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Cross-ventilation of a generic building with various configurations of external and internal openings

BUILDING AND ENVIRONMENT 2022年第PartA期207卷 108447-108447页

作者： Zhang, Xuelin Weerasuriya, A. U. Wang, Jiayao Li, Cruz Y. Chen, Zengshun Tse, K. T. Hang, Jian Sun Yat Sen Univ Sch Atmospher Sci Zhuhai Peoples R China Sun Yat Sen Univ Guangdong Prov Key Lab Climate Change & Nat Disas Zhuhai Peoples R China Southern Marine Sci & Engn Guangdong Lab Zhuhai Zhuhai Peoples R China Hong Kong Univ Sci & Technol Dept Civil & Environm Engn Kowloon Clear Water Bay Hong Kong Peoples R China Chongqing Univ Sch Civil Engn Chongqing Peoples R China

Cross-ventilation is the most effective mode of wind-driven natural ventilation but completely depends on the external openings and internal layout. This study investigates how openings affect cross-ventilation of a generic four-wall space using computational fluid dynamics (CFD) simulation. The building has one to four external openings of two different sizes, and the interior contains various configurations of vertical and horizontal walls with blockage ratios varying between 5% and 20%. Two-opening configurations proved to be tremendously efficient for cross-ventilation;for all similarly sized openings, the two-opening scenario doubles the ventilation rate of the single-opening scenario. Using a larger opening on the windward or leeward surface, the two-opening configuration achieved higher ventilation rates and better indoor wind circulation than both the three- and fouropening configurations. In turn, to enhance cross-ventilation in three- and four-opening configurations, more than one of the openings needs to be larger than the rest. The presence of internal walls always led to smaller ventilation rates than no internal walls;such reduction steadily increased with internal blockage ratio. The reduction in ventilation rates can be minimized by adopting several narrow internal walls instead of one wide vertical wall and positioning horizontally-oriented walls above the opening height.

关键词： Cross-ventilation computational fluid dynamics simulation Exterior design Interior design Blockage ratio

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Usefulness of Inviscid Linear Unsteady Lifting-Line Theory for Viscous Large-Amplitude Problems

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AIAA JOURNAL 2022年第2期60卷 598-609页

作者： Bird, Hugh J. A. Ramesh, Kiran Otomo, Shuji Viola, Ignazio Maria Univ Glasgow Aerosp Sci Div Sch Engn Glasgow G12 8QQ Lanark Scotland Univ Edinburgh Sch Engn Inst Energy Syst Edinburgh EH9 3BF Midlothian Scotland

Unsteady lifting-line theory (ULLT) is a low-order method capable of modeling interacting unsteady and finite wing effects at low computational cost. Most formulations of the method assume inviscid flow and small amplitudes. Although these assumptions might be suitable for small-amplitude aeroelastic problems at high Reynolds numbers, modern engineering applications increasingly involve lower Reynolds numbers, large-amplitude kinematics, and vortex structures that lead to aerodynamic nonlinearities. This paper establishes that ULLT still provides a useful solution for low-Reynolds-number, large-amplitude kinematics problems, by comparing ULLT results against those of experimentally validated computational fluid dynamics simulations at Re = 10,000. Three-dimensional effects stabilize leading-edge vortex (LEV) structures, resulting in a good prediction of whole wing force coefficients by ULLT. Although the inviscid spanwise force distributions are accurate for small-amplitude kinematics, the ULLT cannot model three-dimensional vortical structures, and thus it cannot correctly predict the force distribution due to the LEV. It can, however, predict the shedding of LEVs to a limited extent via the leading-edge suction parameter criterion. This can then be used as an indicator of the usefulness of the force distribution results.

关键词： Freestream Velocity Rectangular Wing computational fluid dynamics simulation Vortex Structure Incompressible Flow Amplitude Kinematics High Aspect Ratio Reynolds Averaged Navier Stokes Wing Tip Lift Coefficient

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Time-Domain Boundary Element Method with Broadband Impedance Boundary Condition

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AIAA JOURNAL 2022年第6期60卷 3661-3670页

作者： Rodio, Michelle E. Hu, Fang Q. Nark, Douglas M. NASA Langley Res Ctr Computat AeroSci Branch Hampton VA 23681 USA NASA Langley Res Ctr NextSilicon HPC Developer Operat Hampton VA 23681 USA Old Dominion Univ Dept Math & Stat Norfolk VA 23529 USA NASA Langley Res Ctr Struct Acoust Branch Hampton VA 23681 USA

