scholarly journals High Frequency Measurement of Temperature and Composition Spots With LITGS

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Francesca De Domenico ◽  
Priyav Shah ◽  
Steven M. Lowe ◽  
Luming Fan ◽  
Paul Ewart ◽  
...  
Keyword(s):  
Frequency Measurement ◽  
Calibration Procedure ◽  
Mean Flow ◽  
Flow Properties ◽  
Time Resolved ◽  
Unsteady Temperature ◽  
Laminar Jet ◽  
The Mean ◽  
Thermal Grating ◽  
Grating Spectroscopy

Temperature and composition spots in a turbulent flow are detected and time-resolved using laser-induced thermal grating spectroscopy (LITGS). A 355 nm wavelength particle image velocimetry laser is operated at 0.5–1 kHz to generate the thermal grating using biacetyl as an absorber in trace amounts. In an open laminar jet, a feasibility study shows that small (≃ 3%) fluctuations in the mean flow properties are well captured with LITGS. However, corrections of the mean flow properties by the presence of the trace biacetyl are necessary to properly capture the fluctuations. The actual density and temperature variation in the flow are determined using a calibration procedure validated using a laminar jet flow. Finally, traveling entropy and composition spots are directly measured at different locations along a quartz tube, obtaining good agreement with expected values. This study demonstrates that LITGS can be used as a technique to obtain instantaneous, unsteady temperature and density variations in a combustion chamber, requiring only limited optical access.

scholarly journals High Frequency Measurement of Temperature and Composition Spots With LITGS

2018 ◽  
Author(s):  
Francesca De Domenico ◽  
Priyav Shah ◽  
Benjamin A. O. Williams ◽  
Paul Ewart ◽  
Steven M. Lowe ◽  
...  
Keyword(s):  
Frequency Measurement ◽  
Calibration Procedure ◽  
Mean Flow ◽  
Flow Properties ◽  
Time Resolved ◽  
Unsteady Temperature ◽  
Laminar Jet ◽  
The Mean ◽  
Thermal Grating ◽  
Grating Spectroscopy

Temperature and composition spots in a turbulent flow are detected and time-resolved using Laser Induced Thermal Grating Spectroscopy (LITGS). A 355 nm wavelength PIV laser is operated at 0.5–1 kHz to generate the thermal grating using biacetyl as an absorber in trace amounts. In a open laminar jet, a feasibility study shows that small (≃ 3%) fluctuations in the mean flow properties are well captured with LITGS. However, corrections of the mean flow properties by the presence of the trace biacetyl are necessary to properly capture the fluctuations. The actual density and temperature variation in the flow are determined using a calibration procedure validated using a laminar jet flow. Finally, travelling entropy and composition spots are directly measured at different locations along a quartz tube, obtaining good agreement with expected values. This study demonstrates that LITGS can be used as a technique to obtain instantaneous, unsteady temperature and density variations in a combustion chamber, requiring only limited optical access.

Influences of Turbulence Boundary Conditions on RANS and URANS Simulations for an Inter-Turbine Duct

2020 ◽  
Author(s):  
Alessio Firrito ◽  
Yannick Bousquet ◽  
Nicolas Binder ◽  
Ludovic Pintat
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Mean Flow ◽  
Time Resolved ◽  
Flow Solution ◽  
Low Pressure Turbine ◽  
Outlet Flow ◽  
Architecture Evolution ◽  
The Mean ◽  
Turbulence Length

Abstract In recent years, lot of turbine research is focused on the study and optimization of inter-turbine ducts, an aero-engine component for which the design is becoming more challenging due to the turbofan architecture evolution. Starting from the early design phase, the knowledge of the component performance and outlet flow pattern is crucial in the design of the low pressure turbine. To improve prediction, multi-row unsteady simulations are deployed. Unfortunately, some questions arise in the use of these simulations, among others the knowledge of the turbulent boundary conditions and the contribution of the unsteady simulations to the flow solution. In this paper steady and time resolved RANS simulations of a turning inter-turbine duct are investigated. Particularly, two questions are addressed. The first one is the influence of the turbulent quantities boundary conditions in the case of a k–ω Wilcox turbulence model in the flow field solution. The second one is the contribution of the unsteadiness to the mean flow prediction. It will be shown that the mean flow depends on inlet turbulence only if the turbulence length scale is relatively high; otherwise the flow field is almost turbulence-invariant. For the unsteady simulations, unsteadiness modifies the mean flow solution only with low inlet turbulence.

