An Experimental Investigation on Internal Flow Characteristics in a Realistic and Entire Coolant Channel With Ribs and Film Holes

2018 ◽  
Author(s):  
Peng Wang ◽  
Jian Pu ◽  
Ren-bin Yu ◽  
Jian-hua Wang ◽  
Bo Wan ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Separation Bubble ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Main Flow ◽  
Particle Image Velocimetry Technique ◽  
Cross Sectional ◽  
Flow Acceleration ◽  
Sharp Bend ◽  
Secondary Vortices

This paper presents an experimental investigation on the flow characteristics within an entire coolant channel of a 2nd stage high pressure (HP) static turbine blade using TRPIV (Time-Resolution Particle Image Velocimetry) technique. The serpentine channel with three passages connected by a sharp bend, a round bend, 2 tip exits, 8 tailing exits and 40 film-holes staggered arranged on pressure side (PS) of the third pass is chosen as specimen, whose cross sections are manufactured to keep the real blade-shape. Ribs with a fixed spacing-to-height of 7 and an angle of 60° to the flow direction are applied on two opposite walls. The experiment is carried out at a fixed inlet Reynolds number of Rein = 23508. The variation process of secondary vortices and the main flow patterns in typical planes of the realistic coolant channel are successfully captured by TRPIV technique. The effects of rib, bend, cross-sectional shape, layout of passages, ejection ratio on the flow characteristics are analyzed and discussed. The following five new phenomena can be obtained. Namely, 1) near the two bend-regions, the rib can reduce the size of separation bubble and generate a new flow-acceleration downstream of the rib. 2) The rib-vortices combined with the mixing vortex caused by the bend and layout of channels, which leads to a new pair of vortices downstream of the bend, and further downstream, in the pair of vortices, the larger vortex presses the smaller vortex to form a new large vortex. This phenomenon has not been captured up to now in simplified ribbed two-pass channels and smooth realistic channels. 3)The development process of the secondary vortices and asymmetric behavior of main flow structure are similar in the regions of the sharp and round bends. 4)The coolant ejection from the tip exit in the sharp bend can decrease the mixing speed of the secondary vortices downstream of the bend. 5)The tip ejection from the trailing edge exits and film holes can reduce of the size of the secondary vortices downstream of the bend.

Pressure Change for Single- and Two-Phase Non-Newtonian Flows through Sudden Contraction in Rectangular Microchannel

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 440
Author(s):  
Masaki Toshimitsu ◽  
Yukihiro Yonemoto ◽  
Akimaro Kawahara
Keyword(s):  
Pressure Distribution ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Pressure Change ◽  
Two Phase ◽  
Rectangular Microchannel ◽  
Cross Sectional ◽  
Contraction Ratio ◽  
Cross Sectional Dimension ◽  
Sudden Contraction

The flow characteristics of the single-phase liquid and the gas–liquid two-phase flows including the Newtonian and non-Newtonian liquids were experimentally investigated in a horizontal rectangular micro-channel with a sudden contraction—specifically the pressure change across the contraction. The rectangular cross-sectional dimension has Wu × Hu (width × height) = 0.99 × 0.50 mm2 on the upstream side of the contraction and Wd × Hd = 0.49 × 0.50 mm2 on the downstream side. The resulting contraction ratio, σA (=Wd/Wu), was 0.5. Air was used as the test gas (in the case of the gas–liquid two-phase flow experiment), distilled water and three kinds of aqueous solution, i.e., glycerin 25 wt%, xanthangum 0.1 wt% and polyacrylamide 0.11 wt% were used as the test liquid. The pressure distribution in the flow direction upstream and downstream of the channel was measured. The pressure change and loss at the sudden contraction were determined from the pressure distribution. In addition, the pressure change data were compared with the calculation by several correlations proposed by various researchers as well as a newly developed correlation in this study. From the comparisons, it was found that calculations by the newly developed correlations agreed well with the measured values within the error of 30%.

