Journal of Fluid Science and Technology最新文献

{"title":"Effects of ambient pressure on cavitation in the nozzle and the discharged liquid jet","authors":"Rubby Prasetya, Akira Sou, Y. Wada, H. Yokohata","doi":"10.1299/JFST.2019JFST0005","DOIUrl":"https://doi.org/10.1299/JFST.2019JFST0005","url":null,"abstract":"Cavitation in the nozzle plays an important role in the atomization of the discharged liquid jet. Because of this, understanding in-nozzle cavitation is very important for the control of spray characteristics. However, in-nozzle cavitation is not fully understood at present, in part because it is affected by various factors, such as fluid properties, injector geometries, and ambient pressure. Although it is obvious that ambient pressure hinders cavitation development in the nozzle, the extent of the effect has not been quantitatively predicted yet. In the present study, visualization of cavitation in an enlarged two-dimensional (2D) transparent nozzle and the discharged liquid jet is carried out under various ambient pressure P a ( P a = 0.1, 0.2, 0.3, 0.4, and 0.5 MPa). From the flow visualization result, an image analysis is carried out to obtain the experimental data on the effects of ambient pressure on cavitation length L c , cavitation width W c , and liquid jet angle θ . Finally, a set of correlations on L c , modified cavitation number σ c , jet angle θ , and the Weber number We at various ambient pressures are proposed, based on the image analysis results.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"1 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2019JFST0005","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66303316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pressure drag and friction drag for truncated pyramids in a turbulent open channel flow","authors":"Mitsuhiro Shintani, Y. Hagiwara","doi":"10.1299/JFST.2019JFST0001","DOIUrl":"https://doi.org/10.1299/JFST.2019JFST0001","url":null,"abstract":"The purpose of this study is to establish a method that more efficiently reduces drags for a three-dimensional object whose surfaces are shaped in some kind of wavy form. We use a truncated pyramid that is a relatively simple three-dimensional object. Experiments were carried out for truncated pyramids covered with flat surfaces or wavy surfaces in a turbulent open channel flow. The total drag was obtained by measuring the force acting on the pyramids. The local wall shear stress was estimated from the local mean velocity profile in the direction normal to the surfaces. The difference between the pressure on the uphill surface and that on the downhill surface of the pyramid was also measured with a pressure difference gauge. It was found that the total drag and the pressure difference for the truncated pyramid covered with the wavy surfaces were at their highest 7.9% and 13.7% lower respectively than the equivalent figures for the truncated pyramid covered with flat surfaces. The reductions of the pressure difference and total drag were caused by the recirculation flow intermittently occurring near the top face and the downhill face of the truncated pyramids.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"1 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2019JFST0001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66302914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigation into far-field drag calculation methods and pseudo total enthalpy generation for airplane CFD","authors":"K. Matsushima, R. Shimizu, Kentaro Goshima","doi":"10.1299/jfst.2019jfst0023","DOIUrl":"https://doi.org/10.1299/jfst.2019jfst0023","url":null,"abstract":"In this study drag calculations were performed for an airplane cruising at transonic speed in a flow-field using two far-field methods. Subjected flow-fields in the calculations were computational fluid dynamics (CFD) results of Reynolds-averaged Navier–Stokes simulation (RANS) around a wing. The objectives were to establish effective means to utilize far-field drag methods and wake flow phenomena as well as report pseudo total enthalpy which peculiarly appeared in the CFD simulation results. The drag calculation was completed using four wake integration equations. The first originated from the equation of the momentum conservation law itself, the second was based on enthalpy variation, the third was based on entropy variation, and the last was a method for induced drag calculation. Drag values resulting from the integrations were compared to those via a near-field method commonly used in CFD. Through the computation and comparison of wake integration drag values, it was proved that the both far-field methods were able to predict a comparably accurate drag value compared to that of the near-field method. In addition, strange inappropriate total enthalpy (pseudo total enthalpy) generation was found in some regions where a flying airplane never affects flow behavior. In the wake integrations, the pseudo total enthalpy generation seems to compensate for the drag value via the first equation. The pseudo total enthalpy generation depends on far-field boundary locations. In summary, wake integrations are promising to provide useful information for accurate drag prediction.