The Effects of Blade 3D Designs in Different Orthogonal Coordinates on the Performance of Compressor Cascades

2014 ◽  
Vol 31 (4) ◽  
Author(s):  
Pengfei Xu ◽  
Xianjun Yu ◽  
Baojie Liu
Keyword(s):  
Aspect Ratio ◽  
Numerical Simulations ◽  
Cascade Model ◽  
Large Aspect Ratio ◽  
3D Design ◽  
Vector Decomposition ◽  
Simulation Results ◽  
Flow Effects ◽  
Superposition Effect ◽  
Orthogonal Coordinates

AbstractThe chordwise based Sweep-Dihedral Coordinates (SDC) and axial-tangential based Axial Sweep-Lean Coordinates (ASLC) are the two widely used coordinates systems for blade 3D design. In order to clarify the relationships between them, some numerical simulations were conducted in a simplified planar cascade model. The cascade model has a large aspect ratio of 3.0 and free-slip endwalls, which are used to minimize the endwall flow effects. The simulation results of totally 9 cases with different blade 3D design schemes, including sweep, dihedral, axial sweep and lean, were analyzed. Firstly, the effects of each type of blade 3D designs were summarized. And then, based on the rule of vector decomposition in an orthogonal coordinates, the effects of blade axial sweep and lean in ASLC were deduced from the effects of blade sweep and dihedral in SDC. It was found that forward/backward axial sweep is combined by positive/negative dihedral and forward/backward sweep, which have opposite trends of effects, resulting in a counterbalance phenomenon. Moreover, positive/negative lean is combined by positive/negative dihedral and forward/backward sweep, which have the same trends of effects, resulting in a superposition effect.

Thermal effect on large-aspect-ratio Couette–Taylor system: numerical simulations

2015 ◽  
Vol 771 ◽  
pp. 57-78 ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang ◽  
Innocent Mutabazi
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Convective Cell ◽  
Base Flow ◽  
Large Aspect Ratio ◽  
Radial Temperature ◽  
Instability Modes ◽  
Momentum And Heat Transfer

We have performed numerical simulations of the flow in a large-aspect-ratio Couette–Taylor system with rotating inner cylinder and with a radial temperature gradient. The aspect ratio was chosen in such a way that the base state is in the conduction regime. Away from the endplates, the base flow is a superposition of an azimuthal flow induced by rotation and an axial flow (large convective cell) induced by the temperature gradient. For a fixed rotation rate of the inner cylinder in the subcritical laminar regime, the increase of the temperature difference imposed on the annulus destabilizes the convective cell to give rise to co-rotating vortices as primary instability modes and to counter-rotating vortices as secondary instability modes. The space–time properties of these vortices have been computed, together with the momentum and heat transfer coefficients. The temperature gradient enhances the momentum and heat transfer in the flow independently of its sign.

Simulation Research on Stress of Polymeric Patterns during Micro Hot Embossing

2011 ◽  
Vol 80-81 ◽  
pp. 339-345 ◽  
Author(s):  
Ting Zhang ◽  
Yong He ◽  
Jian Zhong Fu
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
High Stress ◽  
Hot Embossing ◽  
Duty Ratio ◽  
Simulation Research ◽  
High Stress Concentration ◽  
Simulation Results

The properties of polymeric components made by hot embossing are obviously affected by the geometry of the mold such as the duty ratio, the aspect ratio, width to thickness ratio and the mold cavity position. This paper focuses on numerical simulations with isothermal embossing conditions in order to observe the stress distribution and the stress concentration of the polymeric patterns. The simulation results show that stress concentration in the PMMA resist accumulates at the contact corner between the mold and the polymer, and the location of the stress distribution is mainly on the profile of the replicated patterns. Small duty ratio will result in high stress concentration at the corner of the replicated components. The stress concentration also increases rapidly while the aspect ratio of the mold increases. The thicker the polymer is, the more difficult the adequate flow of the polymer becomes, and the stress concentration rises up. A stress barrier can be used in the mold in order to reduce the stress concentration in the middle of the replicated polymeric patterns.

Control of Vortical Flows Past Open Cavities

2013 ◽  
Vol 332 ◽  
pp. 21-26
Author(s):  
Marius Stoia-Djeska ◽  
Carmen Anca Safta ◽  
Adina Cotuna
Keyword(s):  
Aspect Ratio ◽  
Numerical Simulations ◽  
Compressible Flows ◽  
Leading Edge ◽  
Control Device ◽  
Spanwise Direction ◽  
Large Aspect Ratio ◽  
Pressure Oscillations ◽  
Sustained Oscillations ◽  
Open Cavities

Numerical simulations are used to verify the possibility to mitigate the undesired flow self-sustained oscillations of the compressible flows past open cavities. The simple control device proposed in this work consists in a large aspect ratio wing with an non-symmetric thin airfoil mounted in the spanwise direction of the cavity and located immediately upstream with respect the leading edge of the cavity . The results show that this control device is efficient and diminishes the pressure oscillations.

