Currentmeter Errors under Pulsating flow Conditions

1967 ◽  
Vol 9 (1) ◽  
pp. 45-54 ◽  
Author(s):  
P. Jepson
Keyword(s):  
Unsteady Flow ◽  
Theoretical Approach ◽  
Axial Flow ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Registration Errors ◽  
Flow Fluctuations ◽  
The Mean ◽  
Flow Pulsations

The paper deals with the effect of unsteady flow on the velocity registration of current-meters. In the first section of the paper, experiments are described which show that axial flow pulsations cause currentmeters to over-estimate and that flow fluctuations transverse to the mean velocity generally cause under-registration by amounts depending on the flow and meter parameters. From these tests general comments are made concerning the choice of metering station and to a lesser extent meter design. The second section is theoretical and deals with the effects of axially pulsating flows. It has been possible, using simple aerodynamic principles, to show how the meter design can be improved to minimize registration errors. The agreement between this theoretical approach and the registration errors obtained from experiment is fair.

The Estimation of Discharge in an Experimental Open Channel

2014 ◽  
Vol 905 ◽  
pp. 369-373
Author(s):  
Choo Tai Ho ◽  
Yoon Hyeon Cheol ◽  
Yun Gwan Seon ◽  
Noh Hyun Suk ◽  
Bae Chang Yeon
Keyword(s):  
Unsteady Flow ◽  
River Discharge ◽  
Open Channel ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Velocity Equation ◽  
The Mean ◽  
Loop Form

The estimation of a river discharge by using a mean velocity equation is very convenient and rational. Nevertheless, a research on an equation calculating a mean velocity in a river was not entirely satisfactory after the development of Chezy and Mannings formulas which are uniform equations. In this paper, accordingly, the mean velocity in unsteady flow conditions which are shown loop form properties was estimated by using a new mean velocity formula derived from Chius 2-D velocity formula. The results showed that the proposed method was more accurate in estimating discharge, when compared with the conventional formulas.

An Unsteady Flow Wind Tunnel

1974 ◽  
Vol 25 (2) ◽  
pp. 81-90 ◽  
Author(s):  
J H Horlock
Keyword(s):  
Wind Tunnel ◽  
Unsteady Flow ◽  
Free Stream ◽  
Flow Direction ◽  
Axial Flow ◽  
Mean Velocity ◽  
Low Speed ◽  
The Mean ◽  
Low Speed Wind Tunnel

SummaryA novel low-speed wind tunnel which produces unsteady “gust” flows is described. The walls are sinusoidal in shape and are moved in the flow direction with a velocity Wwless than the mean velocity Wmof the free stream. The tunnel is useful for testing isolated aerofoils and aerofoils in cascade in non-convective gusts (Ww< Wm) so that comparisons with predictions by thin aerofoil theory may be made. However, it does not simulate precisely the unsteady flow that occurs in axial flow turbomachines.

Effect of Annulus Flow Conditions on Turbine Rim Seal Ingestion

2019 ◽  
Author(s):  
Donato M. Palermo ◽  
Feng Gao ◽  
John W. Chew ◽  
Paul F. Beard
Keyword(s):  
Velocity Ratio ◽  
Axial Flow ◽  
Passive Scalar ◽  
External Flow ◽  
Rotor Blades ◽  
Flow Structures ◽  
Flow Conditions ◽  
Sealing Performance ◽  
Annulus Flow ◽  
The Mean

Abstract A systematic study of sealing performance for a chute style turbine rim seal using URANS methods is reported. This extends previous studies from a configuration without external flow in the main annulus to cases with a circumferentially uniform axial flow and vane generated swirling annulus flow (but without rotor blades). The study includes variation of the mean seal-to-rotor velocity ratio, main annulus-to-rotor velocity ratio, and seal clearance. The effects on the unsteady flow structures and the degree of main annulus flow ingestion into the rim seal cavity are examined. Sealing effectiveness is quantified by modeling a passive scalar, and the timescales for the convergence of this solution are considered. It has been found that intrinsic flow unsteadiness occurs in most cases, with the presence of vanes and external flow modifying, the associated flow structures and frequencies. Some sensitivities to the annulus flow conditions are identified. The circumferential pressure asymmetry generated by the vanes has a clear influence on the flow structure but does not lead to higher ingestion rates than the other conditions studied.

