Effect of a Nonlinear Constitutive Relation for Turbulence Modeling on Predicting Flow Separation at Wing-Body Juncture of Transonic Commercial Aircraft

2012 ◽  
Author(s):  
Kazuomi Yamamoto ◽  
Kentaro Tanaka ◽  
Mitsuhiro Murayama
Keyword(s):  
Constitutive Relation ◽  
Flow Separation ◽  
Turbulence Modeling ◽  
Commercial Aircraft ◽  
Nonlinear Constitutive Relation

A convenient formulation of Sadowsky's model for elastic ribbons

2021 ◽  
Vol 477 (2255) ◽  
Author(s):  
Sébastien Neukirch ◽  
Basile Audoly
Keyword(s):  
Differential Equations ◽  
Constitutive Relation ◽  
Classical Problem ◽  
Constitutive Law ◽  
System Of Differential Equations ◽  
Dimensional Model ◽  
Simple Method ◽  
One Dimensional ◽  
Aspect Ratios ◽  
Nonlinear Constitutive Relation

Elastic ribbons are elastic structures whose length-to-width and width-to-thickness aspect ratios are both large. Sadowsky proposed a one-dimensional model for ribbons featuring a nonlinear constitutive relation for bending and twisting: it brings in both rich behaviours and numerical difficulties. By discarding non-physical solutions to this constitutive relation, we show that it can be inverted; this simplifies the system of differential equations governing the equilibrium of ribbons. Based on the inverted form, we propose a natural regularization of the constitutive law that eases the treatment of singularities often encountered in ribbons. We illustrate the approach with the classical problem of the equilibrium of a Möbius ribbon, and compare our findings with the predictions of the Wunderlich model. Overall, our approach provides a simple method for simulating the statics and the dynamics of elastic ribbons.

Active Flow Control of Separated Turbulent Flow Over a Hump Using RANS, DES, and LES

2008 ◽  
Author(s):  
Subhadeep Gan ◽  
Urmila Ghia ◽  
Karman Ghia
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Flow Separation ◽  
Turbulence Modeling ◽  
Active Flow Control ◽  
Separated Flow ◽  
Experimental Results ◽  
Complex Flow ◽  
Active Flow ◽  
Turbulent Separated Flow

Most practical flows in engineering applications are turbulent, and exhibit separation. Losses due to separation are undesirable because they generally have adverse effects on performance and efficiency. Therefore, control of turbulent separated flows has been a topic of significant interest as it can reduce separation losses. It is of utmost importance to understand the complex flow dynamics that leads to flow separation and come up with methods of flow control. In the past, passive flow-control was mostly implemented that does not require any additional energy source to reduce separation losses but it leads to increasing viscous losses at higher Reynolds number. More recent work has been focused primarily on active flow-control techniques that can be turned on and off depending on the requirement of flow-control. The present work is focused on implementing flow control using steady suction in the region of flow separation. The present work is Case 3 of the 2004 CFD Validation on Synthetic Jets and Turbulent Separation Control Workshop, http://cfdval2004.larc.nasa.gov/case3.html, conducted by NASA for the flow over a wall-mounted hump. The flow over a hump is an example of a turbulent separated flow. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case has been successfully simulated by Gan et al., 2007. The flow is simulated at a Reynolds number of 371,600, based on the hump chord length, C, and Mach number of 0.04. The flow control is being achieved via a slot at approximately 65% C by using steady suction. Solutions are presented for the three-dimensional RANS SST, steady and unsteady, turbulence model and DES and LES turbulence modeling approaches. Multiple turbulence modeling approaches help to ascertain what techniques are most appropriate for capturing the physics of this complex separated flow. Second-order accurate time derivatives are used for all implicit unsteady simulation cases. Mean-velocity contours and turbulent kinetic energy contours are examined at different streamwise locations. Detailed comparisons are made of mean and turbulence statistics such as the pressure coefficient, skinfriction coefficient, and Reynolds stress profiles, with experimental results. The location of the reattachment behind the hump is compared with experimental results. The successful control of this turbulent separated flow causes a reduction in the reattachment length, compared with the uncontrolled case. The effects of steady suction on flow separation and reattachment are discussed.

