Structure of Turbulence Around the Trailing Edge of a Rotor Blade

This paper focuses on the structure of turbulence around the trailing edge of a rotor blade operating behind a row of Inlet Guide Vanes (IGVs) located upstream of the rotor. High resolution, two-dimensional Particle Image Velocimetry (PIV) measurements are conducted in a refractive index matched turbomachinery facility that provides unobstructed view of the entire flow field. We focus on a small region around the rotor blade trailing edge, extending from 0.04c upstream of the trailing edge to about 0.1c downstream of it, c being the blade chord length. We examine the phase dependent distribution of turbulent kinetic energy (TKE) and its in-plane components of production rate. Impingement of an IGV wake on the suction surface of a rotor blade, near the trailing edge region, reduces the thickness of the boundary layer within the region impinged by the wake. The resulting increase in phase averaged shear strain rate increases the production rate and causes a striking increase in peak turbulent kinetic energy in the near wake. Streamwise velocity gradients, i.e. compression, also contribute to turbulence production, especially when the boundary layer at trailing edge is relatively thick, i.e. when it is not impinged by the IGV wake.

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Flow Structure and Turbulence in the Tip Region of a Turbomachine Rotor Blade

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27590 ◽

2007 ◽

Author(s):

Francesco Soranna ◽

Yi-Chih Chow ◽

Oguz Uzol ◽

Joseph Katz

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Flow Structure ◽

Turbulent Diffusion ◽

Rotor Blade ◽

Trailing Edge ◽

Left Hand ◽

Tip Leakage ◽

The Subject ◽

Turbulence Production

The flow structure and turbulence in the tip region of a rotor blade operating downstream of a row of Inlet Guide Vanes (IGVs) are investigated experimentally in a refractive index matched facility that provides unobstructed view of the entire flow field. Stereo-PIV measurements are performed in closely spaced radial planes near the blade tip in a region extending from (slightly upstream of) the blade trailing edge to about 40% of the chord downstream of it. The data enable calculations of all the components of the phase-averaged velocity and vorticity vectors, as well as the strain rate, Reynolds stress, and turbulent diffusion tensors. Each rotor blade is confined between two tip-leakage vortices, a right hand vortex (RHV), generated by the subject blade and propagating along its right hand side, and a left hand vortex (LHV), generated by the previous blade in the same row and propagating along the left hand side of the subject blade. In addition, a trailing edge vortex (TEV) lays underneath the LHV and is subject to intense shearing/deformation by the LHV. RHV-induced radial gradients of radial phase-averaged velocity cause negative turbulence production, P, along the RHV-axis, and formation of a region of low P in the gap between the RHV and the blade suction surface. Trends of turbulent kinetic energy k and P within the RHV do not agree due to the effects of advection by the phase-averaged flow. To the left of the blade, shearing of the TEV by the LHV enhances turbulence production in the region between the two vortices and the rotor wake. Trends of turbulent kinetic energy and its production rate are in good agreement and peaks of k and P occur at the same location. As the TEV migrates away from the LHV, shearing effects become weaker and the dominant contributors to production are terms containing vortex-induced radial gradients of axial and radial velocities. Turbulent diffusion is a minor contributor to the evolution of turbulent kinetic energy in the tip region. It is also shown that the tip-leakage flow/vortex deteriorates the rotor blade performance, causing a ∼66% increase in shaft power input (per unit mass flow-rate) in the tip region in comparison with midspan.

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The Effects of Inlet Guide Vane-Wake Impingement on the Boundary Layer and the Near-Wake of a Rotor Blade

Journal of Turbomachinery ◽

10.1115/1.3149282 ◽

2010 ◽

Vol 132 (4) ◽

Cited By ~ 10

Author(s):

Francesco Soranna ◽

Yi-Chih Chow ◽

Oguz Uzol ◽

Joseph Katz

Keyword(s):