scholarly journals Application of Recess Vaned Casing Treatment to Axial Flow Fans

1989 ◽  
Author(s):  
A. R. Azimian ◽  
R. L. Elder ◽  
A. B. McKenzie
Keyword(s):  
Unsteady Flow ◽  
Frequency Response ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Axial Position ◽  
Flow Conditions ◽  
Peak Efficiency ◽  
Stall Margin ◽  
Casing Treatment

The effect of applying a vaned recessed casing treatment to a single stage axial flow fan has been investigated. The influence of the axial position of the recess relative to the rotor leading edge and other geometrical modifications of the vane passage have been examined. Significant improvements in stall margin were observed without (in some builds) loss in peak efficiency. Slow and fast frequency response yawmeter probes have been used in the study to examine both the steady flow conditions and the unsteady flow caused by rotating stall.

Improvement of Aerodynamic Performance of a Combustor Dump Diffuser Using Inclined Walls

2000 ◽  
Author(s):  
Shinji Honami ◽  
Eiichi Yamazaki ◽  
Takaaki Shizawa
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Aerodynamic Performance ◽  
Total Pressure Loss ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Cold Flow ◽  
Inlet Distortion ◽  
Flow Experiment ◽  
The Mean

The combustor diffuser with the deep flame dome in the recent engine results in the large total pressure loss. It is important to obtain both better aerodynamic performance by reduction of total pressure loss and reduced NOx in the exhaust from the combustor, regardless of the inlet flow conditions such as inlet distortion. Installation of an inclined wall within the combustor dump diffuser is suggested in order to improve the aerodynamic performance. A cold flow experiment using Pitot probe surveys in a model of a combustor diffuser shows that the inclined wall is effective in improvement of the total pressure loss, even if the velocity profile at the diffuser inlet is distorted. Furthermore, the flow rate distributions into the branched channels are also improved. The flow mechanism in the inclined wall configuration is clarified from the measurements of the mean velocity and turbulent Reynolds stress by a Laser Doppler Velocimetry (LDV) system.

Wells Turbines With 3-Dimensional Blades: The Performance Under Unsteady Flow Conditions

2015 ◽  
Author(s):  
Manabu Takao ◽  
Katsuya Takasaki ◽  
Tomohiro Tsunematsu ◽  
Miah Md. Ashraful Alam ◽  
Toshiaki Setoguchi
Keyword(s):  
Unsteady Flow ◽  
Flow Separation ◽  
Blade Profile ◽  
Wave Energy Conversion ◽  
Flow Conditions ◽  
Suction Surface ◽  
Wells Turbine ◽  
3 Dimensional ◽  
Profile Changes ◽  
The Mean

The effect of the 3-dimentional (3D) blade on the turbine characteristics of Wells turbines for wave energy conversion has been investigated numerically by a quasi-steady analysis under unsteady flow conditions in this study in order to improve the peak mean efficiency characteristics. The aim of use of the 3D blade is to prevent flow separation on the suction surface near the tip. The chord length is constant in the radius and the blade profile changes gradually from the mean radius to the tip. The proposed blade profiles in the study are NACA0015 from the hub to mean radius and NACA0025 at the tip. The performance of the Wells turbine with 3D blades has been compared with those of the original Wells turbine, i.e., the turbine with 2-dimentional blades. As a result, it was concluded that although the peak mean efficiency of a Wells turbine can be improved by the use of the proposed 3D blade, its blade does not overcome the stall characteristic.

