Characteristics of Turbulence in a Turbofan Stage

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Jeremy Maunus ◽  
Sheryl Grace ◽  
Douglas Sondak ◽  
Victor Yakhot
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dissipation Rate ◽  
Turbulence Models ◽  
Energy Dissipation Rate ◽  
Scale Model ◽  
Length Scale ◽  
Experimental Measurements ◽  
Hot Wire ◽  
Turbofan Engine

Two-equation turbulence models are commonly used in the simulation of turbomachinery flow fields, but there are limited experimental data available to validate the resulting turbulence quantities. Experimental measurements are available from NASA’s Source Diagnostic Test (SDT), a 1/5th scale model representation of the bypass stage of a turbofan engine. Detailed unsteady hot-wire anemometer data were taken at two axial locations between the rotor and fan exit guide vanes (FEGVs). Here, an accurate and consistent procedure is used to obtain the turbulent kinetic energy, dissipation rate, and integral length scale from structure functions calculated using the SDT data. These results are compared to the solutions provided by four proprietary CFD codes that employ two-equation turbulence models. The simulations are shown to predict the turbulent kinetic energy and length scale reasonably well as well as the trend in mean dissipation. The actual mean dissipation rates differ by nearly two orders of magnitude due to a difference in interpretation between the classical definition and what is used in CFD.

Investigation of Calculated Turbulence Parameters for Use in Hybrid Broadband Fan Noise Calculations

2011 ◽  
Author(s):  
Jeremy Maunus ◽  
Sheryl M. Grace ◽  
Douglas L. Sondak ◽  
Victor Yakhot
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dissipation Rate ◽  
Broadband Noise ◽  
Integral Length Scale ◽  
Length Scale ◽  
Noise Prediction ◽  
Cfd Simulations ◽  
Turbofan Engine ◽  
Exhaust Noise

The ability to predict the broadband noise due to fluid-structure interaction in the fan-stage of a turbofan engine could enhance engine design. Currently, fully computational hybrid schemes for coupling RANS flow simulations and linearized Euler acoustic simulations offer a potential broadband noise prediction methodology. The success of the hybrid method depends partly on the ability of RANS to accurately predict the turbulent kinetic energy and the integral length scale. The impact of the accuracy of a RANS simulation on the broadband noise prediction is explored. NASAs Source Diagnostic Test (SDT), a 1/5th scale model representation of the bypass stage of a turbofan engine provides the basis for the computations and validations. The RSI (rotor-stator interaction) code is utilized to compute the fan exit guide vane response and exhaust noise due to the interaction with inflow turbulence. The experimental data for the baseline vane SDT case at the approach condition are analyzed using structure functions to obtain the turbulent kinetic energy, dissipation rate, and integral length scale. These results are compared to the solutions provided by four proprietary CFD codes that employ two-equation turbulence models. The CFD simulations are shown to predict the turbulent kinetic energy well, over-predict mean dissipation rate, and capture the integral length scale moderately well. The broadband exhaust noise computed with RSI based on input derived from the various CFD simulations differ and it is shown that the differences are most strongly dependent upon the variation in the estimation of the integral length scale.

scholarly journals Comment on “Using an ADCP to Estimate Turbulent Kinetic Energy Dissipation Rate in Sheltered Coastal Waters”

2017 ◽  
Vol 34 (6) ◽  
pp. 1387-1390 ◽  
Author(s):  
Ann E. Gargett
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Vertical Velocity ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Vertical Shear ◽  
Length Scale ◽  
Ocean Turbulence ◽  
Large Eddy

AbstractGreene et al. revisit the suggestion that the turbulent kinetic energy dissipation rate could be estimated through a “large-eddy estimate,” employing acoustic measurements of velocity fields associated with the largest energy-containing scales of ocean turbulence. While the large-eddy estimate as originally proposed used vertical velocity and a vertical eddy length scale, Greene et al. chose instead to substitute a horizontal length scale for the latter. This comment argues that combining a horizontal scale for length with a vertical velocity scale produces a large-eddy estimate of the dissipation rate that is accurate only if the energy-containing eddies are isotropic, and that this condition is highly unlikely in naturally occurring ocean turbulence, subject as it is to influences of stratification, vertical shear, and/or the presence of horizontal boundaries. The problem is documented using data from a large-eddy simulation of Langmuir supercells.

