A Unified Theory for the Pressure Change of Sudden Expansions and Contractions Based on the Momentum Balance

2021 ◽  
Author(s):  
Sebastian Müller ◽  
Andreas Malcherek
Keyword(s):  
Control Volume ◽  
Pressure Change ◽  
Sudden Expansion ◽  
Momentum Balance ◽  
Unified Approach ◽  
Pressure Distributions ◽  
Analytical Functions ◽  
Specific Geometry ◽  
Control Volumes ◽  
Pressure Changes

Abstract In this paper a unified approach based on the momentum balance is presented, capable of predicting the pressure change of sudden contractions and sudden expansions. The use of empirically determined correction coefficients is not necessary. Therefore, the momentum balance is derived similarly for both applications but with different control volumes. The control volume takes into account the specific geometry of the hydraulic structure. With a properly chosen control volume, the unified approach requires coefficients that account for the velocity as well as pressure distributions on the boundaries of the control volume. These coefficients can be obtained by parameterizing the results of numerical simulations by simple analytical functions. The numerical model itself is validated by checking the simulated pressure change against calculated or measured pressure changes. It is found that the formulation of the momentum balance for the sudden expansion is more complex compared with the sudden contraction. The prediction of the pressure change of flows through sudden expansions can be improved by applying the momentum balance non-idealized. Most of the correction coefficients originate from an inappropriate application of Bernoulli’s energy conservation principle. Consequently, this leads to a gap between theory and experimental results. The proposed unified approach solely contains physical coefficients that are used to substitute integrals by averaged expressions.

The Analysis of Axial Momentum of the Rotor Tip Flows for Axial Compressors With Circumferential Grooves

2014 ◽  
Author(s):  
Xi Nan ◽  
Feng Lin ◽  
Sichen Wang ◽  
Le Liu ◽  
Ning Ma ◽  
...  
Keyword(s):  
Control Volume ◽  
Underlying Mechanism ◽  
Current Approach ◽  
Momentum Balance ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Onset Condition ◽  
Groove Configurations ◽  
The Stability ◽  
Control Volumes

A new control volume analysis is developed in this paper aiming at assessing the circumferential grooves effectiveness on stability improvement. The underlying mechanism for this approach is based on the hypothesis that the spike stall precursors can be triggered by the forward spillage of the rotor tip leakage flow and the onset condition of such a spillage is determined by the axial momentum balance within the rotor tip region. Control volumes are defined to quantify the axial momentum balance of the whole region where the grooves influence the flow at the rotor tip. The distribution curve of the cumulative axial momentum along the axial chord indicates that the grooves change the rotor tip loading and increase the stability, which is useful to assess the different grooved casings. As an example, multiple-groove configurations for a transonic rotor are analyzed. The results verified the cumulative axial momentum distribution for different grooved casings are in accordance with the stall margin extension variations. Another example is to prescreen the best double-groove configurations for a low speed compressor. By using this current approach, a double-groove configuration was selected and validated by experiments. These examples demonstrate the current approach has great potential in helping pre-screen circumferential grooves. As an important issue, peak efficiency changed by the grooves is discussed in the last section. Entropy production is quantitatively compared with and without grooves.

scholarly journals Unsteady Pressure Distributions on the Impeller Blades of a Centrifugal Pump-Impeller Operating Off-Design

1987 ◽  
Author(s):  
K. Kikuyama ◽  
K. Minemura ◽  
Y. Hasegawa ◽  
E. Asakura ◽  
M. Murakami
Keyword(s):  
Centrifugal Pump ◽  
Leading Edge ◽  
Pressure Change ◽  
Design Flow ◽  
Pump Impeller ◽  
Flow Rates ◽  
Cavitation Inception ◽  
Pressure Distributions ◽  
Periodic Pressure ◽  
Pressure Changes

Pressure distributions on the impeller blades of a centrifugal pump were examined experimentally. The periodic pressure change caused in the suction and delivery pipes by the interaction between the rotating impeller blades and the dividing ridge of the volute casing was small. However, a noticeable cyclic change in the pressure on the blade surface was measured and related to the nonuniform pressure distribution in the volute casing at off-design flow rates. In a lower than normal range of flow rates this pressure fluctuation was largely increased near the leading edge of the blade due to the turbulent fluctuations and the flow separation from the blade surfaces. These periodic pressure changes have a large effect upon cavitation inception along the impeller periphery.