Nozzle Admittance and Damping Analysis Using the LEE Method

2017 ◽  
Vol 34 (1) ◽  
Author(s):  
Wang Mu-xin ◽  
Liu Pei-jin ◽  
Yang Wen-jing ◽  
Wei Xiang-geng
Keyword(s):  
Theoretical Analysis ◽  
Acoustic Energy ◽  
Mean Flow ◽  
Flow Properties ◽  
Linearized Euler Equations ◽  
Oscillation Modes ◽  
Nozzle Size ◽  
Half Angle ◽  
The Mean

AbstractThe nozzle admittance is very important in the theoretical analysis of nozzle damping in combustion instability. The linearized Euler equations (LEE) are used to determine the nozzle admittance with consideration of the mean flow properties. The acoustic energy flux through the nozzle is calculated to evaluate the nozzle damping upon longitudinal oscillation modes. Then the parametric study, involving the nozzle convergent geometry, convergent half angle and nozzle size, is carried out. It is shown that the imaginary part of the nozzle admittance plays a non-negligible role in the determination of the nozzle damping. Under the conditions considered in this work (

An Experimental Study of the Mean Flow and Turbulence Structure Of Cross-Flow Over Tube Bundles

1996 ◽  
Vol 210 (4) ◽  
pp. 317-331 ◽  
Author(s):  
S Balabani ◽  
M Yianneskis
Keyword(s):  
Pressure Drop ◽  
Laser Doppler Anemometry ◽  
Cross Flow ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Time Resolved ◽  
Numerical Predictions ◽  
Dissipation Rates ◽  
Tube Bundles ◽  
The Mean

The velocity characteristics of cross-flow over tube bundles were investigated in a water tunnel. Three tube arrays with a transverse pitch ratio of 3.6 were studied: an in-line and two staggered arrays with longitudinal pitch ratios of 2.1, 1.6 and 2.1 respectively. The mean velocities, turbulence levels, spectra, time and length scales and dissipation rates were determined from ensemble-averaged and time-resolved laser Doppler anemometry (LDA) measurements. The pressure drop across the bundles was also measured. The staggered arrays were found to generate higher levels of turbulence and a higher pressure drop. Turbulence kinetic energy reaches a maximum downstream of the second row in staggered arrays. The wake regions in both geometries are anisotropic with transverse r.m.s. velocities being higher than axial ones. Increasing the longitudinal spacing in the staggered configuration results in lower r.m.s. levels in the wakes and alteration of the recirculation characteristics. A discrete periodicity with a Strouhal number of 0.26 was identified in the 3.6 times 1.6 staggered array which is associated with vortex shedding. Turbulence scales and dissipation rates were estimated and compared with numerical predictions.

scholarly journals Comparative Evaluation of the Rheological Properties, upon Addition of Water, of Three Commercially Available Zinc Oxide Eugenol Impression Materials

2021 ◽  
Vol 10 (23) ◽  
pp. 1788-1793
Author(s):  
Savitha Dandekeri ◽  
Rochelle D’Souza ◽  
Uma Mayoor Prabhu ◽  
Sanath Kumar Shetty ◽  
Karkala Sayed Suhaim ◽  
...  
Keyword(s):  
Zinc Oxide ◽  
Maximum Flow ◽  
Flow Property ◽  
Mean Flow ◽  
Flow Properties ◽  
Zinc Oxide Eugenol ◽  
Impression Materials ◽  
The Mean ◽  
Post Hoc ◽  
Available Zinc

BACKGROUND Zinc oxide eugenol (ZOE) impression paste is commonly used for secondary impression. Water acts as an accelerator to zinc oxide eugenol paste. Study was carried out to determine its flow property and the effect of addition of water on flow properties for different commercially available zinc oxide eugenol impression pastes. We wanted to compare and evaluate the flow properties of ZOE impression paste without water and after addition of water as an accelerator for three different commercially available zinc oxide eugenol impression pastes. METHODS Three commercially available zinc oxide eugenol impression pastes used were - DPI (Dental Product of India), Neogenate (Septodont), IMAGE (Prime Dental Pro.Ltd). A total of 15 discs were made without accelerator and with addition of 1, 2 and 3 drops of water for the three brands of the zinc oxide eugenol paste. Then the flow of each was tested. Data of flow was analysed using one way- ANOVA and post hoc test. RESULTS It was found that the mean flow of zinc oxide eugenol impression paste without the use of accelerator for DPI, Septodont, Image was 4.72 ± 0.56, 4.20 ± 0.75, and 3.50 ± 0.57 respectively. The mean flow of zinc oxide eugenol impression paste with the use of one drop of accelerator for DPI, Septodont, Image was 4.98 ± 0.3493, 4.54 ± 0.6025, and 3.940 ± 0.4722 respectively. With the use of two and three drops of accelerator for DPI was 4.18 ± 0.7259 and 2.68 ± 0.3701, for Septodont was 3.880 ± 0.6907 and 2.32 ± 0.2775 and for Image flow was 3.20 ± 0.5745 and 1.80 ± 0.4000. CONCLUSIONS DPI had the maximum flow as compared to other brands of zinc oxide eugenol impression paste. KEY WORDS Zinc Oxide Eugenol, Impression Material, Flow, and Accelerator

Jet-noise control by fluidic injection from a rotating plug: linear and nonlinear sound-source mechanisms

