Numerical study of the effect of surface wave on turbulence underneath. Part 2. Eulerian and Lagrangian properties of turbulence kinetic energy

2014 ◽  
Vol 744 ◽  
pp. 250-272 ◽  
Author(s):  
Xin Guo ◽  
Lian Shen
Keyword(s):  
Surface Wave ◽  
Kinetic Energy ◽  
Numerical Study ◽  
Turbulence Kinetic Energy ◽  
Pressure Effects ◽  
Wave Turbulence ◽  
Turbulence Energy ◽  
Net Energy ◽  
Production Term ◽  
Near Surface

AbstractThe effect of the rapid distortion of a surface wave on the kinetic energy of turbulence underneath is studied based on the simulation data of Part 1 (Guo & Shen,J. Fluid Mech., vol. 733, 2013, pp. 558–587). In the Eulerian frame, Reynolds normal stresses, which contribute to turbulence kinetic energy, are found to vary with the wave phase. An analysis of their budgets shows that their variation is dominated not only by the normal production term representing the wave straining effect on wave–turbulence energy exchange, but also by pressure effects including the pressure–strain correlation and pressure transport terms. In the Lagrangian frame, the net energy transfer from the wave to turbulence is analysed. It is found to be mainly contributed by the mean Lagrangian effect and the correlation between the Lagrangian fluctuations of the wave and turbulence; the former plays a major role in the overall wave energy dissipation, while the latter is associated with the viscous effect of the wave surface and is appreciable in the near-surface region. Models for various terms in wave–turbulence energy flux are discussed. The decay time scale of swells in oceans estimated from our simulations compares well with the results in the literature.

Three-Dimensional Computations of Turbulent Flow in a Turbine-Rotor Passage

1997 ◽  
Author(s):  
B. Song ◽  
R. S. Amano ◽  
S. Sitarama ◽  
B. Lin
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Isotropic Turbulence ◽  
Numerical Study ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Turbulence Kinetic Energy ◽  
Wall Region ◽  
Staggered Grids

Numerical study on a three-dimensional turbulent flow in a turbine-rotor passage is presented in this paper. The standard k-ε model was used for the first phase of the turbulence computations. The computations were further extended by employing the full Reynolds-stress closure model (RSM). The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The governing equations in a generalized curvilinear coordinate system are discretized by using the SIMPLEC method with non-staggered grids. The oscillations in pressure and velocity due to non-staggered grids are eliminated by using a special interpolation method. The predicted midspan pressure coefficients using the k-ε model and the RSM are compared with the experimental data. It was shown that the present results obtained by using either model are fairly reasonable. Computations were then extended to cover the entire blade-to-blade flow passage, and the three-dimensional effects on pressure and turbulence kinetic energy were evaluated. It was observed that the two turbulence models predict different results for the turbulence kinetic energy. This variation was identified as being related to some non-isotropic turbulence occurring near the blade surface due to the severe acceleration of the flow. It was thus proven that the models based on the RSM give more realistic predictions for highly turbulent cascade flow computations than a Boussinesq viscosity model.

scholarly journals Turbulence Kinetic Energy budget during the afternoon transition – Part 2: A simple TKE model

2015 ◽  
Vol 15 (21) ◽  
pp. 29807-29869 ◽  
Author(s):  
E. Nilsson ◽  
M. Lothon ◽  
F. Lohou ◽  
E. Pardyjak ◽  
O. Hartogensis ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Kinetic Energy ◽  
Dissipation Rate ◽  
Turbulence Kinetic Energy ◽  
Time Varying ◽  
Near Surface ◽  
Surface Buoyancy ◽  
Surface Buoyancy Flux ◽  
Shear Production

