RANS/LES Simulation of Low-Frequency Flow Oscillations on a NACA0012 Airfoil Near Stall

2021 ◽  
Author(s):  
Wei YANG ◽  
Zhaolin FAN ◽  
XiaoBing DENG ◽  
Xiaohui ZHAO
Keyword(s):  
Low Frequency ◽  
Naca0012 Airfoil ◽  
Flow Oscillations

Dynamic Stability of a Water Brake Dynamometer

1998 ◽  
Vol 120 (1) ◽  
pp. 89-96 ◽  
Author(s):  
R. A. Van den Braembussche ◽  
H. Malys
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Lumped Parameter Model ◽  
Stable Operation ◽  
Pressure Oscillations ◽  
Lumped Parameter ◽  
Flow Oscillations ◽  
Brake Dynamometer ◽  
Low Torque ◽  
Frequency Variations

A lumped parameter model to predict the high frequency pressure oscillations observed in a water brake dynamometer is presented. It explains how the measured low frequency variations of the torque are a consequence of the variation in amplitude of the high frequency flow oscillations. Based on this model, geometrical modifications were defined, aiming to suppress the oscillations while maintaining mechanical integrity of the device. An experimental verification demonstrated the validity of the model and showed a very stable operation of the modified dynamometer even at very low torque.

Numerical Simulations of Isothermal Flow in a Swirl Burner

2006 ◽  
Author(s):  
Manuel Garci´a-Villalba ◽  
Jochen Fro¨hlich ◽  
Wolfgang Rodi
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Reacting Flow ◽  
Swirl Burner ◽  
Eddy Simulation ◽  
Pressure Time ◽  
Time Signals ◽  
Flow Oscillations ◽  
Conditional Averaging ◽  
Annular Jets

In this paper; the non-reacting flow in a swirl burner is studied using Large Eddy Simulation. The configuration consists of two unconfined co-annular jets at a Reynolds number of 81500. The flow is characterized by a Swirl number of 0.93. Two cases are studied in the paper differing with respect to the axial location of the inner pilot jet. It was observed in a companion experiment (Bender and Bu¨chner, 2005) that when the inner jet is retracted the flow oscillations are considerably amplified. This is also found in the present simulations. Large-scale coherent structures rotating at a constant rate are observed when the inner jet is retracted. The rotation of the structures leads to vigorous oscillations in the velocity and pressure time signals recorded at selected points in the flow. In addition, the mean velocities, the turbulent fluctuations and the frequency of the oscillations are in good agreement with the experiments. A conditional averaging procedure is used to perform a detailed analysis of the physics leading to the low-frequency oscillations.

EFFECTS OF BOUNDARY-LAYER THICKNESS ON FLOW OSCILLATIONS INSIDE OPEN CAVITIES AT SUPERSONIC SPEEDS

2010 ◽  
Vol 24 (04n05) ◽  
pp. 487-493
Author(s):  
DANG-GUO YANG ◽  
ZHAO-LIN FAN ◽  
JIANG-QIANG LI ◽  
DAN YAO
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Low Frequency ◽  
Cavity Depth ◽  
Oscillation Modes ◽  
Open Cavities ◽  
Flow Oscillations ◽  
Unsteady Characteristics ◽  
Modified Equation

An experiment was conducted in a wind-tunnel to study the internal acoustic field and flow oscillations inside rectangular-box cavities. The length-to-depth ratio of the cavities was 8. The data presented herein was obtained over a Mach number of 1.5 at a Reynolds number of 2.26×107 per meter with different boundary-layer thicknesses of approximately 24 mm and 5.5 mm. The experimental angle of attack, yawing and rolling angles were 0°. The rules were revealed as governing the effects of boundary-layer thickness on flow oscillations and unsteady characteristics by comparing the experimental results with flow oscillation modes predicated by Rossiter's and Heller's modified equation. The results indicate that a decrease in the ratio of boundary-layer thickness to cavity-depth (δ/D) induces flow oscillations amplification, peak oscillation frequency splitting and shifting phenomena of open cavity tones in the low-frequency region.