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"1 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/jfst.2019jfst0023","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66303502","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of diffusing layer thickness on the density-driven natural convection of miscible fluids in porous media: Modeling of mass transport","authors":"Lei Wang, Y. Nakanishi, Alexis Daniel Van Hoang Teston, T. Suekane","doi":"10.1299/JFST.2018JFST0002","DOIUrl":"https://doi.org/10.1299/JFST.2018JFST0002","url":null,"abstract":"In this study, density-driven natural convection in porous media associated with Rayleigh–Taylor instability was visualized by X-ray computed tomography to investigate the effect of the thickness of the diffusing interface on convection. The thickness of the interface was changed by molecular diffusion with time, and the effective diffusivity in a porous medium was estimated. Compared with the thick interface, for the thin interface, many fine fingers formed and extended rapidly in a vertical direction. The onset time of natural convection increased proportionally with the thickness of the interface, being correlated with Rayleigh number and Péclet number. For the thinner initial interface, the finger number density increased more rapidly after onset and reached a higher value. Next, we discussed the mass transport in Rayleigh–Taylor convection to show how dispersion affects mass transport based on finger extension velocity and concentration in fingers. Increasing the interface thickness delayed the onset of convection, while the finger extension velocity remained the same. The reduced finger extension velocity changed nonlinearly with the Péclet number, reflecting the effect of dispersion. High transverse dispersion and longitudinal dispersion quickly reduced finger density. Transverse dispersion between ascending and descending fingers decreased the density; the density decreased linearly along the finger on both sides of the symmetric plane. As a result, the Sherwood number was proportional to the Rayleigh number, whereas the coefficient changed nonlinearly with Péclet number because of dispersion, reflecting the nonlinear dependences of the reduced velocity and the reduced density difference on Péclet number.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"63 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2018JFST0002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66301572","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Control of trailing-edge noise from airfoil using a plasma actuator","authors":"A. Inasawa, Y. Kagawa","doi":"10.1299/JFST.2018JFST0003","DOIUrl":"https://doi.org/10.1299/JFST.2018JFST0003","url":null,"abstract":"gradient were attenuated using downstream installed plasma actuators. They examined both continuous and pulsed-mode operations and showed that the boundary-layer transition could be delayed even by pulsed operation, which has better energy efficiency. Stabilization of the boundary layer in the natural transition over an airfoil, with the aim of tonal noise suppression, was examined by Inasawa et al. (2013), who employed a flush-mounted configuration of actuator electrode in order to minimize the possible interference with Abstract Control of noise generation at an airfoil trailing-edge was conducted using a plasma actuator for an NACA0012 airfoil with an angle of attack of -2° at a chord Reynolds number Re = 1.6×10 5 , where the boundary-layer instability on the pressure side was responsible for the generation of the tonal trailing-edge noise. A thin electrode was installed uniformly in the spanwise direction at the maximum wing thickness location. The actuator was operated in pulsed (burst) mode to excite linear disturbances other than the naturally growing one artificially, and the responses of flow and tonal sound were examined. The naturally radiated tonal trailing-edge noise was found to be replaced by the weaker tonal sound at the bursting frequency when the bursting frequency was near that of the natural tone. It was also demonstrated that when the actuation frequency was far from that of original (natural) sound, the boundary-layer transition was dominated by naturally unstable broadband disturbances, leading to complete suppression of the tonal trailing-edge noise.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"13 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2018JFST0003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66301681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stochastic tsunami inundation flow simulation via polynomial chaos approach","authors":"Wataru Yamazaki, Tatsuya Kato, T. Homma, K. Shimoyama, S. Obayashi","doi":"10.1299/JFST.2018JFST0025","DOIUrl":"https://doi.org/10.1299/JFST.2018JFST0025","url":null,"abstract":"In this research, 2D shallow water equations are expanded by an intrusive polynomial chaos approach for efficient uncertainty quantification in tsunami inundation flows. Uncertainty propagation can be evaluated by solving the expanded 2D shallow water equations, and then probability measures such as mean, standard deviation and probability density function can be obtained for arbitrary variables. An uncertain input is given on its initial condition of water height and/or bathymetry in dam break problems as well as in Thacker’s inundation flow problem. Obtained uncertainty quantification results are compared with (exact) Monte-Carlo simulation results to validate the developed approach. Qualitative agreement can be confirmed between the Monte-Carlo simulation and the developed approach. The computational cost of the developed approach is much more inexpensive than the Monte-Carlo simulation, so that inexpensive/accurate uncertainty quantification can be realized with the developed approach. By using the obtained results, stochastic hazard map considering uncertainties can be generated which will be beneficial to minimize potential damage via inundation flows.