Unsteady Lift for the Wagner Problem of Starting Flow at Very Large Angle of Attack

2015 ◽  
Author(s):  
Juan Li ◽  
Chen-Yuan Bai ◽  
Zi-Niu Wu
Keyword(s):  
Normal Force ◽  
Angle Of Attack ◽  
Large Angle ◽  
Oscillatory Behavior ◽  
Correct Prediction ◽  
Force Coefficient ◽  
Trailing Edge ◽  
A Value ◽  
Starting Flow ◽  
Unsteady Lift

A total vortex force line (TVFL) method has been proposed recently which is capable of studying and understanding the unsteady lift force behavior of inviscid starting flow of a flat plate at an angle of attack (AoA) up to 20 degree. The role of additional leading and trailing edge vortices on the Wagner lift curve has been correctly analyzed. In this paper we consider starting flow at much higher AoAs. By comparing with CFD simulations, we find that the TVFL method, derived originally for lift, predicts well the normal force for large angle of attack up to 40 degree. The oscillatory behavior of the normal force is related to leading and trailing edge vortices in a similar way as the lift oscillation for lower angle of attack. It is shown that apart from the initial singularity, the peak value of the normal force coefficient does not exceed a value around 3. Since the TVFL method can clearly identify the origins of lift increasing or decreasing mechanisms due to vortices, the correct prediction of the normal force for large AoAs means that this method can be used to study flapping flight problems.

scholarly journals Experimental Study of Sand Particle Deposition on a Film-Cooled Turbine Blade at Different Gas Temperatures and Angles of Attack

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 811 ◽  
Author(s):  
Fei Zhang ◽  
Zhenxia Liu ◽  
Zhengang Liu ◽  
Weinan Diao
Keyword(s):  
Turbine Blade ◽  
Film Cooling ◽  
Particle Deposition ◽  
Angle Of Attack ◽  
Large Angle ◽  
Capture Efficiency ◽  
Gas Temperature ◽  
Trailing Edge ◽  
Pressure Surface ◽  
Film Cooling Holes

Particle deposition tests were conducted in a turbine deposition facility with an internally staged single-tube combustor to investigate the individual effect of the gas temperature and angle of attack. Sand particles were seeded to the combustor and deposited on a turbine blade with film-cooling holes at temperatures representative of modern engines. Fuel-air ratios were varied from 0.022 to 0.037 to achieve a gas temperature between 1272 and 1668 K. Results show that capture efficiency increased with increasing gas temperature. A dramatic increase in capture efficiency was noted when gas temperature exceeded the threshold. The deposition formed mostly downstream of the film-cooling holes on the pressure surface, while it concentrated on the suction surface at the trailing edge. Deposition tests at angles of attack between 10° and 40° presented changes in both deposition mass and distribution. The capture efficiency increased with the increase in the angle of attack, and simultaneously the growth rate slowed down. On the blade pressure surface, sand deposition was distributed mainly downstream of the film-cooling holes near the trailing edge in the case of the small angle of attack, while it concentrated on the region around the film-cooling holes near the leading edge, resulting in the partial blockage of holes, in the case of the large angle of attack.

Unsteady aerodynamic characteristics of a morphing wing

2018 ◽  
Vol 91 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Jinwu Xiang ◽  
Kai Liu ◽  
Daochun Li ◽  
Chunxiao Cheng ◽  
Enlai Sha
Keyword(s):  
Lift Coefficient ◽  
Angle Of Attack ◽  
Large Angle ◽  
Unsteady Aerodynamics ◽  
Aerodynamic Characteristics ◽  
Static Case ◽  
Morphing Wing ◽  
Trailing Edge ◽  
Content Type ◽  
Unsteady Aerodynamic