The Application of the Integral Momentum Balance on the Pressure Drop of a Sudden Contraction

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Andreas Malcherek ◽  
Sebastian Müller
Keyword(s):  
Pressure Drop ◽  
Control Volume ◽  
Pressure Coefficient ◽  
Momentum Balance ◽  
Simple Analytical Expression ◽  
Pressure Drops ◽  
Pressure Distributions ◽  
Contraction Ratio ◽  
Sudden Contraction ◽  
New Formulation

Abstract A new approach based on the momentum balance to calculate the pressure drop in turbulent flow through sharp-edged axisymmetric sudden contractions is presented. The momentum balance needs the velocity as well as the pressure distributions on the boundaries of the control volume. These distributions are obtained by a series of numerical simulations with different settings for the discharge, as well as the contraction ratio. The numerical model itself is validated by the comparison of the simulated and measured pressure drops in a laboratory experiment at different positions. To get easily applicable hydraulic formulations for the pressure drop depending on the discharge and the contraction ratio, the missing momentum and pressure coefficients are determined from the simulated velocity and pressure distributions. Only the pressure coefficient shows a dependency on the contraction ratio. After fitting the dependency by a simple analytical expression, a new formulation for the hydraulics of a sharp-edged sudden contraction based solely on momentum balance was obtained. The comparison with own experimental results as well as the classical parameterization of Idelchik show in both cases very good agreement.

Heart Rate Signal Decomposition

2000 ◽  
Vol 39 (02) ◽  
pp. 200-203
Author(s):  
H. Mizuta ◽  
K. Yana
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Pressure Change ◽  
Normal Subjects ◽  
Signal Decomposition ◽  
Large Individual ◽  
Heart Rate Fluctuations ◽  
Type Pattern ◽  
Signal Cancellation ◽  
Pressure Changes

Abstract:This paper proposes a method for decomposing heart rate fluctuations into background, respiratory and blood pressure oriented fluctuations. A signal cancellation scheme using the adaptive RLS algorithm has been introduced for canceling respiration and blood pressure oriented changes in the heart rate fluctuations. The computer simulation confirmed the validity of the proposed method. Then, heart rate fluctuations, instantaneous lung volume and blood pressure changes are simultaneously recorded from eight normal subjects aged 20-24 years. It was shown that after signal decomposition, the power spectrum of the heart rate showed a consistent monotonic 1/fa type pattern. The proposed method enables a clear interpretation of heart rate spectrum removing uncertain large individual variations due to the respiration and blood pressure change.

Study of Toynbee Phenomenon by Combined Intranasopharyngeal and Tympanometric Measurements

1988 ◽  
Vol 97 (2) ◽  
pp. 199-206 ◽  
Author(s):  
Yehuda Finkelstein ◽  
Yuval Zohar ◽  
Yoav P. Talmi ◽  
Nelu Laurian
Keyword(s):  
Middle Ear ◽  
Negative Pressure ◽  
Pressure Change ◽  
Positive Pressure ◽  
New Information ◽  
Pressure Changes ◽  
Rapid Pressure

The Toynbee maneuver, swallowing when the nose is obstructed, leads in most cases to pressure changes in one or both middle ears, resulting in a sensation of fullness. Since first described, many varying and contradictory comments have been reported in the literature concerning the type and amount of pressure changes both in the nasopharynx and in the middle ear. In our study, the pressure changes were determined by catheters placed into the nasopharynx and repeated tympanometric measurements. New information concerning the rapid pressure variations in the nasopharynx and middle ear during deglutition with an obstructed nose was obtained. Typical individual nasopharyngeal pressure change patterns were recorded, ranging from a maximal positive pressure of + 450 to a negative pressure as low as −320 mm H2O.