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"13 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2018JFST0025","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66302476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aerodynamic instability of flare-type membrane inflatable vehicle in suborbital reentry demonstration","authors":"Tatsushi Ohashi, Yusuke Takahashi, H. Terashima, N. Oshima","doi":"10.1299/JFST.2018JFST0020","DOIUrl":"https://doi.org/10.1299/JFST.2018JFST0020","url":null,"abstract":"An inflatable membrane reentry vehicle has been developed as one of the innovative reentry technologies. A suborbital reentry demonstration using a sounding rocket was carried out in 2012. Contrary to the result of a preliminary study, the vehicle always had an angle of attack (AoA) during its reentry. In addition, the amplitude of AoA gradually increased as altitude decreased, and the vehicle rotated vertically under Mach number of 0.1 (M0.1). As a first step to clarify the cause of attitude instability and vertical rotation, the aerodynamic characteristics, that concern static stability, are numerically investigated. Numerical simulations were carried out for the cases of Mach 0.9 (M0.9), 0.6 (M0.6), 0.3 (M0.3), and 0.1 (M0.1) and pitching moment coefficients ( 𝐶 𝑀 ) were obtained. Analysis software “RG-FaSTAR” for M0.9, and “FrontFlow/red” for M0.6, M0.3 and M0.1, are used, respectively. Large eddy simulation (LES) was performed using the standard Smagorinsky model to resolve highly unsteady flow features. Because the slope of 𝐶 𝑀 with respect to AoA was negative for all cases, it was found that the vehicle is statically stable. For M0.9, M0.6 and M0.3 cases, absolute values of 𝐶 𝑀 were almost the same. On the other hand, for M0.1, 𝐶 𝑀 had a particularly large value, because the surface pressure distribution on rear side of the vehicle was different from the other cases. This difference was attributed to the separation point on the lower torus moving backward and turbulence in wake being enhanced with a decrease in Mach number and an increase in the Reynolds number.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"13 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66302638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Measurement of concentration dependency of diffusion coefficient in ethanol-water solution under different storage condition","authors":"A. Komiya, Kengo Sato, J. Okajima","doi":"10.1299/JFST.2018JFST0030","DOIUrl":"https://doi.org/10.1299/JFST.2018JFST0030","url":null,"abstract":"This study focuses on the diffusion phenomena in ethanol-water systems. The diffusion coefficient of ethanol-water systems has a strong concentration dependency originating from intermolecular interactions and the association of molecules in solution. Recently, it has been suggested that flavor variation in whiskey is partly due to different storage conditions that can affect molecular structure variation. To evaluate the molecular structure variation, diffusion coefficient measurements are considered effective. To quantitatively evaluate the variations in the diffusion process and measure the mass diffusion coefficient, the analysis method was improved to measure the concentration field more precisely. Two ethanolic solutions were prepared in this study: one preserved under normal conditions and the other was stored under isothermal conditions for 496 days. By comparing diffusion processes occurring under different storage conditions, the different diffusion coefficients were determined and the effect of storage conditions was discussed. The diffusion coefficient of the ethanolic solution stored under an isothermal condition was smaller than that of the solution stored under normal conditions. of ethanol in water was constant for evaluating the diffusion field. Therefore, for systems with a concentration dependence of mass diffusion coefficients, the measurement of small concentration differences, (where the mass diffusion coefficient was treated as constant), has been performed periodically and the concentration dependency was evaluated using the accumulated data. On the contrary, the proposed method in this study treats the diffusion coefficient as a function of concentration, and the diffusion","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"13 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2018JFST0030","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66302903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of buoyancy on fingering growth activity in immiscible two-phase flow displacements","authors":"Mushlih