Mean Flow Measurements Near the Plane of an Open Rotor Operating with an Inlet Velocity Gradient

1981 ◽  
Vol 103 (2) ◽  
pp. 445-450
Author(s):  
M. L. Billet
Keyword(s):  
Flow Field ◽  
Velocity Profile ◽  
Velocity Gradient ◽  
Vortex Motion ◽  
Field Measurements ◽  
Velocity Data ◽  
Mean Flow ◽  
Flow Measurements ◽  
Inlet Velocity ◽  
Open Rotor

As part of a study on the structure of a trailing vortex, laser doppler anemometer (LDA) measurements were made of the flow field near an open rotor having an inlet velocity gradient. The measurements were made in the 1.22 m dia water tunnel of the Applied Research Laboratory at The Pennsylvania State University. Velocity data were obtained for rotor inlet and outlet flow fields for several different inlet velocity gradients. Velocity data were also obtained downstream of the rotor plane that shows the vortex structure. Flow field measurements show the development of the downstream vortex motion. Small variations in the inlet velocity gradient near the rotor wall caused large differences in the structure of the trailing vortex. In addition, a measured downstream velocity profile is compared with a calculated velocity profile.

Investigation of the Flow Field in a HP Turbine Stage for Two Stator-Rotor Axial Gaps: Part II — Unsteady Flow Field

2006 ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
V. Dossena ◽  
C. Osnaghi
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Dominant Role ◽  
Outer Part ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Flow Measurements

An extensive experimental analysis was carried out at Politecnico di Milano on the subject of unsteady flow in high pressure (HP) turbine stages. In this paper the unsteady flow measured downstream of a modern HP turbine stage is discussed. Traverses in two planes downstream of the rotor are considered and, in one of them, the effects of two very different axial gaps are investigated: the maximum axial gap, equal to one stator axial chord, is chosen to “switch off” the rotor inlet unsteadiness, while the nominal gap, equal to 1/3 of the stator axial chord, is representative of actual engines. The experiments were performed by means of a fast-response pressure probe, allowing for two-dimensional phase-resolved flow measurements in a bandwidth of 80 kHz. The main properties of the probe and the data processing are described. The core of the paper is the analysis of the unsteady rotor aerodynamics; for this purpose, instantaneous snapshots of the rotor flow in the relative frame are used. The rotor mean flow and its interaction with the stator wakes and vortices are also described. In the outer part of the channel only the rotor cascade effects can be observed, with a dominant role played by the tip-leakage flow and by the rotor tip passage vortex. In the hub region, where the secondary flows downstream of the stator are stronger, the persistence of stator vortices is slightly visible in the maximum stator-rotor axial gap configuration, while in the minimum stator-rotor axial gap configuration the interaction with the rotor vortices dominates the flow field. A fair agreement with the wakes and vortices transport models has been achieved. A discussion of the interaction process is reported giving particular emphasis to the effects of the different cascade axial gaps. Some final considerations on the effects of the different axial gap over the stage performances are reported.

Investigation of the Flow Field in a High-Pressure Turbine Stage for Two Stator-Rotor Axial Gaps—Part II: Unsteady Flow Field

2006 ◽  
Vol 129 (3) ◽  
pp. 580-590 ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
V. Dossena ◽  
C. Osnaghi
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Unsteady Flow ◽  
Outer Part ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Flow Measurements

An extensive experimental analysis was carried out at Politecnico di Milano on the subject of unsteady flow in high pressure (HP) turbine stages. In this paper, the unsteady flow measured downstream of a modern HP turbine stage is discussed. Traverses in two planes downstream of the rotor are considered, and, in one of them, the effects of two very different axial gaps are investigated: the maximum axial gap, equal to one stator axial chord, is chosen to “switch off” the rotor inlet unsteadiness, while the nominal gap, equal to 1/3 of the stator axial chord, is representative of actual engines. The experiments were performed by means of a fast-response pressure probe, allowing for two-dimensional phase-resolved flow measurements in a bandwidth of 80kHz. The main properties of the probe and the data processing are described. The core of the paper is the analysis of the unsteady rotor aerodynamics; for this purpose, instantaneous snapshots of the rotor flow in the relative frame are used. The rotor mean flow and its interaction with the stator wakes and vortices are also described. In the outer part of the channel, only the rotor cascade effects can be observed, with a dominant role played by the tip leakage flow and by the rotor tip passage vortex. In the hub region, where the secondary flows downstream of the stator are stronger, the persistence of stator vortices is slightly visible in the maximum stator-rotor axial gap configuration, whereas in the minimum stator-rotor axial gap configuration their interaction with the rotor vortices dominates the flow field. A good agreement with the wakes and vortices transport models has been achieved. A discussion of the interaction process is reported giving particular emphasis to the effects of the different cascade axial gaps. Some final considerations on the effects of the different axial gap over the stage performances are reported.

