Planar Velocity Measurements at 100 kHz in Gas Turbine Combustors With a Continuous Laser Source

This work aims at presenting a novel approach to measure planar velocity in gas turbine combustors at very high sampling frequencies. For this purpose, a continuous wave laser is used in order to illuminate particles that are seeded into the flow. The Mie scattering images are acquired with a high-speed camera at 100 kHz with a constant time between each frame. The velocity fields are then obtained by applying classical PIV algorithms on successive particle scattering images. While this approach has been recently used in other research fields, such as aerodynamics or hydrodynamics, it is relatively new in combustion studies, where pulsed laser systems with higher power levels are usually preferred. The proposed technique is an economical and ergonomic solution to determine velocity fields at very high sampling frequencies. It is highly portable and safe and convenient to use and align. The main drawback is the long image exposure duration due to the low laser energy. This leads to a smearing effect of the captured particles and acts as a low-pass filter. It has the consequence that the PIV algorithm does not determine the displacement of “dots”, but of “traces”. The measurement technique is tested experimentally on a model gas turbine combustor at a laboratory scale. The test is performed in three steps: (1) The instantaneous velocity fields are analysed in order to verify, whether the flame topology is represented correctly. (2) The mean and RMS velocity fields that are obtained with the present technique are compared with those obtained by classic low speed PIV. (3) Instantaneous synthetic Mie scattering fields are generated from a large eddy simulation (LES) on a similar combustor to test the algorithms. The planar velocity fields are calculated from these images and compared for the two techniques. Finally, possible error sources of the new technique are discussed.

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Optimal Design of PID-Based Low-Pass Filter for Gas Turbine Using Intelligent Method

IEEE Access ◽

10.1109/access.2018.2808476 ◽

2018 ◽

Vol 6 ◽

pp. 15335-15345 ◽

Cited By ~ 5

Author(s):

Mohammad Eslami ◽

Mohammad Reza Shayesteh ◽

Majid Pourahmadi

Keyword(s):

Optimal Design ◽

Gas Turbine ◽

Pass Filter ◽

Low Pass Filter ◽

Low Pass

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IMAGE OF THE SURFACE OF GAS TURBINE BLADE AS A DIAGNOSTIC SIGNAL

Acta Mechanica et Automatica ◽

10.2478/ama-2013-0035 ◽

2013 ◽

Vol 7 (4) ◽

pp. 209-214

Author(s):

Józef Błachnio ◽

Iwona Zabrocka

Keyword(s):

Gas Turbine ◽

Turbine Blades ◽

Statistical Parameter ◽

Digital Processing ◽

Pass Filter ◽

Low Pass Filter ◽

Gas Turbine Blades ◽

The Status ◽

Low Pass ◽

Non Destructive

Abstract This paper outlines a non-destructive method that is suitable for evaluation of condition demonstrated by gas turbine blades and is based on digital processing of images acquired from the blade surface in visible light. To enable high clearness of these images the particular attention is paid to the problem of how to provide optimum conditions for investigations and mitigate geometrical distortions of images acquired from maintenance operations. The paper demonstrates that there are relationships between operation lifetime of blades and discoloration of their surfaces due to overheating of the blade material. These relationships are revealed by digital analysis of images acquired for the blade surfaces and expressed as statistical parameter of the first and second order. To improve unambiguity of the analysis results a low-pass filter was applied. It was demonstrated that these relationships are suitable for evaluation how much the status of the blade material microstructure is altered

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Flame Transfer Function Measurement and Instability Frequency Prediction Using a Thermoacoustic Model

Volume 2: Combustion, Fuels and Emissions ◽

10.1115/gt2009-60026 ◽

2009 ◽

Cited By ~ 9

Author(s):

Kyu Tae Kim ◽

Hyung Ju Lee ◽

Jong Guen Lee ◽

Bryan D. Quay ◽

Domenic Santavicca

Keyword(s):

