Improvement of Pressure and Flow Rate Characteristics in a Parallel-Flow-Type Multiple-Passage Channel Flow

2020 ◽  
Vol 2020 (0) ◽  
pp. OS04-11
Author(s):  
Taketo SANNOHE ◽  
Kento SEKI ◽  
Masatoshi SANO
Keyword(s):  
Channel Flow ◽  
Flow Rate ◽  
Parallel Flow ◽  
Flow Type ◽  
Multiple Passage

Air Entrainment and Bubble Generation by a Hydrofoil in a Turbulent Channel Flow

2019 ◽  
Author(s):  
Ichiro Kumagai ◽  
Kakeru Taguchi ◽  
Chiharu Kawakita ◽  
Tatsuya Hamada ◽  
Yuichi Murai
Keyword(s):  
Channel Flow ◽  
Flow Rate ◽  
High Speed ◽  
Air Flow ◽  
Air Entrainment ◽  
Air Bubbles ◽  
Air Flow Rate ◽  
Bubble Generation ◽  
Gas Liquid Flow ◽  
Entrained Air

Abstract Air entrainment and bubble generation by a hydrofoil bubble generator for ship drag reduction have been investigated using a small high-speed channel tunnel with the gap of 20 mm in National Maritime Research Institute (NMRI). A hydrofoil (NACA4412, chord length = 40 mm) was installed in the channel and an air induction pipe was placed above the hydrofoil. The flow rate of the entrained air was quantitatively measured by thermal air flow sensors at the inlet of the air induction pipe. The gas-liquid flow around the hydrofoil was visualized by a backlight method and recorded by a high-speed video camera. As the flow velocity in the channel increased, the negative pressure generated above the suction side of the hydrofoil lowered the hydrostatic pressure in the channel, then the atmospheric air was entrained into the channel flow. The entrained air was broken into small air bubbles by the turbulent flow in the channel. The threshold of air entrainment, the air flow rate, and gas-liquid flow pattern depends on Reynolds number, angle of attack (AOA), and hydrofoil type. We identified at least three modes of air entrainment behavior: intermittent air entrainment, stable air entrainment, and air entrainment with a ventilated cavity. At high flow speed in our experimental condition (9 m/s), a large volume of air bubbles was generated by this hydrofoil system (e.g. air flow rate was 50 l/min for NACA4412 at AOA 16 degrees), which has a high potential to reduce ship drag.

scholarly journals Influence of Topographic Resolution and Accuracy on Hydraulic Channel Flow Simulations: Case Study of the Versilia River (Italy)

2019 ◽  
Vol 11 (13) ◽  
pp. 1630 ◽  
Author(s):  
Luppichini ◽  
Favalli ◽  
Isola ◽  
Nannipieri ◽  
Giannecchini ◽  
...  
Keyword(s):  
Channel Flow ◽  
Flow Rate ◽  
Cross Sections ◽  
Low Cost ◽  
Maximum Flow ◽  
Maximum Flow Rate ◽  
Differential Gps ◽  
Basic Model ◽  
Hydraulic Channel ◽  
Elevation Model

The Versilia plain, a well-known and populated tourist area in northwestern Tuscany, is historically subject to floods. The last hydrogeological disaster of 1996 resulted in 13 deaths and in loss worth hundreds of millions of euros. A valid management of the hydraulic and flooding risks of this territory is therefore mandatory. A 7.5 km-long stretch of the Versilia River was simulated in one-dimension using river cross-sections with the FLO-2D Basic model. Simulations of the channel flow and of its maximum flow rate under different input conditions highlight the key role of topography: uncertainties in the topography introduce much larger errors than the uncertainties in roughness. The best digital elevation model (DEM) available for the area, a 1-m light detection and ranging (LiDAR) DEM dating back to 2008–2010, does not reveal all the hydraulic structures (e.g., the 40 cm thick embankment walls), lowering the maximum flow rate to only 150 m3/s, much lower than the expected value of 400 m3/s. In order to improve the already existing input topography, three different possibilities were considered: (1) to add the embankment walls to the LiDAR data with a targeted Differential GPS (DGPS) survey, (2) to acquire the cross section profiles necessary for simulation with a targeted DGPS survey, and (3) to achieve a very high resolution topography using structure from motion techniques (SfM) from images acquired using an unmanned aerial vehicle (UAV). The simulations based on all these options deliver maximum flow rates in agreement with estimated values. Resampling of the 10 cm cell size SfM-DSM allowed us to investigate the influence of topographic resolution on hydraulic channel flow, demonstrating that a change in the resolution from 30 to 50 cm alone introduced a 10% loss in the maximum flow rate. UAV-SfM-derived DEMs are low cost, relatively fast, very accurate, and they allow for the monitoring of the channel morphology variations in real time and to keep the hydraulic models updated, thus providing an excellent tool for managing hydraulic and flooding risks.

