scholarly journals A Novel Comparative Statistical and Experimental Modeling of Pressure Field in Free Jumps along the Apron of USBR Type I and II Dissipation Basins

Mathematics ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 2155
Author(s):  
Seyed Nasrollah Mousavi ◽  
Daniele Bocchiola
Keyword(s):  
Pressure Field ◽  
Pressure Fluctuations ◽  
Maximum Pressure ◽  
Slab Thickness ◽  
Type I ◽  
Bureau Of Reclamation ◽  
Pressure Transducers ◽  
Large Pressure ◽  
The Us ◽  
Mean Pressure

Dissipation basins are usually constructed downstream of spillways to dissipate energy, causing large pressure fluctuations underneath hydraulic jumps. Little systematic experimental investigation seems available for the pressure parameters on the bed of the US Department of the Interior, Bureau of Reclamation (USBR) Type II dissipation basins in the literature. We present the results of laboratory-scale experiments, focusing on the statistical modeling of the pressure field at the centerline of the apron along the USBR Type I and II basins. The accuracy of the pressure transducers was ±0.5%. The presence of accessories within basinII reduced the maximum pressure fluctuations by about 45% compared to basinI. Accordingly, in some points, the bottom of basinII did not collide directly with the jet due to the hydraulic jump. As a result, the values of pressure and pressure fluctuations decreased mainly therein. New original best-fit relationships were proposed for the mean pressure, the statistical coefficient of the probability distribution, and the standard deviation of pressure fluctuations to estimate the pressures with different probabilities of occurrence in basinI and basinII. The results could be useful for a more accurate, safe design of the slab thickness, and reduce the operation and maintenance costs of dissipation basins.

Unsteady Flow Structure on a Centrifugal Pump: Experimental and Numerical Approaches

2002 ◽  
Author(s):  
Jose´ Gonza´lez ◽  
Carlos Santolaria ◽  
Eduardo Blanco ◽  
Joaqui´n Ferna´ndez
Keyword(s):  
Numerical Model ◽  
Centrifugal Pump ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Side Wall ◽  
Relative Effect ◽  
Pressure Transducers ◽  
Unsteady Pressure ◽  
Blade Passing Frequency ◽  
Wide Range

Both experimental and numerical studies of the unsteady pressure field inside a centrifugal pump have been carried out. The unsteady patterns found for the pressure fluctuations are compared and a further and more detailed flow study from the numerical model developed will be presented in this paper. Measurements were carried out with pressure transducers installed on the volute shroud. At the same time, the unsteady pressure field inside the volute of a centrifugal pump has been numerically modelled using a finite volume commercial code and the dynamic variables obtained have been compared with the experimental data available. In particular, the amplitude of the fluctuating pressure field in the shroud side wall of the volute at the blade passing frequency is successfully captured by the model for a wide range of operating flow rates. Once the developed numerical model has shown its capability in describing the unsteady patterns experimentally measured, an explanation for such patterns is searched. Moreover, the possibilities of the numerical model can be extended to other sections (besides the shroud wall of the volute), which can provide plausible explanations for the dynamic interaction effects between the flow at the impeller exit and the volute tongue at different axial positions. The results of the numerical simulation are focused in the blade passing frequency in order to study the relative effect of the two main phenomena occurring at that frequency for a given position: the blade passing in front of the tongue and the wakes of the blades.

scholarly journals Macro-turbulent characteristcs of pressures in hydraulic jump formed downstream of a stepped spillway

RBRH ◽  
2017 ◽  
Vol 22 (0) ◽  
Author(s):  
Carolina Kuhn Novakoski ◽  
◽  
Eliane Conterato ◽  
Marcelo Marques ◽  
Eder Daniel Teixeira ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
Hydraulic Jump ◽  
Pressure Fluctuations ◽  
Longitudinal Distribution ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Stilling Basin ◽  
Large Pressure ◽  
Skewness Coefficient ◽  
Mean Pressure

