A rigid, coaxial, counter-rotating rotor
We investigate the performance, vibratory loads, and aeroelastic behavior of a rigid, coaxial, counter-rotating rotor system for the development of next-generation vertical lift aircraft. Experiments (in hover) are performed at the rotor test facility, which was designed and built by graduate students in our research group. Measurement of the performance and vibratory loads in both hover and forward flight were completed during a 5-year program funded by the VLRCOE (Vertical Lift Research Center of Excellence) during 2011-2016, and a new 5-year VLRCOE program was kicked off in Fall 2016. Currently, our focus is on the measurement of dynamic inflow in single and coaxial rotor systems, as well as the extraction of reduced order dynamic inflow models from the measured data.
Measurement of transient loads and blade deformation of a coaxial counter rotating rotor
Digital Image Correlation (DIC) techniques calculates full-field deformation of a structure by studying image sequence. A sequence of images is taken by stereoscopic high-speed cameras, discretized into small “sub-set” or “interrogation window”, and compared undeformed and deformed images to find a displacement vector at each interrogation window. The main purpose is to investigate the fundamental aerodynamic and structural dynamic phenomena responsible for the transient loading. This collaborative work with the Technical University of Munich has been presented and published at the 44th European Rotorcraft Forum 2018.
Research personnel: Daiju Uehara
Coaxial rotor wake measurement in hover using Particle Image Velocimetry (PIV)
The flow field of a coaxial, counter-rotating rotor is considerably more complex than that of a conventional isolated single rotor, due to the close proximity of the two rotors rotating in opposite directions. To examine the flow interaction between two rotor wakes during blade passages, flow field visualization measurements were performed using phase-resolved and time-resolved PIV.
Research personnel: Patrick Mortimer
Supersonic Fluid-Structure Interaction of Compliant Panel with Ramp-induced Shock Wave
The interaction between a turbulent boundary layer and an oblique shock wave is known to exhibit low-frequency, unsteady behavior. If the structure at the location of shock interaction is not rigid, but rather a compliant panel, the dynamics of the panel can couple with the shock motion and result in destructive oscillations of the structure. In a supersonic wind tunnel, a set of experiments is performed to analyze the aeroelastic coupling and to investigate its mechanisms. Optical techniques such as digital image correlation, pressure-sensitive paint, and particle image velocimetry are used simultaneously to obtain a full picture of the dynamics of the coupled system.
Research personnel: Marc Eitner
Experimental Testing and Modeling of a Phase-Controlled Stacked Rotor
Electric vertical takeoff and landing (eVTOL) vehicles have experienced increasing interest over recent years. Electrifying aircraft facilitates unique designs concepts to improve vehicle performance over traditional gas-driven systems since distributing power becomes much easier than via mechanical transmission. However, a major drawback from using electrical propulsion is the decreased energy storge from batteries. This research project explores a novel rotorcraft configuration that aims to improve the performance of vertical flight aircraft and facilitate the use of electric power in aviation. The concept utilizes two helicopter rotors stacked on top of each other, each driven by independently-controlled electric motors as shown in Fig. 1. The novelty of the concept is shown by the ability of this system to change thrust in-flight via modifying the geometry of the stacked rotor blades, or more specifically the index angle between the rotor blades, denoted by ϕ in Fig. 2. This is believed to produce less power requirements to vary total rotor thrust than a traditional speed control scheme. This research includes both modeling and experimental testing to predict and validate the performance of this unique aircraft concept. A video of the active index angle control scheme can be seen here.
Research personnel: Matt Asper
Performance and Acoustics of a Stacked Rotor
A stacked rotor, or coaxial co-rotating rotor, employs two two-bladed rotors, spaced axially and azimuthally. The unconventional spacing of blades gives rise to performance and acoustic variation that has benefits for a wide range of applications such as surveillance and Urban Air Mobility. This project was originally funded by Uber Elevate and is now a five-year project with the Vertical Lift Research Center of Excellence (VLRCOE) for 2021-2026. The objective of this research is to measure acoustics and loads in our outdoor facility and to quantify the effects of stacked rotor spacing on flow interactions with Particle Image Velocimetry (PIV).
Research personnel: Chloe Johnson
Full Airframe Sensing Technology for hypersonic vehicles (FAST)
A novel sensing technology is developed that can infer the state of a hypersonic vehicle (such as angle of attack, Mach number, yaw angle,…) from a set of discrete strain and temperature measurements on the inner mold line. Four Universities work with Sandia National Laboratories and Lockheed Martin on this project, which is funded through the AFOSR/NASA University Leadership Initiative program. Dr. Sirohi’s group designs and fabricates multiple models ranging from 1-5 feet in length. The smallest model will be tested in a hypersonic wind tunnel. The larger models will be tested on a benchtop setup, where static and vibratory loads will be applied through force actuators and shakers. Measurements will focus on state-of-the-art fiber-optical sensing technology, as well as camera-based methods such as digital image correlation and pressure sensitive paint.
Research personnel: Aditya Panigrahi