On the Flow and Turbulence Within the Wake and Boundary Layer of a Rotor Blade Located Downstream of an IGV

2003 ◽  
Author(s):  
Yi-Chih Chow ◽  
Oguz Uzol ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Spectral Analysis ◽  
Rotor Blade ◽  
Hot Spot ◽  
Wake Flow ◽  
Mean Flow ◽  
Production Rates ◽  
Near Wake ◽  
Trailing Edge ◽  
Planar Shear

This paper presents detailed experimental data on the flow and turbulence within the wake and boundary layer of a rotor blade operating behind a row of Inlet Guide Vanes (IGVs). The experiments are performed in a refractive index matched facility that provides an unobstructed view of the entire flow field. Results of the high-resolution 2D Particle Image Velocimetry (PIV) measurements are used for characterizing the mean flow, Reynolds stresses, turbulent kinetic energy as well as dissipation and production rates. Dissipation and production rates are high and of the same order of magnitude near the trailing edge, and decrease rapidly with increasing distance from the blade. The trend is reversed in the wake kinking region, resulting in elevated turbulence levels, i.e. a turbulent hot spot. One-dimensional spectral analysis shows that, except for the very near wake and hot-spot regions, the turbulence within the rotor wake can be assumed to be isotropic. Also the directions of the maximum shear strain and shear stress are aligned in that region, i.e. consistent with eddy viscosity type Reynolds stress models. The rotor near wake mainly consists of two parallel layers experiencing planar shear with opposite signs as one would expect to find in a 2D wake. However, orientation differences can extend up to 45° near the trailing edge and the hot-spot. Furthermore, there is substantial mismatch in the location of the local maxima of stresses and strains. The values of S33 are also large there, indicating that the flow is three-dimensional. Rotor boundary layer measurements focus on a region where the IGV wake intersects with the rotor blade. The impingement of the increased axial velocity region in between the IGV wakes causes the thinning of the boundary layer. This is similar to the effect of a turbulent jet impinging on a flat surface. When viewed in the frame of reference of “non-wake” flow regions, the boundary layer thinning can also be attributed to the suction (or “negative jet”) effect of the “slip velocity” present in the IGV wake segments. Spectral analysis shows that the turbulence in the rotor boundary layer is highly anisotropic. As a result, the spectra cannot be used for estimating the dissipation rate.

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

2010 ◽  
Vol 132 (4) ◽  
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.

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

2008 ◽  
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.

Experimental Study of the Structure of a Rotor Wake in a Complex Turbomachinery Flow

2003 ◽  
Author(s):  
Yi-Chih Chow ◽  
Oguz Uzol ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
Shear Stress ◽  
Spectral Analysis ◽  
Shear Strain ◽  
Hot Spot ◽  
Reynolds Shear Stress ◽  
Mean Flow ◽  
Trailing Edge ◽  
Rotor Wake ◽  
Subgrid Scales ◽  
The Mean

Unobstructed PIV measurements within complex turbomachinery flow fields are performed in an optical-refractive-index-matched facility consisting of a 2-stage axial turbomachine. Two different test setups are utilized to demonstrate wake-wake, wake-blade interactions and the associated flow non-uniformities and turbulence. The flow consists of a lattice of interacting wake segments, which are being chopped by the rotor and stator blades. The wake fragments become discontinuous due to the velocity differences across the rotor blades. Striking flow phenomena that occur as a result of this non-uniform flow field, such as turbulent “hot spots” and kinking of the rotor wake are presented at high magnification and samples that are large enough to obtain converged statistics. In this paper we focus on the flow field and turbulence within the rotor wake. One thousand instantaneous realizations at the same phase are used for determining the phase averaged flow and turbulence statistics including Reynolds stresses, turbulence spectra, production, dissipation, and mean strains. Three methodologies are adopted to investigate the details of the rotor wake structure: 1. Local maximization of 2-D shear strain and Reynolds shear stress; 2. 1-D energy spectral analysis; and 3. Subgrid-Scale (SGS) energy budget. Alignment of the local coordinates with direction that maximizes the local shear strain shows that except for the hot spot regions the rotor wake consists of two parallel layers exposed to planar shear strain. The normal strains in this system are significantly lower, indicating that out-of-plane normal straining is much weaker than the in-plane shear (except near the hot spot and close to the trailing edge of the rotor). Significant differences exist in several regions between the orientation of a coordinate system that maximizes the shear strain, and the system that maximizes the Reynolds shear stress, particularly around the hot spot, near the trailing edge, and within the stator wake segments on both sides of the rotor wake. 1-D spectral analysis reveals that the turbulence near the trailing edge is anisotropic and highly dissipative. The dissipation decreases and turbulence becomes more isotropic further away from the trailing edge, but becomes anisotropic again near the hot spot. Spatial filtering of data and measurement of the resulting SGS stresses enable us to examine and compare energy fluxes from the mean flow to the resolved and subgrid scales, as well as from the resolved to the subgrid scales. Due to the limitation in resolution, the present filter scale is 50% of the integral scale (∼wake width). Consequently, the energy flux from the mean flow to the subgrid scales is much higher than flux from the resolved turbulence to the subgrid scales. The production term, representing the energy flux from the mean flow to the resolved scales is typically higher than the flux from the resolved to the subgrid scales. Thus, build-up of large-scale energy occurs in substantial part of the near wake. The dissipation rates estimated from the spectra are everywhere (including the hot spot) of the same order as the overall SGS dissipation rate.