Boundary Layer ◽

Rotor Blade ◽

Guide Vane ◽

Shear Velocity ◽

Inlet Guide Vane ◽

Surface Boundary ◽

Momentum Thickness ◽

Suction Surface ◽

Near Wake ◽

Trailing Edge

This paper examines the response of a rotor blade boundary layer and a rotor near-wake to an impinging wake of an inlet guide vane (IGV) located upstream of the rotor blade. Two-dimensional particle image velocimetry (PIV) measurements are performed in a refractive index matched turbomachinery facility that provides unobstructed view of the entire flow field. Data obtained at several rotor phases enable us to examine the IGV-wake-induced changes to the structure of the boundary layer and how these changes affect the flow and turbulence within the rotor near-wake. We focus on the suction surface boundary layer, near the blade trailing edge, but analyze the evolution of both the pressure and suction sides of the near-wake. During the IGV-wake impingement, the boundary layer becomes significantly thinner, with lower momentum thickness and more stable profile compared with other phases at the same location. Analysis of available terms in the integral momentum equation indicates that the phase-averaged unsteady term is the main contributor to the decrease in momentum thickness within the impinging wake. Thinning of the boundary/shear layer extends into the rotor near-wake, making it narrower and increasing the phase-averaged shear velocity gradients and associated turbulent kinetic energy (TKE) production rate. Consequently, the TKE increases during wake thinning, with as much as 75% phase-dependent variations in its peak magnitude. This paper introduces a new way of looking at the PIV data by defining a wake-oriented coordinate system, which enables to study the structure of turbulence around the trailing edge in great detail.

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Structure of Turbulence Within a Sheared Wake of a Rotor Blade

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2006-98401 ◽

2006 ◽

Author(s):

Francesco Soranna ◽

Yi-Chih Chow ◽

Oguz Uzol ◽

Joseph Katz

Keyword(s):

Shear Stress ◽

Kinetic Energy ◽

Flow Field ◽

Turbulent Kinetic Energy ◽

Production Rate ◽

Rotor Blade ◽

Energy Production ◽

Reynolds Shear Stress ◽

Suction Side ◽

Velocity Fluctuations

Stereoscopic PIV measurements examine the flow structure and turbulence within a rotor near wake located within a non-uniform field generated by a row of Inlet Guide Vanes (IGVs). The experiments are performed in a refractive index matched facility that provides unobstructed view of the entire flow field. The data are acquired at 10 closely spaced radial planes located near mid-span, enabling measurements of all the components of the phase averaged velocity and strain rate, as well as the Reynolds stress and the triple correlation tensors. The rotor wake is sheared and bent towards the pressure (inner) side by a non-uniform flow field generated by IGV wake segments that propagate along the suction and pressure sides of the rotor passage with different speeds. The axial velocity fluctuations increase along the suction/outer side of the wake, while the other components decay. On the pressure/inner part of the bent wake the circumferential velocity fluctuations are higher. The Reynolds shear stress has a complex distribution, but is higher on the suction side. The turbulent kinetic energy is also consistently higher on the outer (suction) side of the wake. This trend is fundamentally different from those observed in prior studies of curved wakes where turbulence is enhanced on the inner side of the wake due to the destabilizing effect of curvature. To explain the difference, we examine the contributors to turbulent kinetic energy production rate in a curvilinear coordinate system aligned with the wake-centerline. The contribution of streamwise curvature to the production rate of turbulent kinetic energy, although consistent with expected trends, is overwhelmed by effects of wake shearing. The primary contributor to turbulent kinetic energy production rate is the product of Reynolds shear stress with cross-stream gradients of streamwise (in a frame of reference relative to the rotor blade) velocity in the wake. The location of peak in turbulent kinetic energy is almost aligned with that of production rate. The turbulence diffusion term opposes the production rate peaks, but also has high values along the edge of the wake.

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The Effects of IGV Wake Impingement on the Boundary Layer and the Near-Wake of a Rotor Blade

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-50598 ◽

2008 ◽

Cited By ~ 1

Author(s):

Francesco Soranna ◽

Yi-Chih Chow ◽

Oguz Uzol ◽

Joseph Katz

Keyword(s):

Boundary Layer ◽

Rotor Blade ◽

Guide Vane ◽

Shear Velocity ◽

Inlet Guide Vane ◽

Surface Boundary ◽

Momentum Thickness ◽

Suction Surface ◽

Near Wake ◽

Trailing Edge

This paper examines the response of a rotor blade boundary layer and a rotor near-wake to an impinging wake of an Inlet Guide Vane (IGV) located upstream of the rotor blade. Two-dimensional Particle Image Velocimetry (PIV) measurements are performed in a refractive index matched turbomachinery facility that provides unobstructed view of the entire flow field. Data obtained at several rotor phases enables us to examine IGV-wake-induced changes to the structure of the boundary layer and how these changes affect the flow and turbulence within the rotor near-wake. We focus on the suction surface boundary layer, near the blade trailing edge, but analyze the evolution of both the pressure and suction sides of the near-wake. During IGV-wake impingement, the boundary layer becomes significantly thinner, with lower momentum thickness and more stable profile compared to other phases at the same location. Analysis of available terms in the integral momentum equation indicates that the phase-averaged unsteady term is the main contributor to the decrease in momentum thickness within the impinging wake. Thinning of the boundary/shear layer extends into the rotor near wake, making it narrower and increasing the phase averaged shear velocity gradients and associated turbulent kinetic energy (TKE) production rate. Consequently, the TKE increases during wake thinning, with as much as 75% phase-dependent variations in its peak magnitude. The paper introduces a new way of looking at PIV data by defining a wake oriented coordinate system which enables to study the structure of turbulence around the trailing edge in great detail.

