On the Impact of the Addition of Steady Flow to Oscillatory Flow in a Diffuser

2008 ◽  
Author(s):  
Cameron V. King ◽  
Barton L. Smith
Keyword(s):  
Pressure Gradient ◽  
Steady Flow ◽  
Oscillatory Flow ◽  
Adverse Pressure Gradient ◽  
Oscillating Flow ◽  
Pressure Measurements ◽  
Minor Losses ◽  
Velocity Pressure ◽  
The Impact ◽  
Diffuser Angle

Separating oscillating and pulsating flows in an internal adverse pressure gradient geometry are studied experimentally. Simultaneous velocity-pressure measurements demonstrate that the minor losses associated with oscillating flow in an adverse pressure gradient geometry can be smaller or larger than for steady flow. The minor losses grow with increasing displacement amplitude in the range 10 < L0/h < 37. Losses decrease with Reδ in the range of 380 < Re < 740. The extent and duration of boundary separation increase with L0/h. It is found that the losses increase with increasing diffuser angle for 12° < θ < 30°. The addition of steady flow can cause the in decrease if the flow becomes more turbulent as a result, or increase when the flow was already turbulent.

Oscillating Flow in Adverse Pressure Gradients

2005 ◽  
Author(s):  
Barton L. Smith ◽  
Kristen V. Mortensen ◽  
Spencer Wendel
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Displacement Amplitude ◽  
Oscillating Flow ◽  
Pressure Gradients ◽  
Pressure Measurements ◽  
Piv Measurements ◽  
Separated Shear Layer ◽  
Minor Losses ◽  
Increasing Function

Separating oscillating flow in an internal adverse pressure gradient geometry is studied experimentally. Phase-locked PIV measurements and simultaneous pressure measurements reveal that during the accelerating portion of the cycle, the flow remains attached in spite of a very large adverse pressure gradient. During the decelerating portion of the cycle, the flow is more prone to separation. The duration and extent of the separation depend strongly on the oscillation displacement amplitude relative to the cross-stream dimension. In some cases, the flow separates but reattaches as the separated shear layer is accelerated temporally. The time-varying pressure measurements are used to determine the resultant minor losses for the flow in each direction. These are found to be an increasing function of displacement amplitude and independent of the Reynolds number.

Time-Resolved PIV and Pressure Measurements of Oscillating and Pulsating Flow in a Rapid Expansion

2007 ◽  
Author(s):  
Barton L. Smith ◽  
Cameron V. King
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Pulsating Flow ◽  
Displacement Amplitude ◽  
Rapid Expansion ◽  
Pressure Measurements ◽  
Time Resolved ◽  
Separated Shear Layer ◽  
Minor Losses ◽  
Pressure And Velocity Measurements

Separating oscillating and pulsating flows in an internal adverse pressure gradient geometry are studied experimentally. Time-resolved PIV measurements and simultaneous pressure measurements reveal that, in oscillating flow, during the accelerating portion of the cycle, the flow remains attached in spite of a very large adverse pressure gradient. During the decelerating portion of the cycle, the flow is more prone to separation. The duration and extent of the separation depend strongly on the oscillation displacement amplitude relative to the cross-stream dimension. In some cases, the flow separates but reattaches as the separated shear layer is accelerated temporally. The time-varying pressure measurements are used to determine the resultant minor losses for the flow in each direction. These are found to be an increasing function of displacement amplitude and a decreasing function of the Reynolds number and can be greater than or less than those for steady flow. Pressure and velocity measurements are presented for pulsating flow with various DC components.

A study of forces, circulation and vortex patterns around a circular cylinder in oscillating flow

1988 ◽  
Vol 196 ◽  
pp. 467-494 ◽  
Author(s):  
E. D. Obasaju ◽  
P. W. Bearman ◽  
J. M. R. Graham
Keyword(s):  
Circular Cylinder ◽  
Steady Flow ◽  
Correlation Length ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Transverse Force ◽  
Vortex Street ◽  
Oscillating Flow ◽  
Time Histories ◽  
Vortex Patterns

Measurements of sectional and total forces and the spanwise correlation of vortex shedding are presented for a circular cylinder in planar oscillatory flow at Keulegan-Carpenter numbers, KC, in the range from about 4 to 55. The viscous parameter β is in the range from around 100 to 1665. Circulation measurements around a circuit close to and enclosing the cylinder, are also presented. A mode-averaging technique was used for both sectional forces and circulation measurements and this gave, for typical modes of vortex shedding, time histories over an average cycle. The transverse force and the circulation tend to fluctuate in sympathy with each other, except around the instant of flow reversal when the force changes sign but the circulation remains high. Values of the strength of shed vortices, estimated from the measured circulation, are found to be comparable with steady-flow results. For KC [lsim ] 30, modes of vortex shedding occur over distinct ranges of KC with spanwise correlation high at the centre of a KC-range for a particular mode of shedding but low at the boundaries. Above KC ≈ 30 the correlation is no longer very sensitive to KC and the correlation length is estimated to be equal to 4.65 cylinder diameters. In the transverse vortex-street regime (8 [lsim ] KC [lsim ] 15) the cylinder was found to experience a steady transverse force, the coefficient of which is estimated to be about 0.5 at KC = 14.