Evaluation of Turbulent Kinetic Energy Dissipation Rate in a Free Jet Flow from PIV Measurements

2012 ◽  
Vol 7 (1) ◽  
pp. 53-69
Author(s):  
Vladimir Dulin ◽  
Yuriy Kozorezov ◽  
Dmitriy Markovich
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Turbulent Velocity ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Piv Measurements ◽  
Free Jet

The present paper reports PIV (Particle Image Velocimetry) measurements of turbulent velocity fluctuations statistics in development region of an axisymmetric free jet (Re = 28 000). To minimize measurement uncertainty, adaptive calibration, image processing and data post-processing algorithms were utilized. On the basis of theoretical analysis and direct measurements, the paper discusses effect of PIV spatial resolution on measured statistical characteristics of turbulent fluctuations. Underestimation of the second-order moments of velocity derivatives and of the turbulent kinetic energy dissipation rate due to a finite size of PIV interrogation area and finite thickness of laser sheet was analyzed from model spectra of turbulent velocity fluctuations. The results are in a good agreement with the measured experimental data. The paper also describes performance of possible ways to account for unresolved small-scale velocity fluctuations in PIV measurements of the dissipation rate. In particular, a turbulent viscosity model can be efficiently used to account for the unresolved pulsations in a free turbulent flow

Assessment of Simple RANS Turbulence Models for Stall Delay Applications at Low Reynolds Number

2017 ◽  
Vol 863 ◽  
pp. 260-265
Author(s):  
M. Arif Mohamed ◽  
Y. Wu ◽  
Martin Skote
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Kinetic Energy ◽  
Dissipation Rate ◽  
Radial Flow ◽  
Turbulence Models ◽  
Energy Dissipation Rate ◽  
Rotating Blade ◽  
Rans Turbulence Models ◽  
Delay Phenomenon

This paper assesses the performance of three two-equation turbulence models viz. the SST k-ω, the RNG and realizable k-εfor the simulations of a rotating blade in a wind tunnel experiment where k, ε and ω are turbulent kinetic energy, dissipation rate and specific dissipation respectively. The experiments showed the stall-delay phenomenon at the inboard of the rotating blade at a Reynolds number of 4800. This trend of suction peaks was captured by all three turbulence models albeit not matching the experimental coefficient of pressure accurately. All three models also showed radial flow at the inboard which is consistent with the experiments while the SST predicted the least k at low wall values.

scholarly journals Using an ADCP to Estimate Turbulent Kinetic Energy Dissipation Rate in Sheltered Coastal Waters

2015 ◽  
Vol 32 (2) ◽  
pp. 318-333 ◽  
Author(s):  
A. D. Greene ◽  
P. J. Hendricks ◽  
M. C. Gregg
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Cell Size ◽  
Dissipation Rate ◽  
Puget Sound ◽  
Acoustic Doppler Current Profiler ◽  
Energy Dissipation Rate ◽  
Integral Scale ◽  
Thorpe Scale

AbstractTurbulent microstructure and acoustic Doppler current profiler (ADCP) data were collected near Tacoma Narrows in Puget Sound, Washington. Over 100 coincident microstructure profiles have been compared to ADCP estimates of turbulent kinetic energy dissipation rate (ϵ). ADCP dissipation rates were calculated using the large-eddy method with theoretically determined corrections for sensor noise on rms velocity and integral-scale calculations. This work is an extension of Ann Gargett’s approach, which used a narrowband ADCP in regions with intense turbulence and strong vertical velocities. Here, a broadband ADCP is used to measure weaker turbulence and achieve greater horizontal and vertical resolution relative to the narrowband ADCP. Estimates of ϵ from the Modular Microstructure Profiler (MMP) and broadband ADCP show good quantitative agreement over nearly three decades of dissipation rate, 3 × 10−8–10−5 m2 s−3. This technique is most readily applied when the turbulent velocity is greater than the ADCP velocity uncertainty (σ) and the ADCP cell size is within a factor of 2 of the Thorpe scale. The 600-kHz broadband ADCP used in this experiment yielded a noise floor of 3 mm s−1 for 3-m vertical bins and 2-m along-track average (≈four pings), which resulted in turbulence levels measureable with the ADCP as weak as 3 × 10−8 m2 s−3. The value and trade-off of changing the ADCP cell size, which reduces noise but also changes the ratio of the Thorpe scale to the cell size, are discussed as well.

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