Transfer Function ◽

Gas Turbine ◽

Critical Role ◽

Flame Length ◽

Operating Conditions ◽

Gas Turbine Combustor ◽

Pass Filter ◽

Low Pass Filter ◽

Turbulent Premixed Flame ◽

Instability Frequency

The dynamic response of a turbulent premixed flame to an acoustic velocity perturbation was experimentally determined in a lean-premixed, swirl-stabilized, lab-scale gas turbine combustor. Fuel was injected far upstream of a choked inlet to eliminate equivalence ratio oscillations. A siren-type modulation device was used to provide acoustic perturbations at the forcing frequency of 100 ∼ 400 Hz. To measure global heat release rate, OH*, CH*, and CO2* chemiluminescence emissions were used. The two-microphone method was utilized to estimate inlet velocity fluctuations, and it was calibrated by direct measurements using a hot wire anemometer under cold-flow conditions. Gain of the flame transfer function (FTF) shows a low pass filter behavior, and it is well-fitted by a second-order model. Phase difference increases quasi-linearly with the forcing frequency. Using the n-τ formulation, gain and phase of FTF were incorporated into an analytic thermoacoustic model in order to predict instability frequencies and corresponding modal structures. Self-excited flame response measurements were also performed to verify eigenfrequencies predicted by the thermoacoustic model. Instability frequency predicted by the thermoacoustic model is supported by experimental results. Two instability frequency bands were measured in the investigated gas turbine combustor at all operating conditions: f ∼ 220 Hz and f ∼ 350 Hz. Results show that the self-excited instability frequency of f ∼ 220 Hz results from the fact that the flames amplify flow perturbations with f = 150 ∼ 250 Hz. This frequency range was observed in the flame transfer function measurements. The other instability frequency of f ∼ 350 Hz occurs because the whole combustion system has an eigenfrequency corresponding to the 1/4-wave eigenmode of the mixing section. This was analytically and experimentally demonstrated. Results also show that the flame length, LCH*max, plays a critical role in determining self-induced instability frequency.

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Aliasing Effects on Nodal Acceleration Output From Nonlinear Finite Element Simulations

10.1115/imece2000-2470 ◽

2000 ◽

Author(s):

Mark O. Neal ◽

Chin-Hsu Lin ◽

J. T. Wang

Keyword(s):

Finite Element ◽

High Frequency ◽

Nonlinear Finite Element ◽

Pass Filter ◽

Low Pass Filter ◽

Low Pass ◽

Frequency Components ◽

Averaging Filter ◽

Very High ◽

Acceleration Output

Abstract Nodal acceleration output from nonlinear finite element crash simulations often contains high frequency components. If this output is not sampled frequently enough the high frequency components will be aliased and the resulting acceleration output will be inaccurate. It is recommended in this paper that a low-pass filter be installed in the crashworthiness finite element codes which would remove the high frequency components of the nodal accelerations before they are sampled for output. This would completely eliminate aliasing error in acceleration output. Prior to this installation, there are several options for reducing the effects of aliasing on acceleration output. One option is to request very high sampling rates for acceleration output; however this will result in very large output files. Another option is to calculate the accelerations by differentiating the output velocities. This option, which effectively is an averaging filter acting on the accelerations, is available in the finite element code DYNA3D. The properties of this filter are examined in this paper and it is shown that this filter is very effective in reducing the effects of aliasing on acceleration output, although it should not be expected to completely eliminate potential aliasing problems. Finally, guidelines are presented for selecting nodes and sampling rates based on local natural frequencies that will reduce the effect of aliasing of the acceleration output.

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Development of an Optical set-up for 3D PIV with a Large Volume

14th International Symposium on Particle Image Velocimetry ◽

10.18409/ispiv.v1i1.138 ◽

2021 ◽

Vol 1 (1) ◽

Author(s):

Haim Abitan ◽

Clara Marika Velta ◽

Yisheng Zhang ◽

Simon Lautrup Ribergård ◽

Jakob Skov Nielsen

Keyword(s):

Laser Beam ◽

Power Density ◽

Pulse Energy ◽

Laser Scanning ◽

Particle Diameter ◽

Mie Scattering ◽

Velocity Fields ◽

Laser Source ◽

Soap Bubbles ◽

Practical Applications

Measurements of 3D volumetric velocity fields are of great theoretical interest with numerous practical applications. These measurements are essential for studying volumetric flows that do not exhibit inherent flow symmetry, such as turbulence or vortex breakdown. In the past decade, several technological innovations facilitated the emergence of 3D-PTV techniques for measuring velocity fields at kHz rate with volumes of interest up to 104 cm3 that contain 300 µm helium-filled soap bubbles. However, when a commercial laser beam with millijoule pulse-energy is expanded and shaped to fill volumes above 102 cm3 for 3D-PTV experiments with 15 µm air filled soap bubbles, one finds that the power density of the laser source is insufficient to generate a signal image. This is because the power density of the laser beam falls inversely with respect to its cross-section area and due to the quadratic dependence of Mie-scattering on the particle diameter. Here, we report of the analysis and development of two optical techniques for extending the volume of measurement in volumetric PTV. In particular, when a volume about 103 cm3 is seeded with 15 µm air-filled soap bubbles and a laser with a pulse energy of few single mJ illuminates it. The first technique uses multi reflections between two opposing parallel mirrors. The second technique is a development of laser scanning PIV for volumetric scanning: The potential to increase the scanned volume is examined by experimenting with an acousto-optic modulator for fast scanning. Furthermore, by employing an off-axis parabolic mirror, we obtain parallel beam scanning, which increases the efficiency and quality of the scanning.

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