Aerodynamic performance analysis and optimization of a turbine duct with low degree of partial admission

2017 ◽  
Vol 232 (5) ◽  
pp. 988-1001 ◽  
Author(s):  
Xiuming Sui ◽  
Wei Zhao ◽  
Xiaolei Sun ◽  
Weiwei Luo ◽  
Qingjun Zhao
Keyword(s):  
Pressure Gradient ◽  
Negative Impact ◽  
Numerical Study ◽  
Flow Behavior ◽  
Adverse Pressure Gradient ◽  
Partial Admission ◽  
Duct Geometry ◽  
Inlet Conditions ◽  
Comparative Results ◽  
The Impact

A partial admission turbine duct with outlet-to-inlet area ratio greater than unity can increase the admission degree of the downstream turbine stage and, thus improve the performance of a multistage turbine with a low partial admission degree. However, the upstream flow structures of ducts, such as secondary flow, especially the circumferential nonuniformities originating from the effect of the partial admission, make the flow in ducts complex. The complexity of the flow has a negative impact on the performance of ducts. In the present investigation, numerical study of the flow behavior within ducts is done to evaluate the effect of the partial admission on the performance of the ducts. The study is carried out with regard to two cases, i.e. which are with the same duct geometry but are at different working conditions to highlight the impact of partial admission on the performance of ducts. Case 1 is used as baseline. It is designed based on circumferential mass-averaged flow conditions at ducts inlet. It causes the circumferential nonuniformities originating from the partial admission to have no impact on the performance of case 1. Case 2, which considers partial admission, is compared with case 1 to know the impact of the partial admission on the performance of ducts, and to give guidelines to design a duct for the partial admission turbines. Since the duct inlet conditions is a result of the interaction between partial admission turbine and duct, a straightforward way to consider the effect of the partial admission is to simulate the flows in ducts and upstream turbines contemporaneously. Comparative results indicate that the mixing of main flow in the admitted channel and the windage fluid from the unadmitted channel occurs at the duct inlet close to the duct circumferential wall. The adverse pressure gradient of case 2 in that region becomes larger than that of case 1. As a result, the flow separates at that region deteriorating the performance of ducts. Based on the simulation results of the previous cases, case 2’s circumferential wall surface, which is along the gas swirling direction is shrunk to accelerate the flow and, thereby, overcome the adverse pressure gradient imposed by the effect of the partial admission. The results show that the separation is restrained and the decrease in total pressure loss is 52.9%.

Experimental investigation of the leading edge vortex formation on unsteady boundary layer

2017 ◽  
Vol 232 (18) ◽  
pp. 3263-3280
Author(s):  
Ali R Davari ◽  
Rezvan Abdollahi ◽  
Ehsaneddin Azimizadeh
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Unsteady Boundary Layer ◽  
Leading Edge Vortex ◽  
Reduced Frequency ◽  
Blade Section ◽  
Edge Vortex ◽  
The Impact

Extensive experimental studies have been performed to investigate the unsteady boundary layer behavior over a plunging wind turbine blade section. The studies have been undertaken at various combinations of reduced frequencies, Reynolds numbers, and locations. A boundary layer rake has been carefully manufactured and utilized for velocity measurements inside the unsteady boundary layer. The measurement has been conducted in pre-static stall conditions. The reduced frequency and free stream velocity have varied from 0.005 to 0.1, and 30 to 60 m/s, respectively. To cover all possible scenarios, the streamwise positions of measurements have been chosen to be in favorable (x/c = 0.37), almost zero (x/c = 0.47), and adverse pressure gradient (x/c = 0.57) regions, on the blade section. The velocity inside the boundary layer has shown high sensitivity to the reduced frequency in the different pressure gradient regions. In some definite test cases, velocity inside boundary layer has shown beating phenomena, which is the result of the periodical appearance of the leading edge vortex. The impact of the leading edge vortex on the velocity has been observed to be more evident, in some cases, in the form of signal beating. This signature has been more evident, as the rake entered the adverse pressure gradient region. In order to quantify this observed phenomenon, the time-dependent velocity data have been transformed into the frequency domain, utilizing the discrete Fourier transformation. Even though the leading edge vortex has been continuously developed on the profile, and then has shed toward the leading edge, during each cycle on a plunging profile, the dominant frequency throughout this process has been measured to be about 4 Hz for this blade section.