Defining the Thermodynamic Efficiency in a Wave Rotor

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Shining Chan ◽  
Huoxing Liu ◽  
Fei Xing
Keyword(s):  
Gas Turbine ◽  
Control Volume ◽  
Thermodynamic Efficiency ◽  
Wave Rotor ◽  
Wave Rotors ◽  
Compression And Expansion ◽  
Efficiency Estimation ◽  
Parametric Analyses ◽  
Control Volumes ◽  
Thermodynamic Processes

A wave rotor enhances the performance of a gas turbine with its internal compression and expansion, yet the thermodynamic efficiency estimation has been troubling because the efficiency definition is unclear. This paper put forward three new thermodynamic efficiency definitions to overcome the trouble: the adiabatic efficiency, the weighted-pressure mixed efficiency, and the pressure pre-equilibrated efficiency. They were all derived from multistream control volumes. As a consequence, they could correct the efficiency values and make the values for compression and expansion independent. Moreover, the latter two incorporated new models of pre-equilibration inside a control volume, and modified the hypothetical “ideal” thermodynamic processes. Parametric analyses based on practical wave rotor data demonstrated that the trends of those efficiency values reflected the energy losses in wave rotors. Essentially, different thermodynamic efficiency definitions indicated different ideal thermal cycle that an optimal wave rotor can provide for a gas turbine, and they were recommended to application based on that essence.

Numerical prediction of the performance of gas-lubricated spiral groove thrust bearings

1997 ◽  
Vol 211 (2) ◽  
pp. 117-128 ◽  
Author(s):  
Y Yue ◽  
T. A. Stolarski
Keyword(s):  
Control Volume ◽  
Numerical Procedure ◽  
Operating Conditions ◽  
Hydrodynamic Bearings ◽  
Thrust Bearings ◽  
Flow Balance ◽  
Control Volumes ◽  
Volume Method ◽  
Spiral Angle ◽  
Spiral Grooves

The objective of this paper is to develop an accurate numerical procedure for the analysis of nominally flat contacts with spiral grooves lubricated by gases. The numerical procedure, which is based on the control-volume method, enables the solutions of the non-linear Reynolds equation to be obtained without limitation in geometry and operating conditions. Satisfactory flow balance was achieved on the control volumes as well as on the whole boundary and the method was proved to be very accurate. Convergence of the method was quick for any compressibility number. Three types of contact with spiral grooves were analysed. They were hydrodynamic bearings without interior chambers, hydrodynamic bearings with interior chambers and hybrid bearings. The effects of spiral angle, groove geometry (length, depth and width) and compressibility on performances were investigated for all possible designs.

Morphodynamic stability and characteristic length scales of bifurcations and confluences loops

2021 ◽  
Author(s):  
Niccolò Ragno ◽  
Marco Redolfi ◽  
Marco Tubino
Keyword(s):  
Froude Number ◽  
Water Surface ◽  
Characteristic Length ◽  
Coupled Model ◽  
Surface Elevation ◽  
Momentum Balance ◽  
Water Surface Elevation ◽  
Control Volumes ◽  
Almost All ◽  
Fluvial Environments

<p>The morphodynamics of multi-thread fluvial environments like braided and anastomosing rivers is fundamentally driven by the continuous concatenation of channel bifurcations and confluences, which govern the distribution of flow and sediment among the different branches that are reconnecting further downstream. Almost all studies performed to date consider the two processes separately, although they frequently appear as closely interconnected. In this work, we tackle the problem of analyzing the coupled morphodynamics of such bifurcation-confluence systems by studying the equilibrium and stability conditions of a channel loop, where flow splits into two secondary anabranches that rejoin after a prescribed distance. Through the formulation of a novel theoretical model for erodible bed confluences based on the momentum balance on two distinct control volumes, we show that the dominating anabranch (i.e. that carrying more water and sediment) is subject to an increase of the water surface elevation that is proportional to the square of the Froude number. This increase in water surface elevation tends to reduce the slope of the dominating branch, which produces a negative feedback that tends to stabilize the bifurcation-confluence system. A linear analysis of the coupled model reveals that the stabilizing effect of the confluence depends on the ratio between the length of the connecting channels and the average water depth, independently of the channel slope and Froude number. Furthermore, the effect of the confluence is potentially able to stabilize the channel loop in conditions where the classic stabilizing mechanism at the bifurcation (i.e. the topographical effect related to the gravitational pull on the sediment transport) is very weak, as expected when most of the sediment is transported in suspension. The identification of a characteristic length scale that produces a coupling between the confluences and bifurcations opens intriguing possibilities for interpreting the self-adjustment of the planform scale of natural multi-thread rivers.</p>

