Software-in-the-loop investigation of wake-vortex-encounter-response of identical multirotor pair with PX4 attitude controller

AIAA SCITECH 2022 Forum

2022

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As the use of multi-rotors is becoming common, understanding how the wake vortices develop and decay from a multi-rotor is important to reduce the effect of wake vortices on other multi-rotors and ensure their safety during operation by applying a wake separation minima. This paper proposes a method of flow simulation in ANSYS Fluent to study the decay of wake vortices from quadrotor propellers as the vortices evolve over distance and time. First, the near-field wake flow from the quadrotor propellers was simulated using Reynolds-Averaged Navier-Stokes (RANS) turbulence model. The velocity profile in the quadrotor frame of reference was then extracted to be applied for a flow simulation using Large Eddy Simulation (LES). The circulation strength as a function of distance could then be calculated, but it was limited by the length of the computational grid due to the wake flow being seen from the quadrotor frame of reference. To change into the stationary frame of reference, the interpolation data from the first stage LES was exported and modified by subtracting the freestream velocity from the velocity component in the freestream direction. The modified interpolation data was then used for the second stage LES, and the circulation strength in terms of time could be calculated from the resulting wake flow. Three cases of flow simulation are presented in this paper: first using 380-mm-diameter propellers based on the SUI Endurance quadrotor propellers with forward flight speed of 6 m/s, second using the 380-mm-diameter propellers with 12 m/s speed, and third using 240-mm-diameter propellers (similar to the propellers of DJI Phantom quadrotor) with 12 m/s speed. Findings regarding the decay of wake vortex from multi-rotor vehicles will help in determining the safe separation distance required to mitigate the hazards due to wake vortex encounters and ensure the safety of multi-rotor vehicles.

Section: Discussionmentioning

confidence: 99%

A Study on Circulation Strength Decay Over Time of Quadrotor Wake Using Large Eddy Simulation

AIAA SCITECH 2022 Forum

2022

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“…The setup can also be improved to obtain a more accurate wind field, for example by employing Large Eddy Simulation (LES) and time-averaging its results [22], applying more realistic terrain and building boundary conditions to acquire detailed atmospheric flow [23], and coupling the meso-scale and micro-scale weather conditions to obtain more accurate inlet boundary condition for the wind field simulation [24][25][26]. In addition, instead of only inferring the wind effect from the flow results, the simulated wind data can be utilized for UAS flight simulation using software-in-the-loop (SITL) [27,28] to study UAS stability and flight behavior when encountering the flow patterns in the urban wind field. Simulation with SITL was previously used to determine the separation requirement between UAS by examining the flight behavior of UAS when encountering the wake vortex from another UAS [29,30].…”

Section: Summary and Future Workmentioning

confidence: 99%

Simulation of Wind Field in a Building Complex for Evaluation of the Wind Effect Along UAS Flight Path

AIAA AVIATION 2023 Forum

2023

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With the use of Unmanned Aerial Systems (UAS) becoming more common, wind field within urban environments becomes significant, and its impact on UAS flight should be examined to ensure UAS operations can be implemented and managed safely with little to no risk of damages and injuries to the inhabitants and infrastructures. This study presents the wind field within the Biopolis building complex in Singapore from steady-state RANS simulation using OpenFOAM v1912. The wind simulation was done using various inlet wind speeds and directions based on the measurements from a weather station near the building complex. After obtaining the velocity field for the whole area, the wind effect on UAS along a given flight path was inferred from the local wind velocity magnitude and direction along the path. When the general wind heading was aligned with the flight path, the local wind and its impact on the UAS along its path had more gradual and less extreme changes than in other cases where the UAS had to fly by crossing through the wake flow of the buildings. Additionally, for flow cases with the same inlet wind direction but different reference speeds, similarity in their results was observed when the wind velocity magnitude was normalized with respect to the velocity magnitude at the inlet boundary. Contours of the wind Turbulence Kinetic Energy (TKE) from the simulation results show that the areas with higher TKE are located around buildings at the most upstream against the wind, and these areas increase in size and TKE levels with higher wind speed.

“…Simulations using LES turbulence modeling would be needed to capture the wake vortex at this extended distance. Indeed, investigation using software-in-the-loop simuations using Pixhawk 4 attitude controller with default tuning and UAS traveling at 10 m/s suggested that separation evaluation would need to take place beyond 𝑋 < 14𝐷 to locate the follow distance that would not resulted in instability of the follower quadrotor UAS [35].…”

Section: B Far-field (Les) Simulaitonmentioning

confidence: 99%

Numerical Investigation on Influence of Fuselage on Multirotor Wake Vortex Structures in Forward Flight

AIAA SCITECH 2022 Forum

2022

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With the increase interest in utilizing multirotor UAS in very low altitude airspace, the safety aspect associated with higher UAS density gains importance. One of the safety consideration is the separation requirements for UAS sharing the airspace, which consists of two major components: wake-based and CNS performance-based. To evaluate the wake-based separation requirements, the wake-field produced by the leading UAS and the resulting encounter response by the follower UAS must be obtained. While previous studies on aircraft wake vortex evolution showed that the fuselage wake have small impact on the overall wake vortex strength and structures, the more distributed lift generation with less distance between the initial formation point of wake vortex to the fuselage could lead to a larger impact. This paper investigates the impact of including multirotor fuselage on simulating the strength and structure of the resulting wake vortex.