The Effect of Airfoil Shape on Trailing Edge Noise

2019 ◽  
Vol 27 (02) ◽  
pp. 1850020 ◽  
Author(s):  
Seongkyu Lee
Keyword(s):  
Boundary Layer ◽  
Noise Source ◽  
Source Region ◽  
Low Frequency ◽  
Suction Side ◽  
Frequency Noise ◽  
Pressure Side ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Naca0012 Airfoil

This paper investigates the effect of airfoil shape on trailing edge noise. The boundary layer profiles are obtained by XFOIL and the trailing edge noise is predicted by a TNO semi-empirical model. In order to investigate the noise source characteristics, the wall pressure spectrum is decomposed into three components. This decomposition helps in finding the dominant source region and the peak noise frequency for each airfoil. The method is validated for a NACA0012 airfoil, and then five additional wind turbine airfoils are examined: NACA0018, DU96-w-180, S809, S822 and S831. It is found that the dominant source region is around 40% of the boundary layer thickness for both the suction and pressure sides for a NACA0012 airfoil. As airfoil thickness and camber increase, the maximum source region moves slightly upward on the suction side. However, the effect of the airfoil shape on the maximum source region on the pressure side is negligible, except for the S831 airfoil, which exhibits an extension of the noise source region near the wall at high frequencies. As airfoil thickness and camber increase, low frequency noise is increased. However, a higher camber reduces low frequency noise on the pressure side. The maximum camber position is also found to be important and its rear position increases noise levels on the suction side.

scholarly journals Mixed-mode dynamics of certain bistable oscillators: behavioural mapping, approximations for motion and links with van der Pol oscillators

2015 ◽  
Vol 471 (2184) ◽  
pp. 20150638 ◽  
Author(s):  
Ivana Kovacic ◽  
Matthew Cartmell ◽  
Miodrag Zukovic
Keyword(s):  
Mixed Mode ◽  
Autonomous Systems ◽  
Low Frequency ◽  
Harmonic Excitation ◽  
Van Der Pol Oscillator ◽  
Van Der Pol ◽  
Restoring Force ◽  
Van Der Pol Oscillators ◽  
Flow Oscillations ◽  
Fast Flow

This study is concerned with a new generalized mathematical model for single degree-of-freedom bistable oscillators with harmonic excitation of low-frequency, linear viscous damping and a restoring force that contains a negative linear term and a positive nonlinear term which is a power-form function of the generalized coordinate. Comprehensive numerical mapping of the range of bifurcatory behaviour shows that such non-autonomous systems can experience mixed-mode oscillations, including bursting oscillations (fast flow oscillations around the outer curves of a slow flow), and relaxation oscillations like a classical (autonomous) van der Pol oscillator. After studying the global system dynamics the focus of the investigations is on cubic oscillators of this type. Approximate techniques are presented to quantify their response, i.e. to determine approximations for both the slow and fast flows. In addition, a clear analogy between the behaviour of two archetypical oscillators—the non-autonomous bistable oscillator operating at low frequency and the strongly damped autonomous van der Pol oscillator—is established for the first time.

Numerical Simulations of Isothermal Flow in a Swirl Burner

2006 ◽  
Vol 129 (2) ◽  
pp. 377-386 ◽  
Author(s):  
M. García-Villalba ◽  
J. Fröhlich ◽  
W. Rodi
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Reacting Flow ◽  
Swirl Burner ◽  
Eddy Simulation ◽  
Pressure Time ◽  
Constant Rate ◽  
Time Signals ◽  
Flow Oscillations ◽  
Conditional Averaging

In this paper, the non-reacting flow in a swirl burner is studied using large eddy simulation. The configuration consists of two unconfined coannular jets at a Reynolds number of 81,500. The flow is characterized by a Swirl number of 0.93. Two cases are studied in the paper differing with respect to the axial location of the inner pilot jet. It was observed in a companion experiment (Bender and Büchner, 2005, Proc. 12 Int. Cong. Sound and Vibration, Lisbon, Portugal) that when the inner jet is retracted the flow oscillations are considerably amplified. This is also found in the present simulations. Large-scale coherent structures rotating at a constant rate are observed when the inner jet is retracted. The rotation of the structures leads to vigorous oscillations in the velocity and pressure time signals recorded at selected points in the flow. In addition, the mean velocities, the turbulent fluctuations, and the frequency of the oscillations are in good agreement with the experiments. A conditional averaging procedure is used to perform a detailed analysis of the physics leading to the low-frequency oscillations.

scholarly journals Low-frequency blood flow oscillations in congestive heart failure and after β1-blockade treatment

2008 ◽  
Vol 76 (3) ◽  
pp. 224-232 ◽  
Author(s):  
A. Bernjak ◽  
P.B.M. Clarkson ◽  
P.V.E. McClintock ◽  
A. Stefanovska
Keyword(s):  
Heart Failure ◽  
Congestive Heart Failure ◽  
Blood Flow ◽  
Low Frequency ◽  
Blood Flow Oscillations ◽  
Flow Oscillations
Sign in / Sign up

Export Citation Format

Share Document