scholarly journals Flow Characteristics of the Medtronic CoreValve: Difficulties Estimating Aortic Valve Cross-Sectional Area Following Transcatheter Aortic Valve Implantation

2015 ◽  
Vol 1 (3) ◽  
pp. 132 ◽  
Author(s):  
Alison Duncan
Keyword(s):  
Aortic Valve ◽  
Transcatheter Aortic Valve Implantation ◽  
Flow Characteristics ◽  
Cross Sectional ◽  
Flow Acceleration ◽  
Transcatheter Aortic Valve ◽  
Sample Position ◽  
Medtronic Corevalve ◽  
Aortic Valve Implantation ◽  
Valve Implantation

Background: Echocardiographic evaluation after transcatheter aortic valve implantation (TAVI) includes estimation of effective<br />orifice area (EOA). EOA calculation depends on sub-valvular stroke volume (SV), which depends on sub-valvular diameter and<br />velocity time integral (VTI). The Medtronic CoreValve area changes throughout its length. We aimed to (i) compare SV at two<br />sites of flow acceleration: ‘pre-stent’ and ‘in-stent, pre-valve’, (ii) assess effects of possible differences in sub-valvular SV on<br />EOA, and (iii) assess agreement of measurement of EOA calculation after CoreValve TAVI.<br />Methods: We studied 43 patients after CoreValve implantation. All had transthoracic echocardiography 5-7 days after TAVI.<br />Sub-valvular SV was measured ‘pre-stent’ and ‘in-stent, pre-valve’. Measurement agreement was assessed by root mean<br />square (RMS) differences and Bland-Altman analyses.<br />Results: SV was consistently higher ‘in-stent, pre-valve’ compared with ‘pre-stent’ (62±20ml vs. 53±19ml, p&lt;0.001), so that<br />EOA was correspondingly larger using ‘in-stent, pre-valve’ measurements (1.7±0.5cm2 vs. 1.4±0.5cm2, p&lt;0.001). Betweenobserver<br />RMS difference for calculation of EOA was higher ‘in-stent, pre-valve’ compared to ‘pre-stent’ (0.53 cm2 vs.<br />0.23cm2, difference from zero 0.17, p=0.002). Though sub-valvular diameter measurements were variable, VTI variability was<br />additionally higher ‘in-stent, pre-valve’ compared to ‘pre-stent’ (0.42cm vs. 0.6cm, difference from zero -1.74, p=0.11).<br />Conclusion: Calculation of EOA after CoreValve TAVI is highly dependent on sub-valvular sample position. EOA may be<br />underestimated using ‘pre-stent’ SV, and overestimated using ‘in-stent, pre-valve’ SV. Limitations in SV reproducibility<br />suggests EOA should be used in conjunction with other indices of valve function in serial assessment of CoreValve function<br />following TAVI.

Numerical Investigation on Heat Transfer and Flow Characteristics of a Confined Circular Cylinder With Slit

2020 ◽  
Vol 12 (5) ◽  
Author(s):  
Liladharsingh Jadon ◽  
Venugopal Arumuru
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Separation Bubble ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Slit Width ◽  
Control Technique ◽  
Aerodynamic Forces ◽  
Passive Flow Control

