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Improvement of the aerodynamic performance by wing flexibility and elytra - hind wing interaction of a beetle during forward flight

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JOURNAL OF THE ROYAL SOCIETY INTERFACE 2013年第85期10卷 20130312-20130312页

作者： Tuyen Quang Le Tien Van Truong Park, Soo Hyung Tri Quang Truong Ko, Jin Hwan Park, Hoon Cheol Byun, Doyoung Korea Inst Ocean Sci & Technol Ansan 425600 South Korea Konkuk Univ Dept Aerosp & Informat Engn Seoul South Korea Konkuk Univ Dept Adv Technol Fus Seoul South Korea Sungkyunkwan Univ Dept Mech Engn Suwon South Korea

In this work, the aerodynamic performance of beetle wing in free-forward flight was explored by a three-dimensional computational fluid dynamics (CFDs) simulation with measured wing kinematics. It is shown from the CFD results that twist and camber variation, which represent the wing flexibility, are most important when determining the aerodynamic performance. Twisting wing significantly increased the mean lift and camber variation enhanced the mean thrust while the required power was lower than the case when neither was considered. Thus, in a comparison of the power economy among rigid, twisting and flexible models, the flexible model showed the best performance. When the positive effect of wing interaction was added to that of wing flexibility, we found that the elytron created enough lift to support its weight, and the total lift (48.4 mN) generated from the simulation exceeded the gravity force of the beetle (47.5 mN) during forward flight.

关键词： beetle elytra forward flight wing interaction wing flexibility computational fluid dynamics simulation

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Flow Topology Around Gas, Liquid, and Three-Dimensional Obstacles in Hypersonic Flow

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AIAA JOURNAL 2012年第1期50卷 100-108页

作者： Asma, C. O. Tirtey, S. Schloegel, F. von Karman Inst Fluid Dynam Turbomachinery Dept B-1640 Rhode St Genese Belgium Univ Queensland St Lucia Qld 4072 Australia

The flow topologies of gas and liquid injections into hypersonic crossflow are compared with the flow topology around three-dimensional rigid obstacles in hypersonic flow. Experimental techniques such as oil flow visualization, infrared thermography, a sublimation technique, and high-speed schlieren photography are applied for a Mach 6 crossing flow on a flat plate. The shock system and the vortex system are visualized and discussed for all cases. Pressure ratios for gas injection, momentum flux ratio for liquid injection, and Reynolds number for three-dimensional obstacles are taken into consideration. The effects of nondimensional numbers on the flow topologies are analyzed. Similarities and differences among different topologies are explained by studying the vortical structures, making use of computational fluid dynamics simulations.

关键词： Transitional Flow Horseshoe Vortex Flow Visualization Techniques Aerodynamic Stability Skin Friction Coefficient Aspect Ratio Shock Layers computational fluid dynamics simulation Hypersonic Wind Tunnels Thermal Protection System

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Numerical simulation of Injection Strategies in a Cavity-Based Supersonic Combustor

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JOURNAL OF PROPULSION AND POWER 2012年第5期28卷 991-999页

作者： Ebrahimi, Houshang B. Malo-Molina, Faure J. Gaitonde, Datta V. Flow Modeling & Simulat Inc Reno NV 89501 USA USAF Res Lab Air Vehicles Directorate Wright Patterson AFB OH 45433 USA Ohio State Univ Columbus OH 43210 USA

High-fidelity simulations with a validated methodology are employed to explore the physical processes associated with different injection strategies on supersonic combustion. The configurations consider a commonly employed open single-cavity flameholder. The effects of different injector locations and injection angles are examined under the constraint that the total fuel mass flow rate is the same. The numerical approach solves the full three-dimensional Navier-Stokes equations, supplemented with a two-equation k-omega turbulence closure. The specific injection locations include 10 different arrangements that examine fuel injection upstream of the cavity, on the backward step, on the cavity bottom wall, and on the downstream ramp. The angles of the fuel port injection slots include combinations of parallel and 27 and 90 deg to the airflow inside the cavity. One case with a closed cavity is also examined for comparison. The simulations are employed to characterize the performance with qualitative and quantitative mixing metrics. Detailed analysis of the results reveals both expected and unexpected findings. As anticipated, the closed cavity performs poorly relative to its open counterpart. However, an injection strategy that enhances the natural circulation pattern of the cavity is found to be superior to one that opposes it. Another counterintuitive finding is that although direct injection of the fuel upstream of the cavity into the main stream results in deeper penetration, the fuel from different injectors remains distinct, with relatively small spanwise mixing. On the other hand, injection on the floor of the cavity results in more diffused fuel distribution.

