velocity ratio
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2021 ◽  
Author(s):  
Zhongyu Shi ◽  
Guanqing Wang ◽  
Xiangxiang Chen ◽  
Lu Wang ◽  
Ning Ding ◽  
...  

Abstract The phenomenon of droplet impact on the immiscible liquid is encountered in a variety of scenarios in nature and industrial production. Despite the exhaustive researches, it is not fully clear how the immiscibility of the droplet with impact liquid affects the crown evolution. The present work experimentally investigates the evolution kinematics of crown formed by a normal impact of camellia oil droplet on immiscible water layer. Based on discussion of dynamic impact behaviors for three critical Weber numbers (We), the radius of crown and its average spreading velocity are compared with those of previous theoretical models to discuss their applicability to the immiscible liquid. The evolution kinematics (morphology and velocity) are analyzed by considering the effects of We and layer thickness. Furthermore, the ability of crown expansion in radical and vertical directions is characterized by a velocity ratio. The results show that our experimental crown radius still follows a square-root function of evolution time, which agrees with the theoretical predictions. The dimensionless average spreading velocity decreases with We and follows a power-law, while the dimensionless average rising velocity remains constant. The velocity ratio is shown to be linearly increasing with We, demonstrating that the rising movement in crown evolution gradually enhances with We. These results are helpful for further investigation on the droplet impact on immiscible liquid layer.


Pomorstvo ◽  
2021 ◽  
Vol 35 (2) ◽  
pp. 308-317
Author(s):  
Erinc Dobrucali

Wind tunnel flow visualization tests were conducted to analyse the efflux velocity impacts and the yaw angle on the smoke dispersion of the exhaust for a generic frigate. An analytical study was also implemented to obtain the exhaust plume trajectories. The 1/100 scale generic frigate, having a platform for helicopters on the aft of the ship, was built and employed during the experimental study. The forward and astern cruises of the frigate were considered. It is found that the plume height and the exhaust gases momentum increase with the velocity ratio. The problem of smoke nuisance was observed for the ratios with low velocity such as K=0.2. The plume was also directed towards the helicopter platform when the yaw angles are higher than 10°. The experimental results are compared with the analytical solutions for three different velocity ratios. The compliance between the experimental and analytical results is found to be consistent.


2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jiaojiao Zhang ◽  
Shengna Liu ◽  
Liancun Zheng

Abstract The turbulent boundary layer (TBL) heat transfer of CuO–water nanofluids on a continuously moving plate subject to convective boundary are investigated. Five different shapes of nanoparticles are taken into account. Prandtl mixing length theory is adopted to divide the TBL into two parts, laminar sub-layer and turbulent region. The numerical solutions are obtained by bvp4c and accuracy is verified with previous results. It is found that the transfer of momentum and heat in the TBL is more obvious in laminar sub-layer than in turbulent region. The rise of velocity ratio parameter increases the velocity and temperature while decreases the local friction coefficient. The heat transfer increases significantly with the increase of velocity ratio parameter, Biot number, and nanoparticles volume fraction. For nanoparticles of different shapes, the heat transfer characteristics are Nu x (sphere) < Nu x (hexahedron) < Nu x (tetrahedron) < Nu x (column) < Nu x (lamina).


2021 ◽  
pp. 1-19
Author(s):  
Cheng Xu ◽  
Ryoichi S. Amano

Abstract Energy savings and emission reductions are essential for internal engines. Turbocharger is critical for engine system performance and emission. In this study, the engine simulation program was used to systematically optimize the engine turbocharger system performance. The velocity ratio concept was used in the engine simulation program to consider the performance impacts of the wheel diameter ratio between compressor and turbine. An integral consideration for both compressor and turbine was proposed to design the new turbocharger. An optimization process was used to design the compressor. The final designs employed Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) solvers for the performance and mechanical integrity assessments. The optimized compressor wheel has different features comparing with conventional designs. In this design, the splitter is not located in the middle between main blades; the compressor wheel exit diameter at shroud is larger than hub. The new compressor was tested on both gas stand and engine. The numerical results are fairly agreed with gas stand tests. The tests showed about 1.2% of the engine BSFC reduction without sacrifice the emission and cost. This study demonstrated that a systematic method in simulation and an integral compress design process could optimize the engine system and improve the engine performance.


2021 ◽  
Author(s):  
Juan He ◽  
Qinghua Deng ◽  
Kun Xiao ◽  
Zhenping Feng

Abstract Impingement cooling can effectively disperse local heat load, but its downstream heat transfer is always reduced due to crossflow effect. In this study, the flow and heat transfer characteristics of impingement cooling with Semi-Circular (SC), Semi-Rectangular (SR), Semi-Diamond (SD) and Semi-Four-pointed Star (SFS) crossflow diverters are compared over the ReD ranging from 3,500 to 14,000 by solving three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with SST k-? turbulence model. It is found that crossflow diverters change the distribution of local jet Reynolds number (ReD,j/ReD) and reduce the mass velocity ratio of downstream crossflow to jet (Gcf/Gj), so they enhance the heat transfer significantly, but also come at the cost of friction loss. Overall evaluation reveals that various crossflow diverters can improve the comprehensive heat transfer performance parameter (F), and the maximum increases are 11.0%, 14.3%, 12.2% and 14.7% for SC, SR, SD and SFS cases respectively. It is noted that the Nusselt number of heated SFS-shaped diverter surface is also the highest. Besides, the influences of streamwise location (L) and thickness (t) of SFS-shaped diverter are also investigated. Results show that the heat transfer and friction loss change a little when the L increases from 2D to 3D, but the heat transfer decreases sharply and friction loss increases seriously when the L increases from 3D to 4D. With respect to the t, it has almost no effect on the flow field and heat transfer.