The Hysteresis Model of Terfenol-D with Magneto-Stress Coupling

2011 ◽  
Vol 121-126 ◽  
pp. 4820-4825
Author(s):  
Ai Hua Meng ◽  
Han Lin He ◽  
Min Kong ◽  
Ming Fan Li
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Constitutive Relation ◽  
Hysteresis Model ◽  
Hysteresis Behavior ◽  
Nonlinear Hysteresis ◽  
Nonlinear Constitutive Relation

The output of Terfenol-D is nonlinear and hysteretic under the effect of magnetic field and prestress. The nonlinear constitutive relation between magnetostriction and magnetization with magneto-stress coupling was built in consideration of the magnetostriction saturation and the prestress correlation. Then, the hysteresis behavior of Terfenol-D was modeled based on the Jiles-Atherton model. The error of magnetostriction between simulations and experimental data is less than 6%. This result indicates that the model can adequately predict the nonlinear hysteresis and magneto-stress coupling character of Terfenol-D.

scholarly journals Damping Energy Dissipation and Parameter Identification of the Bellows Structure Covered with Elastic-Porous Metal Rubber

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Guojian Shen ◽  
Min Li ◽  
Xin Xue
Keyword(s):  
Energy Dissipation ◽  
Dynamic Model ◽  
Constitutive Relation ◽  
Dynamic Properties ◽  
Porous Metal ◽  
Generalized Least Squares ◽  
Restoring Force ◽  
Metal Rubber ◽  
Vibration Parameters ◽  
Nonlinear Constitutive Relation

In order to improve damping energy dissipation of a U-shaped bellows structure, elastic-porous metal rubber as a cover layer was adopted and the corresponding vibration parameters were identified. First, the evolution of energy dissipation characteristics with respect to the changes of amplitude and frequency was investigated through a dynamic experimental test in the bending direction of the covered bellows structure. Second, the conspicuous hysteresis loop characteristics were described while the nonlinear constitutive relation was analytically modelled based on the exact decomposition method. Third, the corresponding parameters on dynamic properties of the covered bellows structure were determined by generalized least-squares estimation. Finally, the prediction results were compared with the measured displacement-restoring force curves to verify the accuracy of the developed dynamic model. The results indicate that the proposed dynamic model associated with the nonlinear constitutive relation for the covered bellows structure can well describe the evolution of the restoring force in terms of amplitude and frequency.

Study on Mechanics Behavior of Human Ear Sound Transmission Based on Nonlinear Constitutive Relation

2013 ◽  
Vol 432 ◽  
pp. 381-385
Author(s):  
Wen Juan Yao ◽  
Bo Te Luo
Keyword(s):  
Tympanic Membrane ◽  
Constitutive Relation ◽  
Middle Ear ◽  
Sound Transmission ◽  
Vibration Velocity ◽  
Human Right ◽  
Amplitude Vibration ◽  
Calculation Results ◽  
Human Ear ◽  
Nonlinear Constitutive Relation

Based on the normal CT scan image of human right ear, numerical model has been established combined with self-compiling program. The nonlinear constitutive relation of real middle ear material has been included, and sound - solid and liquid - solid coupling method have been adopted to simulate the sound transmission process from external auditory canal to tympanic membrane, auditory ossicle chain, and eventually to the inner ear. Frequency response and sound transmission behavior has been obtained, and numerical calculation results have been verified by comparing the calculation results with the experimental data. The amplitude, vibration velocity, and stress distribution of middle ear have been analyzed by the model, and the most easy damage part of the tympanic membrane and ossicular chains owing to stress concentration have been obtained in sound transmission of middle ear, which exposes the inner relationship between mechanical behavior of middle ear and pathological changes.

Numerical prediction of nozzle flow separation: Issue of turbulence modeling

2016 ◽  
Vol 50 ◽  
pp. 31-43 ◽  
Author(s):  
Allamaprabhu Yaravintelimath ◽  
Raghunandan B.N. ◽  
José A. Moríñigo
Keyword(s):  
Flow Separation ◽  
Turbulence Modeling ◽  
Numerical Prediction ◽  
Nozzle Flow
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