Purpose The purpose of this paper is to investigate the unsteady aerodynamic characteristics in the deflection process of a morphing wing with flexible trailing edge, which is based on time-accurate solutions. The dynamic effect of deflection process on the aerodynamics of morphing wing was studied. Design/methodology/approach The computational fluid dynamic method and dynamic mesh combined with user-defined functions were used to simulate the continuous morphing of the flexible trailing edge. The steady aerodynamic characteristics of the morphing deflection and the conventional deflection were studied first. Then, the unsteady aerodynamic characteristics of the morphing wing were investigated as the trailing edge deflects at different rates. Findings The numerical results show that the transient lift coefficient in the deflection process is higher than that of the static case one in large angle of attack. The larger the deflection frequency is, the higher the transient lift coefficient will become. However, the situations are contrary in a small angle of attack. The periodic morphing of the trailing edge with small amplitude and high frequency can increase the lift coefficient after the stall angle. Practical implications The investigation can afford accurate aerodynamic information for the design of aircraft with the morphing wing technology, which has significant advantages in aerodynamic efficiency and control performance. Originality/value The dynamic effects of the deflection process of the morphing trailing edge on aerodynamics were studied. Furthermore, time-accurate solutions can fully explore the unsteady aerodynamics and pressure distribution of the morphing wing.

Separated Flow in a Low-Speed Two-Dimensional Cascade: Part II—Cascade Performance

1993 ◽  
Vol 115 (3) ◽  
pp. 421-434 ◽  
Author(s):  
A. M. Yocum ◽  
W. F. O’Brien
Keyword(s):  
Normal Force ◽  
Full Range ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Leading Edge ◽  
Force Coefficient ◽  
Fundamental Understanding ◽  
Flow Through ◽  
Peak Value ◽  
Made In

This study was conducted for the purpose of providing a more fundamental understanding of separated flow in cascades and to provide performance data for fully stalled blade rows. Cascades of a single blade geometry and a solidity of unity were studied for three stagger angles and the full range of angle of attack extending well into the stalled flow regime. The Reynolds number was also varied for a limited number of cases. Results from velocity and pressure measurements made in the cascade and the overall cascade performance evaluated from these measurements are presented. In addition, results from a numerical simulation of the flow through a cascade of flat plate airfoils are used to illustrate further the effects of blade stagger and to define the correct limits for the cascade performance. The results indicate that the slope of the total pressure loss versus angle of attack curve for the flow immediately downstream of the cascade is steeper for cascades with greater stagger. The normal force coefficient was found to increase to a peak value near the angle of attack where full leading edge stall first occurs. A further increase in angle of attack results in a decline in the normal force coefficient. The peak value of the normal force coefficient is greater and occurs at a higher angle of attack for the cascades with smaller stagger.

scholarly journals Separated Flow in a Low Speed Two-Dimensional Cascade: Part II — Cascade Performance

1992 ◽  
Author(s):  
Adam M. Yocum ◽  
Walter F. O’Brien
Keyword(s):  
Normal Force ◽  
Full Range ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Leading Edge ◽  
Force Coefficient ◽  
Fundamental Understanding ◽  
Flow Through ◽  
Peak Value ◽  
Made In

This study was conducted for the purpose of providing a more fundamental understanding of separated flow in cascades and to provide performance data for fully-stalled blade rows. Cascades of a single blade geometry and a solidity of unity were studied for three stagger angles and the full range of angle of attack extending well into the stalled flow regime. The Reynolds number was also varied for a limited number of cases. Results from velocity and pressure measurements made in the cascade and the overall cascade performance evaluated from these measurements are presented. In addition, results from a numerical simulation of the flow through a cascade of flat plate airfoils are used to further illustrate the effects of blade stagger and to define the correct limits for the cascade performance. The results indicate that the slope of the total pressure loss versus angle of attack curve for the flow immediately downstream of the cascade is steeper for cascades with greater stagger. The normal force coefficient was found to increase to a peak value near the angle of attack where full leading edge stall first occurs. A further increase in angle of attack results in a decline in the normal force coefficient. The peak value of the normal force coefficient is greater and occurs at a higher angle of attack for the cascades with smaller stagger.