Acoustic liners are an effective tool for noise reduction and are characterized by a frequency-dependent impedance value. In this paper, a time-domain boundary element method for acoustic scattering coupled with a broadband impedance boundary condition is studied for the case of no mean flow. A Burton-Miller reformulation of the time domain boundary element method for acoustic scattering is carried out with both the pressure and its surface normal derivative terms retained. A multipole impedance model is converted into the time domain and used for enforcing an impedance boundary condition over a wide range of frequencies. Discretization of the coupled system is described. In particular, the time-domain impedance boundary condition is discretized by the third-order implicit backward difference scheme. Stability of the coupling is assessed by an eigenvalue analysis. Scattering solutions that demonstrate the validity and stability of the numerical method are presented.

关键词： Boundary Integral Equation Acoustic Properties Frequency Domain Numerical Stability Graphics Processing Unit computational fluid dynamics simulation Resonant Frequencies Dirac Delta Function Kelvin Helmholtz Instability NASA Langley Research Center

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Passenger Aircraft Cabin Ventilation - Investigations within the Do728 Research Facility

Passenger Aircraft Cabin Ventilation - Investigations within...

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AIAA Aviation Forum

作者： Schmeling, Daniel Dehne, Tobias Lange, Sven Schiepel, Daniel Shishkin, Andrei German Aerosp Ctr DLR Inst Aerodynam & Flow Technol Dept Ground Vehicles Bunsenstr 10 D-37073 Gottingen Germany Volkswagen AG Dev Aerodynam Postbox 1787 D-38436 Wolfsburg Germany

ISBN: (数字)9781624107047

ISBN: (纸本)9781624107047

The ventilation of passenger aircraft cabins as a subsystem of the environmental control system directly affects the (thermal) passenger comfort and the air quality in the cabin. Additionally, the energy efficiency of the ventilation concept is the third major evaluation parameter. Within the triangle of 'air quality', 'thermal comfort' and 'energy efficiency' the optimal configuration for the specific cabin geometries has to be determined addressing all of the mentioned parameters. Furthermore, the robustness, the capability of integration and the possibility to implement modularization processes are additional evaluation parameters. In the present study, we introduce the Do728 passenger aircraft cabin as potential common research model. Moreover, we present the results of numerical and experimental investigations of two different ventilation concepts within this cabin geometry: mixing ventilation, which is state-of-the-art in all modern passenger aircraft, and cabin displacement ventilation as an alternative concept. The results are discussed in terms of temperature and velocity distributions as well as with regard to the aerosol dispersion in the cabin.

关键词： Aircraft Cabin Common Research Model Energy Efficiency Environmental Control System computational fluid dynamics simulation Reynolds Averaged Navier Stokes Particle Image Velocimetry Digital Twins German Aerospace Center Thermal Convection

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Bayesian calibration of a low order aerodynamic model for the design of unconventional tail empennages

Bayesian calibration of a low order aerodynamic model for th...

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AIAA Aviation Forum

作者： Gori, Giulio Rausa, Andrea Zanotti, Alex Auteri, Franco Guardone, Alberto Politecn Milan Dept Aerosp Sci & Technol Via La Masa 34 I-20156 Milan Italy

ISBN: (数字)9781624107047

ISBN: (纸本)9781624107047

In the frame of the MONNALISA Project of the Clean Sky 2 Joint Undertaking (CSJU), we develop a calibration framework for improving the prediction accuracy of a low-order aerodynamic model. The enhancement is sought with respect to a reference application case, an unconventional "Advanced Rear End" component for the forthcoming generation of ultra-efficient aircraft, which is a specific focus of the MONNALISA Project. The calibration framework develops upon a classical Bayesian inference approach providing not only optimal values for the model parameters, but also a probabilistic characterization in terms of their peculiar probability distribution within well defined bounds. The reference data include both numerical predictions from computational fluid dynamics simulations and experimental measurements collected at the large wind-tunnel facility (GVPM) at Politecnico di Milano.

