at Ma ∞ = 0.2 and Re = 4.1 ×106 m − 1. Planar and stereoscopic Particle Image Velocimetry (PIV) provided statistical turbulence information on the unsteady wake flow with high spatial resolution. Multiple perpendicular regions of interest (ROI) were combined to generate three-dimensional views. Distinct flow patterns emerged that can be interpreted as a rotationally symmetric extension to the wake flow of two-dimensional blunt bodies. In addition, measurements using Constant Temperature Anemometry (CTA) confirmed the turbulence levels and provided time-resolved data. A characteristic dynamic mode at a Strouhal number of St D = 0.21 was revealed. A cluster of multiple, high-fidelity pressure transducers were mounted in the base plane of the model. The analysis of pressure fluctuations verified the dynamic mode and showed its spatial coherence along several circumferential positions.

Tomographic Particle Image Velocimetry Measurements in a Bluff-Body Wake Flow

I N the wake of bluff bodies, flow separation occurs along with phenomena like recirculation, increased turbulence levels, periodic shedding processes, and low-pressure regions. For flow bodies, which cannot avoid such geometries, base drag and buffeting effects can vitally reduce performance and efficiency. This holds true for axisymmetric, cylindrical bodies placed parallel to freestream direction, like the generic rocket configuration considered in the current work. Similar geometries were studied extensively for subsonic freestream conditions, with early studies concentrating on static or time-averaged quantities [1,2]. Following the evolution of both experimental and numerical methods, the unsteadiness of the wake turned into focus. Many studies reported a macroscopic vortex shedding mode at a reduced frequency of StD 0:2 [3–5], that was also detected in hot-wire and dynamic base pressure measurements regarding the present case [6]. The instability of the shear layer is assumed to be a key factor in the shedding mechanism and the wake topology [4]. Correspondingly, Pastoor et al. [7] used zero-net-massflux actuation to actively manipulate the shear layer of a bluff body over wide Reynolds ranges. A possible overall drag reduction of 15% was reported. Perret [8] investigated the wake of a quasitwo-dimensional (2-D) cylinder by means of two-component (2C) particle image velocimetry (PIV) for ReD 1:25 10 [8]. Within the shear layer, a vortex population was detected using the swirling strength criterion. The corresponding structures were both small (<5% of the model diameter) and of high intensity compared to the macroscopic Karman vortices, and, thus, connected to the Kelvin– Helmholtz instabilitymechanism. It was also pointed out that for 2-D measurements, only the planar swirling motion can be taken into account and may be affected or biased by the out-of-plane velocity and inclined vortex axes [8]. Fewer results can be found regarding three-dimensional (3-D) test cases. Deck and Garnier [5] performed both detached and large eddy simulations (DES/LES) on the wake flow of a cylindrical, generic launch vehicle model. The bluff base geometry was prolonged by a Presented at the 41st AIAA Fluid Dynamics Conference and Exhibit, Honolulu, Hawaii, June 27–30, 2011; received 27 November 2011; revision received 10 April 2012; accepted for publication 11 April 2012. Copyright

Active Manipulation of a Rectangular Wing Vortex Wake with Oscillating Ailerons and Winglet-Integrated Rudders

This paper presents results of experimental investigations regarding the vortex wake of a rectangular wing with winglets in a water towing tank. The model comprises ailerons and additional rudders, which are integrated into the winglets. The ailerons and the rudders are able to oscillate around a static deflection to excite inherent short-wavelength instabilities in the vortex system. The Particle Image Velocimetry method is used to investigate the vortex wake up to about 40 spans behind the model. The results show that, depending on the preselected aileron and rudder deflections, an oscillation of correctly chosen frequency leads to a faster decay of the vortex wake in comparison to the statical case.

Influencing Aircraft Wing Vortices

Results presented here were obtained within a project which was part of the Collaborative Research Centre SFB 401 “Flow Modulation and Fluid-Structure Interaction at Airplane Wings” funding from the Deutsche Forschungsgemeinschaft (DFG). The goal of this project was to gain better understanding of aircraft wake vortices in order to investigate possibilities to mitigate the hazard posed by these to following aircraft. To this end wind tunnel testing was undertaken in which the vortex wakes of various wings were measured using hot wire anemometry. It was shown that in the near field, the rolling moment induced on a following aircraft can be significantly reduced by introducing additional turbulence into the wake. Another focus point was the investigation into excitation of short wave instability mechanisms in the vortex wake and their effects in the far field. For these purposes experiments with various models and oscillating control surfaces were conducted in water towing tanks in which the vortex wakes were measured using particle image velocimetry. The results show that for an appropriate multi-vortex system, inherent instabilities can be excited leading to a more rapid vortex decay within the first 30 span lengths behind the model. The effects of these mechanisms further out in the far field are, however, minimal.