Research

Data Enhanced Hybrid Modeling

Hybrid models are seen as occupying a significant niche in unsteady aerodynamics. The objective of hybrid simulation is to formulate the model to capture as much of the fluid dynamics as can be resolved, while modeling that which is unresolved via a RANS formulation.

• Supported by: Air Force Office of Scientific Research (AFOSR)
• Funds: $475K
• Performance period: 2022 – 2025

Dynamic Stall

Dynamic stall is a topic of great interest in unsteady flows since it can lead to aerodynamic forces and moments severe enough to cause catastrophic structural failure. Onset of dynamic stall is of particular interest as that is the point where it is easiest to control. We are working on characterizing stall onset with the aim of developing a universal parameter that can indicate stall-onset and can be used to trigger stall control measures.

• Supported by: National Science Foundation
• Funds: $405K
• Performance period: 2019 – 2023

Ultrasonic Bat Deterrents

Jamming their ultrasound signals through artificially-generated ultrasound can dissuade the bats from specific regions. This idea has been used in active’’ ultrasonic deterrents, e.g., by NRG. We are developing a blade-mounted, passive ultrasonic bat deterrent that generates acoustic power using blade-relative air flow. The fundamental idea is to use the instability of a shear layer and couple it with a resonator to generate high-intensity ultrasound. Tonal sound is generated at the desired frequency by tuning the geometry of the resonator. We have demonstrated both passive and active operation of our deterrent in anechoic wind tunnel and chamber.

• Supported by: Department of Energy
• Funds: $950K
• Performance period: 2018 – 2027

Owl-Inspired Ultra-Quiet Blade Designs

The nocturnal owl is known to have an unusually silent flight. The owl plumage has three unique features that are considered responsible for this acoustic stealth. We are numerically and experimentally investigating the silent flight of the night owl, and developing ways to adapt its unique feather features to enable ultra-quiet aircraft propulsion devices including UAVs. The specific research objectives are to

1. identify the true sources of sound produced in the process of turbulence-airfoil interaction,
2. investigate the unique feather adaptations (hush kit) of the owl that enable its silent flight; quantify their noise benefit and aerodynamic performance penalty, and
3. adapt the owl hush kit to develop ultra-quiet UAVs and jet engines. We have developed and verified a computational framework that can predict aerodynamically generated noise with high accuracy. This framework is now being used to develop and verify novel owl-inspired blade designs.
   • Supported by: National Science Foundation
   • Funds: $500K
   • Performance period: 2016 – 2022

Cable Vibration

Inclined cables in various engineering applications (stay-cable bridges, power conductors, etc.) are prone to damage due to different kinds of wind-induced loads - e.g., vortex-induced vibration (VIV), rain wind-induced (RWI) vibration, flutter, etc. Galloping is an aerodynamic instability characterized by low-frequency, large-amplitude oscillations of cables normal to the wind direction. The galloping phenomenon was first observed for ice/sleet coated power conductors and explained by Den Hartog as caused due to an aerodynamic instability. Dry inclined cable galloping, often referred to as dry cable vibration, can occur for inclined circular cables at high wind speeds even when the cross-section remains axisymmetric. The cause of this instability is understood to be the asymmetry in the flow because of the relative yaw between the cable- and wind directions.

• Supported by: National Science Foundation
• Funds: $338K
• Performance period: 2015 – 2019

Dual-Rotor Wind Turbine

Horizontal axis wind turbines suffer from aerodynamic inefficiencies in the blade root region (near the hub) due to several non-aerodynamic constraints. Aerodynamic interactions between turbines in a wind farm also lead to significant loss of wind farm efficiency. We have developed a new dual-rotor wind turbine (DRWT) technology that aims to mitigate these two losses. One DRWT has been designed using an existing turbine rotor (the NREL 5 MW turbine) for the main rotor. The secondary rotor of the DRWT has been designed using a very high lift-to-drag ratio airfoil. Reynolds Averaged Navier-Stokes computational fluid dynamics simulations have been used to optimize the turbine design. Large eddy simulations confirm the potential of the DRWT to enhance energy capture.

• Supported by: National Science Foundation, Iowa Energy Center
• Funds: $438K
• Performance period: 2014 – 2018

Open Rotor Noise

Open rotor is a next-generation engine architecture being evaluated by NASA in conjunction with Airbus/Boeing and GE/R&R. It has a huge (over 10%) potential fuel burn advantage over conventional turbofan engines. However, the aerodynamic noise from the large, un-ducted fan blades is a concern. We have developed time-linearized RANS based methods in frequency domain to predict tonal noise from open rotors. The common sources are: wake-rotor and vortex-rotor interaction noise. Results from these prediction methods have been validated against data obtained during the recent test campaign run by NASA and GE at the low-speed wind tunnel at NASA Glenn.

• Supported by: Federal Aviation Authority
• Funds: $0K
• Performance period: 2008 – 2013

Aeroacoustics Projects

We have worked on several engine aeroacoustics problems. A few of them are described here.

• Supported by: General Electric
• Funds: $0K
• Performance period: 2006 – 2012