Abstract. A simple model for turbulence kinetic energy (TKE) and the TKE budget is presented for sheared convective atmospheric conditions based on observations from the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. It is based on an idealized mixed-layer approximation and a simplified near-surface TKE budget. In this model, the TKE is dependent on four budget terms (turbulent dissipation rate, buoyancy production, shear production and vertical transport of TKE) and only requires measurements of three input available (near-surface buoyancy flux, boundary layer depth and wind speed at one height in the surface layer). This simple model is shown to reproduce some of the observed variations between the different studied days in terms of near-surface TKE and its decay during the afternoon transition reasonably well. It is subsequently used to systematically study the effects of buoyancy and shear on TKE evolution using idealized constant and time-varying winds during the afternoon transition. From this, we conclude that many different TKE decay rates are possible under time-varying winds and that generalizing the decay with simple scaling laws for near-surface TKE of the form tα may be questionable. The model's errors result from the exclusion of processes such as elevated shear production and horizontal advection. The model also produces an overly rapid decay of shear production with height. However, the most influential budget terms governing near-surface TKE in the observed sheared convective boundary layers are included, while only second order factors are neglected. Comparison between modeled and averaged observed estimates of dissipation rate illustrate that the overall behavior of the model is often quite reasonable. Therefore, we use the model to discuss the low turbulence conditions that form first in the upper parts of the boundary layer during the afternoon transition and are only apparent later near the surface. This occurs as a consequence of the continuous decrease of near-surface buoyancy flux during the afternoon transition. This region of weak afternoon turbulence is hypothesized to be a "pre-residual layer", which is important in determining the onset conditions for the weak sporadic turbulence that occur in the residual layer once near-surface stratification has become stable.

Liquid Turbulence Kinetic Energy Budget of Co-Current Bubbly Flow in a Large Diameter Vertical Pipe

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
M. E. Shawkat ◽  
C. Y. Ching
Keyword(s):  
Kinetic Energy ◽  
Viscous Dissipation ◽  
Energy Budget ◽  
Bubbly Flow ◽  
Turbulence Kinetic Energy ◽  
Wave Number ◽  
Turbulence Energy ◽  
Number Range ◽  
Turbulence Kinetic Energy Budget ◽  
Turbulence Production

The liquid turbulence kinetic energy transfer between the liquid and gas phases was investigated for upward air-water bubbly flow in a 200 mm diameter pipe. The liquid and gas axial momentum equations were analyzed to estimate the interfacial drag from experimental measurements, and hence the liquid turbulence production due to the relative velocity of the bubbles. The liquid turbulence production due to the bubbles was significantly higher than that due to the liquid shear. The liquid turbulence kinetic energy budget indicates that the turbulence production due to the bubbles is approximately balanced by the viscous dissipation, estimated assuming an isotropic turbulence structure, with negligible dissipation due to the bubbles. The liquid turbulence kinetic energy spectra showed an addition of energy at length scales in the range corresponding to the bubble diameter. A model for the turbulence energy production spectra due to the bubbles is proposed and used to investigate the spectral turbulence energy budget. The model indicates that when there is a liquid turbulence augmentation, most of the production occurs in the low wave number range with only a small overlap with the viscous dissipation region. In the case of a turbulence suppression, most of the bubble production occurs in the same wave number range as the viscous dissipation.

scholarly journals Role of Advection of Parameterized Turbulence Kinetic Energy in Idealized Tropical Cyclone Simulations

2021 ◽  
Author(s):  
Xiaomin Chen ◽  
George H. Bryan
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
Prediction Models ◽  
Weather Prediction ◽  
Turbulence Kinetic Energy ◽  
Predictive Equations ◽  
Near Surface ◽  
Vertical Advection ◽  
Pbl Scheme

AbstractHorizontal homogeneity is typically assumed in the design of planetary boundary layer (PBL) parameterizations in weather prediction models. Consistent with this assumption, PBL schemes with predictive equations for subgrid turbulence kinetic energy (TKE) typically neglect advection of TKE. However, tropical cyclone (TC) boundary layers are inhomogeneous, particularly in the eyewall. To gain further insight, this study examines the effect of advection of TKE using the Mellor-Yamada-Nakanishi-Niino (MYNN) PBL scheme in idealized TC simulations. The analysis focuses on two simulations, one that includes TKE advection (CTL) and one that does not (NoADV). Results show that relatively large TKE in the eyewall above 2 km is predominantly attributable to vertical advection of TKE in CTL. Interestingly, buoyancy production of TKE is negative in this region in both simulations; thus, buoyancy effects cannot explain observed columns of TKE in TC eyewalls. Both horizontal and vertical advection of TKE tends to reduce TKE and vertical viscosity (Km) in the near-surface inflow layer, particularly in the eyewall of TCs. Results also show that the simulated TC in CTL has slightly stronger maximum winds, slightly smaller radius of maximum wind (RMW), and ~5% smaller radius of gale-force wind than in NoADV. These differences are consistent with absolute angular momentum being advected to smaller radii in CTL. Sensitivity simulations further reveal that the differences between CTL and NoADV are more attributable to vertical advection (rather than horizontal advection) of TKE. Recommendations for improvements of PBL schemes that use predictive equations for TKE are also discussed.