Characterization of Vortex Dynamics in the Near Wake of an Oscillating Flexible Foil

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Firas F. Siala ◽  
Alexander D. Totpal ◽  
James A. Liburdy
Keyword(s):  
Large Scale ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Wake Flow ◽  
Small Scale ◽  
Mean Flow ◽  
Near Wake ◽  
Trailing Edge ◽  
Swirling Strength ◽  
The Mean

An experimental study was conducted to explore the effect of surface flexibility at the leading and trailing edges on the near-wake flow dynamics of a sinusoidal heaving foil. Midspan particle image velocimetry (PIV) measurements were taken in a closed-loop wind tunnel at a Reynolds number of 25,000 and at a range of reduced frequencies (k = fc/U) from 0.09 to 0.20. Time-resolved and phase-locked measurements are used to describe the mean flow characteristics and phase-averaged vortex structures and their evolution. Large-eddy scale (LES) decomposition and swirling strength analysis are used to quantify the vortical structures. The results demonstrate that trailing edge flexibility has minimal influence on the mean flow characteristics. The mean velocity deficit for the flexible trailing edge and rigid foils remains constant for all reduced frequencies tested. However, the trailing edge flexibility increases the swirling strength of the small-scale structures, resulting in enhanced cross-stream dispersion. Flexibility at the leading edge is shown to generate a large-scale leading edge vortex (LEV) for k ≥ 0.18. This results in a reduction in the swirling strength due to vortex interactions when compared to the flexible trailing edge and rigid foils. Furthermore, it is shown that the large-scale LEV is responsible for extracting a significant portion of energy from the mean flow, reducing the mean flow momentum in the wake. The kinetic energy loss in the wake is shown to scale with the energy content of the LEV.

scholarly journals Near-Wake Observations behind Azimuthally Perforated Disks With Varying Hole Layout and Porosity in Smooth Airstreams at High Reynolds Numbers

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Raf Theunissen ◽  
Robert Worboys
Keyword(s):  
Drag Coefficient ◽  
Experimental Studies ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Mean Flow ◽  
Flow Topology ◽  
Near Wake ◽  
Two Component ◽  
High Reynolds ◽  
Component Particle

Porous disks are commonly encountered in experimental studies dealing with flow through objects such as wind turbines, parachutes, and fluidic devices to regulate pressure and/or downstream turbulence. Perforations are typically staggered and only porosity is altered to attain the required disk drag coefficient, despite a documented influence of topology. Few works have reported, however, to which extent the spatial distribution of the circular perforations affect the mean flow pertaining freestanding disks, and for this reason, this work presents a first, more systematic study focused on the effect of azimuthally varying hole topology and porosity on disk drag and near-wake characteristics. An experimental study performed in airflows of negligible freestream turbulence at Reynolds numbers in the order of 105 is reported and related to the existing literature to ensure reliability. Complementary to drag measurements, near-wake surveys have been performed on a variety of perforation layouts using two-component laser Doppler velocimetry and two-component particle image velocimetry. It is shown that minor changes in perforations can cause drastic changes in near-wake flow topology and no perforation layout can be consistently associated with highest drag. Explicit empirical expressions for drag coefficient linked with the simplified topologies considered have been derived.