ABSTRACT Stilling basins are structures built at the base of the spillway to dissipate energy, by means of a hydraulic jump. Hydraulic jump is a turbulent phenomenon that causes large pressure fluctuation in the stilling basin bottom, and can damage the sink structure through mechanisms such as fatigue, upflit pressure and cavitation. The use of stepped spillways allows the dissipation of a parcel of the energy while the water falls by the spillway, allowing a reduction in the stilling basin’s dimensions and cost. The present article presents the analysis of the longitudinal distribution of mean pressure, pressure fluctuations, skewness coefficient and kurtosis coefficient, derived from tests on physical hydraulic models. Pressure values measured in a stilling basin downstream of a stepped spillway (for Froude numbers between 5 and 8) were compared with data observed in a stilling basin downstream of a smooth spillway with a radius of concordance between the chute and the basin (for Froude numbers between 4.5 and 10). The results of these studies show that the mean pressures and the pressure fluctuation observed in the stilling basin downstream of stepped spillway present maximum values at the spillway’s closest point, differing, thus, from those at the smooth spillway. The longitudinal distribution of skewness and kurtosis coefficients enabled to define the positions for flow detachment start, roller ending and as well as the ending of the influence of the hydraulic jump over the flow.

scholarly journals The Unsteady Pressure Field Over a Turbine Blade Surface: Visualisation and Interpretation of Experimental Data

1997 ◽  
Author(s):  
Roger W. Moss ◽  
Roger W. Ainsworth ◽  
Colin D. Sheldrake ◽  
Robert Miller
Keyword(s):  
Pressure Field ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Surface Flow ◽  
Pressure Transducers ◽  
Root Region ◽  
Flow Features ◽  
Extensive Surface ◽  
Absolute Frame

The unsteady static pressure field over a turbine rotor has been measured in the Oxford Rotor Facility using 78 flush-mounted miniature pressure transducers. This extensive surface coverage allows ensemble-averaged data to be displayed as an animated image. At the mid-height plane the fluctuations are well predicted using the UNSFLO 2-D unsteady code: away from mid-height the data shows large fluctuations. 12 transducers mounted on the blade leading edge show the relative total pressure field entering the blade row; these plus area traverse measurements at rotor exit are used to interpret the surface flow features. Rotor-mounted hot wires show large variations in blade incidence during the wake-passing cycle and allow conversion of blade-relative data into the absolute frame. Large pressure fluctuations in the root region may be explained in terms of a loss core associated with the NGV wake.

Effect of Clocking on the Second Stator Pressure Field of a One and a Half Stage Transonic Turbine

2004 ◽  
Author(s):  
J. Gadea ◽  
R. De´nos ◽  
G. Paniagua ◽  
N. Billiard ◽  
C. H. Sieverding
Keyword(s):  
Pressure Distribution ◽  
Static Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Fast Response ◽  
Time Resolved ◽  
Pressure Transducers ◽  
Static Pressure Distribution ◽  
Transonic Turbine

This paper focuses on the experimental investigation of the time-averaged and time-resolved pressure field of a second stator tested in a one and a half stage high-pressure transonic turbine. The effect of clocking and its influence on the aerodynamic and mechanical behaviour are investigated. The test program includes four different clocking positions, i.e. relative pitch-wise positions between the first and the second stator. Pneumatic probes located upstream and downstream of the second stator provide the time-averaged component of the pressure field. For the second stator airfoil, both time-averaged and time-resolved surface static pressure fields are measured at 15, 50 and 85% span with fast response pressure transducers. Regarding the time-averaged results, the effect of clocking is mostly observed in the leading edge region of the second stator, the largest effects being observed at 15% span. The surface static pressure distribution is changed locally, which is likely to affect the overall performance of the airfoil. The phase-locked averaging technique allows to process the time-resolved component of the data. The pressure fluctuations are attributed to the passage of pressure gradients linked to the traversing of the upstream rotor. The pattern of these fluctuations changes noticeably as a function of clocking. Finally, the time-resolved pressure distribution is integrated along the second stator surface to determine the unsteady forces applied on the vane. The magnitude of the unsteady force is very dependent on the clocking position.