关键词： Combustor Design computational fluid dynamics simulation Fuel Injection Combustion Efficiency Flame Holder Navier Stokes Equations Circulation Patterns Mass Flow Rate Flow Separation Freestream Mach Number

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UPGRADE OF A TRANSVERSE VENTILATION SYSTEM IN A BI-DIRECTIONAL TUNNEL

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THERMAL SCIENCE 2012年第4期16卷 1067-1080页

作者： Vidmar, Peter Petelin, Stojan Luin, Blaz Univ Ljubljana Fac Maritime Studies & Transport Portoroz Slovenia

The Karavanke tunnel forms an important link between Slovenia and Austria. The almost 8 km long tunnel is operated with bi-directional traffic and does not have dedicated escape routes. Moreover, the ventilation in case of fire does not satisfy requirements of the EU Directive 2004/54/EC that specifies the minimum requirements for tunnels in the trans-European road network. The paper present results of the research conducted regarding the possibility of upgrade the existing system in order to reach the required level of safety at lower costs possible. It is shown that with simple but novel adaptations of the ventilation system, a sizeable increase in the overall level of safety can be achieved. The methodology applied is a combination of a simple pipe model for tunnel ventilation and for detailed fluid dynamics analysis the computational fluid dynamics model is used. The existing ventilation system that in fire ventilation extracts smoke from a single duct is replaced with the smoke extraction from both ducts applying four axial fans. The analysis is focused on air/smoke flow through the vents and ducts and on pressure drops calculated over the length of the ventilation duct and its influence on the total flow. The change of the flow condition also has influence on ventilation fan operation point that is investigated in the paper as well.

关键词： tunnel safety computational fluid dynamics simulation pipe model ventilation fire safety

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computational Investigation into the Use of Response Functions for Aerodynamic-Load Modeling

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AIAA JOURNAL 2012年第6期50卷 1314-1327页

作者： Ghoreyshi, Mehdi Jirasek, Adam Cummings, Russell M. USAF Acad Modeling & Simulat Res Ctr Colorado Springs CO 80840 USA USAF Acad Dept Aeronaut Colorado Springs CO 80840 USA

The generation of reduced-order models for the evaluation of unsteady and nonlinear aerodynamic loads are investigated. The reduced-order model considered is an indicial theory based on the convolution of step functions with the derivative of the input signal. The step functions are directly calculated using the results of unsteady Reynolds-averaged Navier-Stokes simulations and a grid-movement tool. Results are reported for a two-dimensional airfoil and an unmanned combat air vehicle configuration. Wind-tunnel data are first used to validate the prediction of static and unsteady coefficients at both low and high angles of attack, with good agreement obtained for all cases. The generation of the aerodynamic models is then described. The focus of the paper next shifts to assess the validity of studied reduced-order models with respect to new maneuvers. This is accomplished by comparison of the model output with time-accurate computational fluid dynamics simulations. Results presented demonstrate the feasibility of the approach for modeling unsteady aerodynamic loads and response-type computational fluid dynamics calculations.

