ANALYSIS OF UNSTEADY CHARACTERISTICS OF THE FLOW FIELD AT HIGH ANGLE OF ATTACK

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1583-1586
Author(s):  
ZHAO LIN FAN ◽  
YUAN JING WANG ◽  
QUAN ZHOU LU
Keyword(s):  
Flow Field ◽  
Angle Of Attack ◽  
Dynamic Measurement ◽  
High Angle ◽  
High Angle Of Attack ◽  
Key Factor ◽  
The Asymmetry ◽  
Unsteady Characteristics ◽  
Energy Components

Energy components in the flow field at high angle of attack were analyzed by the dynamic measurement. The effect of the unsteadiness induced by these components on the flow was analyzed as well. The results showed that the flow itself at high angle of attack is a kind of "vortices behavior" and the effect of unsteadiness on the asymmetry of flow is relatively weak. The key factor that can essentially affect the flow at high angle of attack is the response of the dynamic unsteadiness of the vortices to the unpredictable micro-disturbance coming from near the nose of the model.

Fan-Intake Coupling With Conventional and Short Intakes

2021 ◽  
Author(s):  
E. J. Gunn ◽  
T. Brandvik ◽  
M. J. Wilson
Keyword(s):  
Flow Field ◽  
Potential Flow ◽  
Pressure Ratio ◽  
Current Trend ◽  
Angle Of Attack ◽  
High Angle ◽  
High Angle Of Attack ◽  
Field Distortion ◽  
Intake Flow ◽  
The Impact

Abstract The current trend in civil engine fans towards lower pressure ratio and larger diameter is accompanied by a need to shorten the engine intake length to reduce weight and drag. This paper uses full-annulus, unsteady CFD simulations of two coupled fan-intake configurations to explain the impact of flow field coupling and intake length on fan and intake performance. On-design and off-design operating points are considered at cruise and high angle of attack, respectively. The fan efficiency at cruise is shown to be determined by a trade-off between two effects. Cruise efficiency is reduced by 0.11% with a short intake due to increased potential flow field distortion, which alters the incidence and diffusion of the rotor. This is partially offset by a reduction in casing boundary layer thickness due to lower intake wetted area. At high angle of attack conditions, a short intake leads to increased potential flow field distortion and an earlier onset of intake flow separation due to a higher adverse pressure gradient approaching the fan. Both effects combine to reduce the fan thrust at such conditions, although the fan is shown to remain stable at attack angles up to 35°. The reduction in performance is shown to be dominated by flow separations in the rotor, which increase in size and severity for a given attack angle as the intake length is decreased. The fan is also shown to have a stronger influence on the form of the intake flow field in a short intake, suggesting that it is necessary to model the fan in the intake design process for a successful design.

Detached Eddy Simulation of Complex Separation Flows Over a Modern Fighter Model at High Angle of Attack

2017 ◽  
Vol 22 (5) ◽  
pp. 1309-1332 ◽  
Author(s):  
Yang Zhang ◽  
Laiping Zhang ◽  
Xin He ◽  
Xiaogang Deng ◽  
Haisheng Sun
Keyword(s):  
Flow Field ◽  
Angle Of Attack ◽  
Vortical Flow ◽  
Leeward Side ◽  
Detached Eddy Simulation ◽  
High Angle ◽  
Flow Topology ◽  
High Angle Of Attack ◽  
Eddy Simulation ◽  
Separation Flows

AbstractThis paper presents the simulation of complex separation flows over a modern fighter model at high angle of attack by using an unstructured/hybrid grid based Detached Eddy Simulation (DES) solver with an adaptive dissipation second-order hybrid scheme. Simulation results, including the complex vortex structures, as well as vortex breakdown phenomenon and the overall aerodynamic performance, are analyzed and compared with experimental data and unsteady Reynolds-Averaged Navier-Stokes (URANS) results, which indicates that with the DES solver, clearer vortical flow structures are captured and more accurate aerodynamic coefficients are obtained. The unsteady properties of DES flow field are investigated in detail by correlation coefficient analysis, power spectral density (PSD) analysis and proper orthogonal decomposition (POD) analysis, which indicates that the spiral motion of the primary vortex on the leeward side of the aircraft model is highly nonlinear and dominates the flow field. Through the comparisons of flow topology and pressure distributions with URANS results, the reason why higher and more accurate lift can be obtained by DES is discussed. Overall, these results show the potential capability of present DES solver in industrial applications.

scholarly journals Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

2021 ◽  
Vol 11 (6) ◽  
pp. 2593
Author(s):  
Yasir Al-Okbi ◽  
Tze Pei Chong ◽  
Oksana Stalnov
Keyword(s):  
Boundary Layer ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Shear Instability ◽  
Vortical Flow ◽  
High Angle ◽  
High Angle Of Attack ◽  
Layer Separation ◽  
Aerodynamic Performances

Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence–leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence–leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively.

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