Direct Prediction of Discharge at Supercritical Flow Regime Based on Brink Depth for Inverted Semicircular Channels

2017 ◽  
Vol 143 (9) ◽  
pp. 06017010 ◽  
Author(s):  
Ehsan Abrari ◽  
Mustafa Ergil ◽  
Mohammad Karim Beirami
Keyword(s):  
Flow Regime ◽  
Supercritical Flow ◽  
Brink Depth

Prototype Reynolds Number Vortex-Induced Vibration Tests on a Full-Scale Rigid Riser

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Decao Yin ◽  
Halvor Lie ◽  
Rolf J. Baarholm
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Flow Regime ◽  
Amplitude Ratio ◽  
Flow Regimes ◽  
Offshore Structures ◽  
Full Scale ◽  
Displacement Amplitude ◽  
Small Scale ◽  
Supercritical Flow

Slender offshore structures in deep water subjected to currents may experience vortex-induced vibrations (VIV), which can cause significant fatigue damage. Extensive experimental researches have been conducted to study the VIV in the past several decades. However, most of the experimental works have small-scale models and relatively low Reynolds number (Re)—“subcritical” or even lower Reynolds number regime. There is a lack of full understanding of the VIV in prototype Re flow regime. Applying the results with low Re to a full-scale riser with prototype Re might have uncertainties due to the scaling effects. In addition, the surface roughness of the riser is also an important parameter, especially in critical Re regime, which is the case for prototype risers. In the present study, two full-scale rigid riser models with different surface roughness ratios were tested in the towing tank of MARINTEK in 2014. Stationary tests, pure crossflow (CF) free oscillation tests, and forced/controlled motion tests were carried out. Several conclusions could be made: The drag coefficient is dependent on the Re number and surface roughness ratio. At critical and supercritical flow regimes, the displacement amplitude ratio is less sensitive to Re than that at lower Re. The displacement amplitude ratio in subcritical flow regime is significantly larger than that in critical and supercritical flow regimes. Two excitation regions for the ‘smooth riser’ and one excitation region for the “rough riser” are identified.

Characteristics of free overfall for supercritical flows

2007 ◽  
Vol 34 (2) ◽  
pp. 162-169 ◽  
Author(s):  
Nuray Denli Tokyay ◽  
Dilek Yildiz
Keyword(s):  
Rectangular Channel ◽  
Free Fall ◽  
Horizontal Distance ◽  
Supercritical Flow ◽  
Downstream Flow ◽  
Supercritical Flows ◽  
The Relationship ◽  
End Depth ◽  
Brink Depth ◽  
Free Overfall

The characteristics of supercritical flow at a vertical drop in a rectangular channel are studied experimentally to obtain information that would be valuable to designers of hydraulic structures. The relationship between the ratio of brink depth to the depth of upstream supercritical flow (i.e., end-depth ratio) and the Froude number is determined. Downstream from the vertical drop, the physical characteristics of the falling jet are examined, such as the height of the standing water behind the jet, the maximum horizontal distance of the jet hitting the floor downstream, the height and length of the splashing water, and the horizontal distance where the downstream flow gains uniformity. The energy loss between the drop and stable downstream flow is also studied.Key words: supercritical flow, brink depth, free fall.

Prototype Reynolds Number VIV Tests on a Full-Scale Rigid Riser

2017 ◽  
Author(s):  
Decao Yin ◽  
Halvor Lie ◽  
Rolf J. Baarholm
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Flow Regime ◽  
Amplitude Ratio ◽  
Flow Regimes ◽  
Offshore Structures ◽  
Full Scale ◽  
Displacement Amplitude ◽  
Small Scale ◽  
Supercritical Flow

Slender offshore structures in deep water subjected to currents may experience vortex-induced vibrations (VIV), which can cause significant fatigue damage. Extensive experimental researches have been conducted to study the VIV in the past several decades. However, most of the experimental works have small-scale models and relatively low Reynolds number (Re) - ‘subcritical’ or even lower Reynolds number regime. There is a lack of full understanding the VIV in prototype Re flow regime. Applying the results with low Re to a full scale riser with prototype Re might have uncertainties due to the scaling effects. In addition, the surface roughness of the riser is also an important parameter, especially in prototype Re regime. In present study, two full-scale rigid riser models with different surface roughness ratios were tested in the towing tank of MARINTEK in 2014. Stationary tests, pure cross-flow (CF) free oscillation tests and forced/controlled motion tests were carried out. Several conclusions could be made: • The drag coefficient is dependent on the Re number and surface roughness ratio. • At critical and supercritical flow regimes, the displacement amplitude ratio is less sensitive to Re than that at lower Re. The displacement amplitude ratio in subcritical flow regime is significantly larger than that in critical and supercritical flow regimes. • Two excitation regions for the ‘smooth riser’ and one excitation region for the ‘rough riser’ are identified.