关键词： Aerodynamic Characteristics Lift Coefficient computational fluid dynamics simulation Incompressible Flow Reynolds Averaged Navier Stokes Low Speed Wind Tunnel NACA 0012 Unsteady Aerodynamics Frequency Domain Turbulence Models

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Enhanced Cooling of a Liquid-Fueled Rocket Thrust Chamber by Metal Foams

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JOURNAL OF PROPULSION AND POWER 2012年第2期28卷 434-443页

作者： Bai, Mo Chung, J. N. Univ Florida Dept Mech & Aerosp Engn Gainesville FL 32611 USA

As human beings pursue the deeper space exploration, advanced propulsion systems that deliver super performance and possess increased durability for the next generation spacecraft will be needed, despite current limitations on materials. A promising technology is to fill the current open cooling channels with open-cell metal foams to drastically enhance the cooling of the thrust chamber. After applying the methods developed for the feasibility evaluation, it is found that under equal pressure drop and coolant mass flow rate, the actual amount of increase in the heat transfer coefficient for the foamed channel over the open channel is approximately the same for any given pressure drop, while the percent heat transfer coefficient increase actually decreases with increasing pressure drop from 99% at 841 kPa/m to 48% at 3090 kPa/m. It is also shown that under equal pressure drop and coolant mass flow rate in an actual rocket condition, the heat transfer coefficient of the foamed channel is 49581 W/m(2) K, which is more than 110% enhancement, compared with 23464 W/m(2) K for the open channel. That means that, under the same pressure drop and mass flow rate, the foamed channel has the capability to significantly enhance the cooling for the rocket engine thrust chamber.

关键词： Rocket Thrust Chamber Enhancing Heat Transfer Rate Fuel as Coolant computational fluid dynamics simulation Liquid Propellant Rocket Engine Rockets Chamber Pressure Mass Flow Rate Bipropellants Wall Temperature

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CFD simulation of DEBORA boiling experiments

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ARCHIVES OF THERMOdynamics 2012年第1期33卷 107-122页

作者： Rzehak, Roland Krepper, Eckhard Helmholtz Zentrum Dresden Rossendorf POB 510119 D-01314 Dresden Germany

In this work we investigate the present capabilities of computational fluid dynamics for wall boiling. The computational model used combines the Euler/Euler two-phase flow description with heat flux partitioning. This kind of modeling was previously applied to boiling water under high pressure conditions relevant to nuclear power systems. Similar conditions in terms of the relevant non-dimensional numbers have been realized in the DEBORA tests using dichlorodifluoromethane (R12) as the working fluid. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, bubble size and liquid temperature as well as axial profiles of wall temperature. After reviewing the theoretical and experimental basis of correlations used in the ANSYS CFX model used for the calculations, we give a careful assessment of the necessary recalibrations to describe the DEBORA tests. The basic CFX model is validated by a detailed comparison to the experimental data for two selected test cases. simulations with a single set of calibrated parameters are found to give reasonable quantitative agreement with the data for several tests within a certain range of conditions and reproduce the observed tendencies correctly. Several model refinements are then presented each of which is designed to improve one of the remaining deviations between simulation and measurements. Specifically we consider a homogeneous MUSIG model for the bubble size, modified bubble forces, a wall function for turbulent boiling flow and a partial slip boundary condition for the liquid phase. Finally, needs for further model developments are identified and promising directions discussed.

关键词： Subcooled flow boiling computational fluid dynamics simulation Heat flux partitioning Two-fluid model

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The quantitative effect of an accessory ostium on ventilation of the maxillary sinus

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RESPIRATORY PHYSIOLOGY & NEUROBIOLOGY 2012年第1期181卷 62-73页

作者： Na, Yang Kim, Kyunghun Kim, Sung Kyun Chung, Seung-Kyu Sungkyunkwan Univ Sch Med Samsung Med Ctr Dept Otorhinolaryngol Head & Neck Surg Seoul South Korea Konkuk Univ Dept Mech Engn Seoul 143701 South Korea

