Adjoint-Based Aerodynamic Shape Optimization for Low Reynolds Number Airfoils

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Juanmian Lei ◽  
Jiandong He
Keyword(s):  
Reynolds Number ◽  
Shape Optimization ◽  
Low Reynolds Number ◽  
Boundary Layer Separation ◽  
Small Scale ◽  
Test Case ◽  
Aerodynamic Shape Optimization ◽  
Aerodynamic Shape ◽  
Aerial Vehicles ◽  
Low Reynolds

In the past decades, most of the research studies on airfoil shape design and optimization were focused on high Reynolds number airfoils. However, low Reynolds number airfoils have attracted significant attention nowadays due to their vast applications, ranging from micro-aerial vehicles (MAVs) to small-scale unmanned aerial vehicles. For low Reynolds number airfoils, the unsteady effects caused by boundary layer separation cannot be neglected. In this paper, we present an aerodynamic shape optimization framework for low Reynolds number airfoil that we developed based on the unsteady laminar N–S equation and the adjoint method. Finally, using the developed framework, we performed a test case with NACA0012 airfoil as a baseline configuration and the inverse of lift to drag ratio as the cost function. The optimization was carried out at Re = 10,000 and Ma = 0.2. The results demonstrate the effectiveness of the framework.

Numerical shape optimization in Fluid Mechanics at low Reynolds number

2019 ◽  
Author(s):  
Alexis Courtais ◽  
Francois Lesage ◽  
Yannick Privat ◽  
Pascal Frey ◽  
Abderrazak M. Latifi
Keyword(s):  
Reynolds Number ◽  
Fluid Mechanics ◽  
Shape Optimization ◽  
Low Reynolds Number ◽  
Low Reynolds

A bioinspired Separated Flow wing provides turbulence resilience and aerodynamic efficiency for miniature drones

2020 ◽  
Vol 5 (38) ◽  
pp. eaay8533 ◽  
Author(s):  
Matteo Di Luca ◽  
Stefano Mintchev ◽  
Yunxing Su ◽  
Eric Shaw ◽  
Kenneth Breuer
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Low Reynolds Number ◽  
Substantial Reduction ◽  
Separated Flow ◽  
Small Scale ◽  
Freestream Turbulence ◽  
Flight Duration ◽  
Aerodynamic Efficiency ◽  
Low Reynolds

Small-scale drones have enough sensing and computing power to find use across a growing number of applications. However, flying in the low–Reynolds number regime remains challenging. High sensitivity to atmospheric turbulence compromises vehicle stability and control, and low aerodynamic efficiency limits flight duration. Conventional wing designs have thus far failed to address these two deficiencies simultaneously. Here, we draw inspiration from nature’s small flyers to design a wing with lift generation robust to gusts and freestream turbulence without sacrificing aerodynamic efficiency. This performance is achieved by forcing flow separation at the airfoil leading edge. Water and wind tunnel measurements are used to demonstrate the working principle and aerodynamic performance of the wing, showing a substantial reduction in the sensitivity of lift force production to freestream turbulence, as compared with the performance of an Eppler E423 low–Reynolds number wing. The minimum cruise power of a custom-built 104-gram fixed-wing drone equipped with the Separated Flow wing was measured in the wind tunnel indicating an upper limit for the flight time of 170 minutes, which is about four times higher than comparable existing fixed-wing drones. In addition, we present scaling guidelines and outline future design and manufacturing challenges.

A Study of a Modern Transonic Fan Rotor in a Low Reynolds Number Regime for a Small Turbofan Engine

2013 ◽  
Author(s):  
Toyotaka Sonoda ◽  
Rainer Schnell ◽  
Toshiyuki Arima ◽  
Giles Endicott ◽  
Eberhard Nicke
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Turbofan Engine ◽  
Pressure Surface ◽  
Low Reynolds ◽  
High Reynolds ◽  
Transonic Fan

In this paper, Reynolds effects on a modern transonic low-aspect-ratio fan rotor (Baseline) and the re-designed (optimized) rotor performance are presented with application to a small turbofan engine. The re-design has been done using an in-house numerical optimization system in Honda and the confirmation of the performance was carried out using DLR’s TRACE RANS stage code, assessed with respect to experimental data obtained from a small scale compressor rig in Honda. The baseline rotor performance is evaluated at two Reynolds number conditions, a high Reynolds condition (corresponding to a full engine scale size) and a low Reynolds number condition (corresponding to the small scale compressor rig size), using standard ISA conditions. The performance of the optimized rotor was evaluated at the low Reynolds number condition. The CFD results show significant discrepancies in the rotor efficiency (about 1% at cruise) between these two points due to the different Reynolds numbers. The optimized rotor’s efficiency is increased compared to the baseline. A unique negative curvature region close to the leading edge on the pressure surface of the optimized rotor is one of the reasons why the optimized rotor is superior to the baseline.

scholarly journals Rotation of a low-Reynolds-number watermill: theory and simulations

2018 ◽  
Vol 849 ◽  
pp. 57-75 ◽  
Author(s):  
Lailai Zhu ◽  
Howard A. Stone
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Rotational Symmetry ◽  
Low Reynolds Number ◽  
Rotational Velocity ◽  
Microfluidic Channel ◽  
Hydrodynamic Interactions ◽  
Small Scale ◽  
Low Reynolds

Recent experiments have demonstrated that small-scale rotary devices installed in a microfluidic channel can be driven passively by the underlying flow alone without resorting to conventionally applied magnetic or electric fields. In this work, we conduct a theoretical and numerical study on such a flow-driven ‘watermill’ at low Reynolds number, focusing on its hydrodynamic features. We model the watermill by a collection of equally spaced rigid rods. Based on the classical resistive force (RF) theory and direct numerical simulations, we compute the watermill’s instantaneous rotational velocity as a function of its rod number $N$, position and orientation. When $N\geqslant 4$, the RF theory predicts that the watermill’s rotational velocity is independent of $N$ and its orientation, implying the full rotational symmetry (of infinite order), even though the geometrical configuration exhibits a lower-fold rotational symmetry; the numerical solutions including hydrodynamic interactions show a weak dependence on $N$ and the orientation. In addition, we adopt a dynamical system approach to identify the equilibrium positions of the watermill and analyse their stability. We further compare the theoretically and numerically derived rotational velocities, which agree with each other in general, while considerable discrepancy arises in certain configurations owing to the hydrodynamic interactions neglected by the RF theory. We confirm this conclusion by employing the RF-based asymptotic framework incorporating hydrodynamic interactions for a simpler watermill consisting of two or three rods and we show that accounting for hydrodynamic interactions can significantly enhance the accuracy of the theoretical predictions.

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