The impact of hydrostatic pressure on the result of physiological measurements in various coronary segments

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
A Uveges ◽  
B Tar ◽  
C.S Jenei ◽  
A Agoston ◽  
D Czuriga ◽  
...  
Keyword(s):  
Coronary Artery ◽  
Hydrostatic Pressure ◽  
Pressure Gradient ◽  
Aortic Pressure ◽  
Funding Source ◽  
Pressure Measurements ◽  
Fractional Flow ◽  
Flow Reserve ◽  
The Impact ◽  
Effect Of Hydrostatic Pressure

Abstract Background The effect of hydrostatic pressure on physiological intracoronary measurements is usually ignored in the daily clinical practice. Purpose To investigate the effect of resting Pd/Pa (distal/aortic pressure) and FFR (fractional flow reserve) adjustment based on the calculation of hydrostatic pressure gradient between the coronary orifice and the pressure wire sensor. Methods 41 FFR measurements (between 0.7 and 0.9) were selected. The difference in height of the orifice and the sensor was defined in cm on the basis of 3D coronary reconstruction. The resting Pd/Pa and FFR were adjusted by subtracting the pressure gradient from the distal pressure. Measurements were also performed from 2D lateral projections for each coronary segment visible (n=305). Results In case of the left anterior descending artery (LAD), each segment was located higher (proximal: –13.69±5.4; middle: –46.13±6.1; distal: –56.80±7.7 mm), whereas for the circumflex (CX), lower (proximal: 14.98±8.3; distal: 28.04±6.3 mm) compared to the orifice. In case of the right coronary artery (RCA), the distance from the orifice was much less (proximal: –6.39±2.9; middle: –6.86±7.0; distal: 17.95±6.6 mm). The posterolateral (PL) and posterior descending (PD) branches of the distal RCA were located lower than the orifice (PL: 29.65±6.1; PD: 17.53±6.6 mm). The effect of these distances on pressure ratios at 100 Hgmm aortic pressure was between −0.044 and 0.023. After correction, values of 11 and 5 patients (27% and 12%) stepped the 0.92 Pd/Pa and 0.80 FFR cut-off values, respectively. There was a strong correlation between the 3D and 2D methods (r=0.98; p<0.001). Conclusion The clinical implementation of hydrostatic pressure calculation should be considered during intracoronary pressure measurements. A correction for this parameter may become crucial in case of borderline significant coronary artery stenosis, especially in distal coronary artery segments. Effect of hydrostatic pressure on FFR Funding Acknowledgement Type of funding source: Public grant(s) – EU funding. Main funding source(s): Άron Üveges was supported by the EFOP-3.6.2-16-2017-00006 project. The project is co-financed by the European Union and the European Social Fund.

On the impact of adverse pressure gradient on the supersonic turbulent boundary layer

2016 ◽  
Vol 28 (11) ◽  
pp. 116101 ◽  
Author(s):  
Qian-Cheng Wang ◽  
Zhen-Guo Wang ◽  
Yu-Xin Zhao
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
The Impact

scholarly journals Radiation and Mass Transfer Effects on Inclined MHD Oscillatory Flow for Prandtl-Eyring Fluid through a Porous Channel

2021 ◽  
Vol 26 (4) ◽  
Author(s):  
Wedyan Al-Kaabi ◽  
Dheia G. Salih Al-Khafajy
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Porous Material ◽  
Poiseuille Flow ◽  
Oscillatory Flow ◽  
Fluid Motion ◽  
Oscillating Flow ◽  
Perturbation Approach ◽  
Transfer Effects ◽  
The Impact

The goal of this work is to look at how heat transfer affects the oscillating flow of a hydrodynamically magnetizing Prandtl-Eyring fluid through a porous material under the impact of temperature and concentration under two different engineering conditions: Poiseuille flow and Couette flow. To get an unambiguous formula for fluid motion, we utilized the perturbation approach. Graphs are used to illustrate the findings..

Study on the Flow Characteristics of Shengli Oilfield Super Heavy Oil

2017 ◽  
Vol 10 (1) ◽  
pp. 69-78 ◽  
Author(s):  
Wang Shou-long ◽  
Li Ai-fen ◽  
Peng Rui-gang ◽  
Yu Miao ◽  
Fu Shuai-shi
Keyword(s):  
Pressure Drop ◽  
Pressure Gradient ◽  
Heavy Oil ◽  
Flow Characteristics ◽  
Fluid Viscosity ◽  
Linear Flow ◽  
Start Up ◽  
Non Linear ◽  
Core Permeability ◽  
Velocity Pressure

Objective:The rheological properties of oil severely affect the determination of percolation theory, development program, production technology and oil-gathering and transferring process, especially for super heavy oil reservoirs. This paper illustrated the basic seepage morphology of super heavy oil in micro pores based on its rheological characteristics.Methods:The non-linear flow law and start-up pressure gradient of super heavy oil under irreducible water saturation at different temperatures were performed with different permeable sand packs. Meanwhile, the empirical formulas between start-up pressure gradient, the parameters describing the velocity-pressure drop curve and the ratio of gas permeability of a core to fluid viscosity were established.Results:The results demonstrate that temperature and core permeability have significant effect on the non-linear flow characteristics of super heavy oil. The relationship between start-up pressure gradient of oil, the parameters representing the velocity-pressure drop curve and the ratio of core permeability to fluid viscosity could be described as a power function.Conclusion:Above all, the quantitative description of the seepage law of super heavy oil reservoir was proposed in this paper, and finally the empirical diagram for determining the minimum and maximum start-up pressure of heavy oil with different viscosity in different permeable formations was obtained.

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