Aerodynamic Interaction Effects Between Propellers in Typical eVTOL Vehicle Configurations

Abstract

Many eVTOL concepts are characterized by non-traditional vehicle layouts with distributed propellers. Two propeller interaction types were distinguished in this paper, which investigates how propeller interaction in side-by-side and one-after-another configuration affects performance, in terms of thrust, power, in-plane forces and out-of-plane moments, and how those performance effects depend on axial and lateral propeller spacing. A wind-tunnel experiment was performed with two propeller units, one instrumented with a force/torque sensor, and the other introducing the aerodynamic interaction. Total pressure and planar PIV measurements were taken to investigate slipstream characteristics. A strong dependency of interaction effects on the geometric layout was found. For side-by-side interaction characteristic of vertical takeoff and transition, interaction effects varied from weak at small angle of attack to strong at larger angles. A drop in rear propeller thrust of up to 30% was found at constant advance ratio. Keeping thrust constant resulted in power penalties up to 13% for the two propellers combined. For one-after-another interaction, characteristic of cruise, a maximum reduction

Preliminary Propulsion and Power System Design of a Tandem-Wing Long-Range eVTOL Aircraft

“…The goal of the propulsion design framework is to allow the preliminary study and comparison of different configurations. The analysis focuses around the design of efficient propellers which can provide enough thrust during all phases of the mission, which are [3]: vertical take-off (1); transition from hover to climb (2); climb to cruising altitude (3); cruise (4); loiter in horizontal flight (5); descent (6); transition to hover (7); loiter in hover (8); and landing (9). A schematic of these phases can be seen in Figure 3.…”

“…Propeller-propeller interaction: For the same front and rear wing separation, smaller front propellers with lower slipstream heights allow one to more easily place them such that the propellers on the downstream wing are outside the slipstream of the propellers on the upstream wing. This slipstream ingestion can lead to big losses in thrust from the second row of propellers [7] and increase noise emissions; 5.…”

“…This manuscript elaborates on the propulsion and power system design methodology devised in the Wigeon project as a means of the preliminary design of open rotor eVTOL configurations, which are characterised by the use of innovative distributed propulsion architectures for their propulsion and power systems. Procedures to design efficient propellers are already available in the literature [5,6] and can be applied to eVTOL aircraft; however, the use of these unconventional distributed propulsion configurations, required in order to ensure safety, controllability, and performance during vertical and horizontal flight and the transition between them also results in more difficult performance analysis due to the close coupling between the propulsive and aerodynamic systems, even though analyses of these open rotor distributed propulsion configurations applied to VTOL [7,8] and UAV [9] vehicles are already available in the literature.…”

Experimental Study of the Aerodynamic Interaction between Side-by-Side Propellers in eVTOL Airplane Mode through Stereoscopic Particle Image Velocimetry

“…Similarly, Shukla and Komerath [6] performed stereo PIV measurements to study the interacting wake of a side-by-side configuration made by two mini-drone rotors that were also in the hover condition. Moreover, a very recent work by Stokkermans et al [7] described a comprehensive wind tunnel activity performed over two propellers in both tandem and side-by-side configurations. In particular, in this last work, PIV was dedicated only to the study of the side-by-side interacting flow field characteristic of vertical takeoff and the first stage of transition.…”

“…Despite the efforts found in the literature to gain knowledge on side-by-side propellers, particularly for hover conditions, the literature lacks experimental studies focused on the investigation of interactional flow field that characterise side-by-side configurations in forward flight conditions. As recent works by Zhou et al [5] and Stokkermans et al [7] highlighted the negligible effects of side-by-side interactions on propeller performance for both hover and forward flight conditions, this paper focuses on an investigation of the effects of side-by-side aerodynamic interactions on a propeller wake by means of stereoscopic PIV surveys. The measurements were performed during a wind tunnel campaign and reproduced cruise conditions in order to fill the gap in the literature concerning interactional flow studies of two propeller models in a side-by-side configuration for this flight condition, typical of the eVTOL aircraft airplane mode.…”