André Heider

Investigation of the Propeller Slipstream with Particle Image Velocimetry

The flow around an 8-bladed propeller is analyzed using particle image velocimetry in the Airbus low-speed wind tunnel facility in Bremen, Germany. The propeller is mounted on a half-model equipped with two propellers with opposing rotation directions, where only the outboard propeller is investigated. For two cases with no thrust (C T = 0) and with thrust (C T = 0.1) the propeller slipstream is visualized at several angles of attack. In particular, the development of the slipstream over the wing is investigated with particle image velocimetry derived variables such as mean velocities, fluctuations, and turbulent kinetic energy. A detailed description of the slipstream returns valuable information on the vortical structures and periodic phenomena. An identification of such events is necessary for a future validation with numerical data. It allows for the analysis of parametric cases; first, a comparison between the thrust and no-thrust cases and, second, the effect of an increasing angle of attack. It is found that at the thrust cases, for higher angles of attack, vortices are formed due to interactions in the boundary layer.

Investigations of Sunroof Buffeting in an idealised Generic Vehicle Model - Part I: Experimental Results

This paper is the first of a two-paper series that describes the experimental portion of a long-term, ongoing investigation - carried out by a consortium of the German automotive manufacturers Audi, BMW, Daimler, Porsche and Volkswagen - of the feasibility of predicting buffeting phenomena by means of computational fluid dynamics (CFD). The numerical simulations carried out as part of the study are reported on in the second paper of the series. Sunroof and side-window buffeting is a common phenomenon in passenger cars, and can cause considerable discomfort to the passengers due to the high sound-pressure levels (SPL) that are generated. The general physical mechanism, whereby an unsteady shear layer in the sunroof or window opening induces an acoustic resonance in the passenger compartment, is well-understood. However, experience has shown that making a priori predictions about the tendency of a given configuration to experience buffeting - essential in the early stages of the vehicle design process - with the required degree of reliability and accuracy is not possible. In the vehicle development process, pragmatic design solutions for suppressing buffeting at various wind speeds and geometric configurations are found experimentally. Previous work carried out by members of the consortium has shown that clearly identifying and isolating the individual factors that influence buffeting in real vehicles is very diffcult. They range from the geometry of the sunroof or side window, including small geometric details of the surrounding vehicle parts, to the quality of the oncoming flow, to the arrangement of the internal volume of the vehicle. Moreover, it has been found that the interaction of the fluid flow with the vehicle structure has a particularly large influence on buffeting behaviour and makes the analysis of the individual physical phenomena that contribute to the overall effect very diffcult. In order carry out a systematic analysis of these issues, the consortium devised a long-term project in which the first step, presented in this two-part publication, isolates and investigates only the issues related to fluid dynamics and acoustics, and ensures that the other aforementioned factors influencing buffeting play no role. Rigorous studies of this type which are also directly relevant to vehicle design are not found in the present literature. Only sunroof buffeting was considered in the present study, as the physical mechanism is essentially identical to that of side-window buffeting.

Evaluation of Large-Scale Wing Vortex Wakesfrom Multi-Camera PIV Measurements in Free-Flight Laboratory

Multiple-vortex systems of aircraft wakes have been investigated experimentally in a unique large-scale laboratory facility, the free-flight B20 catapult bench, ONERA Lille. 2D/2C PIV measurements have been performed in a translating reference frame, which provided time-resolved crossvelocity observations of the vortex systems in a Lagrangian frame normal to the wake axis. A PIV setup using a moving multiple-camera array and a variable double-frame time delay has been employed successfully. The large-scale quasi-2D structures of the wake-vortex system have been identified using the QW criterion based on the 2D velocity gradient tensor ∇H u, thus illustrating the temporal development of unequal-strength corotating vortex pairs in aircraft wakes for nondimensional times tU0∕b≲45.

Flight Testing of Alternative Ventilation Systems for Aircraft Cabins

Cabin displacement ventilation (CDV) has been evaluated for the first time in a real passenger aircraft cabin under flight conditions. Two ventilation systems, i.e. pure CDV and a hybrid ventilation (HV) system, which provides 30 % of the total volume flow rate through the lateral mixing ventilation outlets, were tested in an A320 aircraft. While pure CDV was found to provide low air velocities, high heat removal efficiencies and a very good dynamic performance regarding control of the air temperatures, the hybrid system, still allowing for comfortable flow velocities and good heat removal efficiencies, was shown to significantly improve the cooling and heating rates at the cabin surfaces. With both systems, the local temperature in the passenger zone is distributed very homogeneously among the investigated seat and aisle positions.

In-Flight Infrared Thermography for Studies of Aircraft Cabin Ventilation

To improve the convenience of aircraft cabins, Cabin Displacement Ventilation (CDV) was investigated during flight tests in an Airbus A320 with an automatically rotatable infrared camera. For this purpose a programmable, step motor driven infrared camera setup was developed, allowing for time resolved acquisition of the temperatures on the interior cabin surfaces during the whole flights. From the temporal development of the surface temperatures the cooling and heating performance of pure CDV as well as a hybrid system (HV), where 30 % of the fresh air was supplied through the original lateral outlets, was analyzed and characterized. Static measurements reveal a characteristic, yet homogeneous temperature distribution in the cabin for both scenarios, pinpointing to a homogeneous cooling of the heat loads in the whole cabin. In order to study the performance of CDV and HV, dedicated “pull-up” and “pull-down” scenarios, those are abrupt changes of the inflow temperature with the objective to study the heating and cooling dynamics, were conducted during the flight tests. Analysis of time resolved measurements discloses that the cooling performance of the cabin is limited by thermal diffusion of heat inside of the interior cabin materials.

Propeller Slipstream Development

The flow around an 8-bladed propeller is analyzed using Particle Image Ve-locimetry (PIV) in the Airbus Low Speed Wind Tunnel Facility in Bremen, Germany. The propeller is mounted on a half-model equipped with 2 counter-rotating propellers, where only the outboard propeller is investigated. In particular, the development of the slipstream over the wing is investigated with PIV derived variables such as mean velocities, fluctuations and turbulent kinetic energy. A detailed description of the slipstream returns valuable in-formation on areas with separation. For two cases with no thrust (CT = 0) and with thrust (CT = 0.1) several angles of attack in several planes are measured. It allows for the analysis of parametric cases: firstly, a comparison between the thrust and no thrust cases and, secondly, the effect of an increasing angle of attack. It is found that at the thrust cases, for higher an-gles of attack, vortices are formed due to interactions in the boundary layer.