The airflow and gas exchange behaviors of the human maxillary sinus were quantified to better understand the effect of an accessory ostium (AO). An anatomically correct numerical domain was constructed using CT data from a male patient with mild nasal obstruction. For the purpose of comparison, a numerical model without an AO was also generated by artificially removing the AO from the original model using CAD software. A steady-flow field through the nasal cavity was simulated using ANSYS-FLUENT v13.0 with a target flow rate of 250 ml/s. The Volume of fluid (VOF) method was used to investigate the concentration field of nitric oxide (NO) initially filled in the maxillary sinus. The simulation results showed that a transit flow through the maxillary sinus developed in the presence of an AO. As the flow entered the sinus through either a natural or accessory ostium from the middle meatus, the velocity was significantly reduced to a local maximum of approximately 0.034 m/s inside the sinus. This by-pass flow rate through the sinus of 2.186 x 10(-1) to 3.591 x 10(-1) ml/s was a small fraction of the total flow rate inhaled from the nostril, but it effectively changed the local flow topology and led to a larger reduction in NO concentration in the maxillary sinus. This more rapid reduction in NO concentration was due to enhanced ventilation activity afforded by convective transport of the transit stream through the flow path connecting the natural ostium and the AO. The inspiration and expiration phases were qualitatively similar in flow pattern except for the flow direction in the maxillary sinus, suggesting that the AO plays a similar physiological role during both inspiration and expiration in terms of ventilation. (C) 2012 Elsevier BM. All rights reserved.

关键词： Maxillary sinus Accessory ostium Ventilation computational fluid dynamics simulation Nitric oxide Peclet number

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Dynamic Roughness as a Means of Leading-Edge Separation Flow Control

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JOURNAL OF AIRCRAFT 2012年第1期49卷 108-115页

作者： Huebsch, W. W. Gall, P. D. Hamburg, S. D. Rothmayer, A. P. W Virginia Univ Morgantown WV 26506 USA Iowa State Univ Ames IA 50011 USA

A combination of computational simulations (computational fluid dynamics) using two- and three-dimensional commercial flow solvers (FLUENT) and experimental flow visualization is used to show that low-amplitude oscillating distributed surface perturbations (dynamic roughness) can completely suppress leading-edge separation bubbles. computational fluid dynamics simulations show that leading-edge short and long separation bubbles can be suppressed by dynamic roughness, causing the flow to tend toward an attached flow over the entire leading edge. It is shown that the suppression of the separation can be achieved using roughness that is a small fraction of the boundary thickness, providing that the roughness oscillation frequency is sufficiently large. The results also demonstrate an inverse relationship between roughness amplitude and frequency;as the maximum amplitude is increased, the associated frequency to maintain flow control decreased. These results from computational fluid dynamics are corroborated using smoke tunnel visualization experiments for the suppression of a leading-edge short and long separation bubble on a NACA 0012 airfoil with a leading-edge dynamic roughness skin.

关键词： Leading Edges NACA 0012 Tollmien Schlichting waves computational fluid dynamics simulation Aerodynamic Efficiency Boundary Layer Separation Strouhal Number Aerodynamic Flows Turbulence Models Drag Reduction

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computational fluid dynamics ANALYSIS OF HELICAL NOZZLES EFFECTS ON THE ENERGY SEPARATION IN A VORTEX TUBE

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THERMAL SCIENCE 2012年第1期16卷 151-166页

作者： Pourmahmoud, Nader Zadeh, Amir Hassan Moutaby, Omid Bramo, Abdolreza Urmia Univ Dept Mech Engn Orumiyeh Iran

In this article computational fluid dynamics analysis of a 3-D steady-state compressible and turbulent flow has been carried out through a vortex tube. The numerical models use the k-epsilon turbulence model to simulate an axisymmetric computational domain along with periodic boundary conditions. The present research has focused on the energy separation and flow field behavior of a vortex tube by utilizing both straight and helical nozzles. Three kinds of nozzles set include of 3 and 6 straight and 3 helical nozzles have been investigated and their principal effects as cold temperature difference was compared. The studied vortex tubes dimensions are kept the same for all models. The numerical values of hot and cold outlet temperature differences indicate the considerable operating role of helical nozzles, even a few numbers of that in comparing with straight nozzles. The results showed that this type of nozzles causes to form higher swirl velocity in the vortex chamber than the straight one. To be presented numerical results in this paper are validated by both available experimental data and flow characteristics such as stagnation point situation and the location of maximum wall temperature as two important facts. These comparisons showed reasonable agreement.

关键词： vortex tube computational fluid dynamics simulation stagnation point energy separation helical nozzles

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