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Study of Flow Separations over a Two-dimensional Bluff Body

Tongji University-Guangyuan Huang
  • Technical Paper
  • 2020-01-0024
To be published on 2020-03-10 by SAE International in United States
The existence of flow separation over both leading and trailing edges is observed in elongated bluff cylinders. Stepwise variation of the Strouhal number and the change of the unsteady aerodynamic forces have been observed owning to the interaction of two separations. In the present work, flow separations over a two-dimensional (2-D) bluff body at Reynolds number Re=23000 and Mach number M=0.2 is studied numerically. The body, popularly used in vehicle aerodynamic research, presents a rectangular cylinder with a chord-to-thickness ratio c/t=3.64 and a rounded head. The flow field is obtained by direct numerical simulation (DNS) solving 2-D compressible Navier-Stokes equation, together with the state equation of ideal gas. Although the flow at present Reynolds number is three-dimensional and turbulent, we focus on the predominantly 2-D structures, i.e. the separation and the reattachment of the leading-edge shear layer, and the rollup of the trailing-edge shear layer into large-scale vortices. The solution is validated against existing experimental and numerical data. And the difference is discussed. Result shows that the flow is characterized by flow separation at both…
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Investigation of The Effect of Enhanced In-Cylinder Flow on HCCI Combustion in a Rapid Compression and Expansion Machine

Chiba University-Yiwen Zhong, Kazuya Ogawa, Tatsuya Kuboyama, Yasuo Moriyoshi
SUZUKI MOTOR CORPORATION-Kei Yoshimura
  • Technical Paper
  • 2019-32-0528
To be published on 2020-01-24 by Society of Automotive Engineers of Japan in Japan
The purpose of this paper is to find a way to extend the high load limit of homogeneous charge compression ignition (HCCI) combustion. A newly developed rapid compression and expansion machine (RCEM) was employed to reproduce the typical HCCI high load condition. The in-cylinder turbulence was created by the special piston which equipped with a flow guide plate. Meanwhile, the ambient temperature distribution in the cylinder was determined by the wall temperature controlling system which was controlled by the independent coolant passages. In addition, the numerical simulation by using large eddy method coupled with a detailed chemical reaction was conducted as well. The results show that HCCI mode is potential to be improved at high load condition in full consideration of in-cylinder temperature, flow, and turbulence.
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Effect of curvature diameter on secondary flow generation for square channel spiral coil sub-cooled condenser

Sophia University, 7-1, Kioi-cho Chyoda-ku, Tokyo, 102-8554,-Hardeep Singh, Mitsuhisa Ichiyanagi, Takashi Suzuki
  • Technical Paper
  • 2019-01-2315
Published 2019-12-19 by SAE International in United States
This paper oriented towards spiral coil sub-cooled condenser (SCSCC) which is used for the automotive air conditioning system. Therefore, the effect of curvature diameter has been carefully measured by CFD as it reduces/intensify the centrifugal force. This centrifugal force is responsible for Dean vortices and leads to the generation of secondary flow inside the refrigerant. By taking advantage of this secondary flow, the performance of the SCSCC can be improved. CFD analysis comprises curvature diameter from 13mm to 110mm, which varied the Dean number from 7577 to 2605. The author tried to evaluate the complicated phenomena that occurred within the SCSCC. However, the turbulent kinetic energy which is one of the critical factors of heat transfer coefficient illustrates 0.009m2/s2 and 0.006m2/s2 for large and small Dean number, respectively, toward the outer side of the channel. Under the present CFD condition, the secondary flow velocity was largest when using the curvature diameter of 18 mm, which was the medium condition.
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Influences of multi spark discharge on lean ignition for premixed propane/air mixtures under turbulent environment

The University of Tokyo-Taichi Kobayashi, Yuya Yamaki, Shinji Nakaya, Mitsuhiro Tsue
  • Technical Paper
  • 2019-01-2161
Published 2019-12-19 by SAE International in United States
Spark ignition experiments were conducted to investigate effects of multi discharges on ignition of a lean-turbulence mixture. Initial flame kernel developments were observed by Schlieren photography, and discharge characteristics were analyzed by high-speed photography and spectroscopic measurements. Results indicated that the MIE (Minimum Ignition Energy) of the single discharge was lower than that of the multiple one at 100 kPa, and higher at 500 kPa. Each discharge was generated independently when discharge interval was set to 1 ms at 500 kPa, while discharge was occurred continuously at 100 kPa. This discharge characteristics might be related to the ignition performance.
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Vaporization and Turbulence Characteristics of High Pressure Gasoline Sprays Impinging on a Wall

Mazda Motor Corporation-Wu Zhang, Ryosuke Hara, Tatsuya Fujikawa, Masahisa Yamakawa
University of Hiroshima-Tomohiro Watanabe, Yukihiko Ichikawa, Keiya Nishida, Yoichi Ogata
  • Technical Paper
  • 2019-01-2247
Published 2019-12-19 by SAE International in United States
To get a better understanding of the characteristics of the high pressure gasoline sprays impinging on a wall, a fundamental study was conducted in a high-temperature high-pressure constant volume vessel under the simulated engine conditions of in-cylinder pressures, temperatures, and wall temperatures. The injection pressure was varied from 20 to 120 MPa. The spray tip penetration, vapor mass distribution, and vaporization rate were quantitatively measured with the laser absorption-scattering (LAS) technique. The velocity fields of the wall-impinging sprays under vaporizing conditions were measured with the particle image velocimetry (PIV) technique using silicone oil droplets as tracers. The effects of injection pressure and spray/wall interactions on spray characteristics were investigated. The results showed that the increased injection pressure improved penetration, vaporization, and turbulence of the sprays.
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Effect of Injection Amount on Diesel Spray Characteristics of Multi-Hole Nozzle

