Influence of Reynolds Number on the Unsteady Aerodynamics of Integrated Aggressive Intermediate Turbine Duct

2018 ◽  
Vol 27 (3) ◽  
pp. 294-303 ◽  
Author(s):  
Hongrui Liu ◽  
Jun Liu ◽  
Lucheng Ji ◽  
Qiang Du ◽  
Guang Liu ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Unsteady Aerodynamics ◽  
Intermediate Turbine Duct

scholarly journals Lift Generation of an Elliptical Airfoil at a Reynolds Number of 1000

2019 ◽  
Vol 16 (2) ◽  
pp. 6738-6752
Author(s):  
S. Tobing
Keyword(s):  
Reynolds Number ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Two Dimensional ◽  
Hovering Flight ◽  
Number Range ◽  
High Production ◽  
Passenger Aircraft ◽  
3D Wing

Bumblebees cannot fly! That conclusion is likely to be drawn by scientists who analysed the insect using aerodynamics of stationary wings such as that of a passenger aircraft. Looking at the insect again using a newfound understanding of unsteady aerodynamics; it is clear why bumblebees can fly. Bumblebees utilise mechanisms behind unsteady aerodynamics such as leading-edge vortices (LEVs) formation, wake capture, and rapid end-of-stroke rotation to generate forces that enable the insect to fly. This study focuses on two-dimensional (2D) elliptical airfoil. Earlier works found the aerodynamic characteristics of an elliptical airfoil to differ greatly from a conventional airfoil, and that this airfoil shape could generate the counter-rotating vortices used by insects to generate lift. Therefore, this research aims to study the lift generation of a bumblebee-inspired elliptical airfoil in a normal hovering flight. This study focuses on hovering flight with the insect flies in a nearly stationary position, which explains the importance of lift generation to stay aloft. The motion of the elliptical airfoil is inspired by the flapping kinematics of bumblebees at a typical Reynolds number range of . It is found that the current two-dimensional model is capable of capturing the counter-rotating vortices and correlates the formation of these structures to a high production of lift. These results show that bumblebees utilise these counter-rotating vortices to generate lift enough to fly in hovering flight. This results also indicate that flapping 2D elliptical airfoils can be used to investigate their 3D wing counterparts, which translate to a reduced time and computing costs.

Numerical investigation of the effect of triangular cavity on the unsteady aerodynamics of NACA 0012 at a low Reynolds number

2021 ◽  
pp. 095441002110270
Author(s):  
Rajesh Yadav ◽  
Aslesha Bodavula
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Unsteady Aerodynamics ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Accurate Solution ◽  
Low Reynolds Numbers ◽  
State Regime ◽  
Low Reynolds ◽  
Naca 0012

Time accurate numerical simulations were conducted to investigate the effect of triangular cavities on the unsteady aerodynamic characteristics of NACA 0012 airfoil at a Reynolds number of 50,000. Right-angled triangular cavities are placed at 10%, 25% and 50% chord location on the suction and have depths of 0.025c and 0.05c, measured normal to the surface of the airfoil. The second-order accurate solution to the RANS equations is obtained using a pressure-based finite volume solver with a four-equation transition turbulence model, γ–Re θt, to model the effect of turbulence. The two-dimensional results suggest that the cavity of depth 0.025c at 10% chord improves the aerodynamic efficiency ( l/d ratio) by 52%, at an angle of attack of α = 8°, wherein the flow is steady. The shallower triangular cavity when placed at 25%c and 50%c enhances the l/d ratio by only 10% and 17%, respectively, in the steady-state regime of angles of attack between α = 6° and 10°. The deeper cavity also enhances the l/d ratio by up to 13%, 22% and 14% at angles of attack between α = 6° and 10°. Even in the unsteady vortex shedding regime, at α =12° and higher, significant improvements in the time-averaged l/d ratios are observed for both cavity depths. The improvements in l/d ratio in the steady-state, pre-stall regime are primarily because of drag reduction while in the post-stall, unsteady regime, the improvements are because of enhancements in time-averaged C l values. The current finding can thus be used to enhance the aerodynamic performance of MAVs and UAVs that fly at low Reynolds numbers.

Viscous extension of potential-flow unsteady aerodynamics: the lift frequency response problem

2019 ◽  
Vol 868 ◽  
pp. 141-175 ◽  
Author(s):  
Haithem Taha ◽  
Amir S. Rezaei
Keyword(s):  
Reynolds Number ◽  
Stokes Equations ◽  
Unsteady Aerodynamics ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Low Reynolds Numbers ◽  
High Frequencies ◽  
Kutta Condition ◽  
Low Reynolds