Potential Load Reduction Using Airfoils with Variable Trailing Edge Geometry

2005 ◽  
Vol 127 (4) ◽  
pp. 503-516 ◽  
Author(s):  
Thomas Buhl ◽  
Mac Gaunaa ◽  
Christian Bak
Keyword(s):  
Standard Deviation ◽  
Control Algorithm ◽  
Normal Force ◽  
Time Lag ◽  
Turbine Blades ◽  
Angle Of Attack ◽  
Wind Turbine Blades ◽  
Aerodynamic Forces ◽  
Trailing Edge ◽  
Edge Geometry

This paper presents an investigation of the potential for reduction of fluctuating loads on wind turbine blades with the use of flaplike deflectable trailing edges. More specifically, the aeroelastic response of an elastically mounted airfoil section with a deflectable trailing edge is investigated. This is done by coupling a model for the aerodynamic forces on a deforming airfoil with a linear spring/damper model for the elastic deformation of a rigid airfoil to which the forces associated with the deflection of the trailing edge are added. The analysis showed that when the airfoil experienced a wind step from 10to12m∕s the standard deviation of the normal force could be reduced by up to 85% when the flap was controlled by the reading of the airfoil flapwise position and velocity, while reductions of up to 95% could be obtained when the flap was controlled by the reading of the angle of attack. When the airfoil experienced a turbulent wind field, the standard deviation of the normal force could be reduced by 81% for control based on measured angle of attack. The maximum reduction using a combination of flapwise position and velocity was 75%. The maximum deflection of the trailing edge geometry was, in all the considered cases, small enough to justify the use of a potential flow code for calculation of the aerodynamic forces. Calculations showed that the effect of a time lag in the actuators and sensors may drastically reduce the efficiency of the control algorithm. Likewise, the effect of a low maximum actuation velocity reduces the efficiency of the control algorithm. The analysis of the two-dimensional (2D) aeroservoelastic system shown in this paper indicates that the potential of using trailing edge flaps for reduction of fluctuating loads is significant.

Aerodynamic characteristics of a dual-spin projectile with canards

2019 ◽  
Vol 233 (12) ◽  
pp. 4541-4553
Author(s):  
Xiaodong Liu ◽  
Xiaosheng Wu ◽  
Jintao Yin
Keyword(s):  
Mach Number ◽  
Normal Force ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Lateral Force ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Force Coefficient ◽  
Sliding Mesh ◽  
Flow Mechanisms

Based on the three-dimensional Navier–Stokes (N–S) equations, using unsteady numerical technology, flow over a dual-spin projectile was simulated to investigate its aerodynamic characteristics during flight. Spin was achieved via the sliding mesh method. The influence laws of the aftbody spin rate, Mach number, and angle of attack on the aerodynamic characteristics of the projectile are presented, and the flow mechanisms for the laws are revealed. The results demonstrate that the influence of the aftbody spin rate on the normal force coefficient is very small, whereas, on the lateral force coefficient, it is larger. With the increase in the Mach number, the time-averaged normal force coefficient and lateral force coefficient increase, while the fluctuation quantities of the normal force coefficient and the lateral force coefficient decrease. The variation of angle of attack will influence the size, distribution, and interference effect of the shedding vortices.

Supersonic Starting Flow by Accelerated Sinking Movement to Large Angle of Attack

AIAA Journal ◽  
2019 ◽  
Vol 57 (5) ◽  
pp. 1988-2000 ◽  
Author(s):  
Chen-Yuan Bai ◽  
Sheng Li ◽  
Zi-Niu Wu
Keyword(s):  
Angle Of Attack ◽  
Large Angle ◽  
Starting Flow

scholarly journals Comparative Study of Different Turbulence Models for Cavitational Flows around NACA0012 Hydrofoil

2021 ◽  
Vol 9 (7) ◽  
pp. 742
Author(s):  
Minsheng Zhao ◽  
Decheng Wan ◽  
Yangyang Gao
Keyword(s):  
Angle Of Attack ◽  
Large Angle ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Specific Information ◽  
Cloud Cavitation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Shedding Frequency ◽  
Reynolds Average