Abstract Heat transfer and flow characteristics of channel-bounded circular cylinder with a slit vent parallel to the flow direction are numerically investigated using openfoam. The interesting feature of this configuration is the formation of the separation bubble behind the cylinder, which significantly alters the near wake characteristics. In this study, the emphasis is given to understand the effect of the slit on forced convection from the cylinder. Simulations were performed by varying the slit width from 0 to 0.25 (in steps of 0.05) for the range of Reynolds number (Re) 60–240. Re is defined based on the diameter of the cylinder (d) and centerline velocity (Uc) at the inlet of the channel. The influence of s/d and Re on the separation bubble, aerodynamic forces, and heat transfer characteristics are studied in detail. Results demonstrate that the slit can manipulate the flow to mitigate adverse effects of vortex shedding and thus can be used as a passive flow control technique. It was observed that the inclusion of the slit in the cylinder delays the onset of vortex shedding, and it also reduces the fluctuations in aerodynamic forces up to 99%. Compared with the solid cylinder, around 38% increase in vortex shedding frequency, a 16% reduction in drag, and a 10% increase in average Nusselt number is observed when the slit width is 0.25d. It was found that the introduction of slit vent in the cylinder not only enhances the heat transfer along with the reduction in expenditure of pressure loss across the cylinder but also suppresses the fluctuations in aerodynamic forces, which causes vortex-induced vibrations and thus improves structural stability and integrity.

scholarly journals Simulation of Lid-Driven Cavity Flow with Internal Circular Obstacles

2020 ◽  
Vol 10 (13) ◽  
pp. 4583 ◽  
Author(s):  
Tingting Huang ◽  
Hee-Chang Lim
Keyword(s):  
Reynolds Number ◽  
Solid Wall ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Time Model ◽  
Cross Sectional ◽  
Driven Cavity ◽  
Secondary Vortices ◽  
Boltzmann Method

The Lattice Boltzmann method (LBM) has been applied for the simulation of lid-driven flows inside cavities with internal two-dimensional circular obstacles of various diameters under Reynolds numbers ranging from 100 to 5000. With the LBM, a simplified square cross-sectional cavity was used and a single relaxation time model was employed to simulate complex fluid flow around the obstacles inside the cavity. In order to made better convergence, well-posed boundary conditions should be defined in the domain, such as no-slip conditions on the side and bottom solid-wall surfaces as well as the surface of obstacles and uniform horizontal velocity at the top of the cavity. This study focused on the flow inside a square cavity with internal obstacles with the objective of observing the effect of the Reynolds number and size of the internal obstacles on the flow characteristics and primary/secondary vortex formation. The current LBM has been successfully used to precisely simulate and visualize the primary and secondary vortices inside the cavity. In order to validate the results of this study, the results were compared with existing data. In the case of a cavity without any obstacles, as the Reynolds number increases, the primary vortices move toward the center of the cavity, and the secondary vortices at the bottom corners increase in size. In the case of the cavity with internal obstacles, as the Reynolds number increases, the secondary vortices close to the internal obstacle become smaller owing to the strong primary vortices. In contrast, depending on the sizes of the obstacles ( R / L = 1/16, 1/6, 1/4, and 2/5), secondary vortices are induced at each corner of the cavity and remain stationary, but the secondary vortices close to the top of the obstacle become larger as the size of the obstacle increases.

Experimental investigation of the flow characteristics of small orifices and valves in water hydraulics

2002 ◽  
Vol 216 (4) ◽  
pp. 235-245 ◽  
Author(s):  
Zhu Bikai ◽  
Huang Yan ◽  
Zhang Tiehua ◽  
Li Zhuangyun
Keyword(s):  
Experimental Investigation ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Test Results ◽  
Small Opening ◽  
Aspect Ratios ◽  
Water Hydraulics ◽  
Different Shapes ◽  
Large Opening ◽  
Spool Valve

This paper describes an experimental investigation of the flow characteristics of water passing through small sharp-edged cylindrical orifices and valves of different shapes in water hydraulics. The test results using orifices with aspect ratios, l/d, of 1–15 and diameters of 0.8-3 mm show that the flow coefficients in the case of non-cavitating flow are larger than those of flow with cavitation and decrease with increase in the aspect ratio. However, the flow coefficients of flow with cavitation tend to be of constant value close to the contraction coefficient, Cc at small aspect ratios. Orifices with large aspect ratios have the effect of suppressing cavitation. Experimental results concerning the spool valve illustrate that the sharp-edged valve is less cavitation stricken at large opening than at small opening. Throttles with a triangular notch have better anticavitation ability than those with a square notch. The flow of the throttle with a square notch is significantly affected by the flow direction and the shape of the flow passage.