关键词： Aircraft Configurations computational fluid dynamics simulation Wind Tunnel Models Reynolds Averaged Navier Stokes Aerodynamic Performance Aerodynamic Characteristics Wing Configurations computational Modeling Broyden Fletcher Goldfarb Shanno Swept Wing

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Modelling of Transonic Buffet Alleviation via Spoilers

Modelling of Transonic Buffet Alleviation via Spoilers

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AIAA Aviation Forum

作者： Petrocchi, Andrea Barakos, George N. Univ Glasgow Sch Engn CFD Lab Glasgow G12 8QQ Lanark Scotland

ISBN: (数字)9781624107047

ISBN: (纸本)9781624107047

In this work, computational fluid dynamics simulations are carried out to assess the ability of spoilers to alleviate transonic buffet. Spoilers are present on every commercial aircraft and can be used as shock and boundary-layer control devices. The difficulties to model slotted and deployable control surfaces have been overcome by adapting a formulation developped for modelling swinging Gurney flaps to wing spoilers. By adopting virtual spoilers, the separated region formed during buffet is divided. The shock is fixed to an upstream position, and the oscillations are stopped, or alleviated. The effectiveness of this buffet control method is first assessed using 2D computations around aerofoils with different sections and at different flow conditions. The sensitivity to the spoiler deployment angle is studied, and the optimum value based on the aerodynamic performance is determined. Then, computations on an OAT15A unswept wing are carried out to investigate the effect of the spoiler on the 3D buffet dynamics and flow topology.

关键词： Aerodynamic Coefficients Control Surfaces Aerofoil Aerodynamic Performance Buffeting Flows Commercial Aircraft Thickness to Chord Ratio Boundary Layer Control computational fluid dynamics simulation Gurney Flap

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Instability-Based Structural Concept for Rollable Propeller Blades

Instability-Based Structural Concept for Rollable Propeller ...

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AIAA SciTech Forum

作者： Mashin, Annan Kwok, Kawai Univ Cent Florida Dept Mech & Aerosp Engn Orlando FL 32816 USA Purdue Univ Sch Aeronaut & Astronaut W Lafayette IN 47907 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

Launching aircraft in highly constrained environments such as battlefields and undersea severely limits the dimension of the aerodynamic surfaces, limiting the range and efficiency. Deployable structures that can be packaged within small volumes for launch and expand rapidly and extensively midair for cruise present an effective solution to achieve performance while satisfying the stringent launch constraints. This paper introduces a novel structural concept for a rollable propeller blade, which results from combining a rollable skin and a rollable inner spar. The blade can be rolled up for packaging within a confined volume while maintaining sufficient stiffness when deployed in air. The design concept is based on the principle of propagating instability in thin-shell structures to achieve fast deployment without external actuation. The structural architecture design, prototype manufacturing, computational fluid dynamics and structural analysis, and propeller testing are presented to prove the concept. The proposed concept offers enhanced take-off and launching flexibility for aerial vehicles.

关键词： Propeller Blades computational fluid dynamics simulation Thin Shell Structure Structural Analysis Deployable Structures Blade Element Theory Finite Element Analysis High Aspect Ratio Airfoil Profiles Thin Films

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Effect of the pressure balance device on the flow characteristics of a pump-turbine

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY 2022年第8期236卷 1533-1543页

作者： Cao, Jingwei Luo, Yongyao Zhuang, Jianling Li, Xiangyang Wang, Zhengwei Tsinghua Univ Dept Energy & Power Engn Beijing 100084 Peoples R China Fujian Xianyou Pumped Storage Co Ltd Xianyou Fujian Peoples R China

Pump-turbine plays a significant role in the pumped storage station, and it is troubled by unreasonable hydraulic thrust. Some pressure balance devices have been adopted to ensure the safety of the pump-turbine unit, but the effect mechanism has not been numerical studied. This paper establishes the CFD model of the flow passage of a pump-turbine, wherein the crown gap, band gap, pressure balance pipe, and the discharge ostium are considered. Then, the flow characteristics of the pump-turbine at four typical operating conditions in turbine mode are calculated in transient scheme, and the numerical results agree with the experimental results. Finally, the effect of the pressure balance pipe and the discharge ostium on the pressure pulsation and the hydraulic thrust is discussed. The results show that the pressure balance pipe causes the direction of the axial hydraulic thrust to change from downward to upward, and the discharge ostium helps reducing the axial hydraulic thrust to a reasonable range. The pressure balance pipe and the discharge ostium have little effect on the radial hydraulic thrust. The pressure pulsation analysis provides a basis for revealing the mechanism of the hydraulic thrust frequency, and the rotor-stator interaction frequency exists in the axial hydraulic thrust. This paper provides a deeper knowledge of the impact mechanism of the pressure balance pipe and discharge ostium on the flow characteristics of the pump-turbine, which could contribute to future designs of the pump-turbine units, and is helpful for improving the safety of the pumped storage unit.

