scholarly journals Dynamical mode decomposition of Gurney flap wake flow

2011 ◽  
Vol 1 (1) ◽  
pp. 012002 ◽  
Author(s):  
Chong Pan ◽  
Dongsheng Yu ◽  
Jinjun Wang
Keyword(s):  
Wake Flow ◽  
Mode Decomposition ◽  
Gurney Flap ◽  
Dynamical Mode

scholarly journals Using dynamical mode decomposition to extract the limit cycle dynamics of modulated turbulence in a plasma simulation

2019 ◽  
Vol 61 (11) ◽  
pp. 112001 ◽  
Author(s):  
M Sasaki ◽  
Y Kawachi ◽  
R O Dendy ◽  
H Arakawa ◽  
N Kasuya ◽  
...  
Keyword(s):  
Limit Cycle ◽  
Plasma Simulation ◽  
Mode Decomposition ◽  
Dynamical Mode

Characterization of the rear wake of a SUV with extensions and without extensions

2016 ◽  
Vol 231 (9) ◽  
pp. 1294-1302 ◽  
Author(s):  
Simone Sebben ◽  
Lennert Sterken ◽  
Thies Wölken
Keyword(s):  
Aerodynamic Resistance ◽  
Wake Flow ◽  
Bluff Bodies ◽  
Pressure Drag ◽  
Passenger Vehicles ◽  
Mode Decomposition ◽  
Structure Sensitive ◽  
The Difference ◽  
Proper Orthogonal

Passenger vehicles are considered to be bluff bodies, and therefore their total aerodynamic resistance is dominated by the pressure drag, which is basically the difference between the stagnation pressure at the front and the pressure at the base. In particular, the base wake of a vehicle has a significant influence on the total drag, and the ways to reduce and to control the drag have been the subject of numerous investigations. The present work focuses on the identification and analysis of unsteady-flow structures acting on the base wake of a sport utility vehicle with rear-end extensions and without rear-end extensions. Tapered extensions have proved to be an effective way to reduce the drag since they act as a truncated boat-tailing device which improves the pressure recovery zone and reduces the wake size. In this investigation, wind tunnel experiments and computational fluid dynamics were used to study the forces acting on the vehicle and the non-stationary behaviour of the rear wake flow. For analysis of the unsteady base pressures, a data-structure-sensitive filtering approach based on empirical mode decomposition in combination with fast Fourier transform and proper orthogonal decomposition was used. The numerical results and the experimental results complement each other well, and both revealed an antisymmetric mode in the transverse plane related to a flapping of the wake at a Strouhal number of around 0.23. Furthermore, a pumping effect, which is a main contributor to the drag, was observed at Strouhal values of between 0.04 and 0.07. This is in good agreement with the results from the research on more simplified model shapes. The rear extensions proved to be a productive way to reduce the drag coefficient and the magnitude of the wake flapping for the yaw angles investigated.

Some Aspects of the Aerodynamics of Gurney Flaps on a Double-Element Wing

2000 ◽  
Vol 123 (1) ◽  
pp. 99-104 ◽  
Author(s):  
David Jeffrey ◽  
Xin Zhang ◽  
David W. Hurst
Keyword(s):  
Laser Doppler Anemometry ◽  
Separated Flow ◽  
Surface Flow ◽  
Wake Flow ◽  
Single Element ◽  
Suction Surface ◽  
Gurney Flaps ◽  
Gurney Flap ◽  
Flow Features ◽  
Flap Deflection

Gurney flaps of different heights have been fitted to a generic double-element wing, and the effects at two typical flap angles have been observed using force and pressure measurements, and by performing flow surveys using Laser Doppler Anemometry. At a low flap setting angle of 20 deg the suction-surface flow remains attached to the trailing edge of the flap, and vortex flow features and perturbation velocities are all similar to those observed when Gurney flaps are fitted to single element wings. At a high flap deflection of 50 deg there is an extensive region of separated flow over the flap, yet the Gurney flap still alters the flow structure. The measurements suggest that the wake flow behind the Gurney flap consists of a von Karman vortex street of alternately shed vortices. The effects of the Gurney flap on the lift, zero-lift drag, and pressure distributions are reported, and the differences between the trends observed for single-element wings are discussed.