scholarly journals Comparative Analysis of Different Mobile LiDAR Mapping Systems for Ditch Line Characterization

2021 ◽  
Vol 13 (13) ◽  
pp. 2485
Author(s):  
Yi-Chun Lin ◽  
Raja Manish ◽  
Darcy Bullock ◽  
Ayman Habib
Keyword(s):  
Flow Direction ◽  
Sediment Accumulation ◽  
Digital Terrain Model ◽  
Vertical Direction ◽  
Point Clouds ◽  
Lidar Data ◽  
Cross Sectional ◽  
Premature Failure ◽  
3D Point Clouds ◽  
Mapping Systems

Maintenance of roadside ditches is important to avoid localized flooding and premature failure of pavements. Scheduling effective preventative maintenance requires a reasonably detailed mapping of the ditch profile to identify areas in need of excavation to remove long-term sediment accumulation. This study utilizes high-resolution, high-quality point clouds collected by mobile LiDAR mapping systems (MLMS) for mapping roadside ditches and performing hydrological analyses. The performance of alternative MLMS units, including an unmanned aerial vehicle, an unmanned ground vehicle, a portable backpack system along with its vehicle-mounted version, a medium-grade wheel-based system, and a high-grade wheel-based system, is evaluated. Point clouds from all the MLMS units are in agreement within the ±3 cm range for solid surfaces and ±7 cm range for vegetated areas along the vertical direction. The portable backpack system that could be carried by a surveyor or mounted on a vehicle is found to be the most cost-effective method for mapping roadside ditches, followed by the medium-grade wheel-based system. Furthermore, a framework for ditch line characterization is proposed and tested using datasets acquired by the medium-grade wheel-based and vehicle-mounted portable systems over a state highway. An existing ground-filtering approach—cloth simulation—is modified to handle variations in point density of mobile LiDAR data. Hydrological analyses, including flow direction and flow accumulation, are applied to extract the drainage network from the digital terrain model (DTM). Cross-sectional/longitudinal profiles of the ditch are automatically extracted from the LiDAR data and visualized in 3D point clouds and 2D images. The slope derived from the LiDAR data turned out to be very close to the highway cross slope design standards of 2% on driving lanes, 4% on shoulders, and a 6-by-1 slope for ditch lines.

Pressure Distributions in the Tip Clearance Region of an Unshrouded Axial Turbine as Affecting the Problem of Tip Burnout

1987 ◽  
Author(s):  
Jeffery P. Bindon
Keyword(s):  
Separation Bubble ◽  
Low Pressure ◽  
High Heat ◽  
Tip Clearance ◽  
Small Scale ◽  
Narrow Strip ◽  
Pressure Surface ◽  
High Heat Transfer ◽  
Axial Turbines ◽  
Secondary Vortices

The pressure distribution in the tip clearance region of a 2D turbine cascade was examined with reference to unknown factors which cause high heat transfer rates and burnout along the edge of the pressure surface of unshrouded cooled axial turbines. Using a special micro-tapping technique, the pressure along a very narrow strip of the blade edge was found to be 2.8 times lower than the cascade outlet pressure. This low pressure, coupled with a thin boundary layer due to the intense acceleration at gap entry, are believed to cause blade burnout. The flow phenomena causing the low pressure are of very small scale and do not appear to have been previously reported. The ultra low pressure is primarily caused by the sharp flow curvature demanded of the leakage flow at gap entry. The curvature is made more severe by the apparent attachement of the flow around the corner instead of immediately separating to increase the radius demanded of the flow. The low pressures are intensified by a depression in the suction corner and by the formation of a separation bubble in the clearance gap. The bubble creates a venturi action. The suction corner depression is due to the mainstream flow moving round the leakage and secondary vortices.

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