The application of the Kutta condition to unsteady flows has been controversial over the years, with increased research activities over the 1970s and 1980s. This dissatisfaction with the Kutta condition has been recently rejuvenated with the increased interest in low-Reynolds-number, high-frequency bio-inspired flight. However, there is no convincing alternative to the Kutta condition, even though it is not mathematically derived. Realizing that the lift generation and vorticity production are essentially viscous processes, we provide a viscous extension of the classical theory of unsteady aerodynamics by relaxing the Kutta condition. We introduce a trailing-edge singularity term in the pressure distribution and determine its strength by using the triple-deck viscous boundary layer theory. Based on the extended theory, we develop (for the first time) a theoretical viscous (Reynolds-number-dependent) extension of the Theodorsen lift frequency response function. It is found that viscosity induces more phase lag to the Theodorsen function particularly at high frequencies and low Reynolds numbers. The obtained theoretical results are validated against numerical laminar simulations of Navier–Stokes equations over a sinusoidally pitching NACA 0012 at low Reynolds numbers and using Reynolds-averaged Navier–Stokes equations at relatively high Reynolds numbers. The physics behind the observed viscosity-induced lag is discussed in relation to wake viscous damping, circulation development and the Kutta condition. Also, the viscous contribution to the lift is shown to significantly decrease the virtual mass, particularly at high frequencies and Reynolds numbers.

Unsteady aerodynamics of a pitching-flapping-perturbed revolving wing at low Reynolds number

2018 ◽  
Vol 30 (5) ◽  
pp. 051903 ◽  
Author(s):  
Long Chen ◽  
Jianghao Wu ◽  
Chao Zhou ◽  
Shih-Jung Hsu ◽  
Bo Cheng
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Unsteady Aerodynamics ◽  
Low Reynolds

On Some Aspects of Unsteady Aerodynamics and Vortex Induced Oscillations of Elliptic Cylinders at Subcritical Reynolds Number

1978 ◽  
Vol 100 (2) ◽  
pp. 354-362 ◽  
Author(s):  
V. J. Modi ◽  
L. Ieong
Keyword(s):  
Reynolds Number ◽  
Wind Velocity ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Number Range ◽  
Extensive Test ◽  
Number Variation ◽  
In The Beginning

The paper presents results of an extensive test program aimed at better understanding of unsteady aerodynamics and vortex induced oscillations of a family of two dimensional elliptic cylinders in the Reynolds number range of 3 × 104 – 105. In the beginning, results on Strouhal number variation with cylinder eccentricity and angle of attack are presented which can be used to predict critical resonant velocity once the structural properties are identified. This is followed by the data on the fluctuating pressure at the surface of the cylinders which suggest their three dimensional character and significant dependence on the Reynolds number. However, the unsteady, sectional lift coefficient, obtained through integration of the pressure data, is virtually independent of the spanwise location. The correlation of phase between unsteady pressure signals along the span showed parabolic character of the vortexline at zero angle of attack of the model, but the vortexline tends to be straight and its alignment with the model improves as the angle of attack increases. On the other hand, the presence of end gaps (between the model and tunnel walls) results in a parabolic vortexline at all angles of attack. During the vortex excited oscillations, the familiar ‘capture’ phenomenon is exhibited where the vortex shedding frequency is controlled by the cylinder vibration over a finite range of wind velocity. Detailed measurements of cylinder and Strouhal frequencies, displacement amplitude and phase angle as functions of wind velocity, cylinder eccentricity and angle of attack provide information which should prove useful during design of such structural members.

scholarly journals A Computational Investigation of Unsteady Aerodynamics of Insect-Inspired Fixed Wing Micro Aerial Vehicle’s 2D Airfoil

2014 ◽  
Vol 2014 ◽  
pp. 1-7
Author(s):  
Somashekar V
Keyword(s):  
Reynolds Number ◽  
Control Volume ◽  
Unsteady Aerodynamics ◽  
Aerodynamic Characteristics ◽  
Research Field ◽  
Drag Coefficients ◽  
Unsteady Aerodynamic ◽  
Air Vehicle ◽  
Lift And Drag ◽  
2D Airfoil

A Micro air vehicle (MAV) is defined as class of unmanned air vehicle (UAV) having a linear dimension of less than 15 centimeters and a mass of less than 100 grams with flight speeds of 6 to 12 meters per second. MAVs fall within a Reynolds number (Re) range of 50,000 and 120,000, in which many causes of unsteady aerodynamic effects are not fully understood. The research field of low Reynolds number aerodynamics is currently an active one, with many defence organizations, universities, and corporations working towards a better understanding of the physical processes of this aerodynamic regime. In the present work, it is proposed to study the unsteady aerodynamic analysis of 2D airfoil using CFD software and Xfoil panel code method. The various steps involved in this work are geometric modelling using CATIA V5R17, meshing using ICEM CFD, and solution and postprocessing through FLUENT. The finite control volume analysis and Xfoil panel code method has been carried out to predict aerodynamic characteristics such as lift coefficients, drag coefficients, moment coefficients, pressure coefficients, and flow visualization. The lift and drag coefficients were compared for all the simulations with experimental results. It was observed that for the 2D airfoil, lift and drag both compared well for the midrange angle of attack from −10 to 15 degree AOA.

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