Modular Flow Structure Design for a Single-Phase Manifold Microchannel Cold Plate

2015 ◽  
Author(s):  
Feng Zhou ◽  
Yan Liu ◽  
Shailesh N. Joshi ◽  
Yanghe Liu ◽  
Ercan M. Dede
Keyword(s):  
Flow Rate ◽  
Modular Design ◽  
Parallel Flow ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Cold Plate ◽  
Cooling Performance ◽  
Plate Design ◽  
Flow Configurations ◽  
Manifold Microchannel

The present work is generally related to the design of a manifold microchannel heat sink with high modularity and performance for electronics cooling, utilizing two well established (i.e., jet impingement and channel flow) cooling technologies. The present cold plate design provides flexibility to assemble manifold sections in five different configurations to reach different flow structures, and thus different cooling performance, without redesign. The details of the modular manifold and possible configurations of a cold plate comprising three manifold sections are shown herein. A conjugate flow and heat transfer 3-D model is developed for each configuration of the cold plate to demonstrate the merits of each modular design. Parallel flow configurations are used to satisfy a uniform cooling requirement from each module, but a “U-shape” parallel flow “base” configuration cools the modules more uniformly than a “Z-shape” flow pattern due to intrinsic pressure distribution characteristics. A serial fluid flow configuration requires the minimum coolant flow rate with a gradually increasing device temperature along the flow direction. Two mixed (i.e., parallel + serial flow) configurations achieve either cooling performance similar to the “U-shape” configuration with slightly more than half of the coolant flow rate, or cooling of a specific module to a much lower temperature level. Generally speaking, the current cold plate design significantly extends its application to different situations with different cooling requirements.

Turbulence in transient channel flow

2013 ◽  
Vol 715 ◽  
pp. 60-102 ◽  
Author(s):  
S. He ◽  
M. Seddighi
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Channel Flow ◽  
Flow Rate ◽  
Bypass Transition ◽  
Turbulent Structures ◽  
Turbulent Spots ◽  
Transient Channel ◽  
Transitional Phase

AbstractDirect numerical simulations (DNS) are performed of a transient channel flow following a rapid increase of flow rate from an initially turbulent flow. It is shown that a low-Reynolds-number turbulent flow can undergo a process of transition that resembles the laminar–turbulent transition. In response to the rapid increase of flow rate, the flow does not progressively evolve from the initial turbulent structure to a new one, but undergoes a process involving three distinct phases (pre-transition, transition and fully turbulent) that are equivalent to the three regions of the boundary layer bypass transition, namely, the buffeted laminar flow, the intermittent flow and the fully turbulent flow regions. This transient channel flow represents an alternative bypass transition scenario to the free-stream-turbulence (FST) induced transition, whereby the initial flow serving as the disturbance is a low-Reynolds-number turbulent wall shear flow with pre-existing streaky structures. The flow nevertheless undergoes a ‘receptivity’ process during which the initial structures are modulated by a time-developing boundary layer, forming streaks of apparently specific favourable spacing (of about double the new boundary layer thickness) which are elongated streamwise during the pre-transitional period. The structures are stable and the flow is laminar-like initially; but later in the transitional phase, localized turbulent spots are generated which grow spatially, merge with each other and eventually occupy the entire wall surfaces when the flow becomes fully turbulent. It appears that the presence of the initial turbulent structures does not promote early transition when compared with boundary layer transition of similar FST intensity. New turbulent structures first appear at high wavenumbers extending into a lower-wavenumber spectrum later as turbulent spots grow and join together. In line with the transient energy growth theory, the maximum turbulent kinetic energy in the pre-transitional phase grows linearly but only in terms of ${u}^{\ensuremath{\prime} } $, whilst ${v}^{\ensuremath{\prime} } $ and ${w}^{\ensuremath{\prime} } $ remain essentially unchanged. The energy production and dissipation rates are very low at this stage despite the high level of ${u}^{\ensuremath{\prime} } $. The pressure–strain term remains unchanged at that time, but increases rapidly later during transition along with the generation of turbulent spots, hence providing an unambiguous measure for the onset of transition.

Hydraulics of steeppass fishways

1991 ◽  
Vol 18 (6) ◽  
pp. 1024-1032 ◽  
Author(s):  
N. Rajaratnam ◽  
C. Katopodis
Keyword(s):  
Experimental Study ◽  
Velocity Profile ◽  
Channel Flow ◽  
Flow Rate ◽  
Open Channel ◽  
Maximum Velocity ◽  
Open Channel Flow ◽  
Width Ratio ◽  
Hydraulic Design ◽  
Theoretical Considerations

This paper presents the results of an experimental study on the hydraulics of steeppass fishways. Using theoretical considerations and experimental observations, an expression has been developed that relates the flow rate, slope of the fishway, and depth of flow. It was also found that the characteristic (similarity) velocity profile found earlier, for smaller values of depth to width ratio,y0/b, with the maximum velocity near the bottom, changes to a rather symmetrical profile with the maximum velocity occurring somewhere near the mid-depth for larger values of y0/b. A correlation has also been found for the maximum velocity. This paper also includes some observations on the M-type backwater curves that would appear in the fishway when the tailwater depths exceed uniform flow depths. Key words: fishways, hydraulics, turbulent flow, open-channel flow, hydraulic design.

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