Georg Eitelberg

Experimental investigation of propeller induced ground vortex under headwind condition

During the ground operation of propeller aircraft, the interaction between the ground and the flow field produced by the propeller may lead to the generation of a vortex originating on the ground. Such ground induced vortex results in non-uniform inflow into the propeller disk. Furthermore, the vortex may raise debris from the ground that may damage the blades, decreasing their life time. For this phenomenon, the flow field near the ground is of interest because it provides information on the strength of the vortex before it is being ingested by the propeller. To obtain insight into the origins and the development of the ground vortex, velocity measurements have been performed in the flow field produced by a scaled propeller model using a three-component PIV system on a plane parallel to the ground and in the proximity of it. The velocities in the test plane suggest that a horseshoe vortex is formed above the ground which is built to help understand the flow topology of ground vortices. The vortex/no-vortex domain boundary which is relied upon the presence of node and saddle points in the time averaged flow is presented. The effect of varying the thrust coefficient of the propeller has been assessed under headwind conditions. The averaged strength of the maximum wall normal vortex is compared at different thrust coefficients. The results show that average levels of vortex strength increases up to a maximum and then decreases to achieve a plateau. The pressure under the propeller is measured and the mean value of pressure gradient magnitude keeps increasing as thrust coefficient increases. Vortex wandering is observed at all test conditions in both the lateral and the longitudinal directions for all test conditions. The influence of the ground induced non-uniform inflow upon the propeller performances is found to be negligible.

Aerodynamic and Aeroacoustic Effects of Pylon Trailing Edge Blowing on Pusher Propeller Installation

The aerodynamic and aeroacoustic effects of pylon trailing edge blowing on the propulsive performance and noise emissions of a propeller installed in a pusher configuration were studied in a wind tunnel. A propeller model and a pylon equipped with a trailing edge blowing system were installed in the large low-speed facility of the German-Dutch wind-tunnels (DNW-LLF). Particle image velocimetry measurements of the flow field downstream of the pylon confirmed a wake re-energization obtained through blowing, with a momentum deficit recovery of 80% compared to the unblown case. For the symmetric inflow conditions considered, the effect of pylon installation on the propulsive performance was found small. Increases in thrust and torque of 1% up to 6% were measured at high and low thrust settings, which was comparable to the measurement variability. Acoustic data obtained using out-of-flow microphones confirmed the strong interaction effects resulting from the installation of the upstream pylon, with an increase in noise levels due to the presence of the pylon of up to 12 dB at a medium propeller thrust setting. The application of pylon trailing edge blowing successfully eliminated the installation effects, resulting in noise levels equal to those of the isolated propeller over the entire axial directivity range. At higher thrust settings the change in blade angle of attack due to the pylon wake impingement is smaller, and the steady blade loads are larger compared to the unsteady loads experienced during the wake passage. Consequently, in this operating regime the propeller noise emissions were dominated by steady sources for all but the most upstream observer positions.

Spatial-temporal and modal analysis of propeller induced ground vortices by particle image velocimetry

During the ground operation of aircraft, there is potentially a system of vortices generated from the ground toward the propulsor, commonly denoted as ground vortices. Although extensive research has been conducted on ground vortices induced by turbofans which were simplified by suction tubes, these studies cannot well capture the properties of ground vortices induced by propellers, e.g., the flow phenomena due to intermittent characteristics of blade passing and the presence of slipstream of the propeller. Therefore, the investigation of ground vortices induced by a propeller is performed to improve understanding of these phenomena. The distributions of velocities in two different planes containing the vortices were measured by high frequency Particle Image Velocimetry. These planes are a wall-parallel plane in close proximity to the ground and a wall-normal plane upstream of the propeller. The instantaneous flow fields feature highly unsteady flow in both of these two planes. The spectral analysis is co...

The Effects of Swirl Recovery Vanes on Single-Rotation Propeller Aerodynamics and Aeroacoustics

A preliminary assessment of the aerodynamic and aeroacoustic impact of swirl recovery vanes (SRVs) installed downstream of a single-rotating propeller model was performed at the large low-speed facility of the German-Dutch wind tunnels (DNW-LLF). The SRVs are designed to recover the swirl in the rotor slipstream, thereby increasing the propulsive efficiency without the added complexity of contra-rotating systems. The performance data acquired with a rotating shaft balance showed that the upstream effect of the SRVs on the time-averaged rotor performance was negligible. Particle image velocimetry measurements in the slipstream of the propeller with and without SRVs substantiated the efficacy of the vanes in reducing the swirl in the propeller slipstream. Integrated in the radial direction, installation of the vanes reduced the swirl kinetic energy by 50% at a medium propeller thrust setting. An additional slipstream contraction was observed with vanes installed. The acoustic data measured with out-of-flow microphones showed that installation of the SRVs increased the total sound pressure levels by 2 to 6 dB compared to the isolated propeller.

