Three-component Velocity Data Research Articles

Wake Dynamics of Complex Turning Vanes Using Time-Resolved Particle Image Velocimetry Measurements

Abstract The use of turning vanes spans multiple engineering disciplines such as aerospace, ocean, and biomedical to effectively turn an otherwise uniform flowfield and achieve desired downstream flow angles. The presented work investigates the wake dynamics generated by sets of complex turning vanes which contained nonaxisymmetric geometries, spanwise variations in turning angle, and multiple vane junctions. Time-resolved particle image velocimetry (TR-PIV) measurements were performed to collect three-component velocity data downstream of the vane pack geometries. As the vanes contained blunt trailing edges (TEs), large-scale periodic structures (von Kármán vortices) dominated the unsteady wakes. Two postprocessing methods, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), were employed to extract the wake energy or enstrophy content, corresponding spatial modes, and associated frequencies. This was completed for various parameters such as Reynolds number, vane turning angle, and vane trailing edge thickness. Spatial POD analyses showed that zero-turning vanes contained similar dynamics to that of a circular cylinder, and the total wake energy distributions were affected by freestream velocity. A spectral POD analysis in the wake of vane junctions found that the junction flow contained significant coherent content and gave some insight into the mean flow. Finally, vane parameters such as turning angle and TE thickness were found to play a large role in modifying the enstrophy content of the large-scale shedding modes.

Turbulence Anisotropy Investigations in an Internal Combustion Engine

Abstract The assumption of isotropic turbulence is commonly incorporated into models of the internal combustion engine (ICE) in-cylinder flows. While preliminary analysis with two-dimensional (2D) velocity data indicates that the turbulence may tend to isotropy as the piston approaches top-dead-center (TDC), the validity of this assumption has not been fully investigated, partially due to the lack of three-component velocity data in ICEs. In this work, the velocity was measured using two-dimensional, three-component (2D-3C) particle image velocimetry in a single-cylinder, motored, research engine to investigate the evolution of turbulence anisotropy throughout the compression stroke. Invariants of the Reynolds stress anisotropy tensor were calculated and visualized, through the Lumley triangle, to investigate turbulence states. Results showed the turbulence to be mostly anisotropic, with preferential tendency toward 2D axisymmetry at the beginning of the compression stroke and approaching-isotropy near top-dead-center. Findings provide new insights into turbulence in dynamic, bounded flows to assist with the development of physics-based, quantitative models.

Laser Doppler Velocimetry Characterization of Unsteady Vaned Diffuser Flow in a Centrifugal Compressor

Abstract Modern turbomachinery faces increased performance demands in terms of efficiency, compactness, and pressure-rise. Advancements in computational technology have allowed numerical methods to become the backbone of design development efforts. However, the unique complexities of centrifugal compressor flow-fields pose difficult computational problems. As such, advanced experimental methods must be used to obtain high-quality data sets to further inform, improve, and validate computational methods in complex flow regimes. A recent experimental work on a high-speed centrifugal compressor has provided detailed, unsteady, three-component velocity data using laser Doppler velocimetry. A passage vortex is present, and its nascent tied to the increased incidence at mid-span associated with impeller wake flow. This vortex begins in the hub-pressure side corner and grows to fill the passage and become temporally stable. The vortex development is unsteady in nature, and the unsteady effects persist 40% downstream of the throat. Distinct jet and wake flow patterns from the impeller also do not agglomerate until 40% downstream of the throat. Additionally, the critical impact of the unsteady flow development on the time-averaged flow-field is explained.

Estimation of In Situ 3-D Particle Distributions From a Stereo Laser Imaging Profiler

In this paper, an image processing system for estimating 3-D particle distributions from stereo light scatter images is described. The system incorporates measured, three-component velocity data to mitigate particle blur associated with instrument motion. An iterative background estimation algorithm yields a local threshold operator that dramatically reduces bias in particle counts over the full image field. Algorithms are tested on simulated particle distributions and data from an open-ocean profile collected near the Santa Barbara Channel Islands, CA. They yield over a 50% reduction in root-mean-squared error in particle size estimates, and a 30% reduction in the magnitude of the motion blur point spread function. In situ particle distributions are estimated and compared to several models. It is demonstrated that quantitative, 3-D particle distributions can be accurately estimated from these data for particles with diameter larger than 4 pixels (0.8 mm).

Enhanced Vertical Inhomogeneity in Turbulent Rotating Convection

In this Letter we report experimental evidence that rotation enhances vertical inhomogeneity in turbulent convection, in spite of the increased columnar flow ordering under rotation. Measurements using stereoscopic particle image velocimetry have been carried out on turbulent rotating convection in water. At constant Rayleigh number Ra=1.11 x 10(9) several rotation rates have been used, so that the Rossby number takes values from Ro=infinity (no rotation) to 0.09 (strong rotation). The three-component velocity data, obtained at two vertical positions, are used to investigate the anisotropy of the flow through the invariants of the Reynolds-stress anisotropy tensor and the Lumley triangle, as well as to correlate the vertical velocity and vorticity. In the center plane rotation causes the turbulence to be "rodlike," while closer to the top plate a trend toward isotropy is observed.

Combined PIV and DGV applied to a pressurized gas turbine combustion facility

This paper provides an overview of flow field measurements on a pressurized generic combustor that shares typical features of realistic gas turbine combustors. Both Doppler global velocimetry (DGV) and particle image velocimetry (PIV) were applied in parallel to achieve volumetric, three-component velocity data sets of the reacting flow field at pressures of 2 and 10 bar with 700 K pre-heating. Limited optical access to the mixing zone required a combination of PIV and DGV to obtain averaged three-component velocity data from a single viewing direction. The acquired volume data sets of the time-averaged flow in the mixing zone contain about 40 parallel planes spaced at 2 mm with a spatial resolution of 1.2 × 1.2 mm2 each. Difficulties encountered in the application of stereoscopic PIV to a simple atmospheric generic combustor illustrate the advantage of the combined PIV–DGV technique.

Detection of anomalous seismic phases by the wavelet transform

SUMMARY Strong motion data at La Union, one of three near-fault stations of the Michoacan, Mexico, earthquake in 1985, are analysed by a wavelet transform in order to identify a clear later energy arrival whose frequency content and particle motion are quite different from the main part of the seismograms. We used an orthonormal set of analysing wavelets, a discrete wavelet transform, proposed by Meyer and Yamada, with which an efficient computational procedure can be achieved utilizing the fast Fourier transform. Results of an application of the above wavelet transform to three-component velocity data of La Union are summarized as follows. A vertical seismogram does not contain any distinguishable later energy arrivals for the entire frequency range recorded. The major energy arrives in the time interval between 10 and 30 s. In contrast, an east-west component seismogram shows a peculiar later arrival more than 10 s later than the main energy arrival, and our wavelet analysis shows that this later phase is characterized by an arrival time of 38 s and a frequency range from 0.1 to 1 Hz where the amplitude of the later phase is even larger than the main part. This example clearly demonstrates the potential of wavelet transforms to identify objectively any phase in seismograms localized in both time and frequency. From the information on its particle motion, the above phase corresponds to a heterogeneous and delayed break of one stronger portion on a fault on which the rupture was very smooth or ‘crack-like’ elsewhere.