关键词： Pump-turbine computational fluid dynamics simulation pressure pulsation hydraulic thrust

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An Experimental Study of CO2 Thermochemical Nonequilibrium

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AIAA JOURNAL 2022年第3期60卷 1283-1292页

作者： Gu, Sangdi Morgan, Richard G. McIntyre, Timothy J. Brandis, Aaron M. Univ Queensland Ctr Hyperson Sch Mech & Min Engn Brisbane Qld 4072 Australia Univ Queensland Ctr Hyperson Sch Math & Phys Brisbane Qld 4072 Australia NASA Ames AMA Aerothermodynam Branch Mountain View CA 94035 USA Hong Kong Polytech Univ Dept Aeronaut & Aviat Engn Kowloon Hong Kong Peoples R China

An experimental study of CO2 flows subjected to expanding conditions relevant to Mars entry is presented. A condition with a nominal velocity of 4.0 km/s was generated in the X2 expansion tunnel. Midwavelength infrared emission measurements of the 4.3 and 2.7 mu m bands were made over both a two-dimensional wedge model and for the freestream. Consistent results in the characterization of the freestream were obtained from pressure and spectroscopic measurements. The rotational and vibrational temperatures estimated in the wedge flow using the 2.7 mu m band were consistent with those estimated from the 4.3 mu m band. The difference between the CO2 translational-rotational temperature and the CO2 vibrational temperature was shown to be small in the freestream and expanding flow over the wedge model: less than 10%. Using vibrational relaxation rates tuned for postshock conditions, computational fluid dynamics simulations significantly overestimated the thermal nonequilibrium in the expanding flow, but not in the postshock (compressive) flow. This observation is consistent with past results for N-2 and CO, as well as CO2 at lower temperatures.

关键词： Freestream Conditions Nonequilibrium Flows Thermal Nonequilibrium computational fluid dynamics simulation Emission Spectrum Spectroscopy Energy Distribution Static Pressure Pressure Transducers Pitot Probes

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Machining performance evaluation under recently developed sustainable HAJM process of zirconia ceramic using hot SiC abrasives: An experimental and simulation approach

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 2022年第2期236卷 1009-1035页

作者： Pradhan, Subhadip Das, Sudhansu Ranjan Jena, Pankaj Charan Dhupal, Debabrata Veer Surendra Sai Univ Technol Dept Prod Engn Sambalpur 768018 Odisha India

The proposed research work accomplishes the experimental study and computational fluid dynamics (CFD) technique for erosive footprint prediction extent in hot abrasive jet machining (HAJMing) constraints on target surface erosion rate, surface roughness of intricately shaped tapered holes generation. The CFD-obtained footprints were in superior agreement with experimentally measured data. HAJMing process uses a relatively high speed air-hot abrasive stream to produce both high accuracy micro-channels and tapered holes. HAJM also defines itself phenomenal competence over all advanced manufacturing techniques due to its growing demands for better surface reliability with defects (mostly stress, heat) free surfaces. Zirconia is widely accepted and associated in the non-conventional machining processes and industries with the years of track on record of proven performance in a vast number of brittle materials. Most perceptible act in this research is the selection of abrasive particle to achieve the appropriate intricate shaped holes on zirconia ceramic with hot silicon carbide (SiC) abrasives. Machining of these features are done with varying the abrasive temperature. Optical microscopic view was considered for the generation of machined holes during HAJMing. All the experimental data were presented to study the effect of machining constraints on target surface erosion rate and surface roughness using HAJMing. Single impact experiments were executed to measure the target surface erosion due to impact of individual hot silicon carbide abrasive particles. An experimental setup has been designed to conduct the machining trials using Box-Behnken design of experiments. It is also shown that the generated workpiece surface contour and erosion rate are the function of machining constraints which have a negligible influence on air-abrasive flow characteristics. This research work also deals with the sustainability assessment under environmental-friendly hot abrasive-assisted m

关键词： Hot abrasive jet machine zirconia ceramic silicon carbide computational fluid dynamics simulation scanning electron microscopic study sustainability assessment

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