2016 ◽  
Vol 788 ◽  
pp. 358-380 ◽  
Author(s):  
Maxime Kœnig ◽  
Kenzo Sasaki ◽  
André V. G. Cavalieri ◽  
Peter Jordan ◽  
Yves Gervais
Keyword(s):  
Coherent Structures ◽  
Stereoscopic Particle Image Velocimetry ◽  
Linear Stability Theory ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Wave Interactions ◽  
Time Resolved ◽  
Source Mechanisms ◽  
The Mean ◽  
Flow Deformation

We present a study of the turbulent and acoustic fields of subsonic jets, controlled by means of a novel actuator that introduces perturbations via steady-fluidic actuation from a rotating centrebody. The actuation can produce louder or quieter jets, and these are analysed using time-resolved stereoscopic particle image velocimetry and a hot-wire anemometer. We place the analysis in the framework of wavepackets and linear stability theory, whence we show, using solutions of the linear parabolised stability equations, that the quieter flows can be understood to result from a mean-flow deformation that modifies wavepacket dynamics, and in particular their phase velocities, which are significantly reduced. The mean-flow deformation is shown, by a triple decomposition, to be due to the generation of Reynolds stresses associated with incoherent turbulence (rather than coherent structures) which arises when the actuation energises the flow with a frequency–azimuthal wavenumber (${\it\omega}$–$m$) combination to which the mean flow is stable. When the actuation excites the flow with an ${\it\omega}$–$m$ combination to which the mean flow is unstable, the response is dominated by coherent structures, whose rapid growth takes them beyond the linear limit, where they undergo quadratic wave interactions and lead, consequently, to a louder flow.

scholarly journals Dynamics of Midlatitude Tropopause Height in an Idealized Model

2011 ◽  
Vol 68 (4) ◽  
pp. 823-838 ◽  
Author(s):  
Pablo Zurita-Gotor ◽  
Geoffrey K. Vallis
Keyword(s):  
Baroclinic Instability ◽  
Equation Model ◽  
Tropopause Height ◽  
Mean Flow ◽  
Flow Properties ◽  
Primitive Equation ◽  
Conservation Of Energy ◽  
Primitive Equation Model ◽  
Eddy Transport ◽  
The Mean

Abstract This paper investigates the factors that determine the equilibrium state, and in particular the height and structure of the tropopause, in an idealized primitive equation model forced by Newtonian cooling in which the eddies can determine their own depth. Previous work has suggested that the midlatitude tropopause height may be understood as the intersection between a radiative and a dynamical constraint. The dynamical constraint relates to the lateral transfer of energy, which in midlatitudes is largely effected by baroclinic eddies, and its representation in terms of mean-flow properties. Various theories have been proposed and investigated for the representation of the eddy transport in terms of the mean flow, including a number of diffusive closures and the notion that the flow evolves to a state marginally supercritical to baroclinic instability. The radiative constraint expresses conservation of energy and so must be satisfied, although it need not necessarily be useful in providing a tight constraint on tropopause height. This paper explores whether and how the marginal criticality and radiative constraints work together to produce an equilibrated flow and a tropopause that is internal to the fluid. The paper investigates whether these two constraints are consistent with simulated variations in the tropopause height and in the mean state when the external parameters of an idealized primitive equation model are changed. It is found that when the vertical redistribution of heat is important, the radiative constraint tightly constrains the tropopause height and prevents an adjustment to marginal criticality. In contrast, when the stratification adjustment is small, the radiative constraint is only loosely satisfied and there is a tendency for the flow to adjust to marginal criticality. In those cases an alternative dynamical constraint would be needed in order to close the problem and determine the eddy transport and tropopause height in terms of forcing and mean flow.

Simple explicit model of liquid mean flow in region above axial impeller

1985 ◽  
Vol 50 (11) ◽  
pp. 2396-2410
Author(s):  
Miloslav Hošťálek ◽  
Ivan Fořt
Keyword(s):  
Vortex Flow ◽  
Flow Model ◽  
Quantitative Agreement ◽  
Mean Flow ◽  
Flat Bottom ◽  
Proposed Model ◽  
Minimum Number ◽  
The Mean ◽  
Model Equations ◽  
Radial Circulation

The study describes a method of modelling axial-radial circulation in a tank with an axial impeller and radial baffles. The proposed model is based on the analytical solution of the equation for vortex transport in the mean flow of turbulent liquid. The obtained vortex flow model is tested by the results of experiments carried out in a tank of diameter 1 m and with the bottom in the shape of truncated cone as well as by the data published for the vessel of diameter 0.29 m with flat bottom. Though the model equations are expressed in a simple form, good qualitative and even quantitative agreement of the model with reality is stated. Apart from its simplicity, the model has other advantages: minimum number of experimental data necessary for the completion of boundary conditions and integral nature of these data.

Sign in / Sign up

Export Citation Format

Share Document