The Origin of Aeolian Dunes – PIV measurements of flow structure over early stage protodunes in a refractive-index-matching flume

2020 ◽  
Author(s):  
Nathaniel Bristow ◽  
James Best ◽  
Kenneth Christensen ◽  
Matthew Baddock ◽  
Giles Wiggs ◽  
...  
Keyword(s):  
Refractive Index ◽  
Flow Field ◽  
Turbulent Flow ◽  
Fixed Bed ◽  
Field Measurements ◽  
Morphological Development ◽  
Flow Measurements ◽  
Early Stages ◽  
Aeolian Dunes ◽  
Turbulent Flow Field

<p>Understanding the initiation of aeolian dunes poses significant challenges due to the strong couplings between turbulent fluid flow, sediment transport, and bedform morphology. While much is known concerning the dynamics of more mature bedforms, open questions remain as to how protodunes are formed, as well as the mechanisms by which they continue to evolve. The structure of the turbulent flow field drives the mobilization or deposition of sediment, thus controlling the initial formation of sand patches, yet is also strongly influenced itself by local conditions such as surface roughness and moisture. Furthermore, an additional feedback on the flow and transport is exerted by the sand patches themselves once they begin to form.</p><p>As protodunes begin to develop from this initial deposition, their morphologies possess unique characteristics involving a reverse asymmetry of the stoss and lee sides, wherein the crest begins upstream, close to the toe, and gradually shifts downstream toward the "regular" asymmetric profile exhibited by more mature dunes. However, these early stages of development also involve very gentle slopes and low profiles which make field measurements of the associated flow particularly challenging.</p><p>The current research effort involves a combination of field measurements, documenting the initiation and morphological development of sand patches and protodunes, in concert with detailed measurements of the flow-form interactions in a laboratory flume. The work presented herein focuses primarily on experiments conducted in a unique flow facility wherein high-resolution measurements of the turbulent flow field associated with the early stages of protodune development are obtained utilizing particle-image velocimetry (PIV) in a refractive-index-matched (RIM) environment. The RIM technique facilitates flow measurements extremely close to model surfaces as well as unimpeded optical access which are critical to understanding the flow-form coupling. A series idealized, fixed-bed models are fabricated to mimic the key morphological characteristics of early protodune development observed in the field, and the flow measurements associated with them are analyzed to reveal the mechanisms controlling the bedform dynamics.</p>

scholarly journals Assessing theoretical flow velocity profile and resistance in gravel bed rivers by field measurements

2018 ◽  
Vol 49 (4) ◽  
pp. 220-227 ◽  
Author(s):  
Vito Ferro ◽  
Paolo Porto
Keyword(s):  
Velocity Profile ◽  
Flow Velocity ◽  
Froude Number ◽  
Flow Resistance ◽  
Field Measurements ◽  
Mean Flow ◽  
Gravel Bed ◽  
Wide Range ◽  
Gravel Bed Rivers ◽  
Resistance Equation

Previous studies showed that integrating a power velocity profile, deduced applying dimensional analysis and the incomplete self-similarity condition, the flow resistance equation for open channel flow can be obtained. At first, in this paper the relationship between the Γ function of the power velocity profile, the channel slope and the Froude number, which was already empirically introduced in a previous paper, is now theoretically deduced. Then this relationship is calibrated using the field measurements of flow velocity, water depth and bed slope carried out in 101 reaches of gravel bed rivers available by literature. The proposed relationship for estimating Γ function and the theoretical flow resistance equation are also tested by an independent dataset of 104 reaches of some gravel bed rivers (Fiumare) in Calabria region. Finally, the theoretically-based relationship for estimating the Γ function is calibrated by the overall available database (205 reaches). In this way the three coefficients of the theoretically based Γ function are estimated for a wide range of slopes (0.1%-6.19%) and hydraulic conditions (Froude number values ranging from 0.08 to 1.25). In conclusion, the analysis shows that the Darcy-Weisbach friction factor for gravel bed rivers can be accurately estimated by the approach based on a power-velocity profile and the theoretically-based relationship proposed for estimating Γ function. The analysis also points out a performance in estimating mean flow velocity better than that obtained in a previous study carried out by the authors.

An Experimental Flow Study of the Pitching Oscillating Airfoil Using the PIV Technique

2015 ◽  
Vol 733 ◽  
pp. 562-565
Author(s):  
Xuan Xiong ◽  
Xiao Ming Ye ◽  
Kai Wang
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Velocity Profile ◽  
Wind Tunnel Experiment ◽  
Experimental Results ◽  
Velocity Data ◽  
Piv Technique ◽  
Oscillating Airfoil ◽  
Flow Study

A wind tunnel experiment is carried out employing 2D-PIV technique to visualize the qualitative flow field and to obtain the quantitative velocity profile respectively in the wake of 1 Hz pitching oscillating airfoil of 6 degrees amplitude. In order to validate the experiment for future’s study, the experimental velocity data are compared to relative CFD ones. The CFD results are obtained from a code called Map Flow that is able to deal with the flow around pitching and plunging oscillating airfoil. From the vortices maps it is shown that the experimental results and CFD ones are well compared with respect to the size and the shape of the vortices patterns. Quantitatively, the differences between experiment and CFD with respect to the velocity profile are acceptable.