Aerodynamic interaction effects of tip-mounted propellers installed on the horizontal tailplane

This paper addresses the effects of propeller installation on the aerodynamic performance of a tailplane featuring tip-mounted propellers. A model of a low aspect ratio tailplane equipped with an elevator and a tip-mounted propeller was installed in a low-speed wind-tunnel. Measurements were taken with an external balance and surface pressure taps to determine the aerodynamic characteristics of the tailplane, while the flowfield in the wake of the model was investigated using particle-image velocimetry. The experimental data are supported by CFD analyses, involving both transient simulations of the full-blade configuration and steady-state simulations the propeller replaced by an actuator-disk model. The upstream effects on the propeller time-average and time-accurate thrust and normal-forces are found to be limited for different tailplane operating conditions. It is shown that for a given propeller rotation direction, the load distribution on the tailplane is highly dependent on the direction of elevator deflection. The rotation direction of the tailplane tip-vortex relative to the propeller swirl therefore significantly affects the integral loads on the tailplane, resulting in differences in the normal-force gradient and elevator effectiveness.

Tractor Propeller-Pylon Interaction, Part II: Mitigation of Unsteady Pylon Loading by Application of Leading-Edge Porosity

Citation (APA) Della Corte, B., Sinnige, T., de Vries, R., Avallone, F., Ragni, D., Eitelberg, G., & Veldhuis, L. (2017). Tractor Propeller-Pylon Interaction, Part II: Mitigation of Unsteady Pylon Loading by Application of LeadingEdge Porosity. In 55th AIAA Aerospace Sciences Meeting: Grapevine, Texas [AIAA 2017-1176] American Institute of Aeronautics and Astronautics Inc. (AIAA). https://doi.org/10.2514/6.2017-1176

Pusher-Propeller Installation Effects in Angular Inflow

Pylon-mounted pusher propellers suffer from installation effects due to the interaction between the pylon and the propeller. The impact of angular inflow on these installation effects was quantified at the Large Low-Speed Facility of the German-Dutch wind tunnels (DNW-LLF). Particle-image-velocimetry measurements showed that the pylon wakes width and velocity deficit were hardly affected by the introduction of a six-degree sideslip angle. Application of pylon trailing-edge blowing reduced the integral velocity deficit in the wake by up to 65%. Evaluations of the surface pressures on the blades confirmed the sinusoidal loading behavior in angular inflow and the impulsive loading peak due to the pylon-wake encounter. The circumferential velocity components induced by the pylon tip vortex strongly affected the steady-state propeller performance by modifying the effective advance ratio sensed by the blades. Increased performance was measured when the rotation direction of the pylon tip vortex was opposite to that of the propeller. Angular inflow affected the propeller noise emissions due to the resulting unsteady blade loads and the circumferential variation of the effective Mach number of the blade sections. The installation of the pylon added a noise source due to the unsteady blade loads caused by the pylon-wake encounter. Depending on the sideslip angle, application of blowing eliminated a large part of the installation noise penalty, despite remaining non-uniformities in the blown wake profiles.

Analysis of propeller-induced ground vortices by particle image velocimetry

The interaction between a propeller and its self-induced vortices originating on the ground is investigated in a scaled experiment. The velocity distribution in the flow field in two different planes containing the self-induced vortices is measured by particle image velocimetry (PIV). These planes are a wall–parallel plane in close proximity to the ground and a wall–normal plane just upstream of the propeller. Based on the visualization of the flow field in these two planes, the occurrence of ground vortices and its domain boundary are analysed. The elevation of the propeller from the ground and the thrust of the propeller are two parameters that determine the occurrence of ground vortices. The main features of the propeller inflow in the presence of the ground vortices are highlighted. Moreover, the analysis of the non-uniform inflow in the azimuthal direction shows that with increasing the propeller thrust coefficient and decreasing the elevation of the propeller above the ground, the variation of the inflow angle of the blade increases.Graphical Abstract

Numerical analysis of propeller induced ground vortices by actuator disk model

During the ground operation of aircraft, the interaction between the propulsor-induced flow field and the ground may lead to the generation of ground vortices. Utilizing numerical approaches, the source of vorticity entering ground vortices is investigated. The results show that the production of wall-parallel components of vorticity has a strong contribution from the wall-parallel components of the pressure gradient on the wall, which is generated by the action of the propulsor. This mechanism is a supplementation for the vorticity transported from the far-field boundary layer, which has been assumed the main vorticity source in a number of previous publications. Furthermore, the quantitative prediction of the occurrence of ground vortices is performed from the numerical results. As the distance of the propeller form the ground decreases, and as the thrust of the propeller increases, ground vortices are generated from the ground and enter the propeller. In addition, the vortices which exist near the ground but does not enter the propeller plane are observed and visualized by three-dimensional data.Graphical abstract

Unsteady Pylon Loading Caused by Propeller-Slipstream Impingement for Tip-Mounted Propellers

An experimental analysis was performed of the unsteady aerodynamic loading caused by the impingement of a propeller slipstream on a downstream lifting surface. When installed on an aircraft, this unsteady loading results in vibrations that are transmitted to the fuselage and are perceived inside the cabin as structure-borne noise. A pylon-mounted tractor–propeller configuration was installed in a low-speed wind tunnel at Delft University of Technology. Surface-microphone and particle-image-velocimetry measurements were taken to quantify the pressure fluctuations on the pylon and visualize the impingement phenomena. It was confirmed that the propeller tip vortex is the dominant source of pressure fluctuations on the pylon. Along the path of the tip vortex on the pylon, a periodic pressure response occurs with strong harmonics. The amplitude of the pressure fluctuations increases with increasing thrust setting, whereas the unsteady lift coefficient displays a nonmonotonic dependency on the propeller thrust....