Fluctuation of Air-Water Two-Phase Flow in Horizontal and Inclined Water Pipelines

2005 ◽  
Vol 129 (1) ◽  
pp. 1-14 ◽  
Author(s):  
A. R. Kabiri-Samani ◽  
S. M. Borghei ◽  
M. H. Saidi
Keyword(s):  
Slug Flow ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Digital Camera ◽  
Air Entrainment ◽  
Maximum Pressure ◽  
Water Mixture ◽  
Two Phase ◽  
Cross Sectional ◽  
Pressure Transducers

Air in water flow is a frequent phenomenon in hydraulic structures. The main reason for air entrainment is vortices at water intakes, pumping stations, tunnel inlets, and so on. The accumulated air, in a conduit, can evolve to a different flow pattern, from stratified to pressurized. Among different patterns, slug is most complex with extreme pressure variations. Due to lack of firm relations between pressure and influential parameters, study of slug flow is very important. Based on an experimental model, pressure fluctuations inside a circular, horizontal, and inclined pipe (90mm inside diameter and 10m long) carrying tow-phase air-water slug flow has been studied. Pressure fluctuations were sampled simultaneously at different sections, and longitudinal positions. The pressure fluctuations were measured using differential pressure transducers (DPT), while behavior of the air slug was studied using a digital camera. The objective of the paper is to predict the pressure variation in a pipeline or tunnel, involving resonance and shock waves experimentally. The results show that the more intensive phase interaction commences stronger fluctuations. It is shown, that the air-water mixture entering the pipe during rapid filling of surcharging can cause a tremendous pressure surge in the system and may eventually cause failure of the system (e.g., the maximum pressure inside the pipe would reach up to 10 times of upstream hydrostatic pressure as suggested by others too). Relations for forecasting pressure in these situations are presented as a function of flow characteristics, pipe geometry, longitudinal, and cross-sectional positions and head water.

The Effect of the Operating Point on the Pressure Fluctuations at the Blade Passage Frequency in the Volute of a Centrifugal Pump

2002 ◽  
Vol 124 (3) ◽  
pp. 784-790 ◽  
Author(s):  
Jorge L. Parrondo-Gayo ◽  
Jose´ Gonza´lez-Pe´rez ◽  
Joaquı´n Ferna´ndez-Francos
Keyword(s):  
Centrifugal Pump ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Strong Increase ◽  
Flow Rates ◽  
Blade Passage ◽  
Pressure Transducers ◽  
Leading Role ◽  
Dynamic Forces ◽  
Response Pressure

An experimental investigation is presented which analyzes the unsteady pressure distribution existing in the volute of a conventional centrifugal pump with a nondimensional specific speed of 0.48, for flow-rates from 0% to 160% of the best-efficiency point. For that purpose, pressure signals were obtained at 36 different locations along the volute casing by means of fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the blade passage frequency, regarding both amplitude and phase delay relative to the motion of the blades. Also, the experimental data obtained was used to adjust the parameters of a simple acoustic model for the volute of the pump. The results clearly show the leading role played by the tongue in the impeller-volute interaction and the strong increase in the magnitude of dynamic forces and dipole-like sound generation in off-design conditions.

Dynamic Analysis of Tilting-Pad Journal Bearing—Influence of Pad Deformations

1994 ◽  
Vol 116 (3) ◽  
pp. 621-627 ◽  
Author(s):  
H. Desbordes ◽  
M. Fillon ◽  
C. Chan Hew Wai ◽  
J. Frene
Keyword(s):  
Film Thickness ◽  
Pressure Field ◽  
Journal Bearing ◽  
Maximum Pressure ◽  
Tilting Pad ◽  
Minimum Film Thickness ◽  
Dimensional Finite Element ◽  
The One ◽  
Tilting Pad Journal Bearing ◽  
Tilting Pad Journal Bearings

A theoretical nonlinear analysis of tilting-pad journal bearings is presented for small and large unbalance loads under isothermal conditions. The radial displacements of internal pad surface due to pressure field are determined by a two-dimensional finite element method in order to define the actual film thickness. The influence of pad deformations on the journal orbit, on the minimum film thickness and on the maximum pressure is studied. The effects of pad displacements are to decrease the minimum film thickness and to increase the maximum pressure. The orbit amplitude is also increased by 20 percent for the large unbalance load compared to the one obtained for rigid pad.