Turbomachinery Flow Measurements Using Long-Nose Probes

2003 ◽  
Author(s):  
A. Doukelis ◽  
K. Mathioudakis
Keyword(s):  
Flow Field ◽  
Field Measurements ◽  
Laser Doppler Anemometer ◽  
Frame Of Reference ◽  
Measuring Technique ◽  
Flow Measurements ◽  
Pneumatic Measuring ◽  
Stationary Frame ◽  
Annular Cascade ◽  
Long Nose

The present work provides a detailed account of a pneumatic measuring technique appropriate for flow field measurements in turbomachinery configurations, making use of long-nose 5-hole probes. The way of obtaining flow quantities in a frame of reference on the sensing head of the probe is first addressed. Transformation of velocity co-ordinates from the probe frame to a stationary frame, customary for turbomachinery flows, is then discussed. Sources of error are also discussed, with particular attention on those that can be introduced by the nose geometry and the co-ordinate transformations. The potential of the measuring technique is demonstrated by presenting the application of the technique for measurements in an annular cascade facility. The results are compared to results obtained by a 3-D Laser-Doppler Anemometer.

scholarly journals Heat Transfer Behaviour and Flow Field Characterisation of Impinging Synthetic Jets for a Wide Range of Parameters

2010 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
High Speed ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Flow Measurements ◽  
Wide Range

Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets. Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics. High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.

scholarly journals Flow in a Centrifugal Fan of the Squirrel Cage Type

1989 ◽  
Author(s):  
R. J. Kind ◽  
M. G. Tobin
Keyword(s):  
Flow Field ◽  
Reverse Flow ◽  
Field Measurements ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Squirrel Cage ◽  
Flow Through ◽  
The Mean

This paper presents the results of performance measurements and detailed measurements of the mean flow field at rotor inlet and rotor exit in three squirrel cage fan configurations. The flow-field measurements were taken with a five-hole probe and yield total pressure, static pressure and the three components of velocity. Measurements were taken for two casing throat areas and for two different rotors. For each configuration the flow field was measured for flow rates below, near and above the best-efficiency point. Flow patterns are complex and there is reverse flow through the rotor blading even at the best-efficiency operating condition. Although complex, the main features of flow behaviour can be understood. They were common to all three fan configurations.

Secondary Flow Measurements in a Turbine Cascade With High Inlet Turbulence

1992 ◽  
Vol 114 (1) ◽  
pp. 173-183 ◽  
Author(s):  
D. G. Gregory-Smith ◽  
J. G. E. Cleak
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Flow Region ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Flow Measurements ◽  
Frequency Spectra ◽  
The Mean ◽  
End Wall

Measurements of the mean and turbulent flow field have been made in a cascade of high turning turbine rotor blades. The inlet turbulence was raised to 5 percent by a grid placed upstream of the cascade, and the secondary flow region was traversed within and downstream of the blades using a five-hole probe and crossed hot wires. Flow very close to the end wall was measured using a single wire placed at several orientations. Some frequency spectra of the turbulence were also obtained. The results show that the mean flow field is not affected greatly by the high inlet turbulence. The Reynolds stresses were found to be very high, particularly in the loss core. Assessment of the contributions to production of turbulence by the Reynolds stresses shows that the normal stresses have significant effects, as do the shear stresses. The calculation of eddy viscosity from two independent shear stresses shows it to be fairly isotropic in the loss core. Within the blade passage, the flow close to the end wall is highly skewed and exhibits generally high turbulence. The frequency spectra show no significant resonant peaks, except for one at very low frequency, attributable to an acoustic resonance.

Flow in a Centrifugal Fan of the Squirrel-Cage Type

1990 ◽  
Vol 112 (1) ◽  
pp. 84-90 ◽  
Author(s):  
R. J. Kind ◽  
M. G. Tobin
Keyword(s):  
Flow Field ◽  
Reverse Flow ◽  
Flow Behavior ◽  
Field Measurements ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Mean Flow ◽  
Squirrel Cage ◽  
Flow Through ◽  
The Mean

This paper presents the results of performance measurements and detailed measurements of the mean flow field at rotor inlet and rotor exit in three squirrel-cage fan configurations. The flow-field measurements were taken with a five-hole probe and yield total pressure, static pressure, and the three components of velocity. Measurements were taken for two casing throat areas and for two different rotors. For each configuration the flow field was measured for flow rates below, near, and above the best-efficiency point. Flow patterns are complex and there is reverse flow through the rotor blading even at the best-efficiency operating condition. Although complex, the main features of flow behavior can be understood. They were common to all three fan configurations.

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