Numerical Investigation of the Flow Around a Generic Car Using Dynamic Mode Decomposition

2014 ◽  
Author(s):  
Martin Peichl ◽  
Steffen Mack ◽  
Thomas Indinger ◽  
Friedhelm Decker
Keyword(s):  
Vector Fields ◽  
Three Dimensional ◽  
Wake Flow ◽  
Dynamic Mode Decomposition ◽  
Wind Tunnels ◽  
Dynamic Mode ◽  
Dynamic Information ◽  
Cfd Simulations ◽  
Mode Decomposition ◽  
Vortex Systems

The drag of a car is highly dependent on the topology of its complex wake system. Small changes in the shape of the car, that do not have a big effect when considered separately, can lead to significant changes in the total drag when the vortex systems of the changed part of the car body interact with the wake vortices. To understand these interferences, a method is necessary that decomposes the flow based on dynamic information. In this paper, the feasibility of using the Dynamic Mode Decomposition (DMD) to analyze the dynamic behavior of the wake flow of a car is investigated. The DMD is found to extract useful information from the flow when applied to three dimensional velocity vector fields. The CFD simulations are validated by yet unpublished experimental results from experiments in two different wind tunnels.

scholarly journals Dynamic mode decomposition of numerical and experimental data

2010 ◽  
Vol 656 ◽  
pp. 5-28 ◽  
Author(s):  
PETER J. SCHMID
Keyword(s):  
Degrees Of Freedom ◽  
Large Scale ◽  
Plane Channel ◽  
Transport Processes ◽  
Wake Flow ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Complex Flow ◽  
Mode Decomposition ◽  
Plane Channel Flow

The description of coherent features of fluid flow is essential to our understanding of fluid-dynamical and transport processes. A method is introduced that is able to extract dynamic information from flow fields that are either generated by a (direct) numerical simulation or visualized/measured in a physical experiment. The extracted dynamic modes, which can be interpreted as a generalization of global stability modes, can be used to describe the underlying physical mechanisms captured in the data sequence or to project large-scale problems onto a dynamical system of significantly fewer degrees of freedom. The concentration on subdomains of the flow field where relevant dynamics is expected allows the dissection of a complex flow into regions of localized instability phenomena and further illustrates the flexibility of the method, as does the description of the dynamics within a spatial framework. Demonstrations of the method are presented consisting of a plane channel flow, flow over a two-dimensional cavity, wake flow behind a flexible membrane and a jet passing between two cylinders.

scholarly journals Effects of Bogies on the Wake Flow of a High-Speed Train

2019 ◽  
Vol 9 (4) ◽  
pp. 759 ◽  
Author(s):  
Wen Liu ◽  
Dilong Guo ◽  
Zijian Zhang ◽  
Dawei Chen ◽  
Guowei Yang
Keyword(s):  
High Speed ◽  
Wake Flow ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Wake Flows ◽  
Delayed Detached Eddy Simulation ◽  
Mode Decomposition ◽  
Unsteady Characteristics

The wake region of high-speed trains is an area of complex turbulent flow characterized by the periodic generation and shedding of vortices, which causes discomfort to passengers and affects the stability and safety of the train. In this study, the unsteady characteristics of the wake flows of three 1:1 scale China Railway High-Speed 380A (CRH380A) high-speed train models with different degrees of simplification were numerically investigated using the improved delayed detached eddy simulation (IDDES) method. Analyses of the aerodynamic forces, train-induced slipstream, and turbulent kinetic energy (TKE) were conducted to determine the effects of the bogies on the wake flow of the high-speed train. It was found that the existence of bogies on the bottom of the train, especially the last bogie, not only enhanced the wake flow but also introduced large perturbances into the wake flow. Moreover, the generation and evolution of the vortices in the wake flows were determined by analyzing the instantaneous flow fields and coherent flow structures that were obtained by the dynamic mode decomposition (DMD) method. The results showed that a pair of large, counter-rotating streamwise vortices in the real model of the high-speed train was generated by the cowcatcher and their intensity was significantly enhanced by perturbances that were introduced by the bogies on the bottom of the train.

Clarifying Low-Frequency Variatoions Phenomenon Using a Novel Mode Decomposition Method

2006 ◽  
Vol 22 (3) ◽  
pp. 193-198 ◽  
Author(s):  
C.-T. Wang
Keyword(s):  
Finite Number ◽  
Vortex Shedding ◽  
Characteristic Time ◽  
Decomposition Method ◽  
Decomposition Analysis ◽  
Low Frequency ◽  
Wake Flow ◽  
Data Set ◽  
Mode Decomposition ◽  
Frequency Variations

AbstractLow-frequency variations in wake flow are complex and many aspects of its behavior remain poorly understood. A mode decomposition method developed by Huang et al is utilized herein because it can decompose any complicated data set into a finite number of intrinsic modes without distorting their original characteristics. The results of decomposition analysis of the measured base pressure signals reveal that a finite number of various kinds of flow structure modes, with their own characteristic time scales, coexist with the residue that exhibits most of the low-frequency variations in flow at Re = 11760 and 31600, respectively. As the Reynolds number increases, the decomposition method yields more components. Results also show exactly the vortex shedding structure in an intrinsic mode and the low-frequency variations that appear in the residue during vortex shedding process.

Sign in / Sign up

Export Citation Format

Share Document