Tail shapes lead to different propulsive mechanisms in the body/caudal fin undulation of fish

2020 ◽  
pp. 095440622096768
Author(s):  
Jialei Song ◽  
Yong Zhong ◽  
Ruxu Du ◽  
Ling Yin ◽  
Yang Ding
Keyword(s):  
Numerical Simulation ◽  
Aspect Ratio ◽  
High Efficiency ◽  
The Body ◽  
Caudal Fin ◽  
Fish Model ◽  
Swimming Efficiency ◽  
Simulation Results ◽  
Propulsive Mechanism ◽  
High Depth

In this paper, we investigate the hydrodynamics of swimmers with three caudal fins: a round one corresponding to snakehead fish ( Channidae), an indented one corresponding to saithe ( Pollachius virens), and a lunate one corresponding to tuna ( Thunnus thynnus). A direct numerical simulation (DNS) approach with a self-propelled fish model was adopted. The simulation results show that the caudal fin transitions from a pushing/suction combined propulsive mechanism to a suction-dominated propulsive mechanism with increasing aspect ratio ( AR). Interestingly, different from a previous finding that suction-based propulsion leads to high efficiency in animal swimming, this study shows that the utilization of suction-based propulsion by a high- AR caudal fin reduces swimming efficiency. Therefore, the suction-based propulsive mechanism does not necessarily lead to high efficiency, while other factors might play a role. Further analysis shows that the large lateral momentum transferred to the flow due to the high depth of the high- AR caudal fin leads to the lowest efficiency despite the most significant suction.

Modulation instability in nonlinear chiral fiber

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Demissie Jobir Gelmecha ◽  
Ram Sewak Singh
Keyword(s):  
Theoretical Model ◽  
Numerical Simulations ◽  
Pulse Propagation ◽  
Modulation Instability ◽  
Constitutive Relations ◽  
Gain Spectrum ◽  
Circularly Polarized ◽  
Left Handed ◽  
Simulation Results ◽  
The Difference

AbstractIn this paper, the rigorous derivations of generalized coupled chiral nonlinear Schrödinger equations (CCNLSEs) and their modulation instability analysis have been explored theoretically and computationally. With the consideration of Maxwell’s equations and Post’s constitutive relations, a generalized CCNLSE has been derived, which describes the evolution of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components propagating through single-core nonlinear chiral fiber. The analysis of modulation instability in nonlinear chiral fiber has been investigated starting from CCNLSEs. Based on a theoretical model and numerical simulations, the difference on the modulation instability gain spectrum in LCP and RCP components through chiral fiber has been analyzed by considering loss and chirality into account. The obtained simulation results have shown that the loss distorts the sidebands of the modulation instability gain spectrum, while chirality modulates the gain for LCP and RCP components in a different manner. This suggests that adjusting chirality strength may control the loss, and nonlinearity simultaneously provides stable modulated pulse propagation.

scholarly journals A modular framework to generate robust biped locomotion: from planning to control

2021 ◽  
Vol 3 (9) ◽  
Author(s):  
Mohammadreza Kasaei ◽  
Ali Ahmadi ◽  
Nuno Lau ◽  
Artur Pereira
Keyword(s):  
Numerical Simulations ◽  
Predictive Control ◽  
Biped Locomotion ◽  
Input Output ◽  
Dynamics Model ◽  
Biped Robots ◽  
The Core ◽  
Simulation Results ◽  
Reference Trajectories ◽  
Modular Framework

AbstractBiped robots are inherently unstable because of their complex kinematics as well as dynamics. Despite many research efforts in developing biped locomotion, the performance of biped locomotion is still far from the expectations. This paper proposes a model-based framework to generate stable biped locomotion. The core of this framework is an abstract dynamics model which is composed of three masses to consider the dynamics of stance leg, torso, and swing leg for minimizing the tracking problems. According to this dynamics model, we propose a modular walking reference trajectories planner which takes into account obstacles to plan all the references. Moreover, this dynamics model is used to formulate the controller as a Model Predictive Control (MPC) scheme which can consider some constraints in the states of the system, inputs, outputs, and also mixed input-output. The performance and the robustness of the proposed framework are validated by performing several numerical simulations using MATLAB. Moreover, the framework is deployed on a simulated torque-controlled humanoid to verify its performance and robustness. The simulation results show that the proposed framework is capable of generating biped locomotion robustly.

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