2021 ◽  
pp. 152660282110648
Author(s):  
Edward Choke ◽  
Tjun Yip Tang ◽  
Eilane Peh ◽  
Karthikeyan Damodharan ◽  
Shin Chuen Cheng ◽  
...  

Introduction: Sirolimus coated balloon (SCB) is a promising treatment option to prevent restenosis for peripheral arterial occlusive disease (PAOD). This is a pilot first-in-human study of MagicTouch percutaneous transluminal angioplasty (PTA) SCB for treatment of PAOD for both femoropopliteal and below the knee arteries (BTK). Material and Methods: Xtreme Touch-Neo [MagicTouch PTA] Sirolimus Coated Balloon (XTOSI) pilot study is a prospective, single-arm, open-label, single-center trial evaluating MagicTouch PTA SCB for symptomatic PAOD. Primary endpoint was defined as primary patency at 6 months (duplex ultrasound peak systolic velocity ratio ≤2.4). Secondary endpoints included clinically driven target lesion revascularization (CD-TLR), amputation free survival (AFS), all-cause mortality, and limb salvage success. Results: Fifty patients were recruited. The mean age was 67 (n=31 [62%] males). SCB was applied to femoropopliteal in 20 patients (40%) and BTK in 30 patients (60%). Majority of treatments (94%) were performed for limb salvage indications (Rutherford scores 5 or 6). This was a high risk cohort, in which 90% had diabetes, 36% had coronary artery disease, 20% had end stage renal failure, and American Society of Anaesthesiologists (ASA) score was 3 or more in 80%. Mean lesion length treated was 227±81 mm, of which 36% were total occlusions. Technical and device success were both 100%. At 30 days, mortality was 2% and major limb amputation was also 2%. Six-month primary patency was 80% (88.2% for femoropopliteal; 74% for BTK). At 12 months, freedom from CD-TLR was 89.7% (94.1% for femoropopliteal; 86.3% for BTK), AFS was 81.6% (90.0% for femoropopliteal; 75.9% for BTK), all-cause mortality was 14.3% (10.0% for femoropopliteal; 17.2% for BTK), and limb salvage success was 92.9% (94.4% for femoropopliteal; 91.7% for BTK). There was a statistically significant increase between baseline and 6-month toe pressures for both femoropopliteal (57.3±23.3 mm Hg vs 82.5±37.8 mm Hg; p<.001) and BTK lesions (52.8±19.2 mm Hg vs 70.7±37 mm Hg; p<.037). At 12 months, wound healing rate was 33/39 (84.6%). Conclusions: MagicTouch PTA SCB in the XTOSI study showed promising 6-month primary patency and encouraging 12-month freedom from CD-TLR, AFS, and limb salvage rates. No early safety concerns were raised. Randomized trials are needed to investigate the safety and efficacy of SCB for treatment of PAOD.


2021 ◽  
Vol 2 (1) ◽  
pp. 31-40
Author(s):  
Seyed Mehdi Mousavi ◽  
◽  
Mohammadreza Nademi Rostami ◽  
Mohammad Yousefi ◽  
Saeed Dinarvand ◽  
...  

In this analysis, the flow and heat transfer characteristics of an aqueous hybrid nanofluid with TiO2 and Cu as the nanoparticles past a horizontal slim needle in the presence of thermal radiation effect is investigated. We hope that the present research is applicable in fiber technology, polymer ejection, blood flow, etc. The Prandtl number of the base fluid is kept constant at 6.2. The needle is considered thin when its thickness does not exceed that of the boundary layer over it. Using the similarity transformation method, the governing PDEs are transformed to a set of non-linear ODEs. Then, the converted ODEs are numerically solved with help of bvp4c routine from MATLAB. Results indicate that the dual similarity solutions are obtained only when the slim needle moves in the opposite direction of the free stream. In addition, the first solutions are stable and physically realizable. Besides, the second nanoparticle's mass and also the magnetic parameter lead to decrease the range of the velocity ratio parameter for which the solution exists.


Geosciences ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 510
Author(s):  
Takaji Kokusho ◽  
Tomohiro Ishizawa

A number of vertical array records during eight destructive earthquakes in Japan are utilized, after discussing criteria for desirable requirements of vertical arrays, to formulate seismic amplification between ground surface and outcrop base for seismic zonation. A correlation between peak spectrum amplification and Vs (S-wave velocity) ratio (base Vs/surface Vs) was found to clearly improve by using Vs in an equivalent surface layer wherein predominant frequency or first peak is exerted, though the currently used average Vs in top 30 m is also meaningful, correlating positively with the amplification. We also found that soil nonlinearity during strong earthquakes has only a marginal effect even in soft soil sites on the amplification between surface and outcrop base except for ultimate soil liquefaction failure, while strong nonlinearity clearly appears in the vertical array amplification between surface and downhole base. Its theoretical basis has been explained by a simple study on a two-layered system in terms of radiation damping and strain-dependent equivalent nonlinearity.


2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ved Prakash ◽  
Sunil Chandel ◽  
Dineshsingh G. Thakur ◽  
Mukesh Prakash Mishra ◽  
R. K. Mishra

Abstract The present study performed a three-dimensional numerical analysis on an adiabatic flat plate with forward injection holes for multi-zone film cooling. The cooling holes were divided into three-zone, and the cold air was supplied from cylindrical holes at a velocity ratio of 0.5 and 1.5 with 30° inclination to the primary flow. The effect of multi-zone arrangement in film cooling effectiveness is studied, and a comparison between two-zone and three-zone arrangement has been made. Results show that the three-zone arrangement helps achieve better film cooling effectiveness than the two-zone arrangement due to the uniform flow of coolant at a higher velocity ratio. It also reduces the mass flow rate of secondary flow by decreasing the number of cylindrical holes in the perforated plate.


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