Comparison of Subcritical and Supercritical Flow Patterns Within Triangular Channels Along the Side Weir

2016 ◽  
Vol 17 (7-8) ◽  
pp. 361-368 ◽  
Author(s):  
Hamed Azimi ◽  
Saeid Shabanlou
Keyword(s):  
Flow Regime ◽  
Transverse Velocity ◽  
Longitudinal Velocity ◽  
Side Weir ◽  
Supercritical Flow ◽  
Subcritical Regime ◽  
Triangular Channel ◽  
Diversion Channel ◽  
Side Walls ◽  
Side Weirs

AbstractSide weirs with triangular channel are used as flow controlling devices in draining and irrigation networks. By installing a side weir on the main conduits side walls, the runoff overflows from the weir and are conducted toward the diversion channel. In this study, changing of the flow free surface and the turbulence of the flow field in triangular channels with side weir are numerically simulated using volume of fluid (VOF) scheme and RNG k–ε turbulence model. In the present paper, the pattern of the spatially varied flow with decreasing discharge in both subcritical and supercritical flow regimes for triangular channels with side weirs was simulated. The present numerical model has precisely predicted the changes of the water surface and the specific energy. In subcritical regime, the flow depth is from the beginning of the weir toward its end is followed by an increase and in supercritical conditions is followed by a reduction in depth. For both subcritical and supercritical regimes, a drop in the surface in the first third of the weir’s opening and a surface jump in the final third of its length has occurred. Along the mentioned surface jump the amount of the kinetic energy increases and the potential energy reduces. According to results of the simulation, the maximum longitudinal velocity for subcritical flow regime occurs in the first third of the length of the side weir and for supercritical flow regime, almost in the middle of the weir opening happens. In both subcritical and supercritical regimes, the maximum transverse velocity has occurred in the final third of the length of the side weir.

scholarly journals Flow regime changes at hydraulic jumps in an open Venturi channel for Newtonian fluid

2017 ◽  
Vol 9 (4) ◽  
pp. 169-179 ◽  
Author(s):  
Prasanna Welahettige ◽  
Bernt Lie ◽  
Knut Vaagsaether
Keyword(s):  
Flow Regime ◽  
Newtonian Fluid ◽  
Triple Point ◽  
Hydraulic Jump ◽  
Experimental Results ◽  
Hydraulic Jumps ◽  
Flow Depth ◽  
Supercritical Flow ◽  
Subcritical Flow ◽  
Regime Changes

The aim of this paper is to study flow regime changes of Newtonian fluid flow in an open Venturi channel. The simulations are based on the volume of fluid method with interface tracking. ANSYS Fluent 16.2 (commercial code) is used as the simulation tool. The simulation results are validated with experimental results. The experiments were conducted in an open Venturi channel with water at atmospheric condition. The inlet water flow rate was 400 kg/min. The flow depth was measured by using ultrasonic level sensors. Both experiment and simulation were done for the channel inclination angles 0°, −0.7°, and −1.5°. The agreement between computed and experimental results is satisfactory. At horizontal condition, flow in the channel is supercritical until contraction and subcritical after the contraction. There is a hydraulic jump separating the supercritical and subcritical flow. The position of the hydraulic jump oscillates within a region of about 100 mm. Hydraulic jumps coming from the contraction walls to the upstream flow are the main reasons for the conversion of supercritical flow into subcritical flow. An “oblique jump” can be seen where there is a supercritical flow in the contraction. There is a triple point in this oblique jump: the triple point consists of two hydraulic jumps coming from the contraction walls and the resultant wave. The highest flow depth and the lowest velocity in the triple point are found at the oblique jump.

Dimensionless Discharge in Supercritical Flow Regime for Different Sizes of Cutthroat Flumes

2016 ◽  
Vol 41 (10) ◽  
pp. 4235-4245 ◽  
Author(s):  
Shrikant A. Tekade ◽  
Avinash D. Vasudeo ◽  
Aniruddha D. Ghare ◽  
Ramesh N. Ingle
Keyword(s):  
Flow Regime ◽  
Supercritical Flow

Discharge Coefficient of Rectangular Side Weirs on Circular Channels

2016 ◽  
Vol 17 (7-8) ◽  
pp. 391-399 ◽  
Author(s):  
Hamed Azimi ◽  
Saeid Shabanlou ◽  
Isa Ebtehaj ◽  
Hossein Bonakdari
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Flow Regime ◽  
Discharge Coefficient ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Energy Difference ◽  
Surface Flow ◽  
Side Weir ◽  
Supercritical Flow

AbstractIn this study, the flow turbulence and variations of the supercritical free surface flow in a circular channel along a side weir are simulated as three dimensional using the RNG k-ε turbulence model and volume of fluid (VOF) scheme. Comparison between the numerical model and experimental measurements shows that the numerical model simulates the free surface flow with good accuracy. According to the numerical model results, the specific energy variations along the side weir for the supercritical flow regime are almost constant and the energy drop is not significant but by increasing the side weir length the energy difference between the side weir upstream and downstream increases. Next, using the nonlinear regression (NLR) and analysis of the simulation results, some relationships for calculating the discharge coefficient of side weir on circular channels in supercritical flow regime are provided.

Measurement of flow in supercritical flow regime using cutthroat flumes

Sadhana ◽  
2016 ◽  
Vol 41 (2) ◽  
pp. 265-272 ◽  
Author(s):  
SHRIKANT A TEKADE ◽  
AVINASH D VASUDEO ◽  
ANIRUDDHA D GHARE ◽  
RAMESH N INGLE
Keyword(s):  
Flow Regime ◽  
Supercritical Flow
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