Fukuoka Institute of Technology-Keisuke Komada
IRS Corporation-Manabu Saito
  • Technical Paper
  • 2019-01-2284
Published 2019-12-19 by SAE International in United States
A laser 2-focus velocimeter(L2F) has been utilized for the measurements of the velocity and size of droplets in diesel fuel sprays injected from a 6-hole nozzle. The fuel was stored once in a common rail and was injected intermittently to the atmosphere by using a solenoid injector. The diameter of the nozzle orifice was 0.165 mm. The injection pressure was 60 MPa. The injector solenoid was driven by the current having a waveform consisted of 3 stages; boot, pull, and hold. The injection amounts were set at 0.8, 2.9, 3.9 and 4.7mg by changing the durations of the pull stage and the hold stage. The L2F measurement was conducted at 10 mm downstream from the nozzle exit. The fluctuation intensity of the droplet velocity was found to be larger under the smaller injection amount. It was clearly shown that the arithmetic mean droplet size under the smaller injection amount was smaller than that under the larger injection amount during the hold current duration. There was a negative correlation between the droplet size and the droplet…
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Impact of Wheel-Housing on Aerodynamic Drag and Effect on Energy Consumption on an Electric Bus Body

ARAI Academy-Amitabh Das, Yash Jain
Automotive Research Association of India-Mohammad Rafiq Agrewale, Kamalkishore Vora
  • Technical Paper
  • 2019-28-2394
Published 2019-11-21 by SAE International in United States
Role of wheel and underbody aerodynamics of vehicle in the formation of drag forces is detrimental to the fuel (energy) consumption during the course of operation at high velocities. This paper deals with the CFD simulation of the flow around the wheels of a bus with different wheel housing arrangements. Based on benchmarking, a model of a bus is selected and analysis is performed. The aerodynamic drag coefficient is obtained and turbulence around wheels is observed using ANSYS Fluent CFD simulation for different combinations of wheel-housing- at the front wheels, at the rear wheels and both in the front and rear wheels. The drag force is recorded and corresponding influence on energy consumption of a bus is evaluated mathematically. A comparison is drawn between energy consumption of bus body without wheel housing and bus body with wheel housing. The result shows a significant reduction in drag coefficient and fuel consumption.
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Winglet Design and Analysis for Cessna 152 - A Numerical Study

SRM Institute of Science and Technology-Vivek Saini, Nagarajan Sunil Bhargav, Yallur Mohiddinsha, Sundararaj Senthilkumar
Published 2019-10-11 by SAE International in United States
During flight an emergent circulatory flow pattern named vortex is observed at wing tips producing induced drag. An approach to reduce this effect is by implementing winglets. Winglets are small wing-like lifting surfaces, fitted at the tip of some wings, usually with the objective of decreasing trailing vortex drag and thereby increasing the aerodynamic efficiency of the wing. The aim of the project is to design and analyze the effect of winglets for Cessna 152 by varying the cant angle and sweep angle. This model has been selected since it provides a good choice for Pilots first airplane. A baseline wing model was designed in CATIA V5, correspondingly wings with winglet models were designed with a fixed taper ratio of 0.2 and different cant and sweep angles. The lift to drag ratio is evaluated at different angles of attack by varying winglet design parameters. Different wing configurations with various Cant and Sweep angles were analyzed at sea level conditions using K-ω SST turbulent model in ANSYS FLUENT and best winglet with desired characteristics for optimum…
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CFD Simulation on Turbulent Forced Convection of Copper Oxide (CuO) -Water Nanofluids in a Horizontal Circular Pipe

John Deere India Pvt, Ltd.-Nitin Dewangan, Nitin Kattula
Published 2019-10-11 by SAE International in United States
The present study provides a detailed investigation on simulation of Copper oxide nanofluids in a simple horizontal circular pipe considering turbulent forced convection, with a constant heat flux boundary condition. The simulation is carried out using three different models available in fluent viz. Newtonian single phase model, Eulerian-mixture and Eulerian-Eulerian multiphase models. The Reynold number of the flow is varied along with volume concentration of nanoparticles varying form low to high. Nanofluids rheology is studied by considering standard k-ε two equation turbulence model with enhanced wall treatment considering appropriate wall y+ values. The effective temperature dependent thermo-physical properties for nanofluids were seized from the literatures. The results from the simulation clearly showed an increase in the heat transfer characteristics with the addition of nanoparticles compared to that of base fluid alone. Eulerian-Mixture model predicted the Nusselt number near to that of the experimental results from literature.
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Increase of Compressor Performance through the Use of Microstructures

Bionic Surface Technologies GmbH-Mikel Garcia de Albeniz, Peter Adrian Leitl
RINA-Emiliano Costa, Stefano Barberis
Published 2019-10-07 by SAE International in United States
Turbomachinery efficiency is becoming more and more relevant in order to reduce fuel consumption and mechanical wear of machines at the purpose of increasing their environmental sustainability and reliability. Optimized material identification and design is therefore of paramount importance. This paper describes how turbomachines can be optimized thanks to the effect of microstructures suitably created over the shapes of their constituting components in order to increase the overall efficiency via a simple coating solution. These structures, called riblets, consist of tiny streamwise grooved surfaces which are such to reduce drag in the turbulent boundary layer. Theoretical, numerical and experimental experiences gave a first estimation of the impact of riblets in industrial compressors. In this case, the riblet structures reduce the aerodynamic shear stress losses. The areas of higher interest are the diffuser and the volute, where the higher losses happen. The optimal size, position and effect on performance were analysed via simulation. The use of such an effective numerical means may give a precise evaluation about benefits in terms of efficiency increase as well as…
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