Confined Jet Mixing for Nonseparating Conditions

1971 ◽  
Vol 93 (3) ◽  
pp. 333-347 ◽  
Author(s):  
E. Razinsky ◽  
J. A. Brighton
Keyword(s):  
Reynolds Stress ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Lower Velocity ◽  
Jet Mixing ◽  
Air Jet ◽  
Air Stream ◽  
Constant Diameter ◽  
Diameter Pipe ◽  
The Mean

The mixing of an air jet with a lower-velocity air stream is described. The mixing takes place in a constant diameter pipe, and the flow is investigated from the inlet where the jet and secondary velocities are uniform (but different) to a location downstream where the flow is fully developed. Measurements are made of (1) the wall static pressure, (2) the mean velocity, (3) the turbulence velocities and Reynolds stress throughout the flow field for different velocity ratios and diameter ratios. This work differs from previous investigations in that a wider range of flow conditions is considered, i.e., different diameter and velocity ratios in addition to the flow in the latter stages of mixing. Also, the turbulence velocities and Reynolds stress as determined throughout the flow are described.

scholarly journals DRAG COEFFICIENT OF VEGETATION IN FLOW MODELING

2012 ◽  
Vol 1 (33) ◽  
pp. 4
Author(s):  
Zhan Hu ◽  
M. Stive ◽  
T. Zitman ◽  
T. Suzuki
Keyword(s):  
Drag Coefficient ◽  
Numerical Models ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Local Flow ◽  
Rigid Vegetation ◽  
Flow Through ◽  
The Mean ◽  
Empirical Coefficients

Flow through vegetation has a significant impact on sediment transport and ecosystem robustness in the coastal and fluvial environment. Numerical models (Nepf and Vivoni, 2000; Uittenbogaaard, 2003) have been developed to simulate this type of flow. The success of these models depends on proper characterization of the main processes and appropriate setting of pre-defined empirical coefficients. Among others, the drag coefficient CD is one of the most important coefficients, which influences the mean velocity and the turbulence characteristics (Nepf and Ghisalberti, 2008). Tanino and Nepf (2008) and Cheng (2011) have derived empirical relationships of CD for flow through emerged rigid vegetation. Both studies confirm that CD is related to canopy properties (plants density, diameter, etc.) as well as flow conditions. However, in both studies CD is estimated by simply equating the vegetation drag force to the water level gradient. Bed shear stress and Reynolds stress were ignored. More importantly, the CD provided by these expressions is depth averaged, which is not suitable for modelling flow and canopy that both vary in vertical (Nepf and Vivoni, 2000). In this study, the CD relation proposed by Cheng (2011) is modified. This new relation depends on the local flow conditions and canopy properties in the vertical. Further, this relation is implemented in an iterative scheme of a 1DV flow model. The modelling results are compared with experiment data of flow through emerged and submerged rigid vegetation. Our results show that when special defined Reynolds number is small, this relation performs less well compare to that when it is larger.

scholarly journals On Wind-induced Flows in Closed Channels

1967 ◽  
Vol 20 (1) ◽  
pp. 1
Author(s):  
CHJ Johnson
Keyword(s):  
Shear Stress ◽  
Turbulent Viscosity ◽  
Surface Slope ◽  
Flow Conditions ◽  
Closed Channel ◽  
Mean Velocity ◽  
Induced Flow ◽  
The Mean ◽  
Stress Profiles ◽  
Wind Induced Flow

The mean velocity and shear-stress profiles for a wind-induced flow in a closed channel with constant surface slope are first derived using a turbulent viscosity constructed by dimensional arguments. Using a perturbation analysis based on the fact that the surface slope is small, these results are extended to the case where the surface slope, and hence flow conditions generally, are allowed to vary in a downwind direction. Explicit results are obtained for the velocity and shear-stress profiles and also for the surface slope as a function of distance downwind. The results agree quite well with experiment, although better agreement would probably be obtained by using a more elaborate turbulent iscosity_

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