Comparison of Mixture and Multifluid Models for In-Nozzle Cavitation Prediction

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Michele Battistoni ◽  
Sibendu Som ◽  
Douglas E. Longman
Keyword(s):  
Mixture Model ◽  
Bubble Dynamics ◽  
National Laboratory ◽  
Pressure Fluctuations ◽  
Argonne National Laboratory ◽  
Numerical Approach ◽  
Fuel Injectors ◽  
Cavitation Inception ◽  
Noncondensable Gases ◽  
Large Pressure

Fuel injectors often feature cavitation because of large pressure gradients, which in some regions lead to extremely low pressures. The main objective of this work is to compare the prediction capabilities of two multiphase flow approaches for modeling cavitation in small nozzles, like those used in high-pressure diesel or gasoline fuel injectors. Numerical results are assessed against quantitative high resolution experimental data collected at Argonne National Laboratory using synchrotron X-ray radiography of a model nozzle. One numerical approach uses a homogeneous mixture model with the volume of fluid (VOF) method, in which phase change is modeled via the homogeneous relaxation model (HRM). The second approach is based on the multifluid nonhomogeneous model and uses the Rayleigh bubble-dynamics model to account for cavitation. Both models include three components, i.e., liquid, vapor, and air, and the flow is compressible. Quantitatively, the amount of void predicted by the multifluid model is in good agreement with measurements, while the mixture model overpredicts the values. Qualitatively, void regions look similar and compare well with the experimental measurements. Grid converged results have been achieved for the prediction of mass flow rate while grid-convergence for void fraction is still an open point. Simulation results indicate that most of the vapor is produced at the nozzle entrance. In addition, downstream along the centerline, void due to expansion of noncondensable gases has been identified. The paper also includes a discussion about the effect of turbulent pressure fluctuations on cavitation inception.

scholarly journals Pressure-Time Study of Slow Burning Rate Ap/HTPB Based Composite Propellant by Using Closed Vessel Test (CVT)

2018 ◽  
Vol 778 ◽  
pp. 268-274
Author(s):  
Amir Mukhtar ◽  
Habib Nasir ◽  
Hizba Waheed
Keyword(s):  
Time History ◽  
Toluene Diisocyanate ◽  
Solid Loading ◽  
Maximum Pressure ◽  
Burning Time ◽  
Closed Vessel ◽  
Composite Propellant ◽  
Powder Charge ◽  
Pressure Buildup ◽  
Pressure Transducers

The Closed vessel (CV) is an equipment used to study the ballistic parameters by recording burning time history, pressure buildup during the process and vivacity of the propellants. It is an apparatus which consists of strong pressure vessel, piezo-electric pressure transducers, sensors and dedicated software. To save time and resources this method is employed instead of dynamic firing while doing research and development of propellants. A measured amount of propellant charge is loaded in the vessel and fired remotely. Ignition is provided by the filament which ignites the black powder charge. In this study, we have used Closed Vessel Tests (CVT) for the first time for recording the ballistic parameters of slow burning composite rocket propellant. We developed a set of composite solid propellant samples containing a mixture of bimodal Ammonium Perchlorate (AP) as an oxidizer, Hydroxy-terminated Polybutadiene (HTPB) as a binder as well as fuel, Dioctyl Sebacate (DOS) as plasticizer, 1-(2-methyl) Aziridinyl Phosphine Oxide (MAPO) as bonding agent and Toluene Diisocyanate (TDI) as curator. Samples were developed by changing the solid loading percentage of bimodal AP particles. By increasing the percentage of AP, the oxidizer-fuel ratio (O/F) increases which effects the ballistic parameters. It is observed that maximum pressure and vivacity increases with increase in solid filler in the propellants. As quantity of AP increases, rate of rise of pressure also increases. CVT firing of each sample was done three times to obtain average burning time and pressure buildup history to evaluate the effect of oxidizer loadings on ballistic parameters of the composite propellant.

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