The present work focuses on the comparison of the numerical simulation of sheet/cloud cavitation with the Reynolds Average Navier-Stokes and Large Eddy Simulation(RANS and LES) methods around NACA0012 hydrofoil in water flow. Three kinds of turbulence models—SST k-ω, modified SST k-ω, and Smagorinsky’s model—were used in this paper. The unstable sheet cavity and periodic shedding of the sheet/cloud cavitation were predicted, and the simulation results, namelycavitation shape, shedding frequency, and the lift and the drag coefficients of those three turbulence models, were analyzed and compared with each other. The numerical results above were basically in accordance with experimental ones. It was found that the modified SST k-ω and Smagorinsky turbulence models performed better in the aspects of cavitation shape, shedding frequency, and capturing the unsteady cavitation vortex cluster in the developing and shedding period of the cavitation at the cavitation number σ = 0.8. At a small angle of attack, the modified SST k-ω model was more accurate and practical than the other two models. However, at a large angle of attack, the Smagorinsky model of the LES method was able to give specific information in the cavitation flow field, which RANS method could not give. Further study showed that the vortex structure of the wing is the main cause of cavitation shedding.

Development of the Third Darrieus Blade of Sultan Wind Turbine for Low Wind Speed

2015 ◽  
Vol 758 ◽  
pp. 13-19 ◽  
Author(s):  
Erwin ◽  
Slamet Wiyono ◽  
Erny Listijorini ◽  
Rina Lusiani ◽  
Tresna P. Soemardi
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Angle Of Attack ◽  
Optimum Combination ◽  
Chord Length ◽  
The Third ◽  
Low Wind Speed ◽  
A Value ◽  
Power Turbine ◽  
Naca 0012

Use of NACA 0012 at the Sultan Wind Turbine prototype provide value coefficient power turbine at wind speed 5.5 m / s by 0017 , wind speed 6.1 m / s at 0.015 , wind speed 7.7 m / s at 0.016 , wind speed 6.5 m / s for 0018 and wind speed 6.2 m / s by 0017 . Where the value of the highest efficiency obtained at a speed of 6.5 m / s at 0.018 . This result is not as expected to generate sufficient energy.The next development carried out investigations on some kind of airfoil, from investigations obtained by using Qblade software that NACA 6612 has a value of 1.78 CL at 15 degrees angle of attack is the largest of all the airfoil .In this research, NACA 6612 will be simulated with a variable chord length, angle of attack, and wind speed, of these three variables will be created which will map graphics 3d sliding value of the ratio of the 3 variables, this graph will give recommendations most optimum combination of variables to types are mapped wind speed throughout the year, to produce optimum power.Optimum combination of NACA 6612 with wind speed varied from 2-7 m/s is chord length 30 cm and angle of attack 7 degree.

Calculations of unsteady viscous flow past a circular cylinder

1958 ◽  
Vol 4 (1) ◽  
pp. 81-86 ◽  
Author(s):  
R. B. Payne
Keyword(s):  
Circular Cylinder ◽  
Viscous Fluid ◽  
Numerical Solution ◽  
Viscous Flow ◽  
Steady Flow ◽  
Reynolds Numbers ◽  
A Value ◽  
Unsteady Viscous Flow ◽  
Starting Flow ◽  
Forward Integration

A numerical solution has been obtained for the starting flow of a viscous fluid past a circular cylinder at Reynolds numbers 40 and 100. The method used is the step-by-step forward integration in time of Helmholtz's vorticity equation. The advantage of working with the vorticity is that calculations can be confined to the region of non-zero vorticity near the cylinder.The general features of the flow, including the formation of the eddies attached to the rear of the cylinder, have been determined, and the drag has been calculated. At R = 40 the drag on the cylinder decreases with time to a value very near that for the steady flow.

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