A Turbulent Boundary Layer Flow Over an Open Shallow Cavity

2016 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Vector Fields ◽  
Turbulence Models ◽  
Leading Edge ◽  
Field Measurements ◽  
Recirculation Region ◽  
Mean Flow ◽  
Trailing Edge ◽  
Cavity Depth

Particle Image Velocimetry (PIV) was used to study the flow structure and turbulence, upstream, over, and downstream a shallow open cavity. Three sets of PIV measurements, corresponding to a turbulent incoming boundary layer and a cavity length-to-depth ratio of four, are reported. The cavity depth based Reynolds numbers were 21,000; 42,000; and 54,000. The selected flow configuration and well characterized inflow conditions allow for straightforward assessment of turbulence models and numerical schemes. All mean flow field measurements display a large flow recirculation region, spanning most of the cavity and a smaller, counter-rotating, secondary vortex, immediately downstream of the cavity leading edge. The Galilean decomposed instantaneous velocity vector fields, clearly demonstrate two distinct modes of interaction between the free shear and the cavity trailing edge. The first corresponds to a cascade of vortical structures emanating from the tip of the leading edge of the cavity that grow in size as they travel downstream and directly interact with the trailing edge, i.e., impinging vortices. The second represents vortices that travel above the trailing edge of the cavity, i.e., non-impinging vortices. In the case of impinging vortices, a strong, large scale region of recirculation forms inside the cavity and carries the flow disturbances, arising from the impingement of vortices on the trailing edge of the cavity, upstream in a manner that interacts with and influences the flow as it separates from the cavity leading edge.

Structure of Turbulence Around the Trailing Edge of a Rotor Blade

2007 ◽  
Author(s):  
Francesco Soranna ◽  
Yi-Chih Chow ◽  
Oguz Uzol ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Production Rate ◽  
Rotor Blade ◽  
Streamwise Velocity ◽  
Small Region ◽  
Shear Strain Rate ◽  
Suction Surface ◽  
Trailing Edge

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.

Near-Wake Flow Dynamics Resulting from Trailing Edge Spanwise Perturbation

2008 ◽  
Author(s):  
L Doddipatla ◽  
H Hangan ◽  
V Durgesh ◽  
J Naughton
Keyword(s):  
Flow Dynamics ◽  
Wake Flow ◽  
Near Wake ◽  
Trailing Edge

Development of the turbulent near wake of a tapered thick flat plate

1988 ◽  
Vol 189 ◽  
pp. 135-163 ◽  
Author(s):  
A. Haji-Haidari ◽  
C. R. Smith
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Wall Region ◽  
Turbulence Structure ◽  
Near Wake ◽  
Growth Region ◽  
Trailing Edge ◽  
Centreline Velocity ◽  
Hot Film

The velocity field and turbulence structure in the near wake of a thick flat plate with a tapered trailing-edge geometry are examined using both hydrogen-bubble flow visualization and hot-film anemometry measurements. Tests were conducted for Re1 = 8.5 × 105 in the region 0 < x+ < 6400 behind the trailing edge. The probe and visualization results indicate a similarity between both (i) velocity and turbulence structure variations wih x+ in the near wake, and (ii) the corresponding changes in similar flow characteristics with y+ within a turbulent boundary layer. In particular, visualization data in the vicinity of the wake centreline reveal the existence of strong streamwise flow structures in the region close (x+ < 270) to the trailing edge. The streamwise orientation of the observed structures diminishes as x+ increases. From hot-film measurements, two separate regions along the wake centreline can be distinguished: (i) a linear growth region which extends over 0 < x+ < 100, wherein the centreline velocity varies linearly with x+; and (ii) a logarithmic growth region for x+ > 270, wherein the centreline velocity varies as log x+. The similarity in behaviour between these regions and the comparable wall region of a turbulent boundary layer suggests the existence of a common functionality. This similarity is demonstrated by a simple linear relationship of the form y+ = Kx+, which is shown to approximately collapse the velocity behaviour both across a turbulent boundary layer and along the wake centreline to a unified set of empirical relationships.

Sign in / Sign up

Export Citation Format

Share Document