Muharrik, T. Suekane, Anindityo Patmonoaji","doi":"10.1299/JFST.2018JFST0006","DOIUrl":"https://doi.org/10.1299/JFST.2018JFST0006","url":null,"abstract":"Immiscible displacement processes have been investigated for decades to understand their applications, such as geosequestration of CO 2 and enhanced oil recovery, in detail. In this study, the effect of buoyancy on fingering growth activity during a drainage process was investigated under the competitive influence of buoyancy, capillary, and viscous forces. A packed bed of glass microbeads was used as a porous medium for immiscible fluid pairing of silicon oil and water as a non-wetting phase (NWP) and wetting phase (WP), respectively. The time lapse 3D structure of finger development was visualized for a Bond number Bo range of 3.84 × 10 −4 to 3.45 × 10 −3 and a capillary number Ca range of 4.30 × 10 −9 to 4.30 × 10 −7 using an X-ray CT scanner. Three instability regimes—capillary fingering, transition, and gravity fingering enhanced by buoyancy forces—were successfully observed. The crossover from capillary fingering to gravity fingering was observed at Bo values between 1.53 × 10 −3 and 3.45 × 10 −3 . The gravity fingering structure was observed at Bo = 3.45 × 10 −3 and Ca = 4.30 × 10 −7 . Under gravity fingering conditions, the pressure of the NWP to displace the WP is highest at the tip of the most advanced finger because the buoyancy force is relatively higher than the capillary force. Consequently, massive new invasions were induced near the tip of the most advanced finger. As a result, the fingers vertically extended with a streak-like structure, and the diameter of the fingers was as small as single-pore sizes. The NWP saturation at breakthrough was low and fluctuated in the z direction. The WP was merely trapped as an isolated cluster. Under capillary fingering conditions ( Bo < 1.53 × 10 −3 ), the fingers not only grew near the tip of the most advanced finger but also grew far below the tip. Some fingers extended to link pores with a small diameter of approximately single-pore size and developed in a horizontal direction, i.e., in the negative z direction as well as in the z direction. The size of trapped WP clusters was distributed from single-pore size to large size, connecting several pores. A skewed distribution of saturation was shown at the breakthrough for low Ca because of competition between capillary fingering and gravity fingering. At high Ca , the pressure gradient established along the z direction as a result of viscous shear force resulted in a gradual decrease in the saturation profile in the z direction. −3 −3 fingering","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"13 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2018JFST0006","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66301540","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An experimental investigation of the behavior of oil jets injected by a 90° curved circular nozzle","authors":"A. Nakashima, G. Nitta, K. Nishida, H. Hongou, H. Yokohata, Y. Ogata","doi":"10.1299/JFST.2018JFST0007","DOIUrl":"https://doi.org/10.1299/JFST.2018JFST0007","url":null,"abstract":"Abstract The high efficiency cooling of pistons in internal combustion engines by oil jets has recently received widespread attention. To date, curved circular oil jet nozzles have been commonly employed. However, although liquid jets from straight circular nozzles have been studied, there are few reports regarding the characteristics of liquid jets injected by curved circular nozzles. The present work therefore examined the characteristics of oil jets, such as jet width and interfacial fluctuations, following injection via either a 90° curved circular nozzle or straight circular nozzle into a stationary atmosphere. Oil jet parameters were assessed at Reynolds numbers from 1000 to 3000 and the jet interfaces were visualized using a background illumination method in conjunction with a high-speed camera. The oil jet injected from the curved nozzle exhibits more complex behavior compared with that from the straight nozzle. The cross section of the jet from the curved nozzle perpendicular to the direction of movement gradually expanded from a circular shape to an elliptical shape in the downstream direction. The side corresponding to the long diameter of this elliptical jet shape was also observed to switch depending on the Reynolds number. At the inner and outer side interfaces, the outer side interface became larger than the inner side interface at the Reynolds number of 1500 or less. However, the inner side interface became greater than the outer side interface at the Reynolds number of 2000 or more. The effects of the velocity distribution following the bend in the curved nozzle on oil jet behavior were examined by stereoscopic particle image velocimetry. The nozzle internal flow evidently generated movement from the outer side toward the inner side at the Reynolds number of 2000, while flow toward the inner side was dominant when the Reynolds number was 2500.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":"12 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1299/JFST.2018JFST0007","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66301664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}