Association between ibrutinib treatment and hypertension

Heart ◽  
2021 ◽  
pp. heartjnl-2021-319110
Author(s):  
Dae Hyun Lee ◽  
Fahad Hawk ◽  
Kieun Seok ◽  
Matthew Gliksman ◽  
Josephine Emole ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Systolic Blood Pressure ◽  
Repeated Measures ◽  
Treatment Initiation ◽  
Kinase Inhibitor ◽  
Pressure Change ◽  
Exact Test ◽  
N 93 ◽  
Pressure Changes ◽  
Over Time

BackgroundIbrutinib is a tyrosine kinase inhibitor most commonly associated with atrial fibrillation. However, additional cardiotoxicities have been identified, including accelerated hypertension. The incidence and risk factors of new or worsening hypertension following ibrutinib treatment are not as well known.MethodsWe conducted a retrospective study of 144 patients diagnosed with B cell malignancies treated with ibrutinib (n=93) versus conventional chemoimmunotherapy (n=51) and evaluated their effects on blood pressure at 1, 2, 3 and 6 months after treatment initiation. Descriptive statistics were used to compare baseline characteristics for each treatment group. Fisher’s exact test was used to identify covariates significantly associated with the development of hypertension. Repeated measures analyses were conducted to analyse longitudinal blood pressure changes.ResultsBoth treatments had similar prevalence of baseline hypertension at 63.4% and 66.7%, respectively. There were no differences between treatments by age, sex and baseline cardiac comorbidities. Both systolic and diastolic blood pressure significantly increased over time with ibrutinib compared with baseline, whereas conventional chemoimmunotherapy was not associated with significant changes in blood pressure. Baseline hypertensive status did not affect the degree of blood pressure change over time. A significant increase in systolic blood pressure (defined as more than 10 mm Hg) was noted for ibrutinib (36.6%) compared with conventional chemoimmunotherapy (7.9%) at 1 month after treatment initiation. Despite being hypertensive at follow-up, 61.2% of patients who were treated with ibrutinib did not receive adequate blood pressure management (increase or addition of blood pressure medications). Within the ibrutinib group, of patients who developed more than 20 mm Hg increase in systolic blood pressure, only 52.9% had hypertension management changes.ConclusionsIbrutinib is associated with the development of hypertension and worsening of blood pressure. Cardiologists and oncologists must be aware of this cardiotoxicity to allow timely management of blood pressure elevations.

Application and Research of Rotate-Lookup-Summation in Robot Motion

2011 ◽  
Vol 467-469 ◽  
pp. 186-191
Author(s):  
Hao Bin Shi ◽  
Wen Jie Dong
Keyword(s):  
Control Volume ◽  
Dimensional Space ◽  
Control Variable ◽  
Control Process ◽  
Controlling Factors ◽  
Dimensional Control ◽  
Control Factors ◽  
Look Up Table ◽  
New Research ◽  
Control Volumes

How to exercise reasonable motion control on robot becomes a new research focus in robot technology research. This paper proposes the Rotate-Lookup-Summation according to the deficiency of traditional look-up table. This method first confirm the controlling factors P1，P2….Pn that would affect the control volume Z, and then the multi-dimensional control volumes and multi-dimensional control factors would be projected to sub-dimensional space. Finally, the same controlling factors of different sub-dimensional space would be rotated to a single sub-dimensional space and establish a corresponding table. According to the single sub-dimensional space value of the controlling factors, the corresponding control variable could be found in table and eventually complete the control process. Experiments show that the method could ensure the integrity and accuracy of table, reduce the table memory capacitance and lookup time, so as to realize the control of look-up table in micro-device.

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