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Assessing the Horizontal Homogeneity of the Atmospheric Boundary Layer (HHABL) Profile Using Different CFD Software

Atmosphere ◽

10.3390/atmos11101138 ◽

2020 ◽

Vol 11 (10) ◽

pp. 1138

Author(s):

Islam Abohela ◽

Elsa Aristodemou ◽

Abas Hadawey ◽

Raveendran Sundararajan

Keyword(s):

Boundary Layer ◽

Kinetic Energy ◽

Atmospheric Boundary Layer ◽

Turbulent Kinetic Energy ◽

Dissipation Rate ◽

Streamwise Velocity ◽

Computational Domain ◽

Wall Function ◽

Wall Boundary Conditions ◽

Inlet Conditions

One of the main factors affecting the reliability of computational fluid dynamics (CFD) simulations for the urban environment is the Horizontal Homogeneity of the Atmospheric Boundary Layer (HHABL) profile—meaning the vertical profiles of the mean streamwise velocity, the turbulent kinetic energy, and dissipation rate are maintained throughout the streamwise direction of the computational domain. This paper investigates the preservation of the HHABL profile using three different commercial CFD codes—the ANSYS Fluent, the ANSYS CFD, and the Siemens STAR-CCM+ software. Three different cases were considered, identified by their different inlet conditions for the inlet velocity, turbulent kinetic energy, and dissipation rate profiles. Simulations were carried out using the RANS k-ε turbulence model. Slight variations in the eddy viscosity models, as well as in the wall boundary conditions, were identified in the different software, with the standard wall function with roughness being implemented in the Fluent applications, the scalable wall function with roughness in the CFX applications, and the blended wall function option in the STAR-CCM+ simulations. There was a slight difference in the meshing approach in the three different software, with a prism-layer option in the STAR-CCM+ software, which allowed a finer mesh near the wall/ground boundary. The results show all three software are able to preserve the horizontal homogeneity of the ABL—less than 0.5% difference between the software—indicating very similar degrees of accuracy.

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Spatiotemporal Dynamics of the Kinetic Energy in the Atmospheric Boundary Layer from Minisodar Measurements

Atmosphere ◽

10.3390/atmos12040421 ◽

2021 ◽

Vol 12 (4) ◽

pp. 421

Author(s):

Alexander Potekaev ◽

Liudmila Shamanaeva ◽

Valentina Kulagina

Keyword(s):

Boundary Layer ◽

Kinetic Energy ◽

Atmospheric Boundary Layer ◽

Turbulent Kinetic Energy ◽

Time Of Day ◽

Linear Increase ◽

Spatiotemporal Dynamics ◽

Intermediate Layers ◽

Subsequent Decrease ◽

Stable Atmospheric Boundary Layer

Spatiotemporal dynamics of the atmospheric kinetic energy and its components caused by the ordered and turbulent motions of air masses are estimated from minisodar measurements of three velocity vector components and their variances within the lowest 5–200 m layer of the atmosphere, with a particular emphasis on the turbulent kinetic energy. The layered structure of the total atmospheric kinetic energy has been established. From the diurnal hourly dynamics of the altitude profiles of the turbulent kinetic energy (TKE) retrieved from minisodar data, four layers are established by the character of the altitude TKE dependence, namely, the near-ground layer, the surface layer, the layer with a linear TKE increase, and the transitive layer above. In the first layer, the most significant changes of the TKE were observed in the evening hours. In the second layer, no significant changes in the TKE values were observed. A linear increase in the TKE values with altitude was observed in the third layer. In the fourth layer, the TKE slightly increased with altitude and exhibited variations during the entire observation period. The altitudes of the upper boundaries of these layers depended on the time of day. The MKE values were much less than the corresponding TKE values, they did not exceed 50 m2/s2. From two to four MKE layers were distinguished based on the character of its altitude dependence. The two-layer structures were observed in the evening and at night (under conditions of the stable atmospheric boundary layer). In the morning and daytime, the four-layer MKE structures with intermediate layers of linear increase and subsequent decrease in the MKE values were observed. Our estimates demonstrated that the TKE contribution to the total atmospheric kinetic energy considerably (by a factor of 2.5–3) exceeded the corresponding MKE contribution.

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