scholarly journals Effect of Cooling Air on Swirl Combustor

1970 ◽  
Vol 37 ◽  
pp. 1-9
Author(s):  
Showkat Jahan Chowdhury ◽  
Md. Shiblee Noman
Keyword(s):  
Kinetic Energy ◽  
Swirling Flow ◽  
Numerical Study ◽  
Control Volume ◽  
Turbulence Kinetic Energy ◽  
Mixing Rate ◽  
Swirl Combustor ◽  
Practical Applications ◽  
Air Jet ◽  
Cooling Air

This paper presents the numerical study of the turbulent swirling flow in a combustor and the effect of cooling air, which has practical applications in industrial furnaces and jet engines. Cooling air is used to protect the combustor wall from burnout, while allowing the combustion to occur at higher temperature. The governing differential equations using k - ε turbulence model closure are solved by a control-volume based iterative finite difference technique. Computations are done for constant vane angle type swirl generation at inlet. Different swirl numbers up to 1.5 are considered. To study the effect of cooling air on the combustor performance, calculations are repeated for two different velocities of the cooling air jet. The predicted distribution of the mean axial and tangential velocities, turbulence kinetic energy and streamline plots are discussed in the article. With the increase of swirl strength, secondary on-axis recirculation due to swirl is observed. The swirl produces larger turbulence kinetic energy and enhances mixing rate, thus require shorter combustor length. The interaction between the non-swirling cooling air and swirling core flow also increases the generation of turbulence kinetic energy and mixing rate. The capability of the computational model for predicting recirculating flows is tested by comparing the results with available experimental data and found to have reasonable matching.Journal of Mechanical Engineering Vol.37 June 2007 pp.1-9doi:10.3329/jme.v37i0.811

scholarly journals Turbulence kinetic energy budget during the afternoon transition – Part 1: Observed surface TKE budget and boundary layer description for 10 intensive observation period days

2016 ◽  
Vol 16 (14) ◽  
pp. 8849-8872 ◽  
Author(s):  
Erik Nilsson ◽  
Fabienne Lohou ◽  
Marie Lothon ◽  
Eric Pardyjak ◽  
Larry Mahrt ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulence Kinetic Energy ◽  
Scale Model ◽  
Near Surface ◽  
Local Parametrization ◽  
Non Local ◽  
Intensive Observation ◽  
Surface Production ◽  
Observation Period

Abstract. The decay of turbulence kinetic energy (TKE) and its budget in the afternoon period from midday until zero-buoyancy flux at the surface is studied in a two-part paper by means of measurements from the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign for 10 intensive observation period days. Here, in Part 1, near-surface measurements from a small tower are used to estimate a TKE budget. The overall boundary layer characteristics and mesoscale situation at the site are also described based upon taller tower measurements, radiosoundings and remote sensing instrumentation. Analysis of the TKE budget during the afternoon transition reveals a variety of different surface layer dynamics in terms of TKE and TKE decay. This is largely attributed to variations in the 8 m wind speed, which is responsible for different amounts of near-surface shear production on different afternoons and variations within some of the afternoon periods. The partitioning of near-surface production into local dissipation and transport in neutral and unstably stratified conditions was investigated. Although variations exist both between and within afternoons, as a rule of thumb, our results suggest that about 50 % of the near-surface production of TKE is compensated for by local dissipation near the surface, leaving about 50 % available for transport. This result indicates that it is important to also consider TKE transport as a factor influencing the near-surface TKE decay rate, which in many earlier studies has mainly been linked with the production terms of TKE by buoyancy and wind shear. We also conclude that the TKE tendency is smaller than the other budget terms, indicating a quasi-stationary evolution of TKE in the afternoon transition. Even though the TKE tendency was observed to be small, a strong correlation to mean buoyancy production of −0.69 was found for the afternoon period. For comparison with previous results, the TKE budget terms are normalized with friction velocity and measurement height and discussed in the framework of Monin–Obukhov similarity theory. Empirically fitted expressions are presented. Alternatively, we also suggest a non-local parametrization of dissipation using a TKE–length scale model which takes into account the boundary layer depth in addition to distance above the ground. The non-local formulation is shown to give a better description of dissipation compared to a local parametrization.

scholarly journals Spatiotemporal Variability of Turbulence Kinetic Energy Budgets in the Convective Boundary Layer over Both Simple and Complex Terrain

2017 ◽  
Vol 56 (12) ◽  
pp. 3285-3302 ◽  
Author(s):  
Raj K. Rai ◽  
Larry K. Berg ◽  
Mikhail Pekour ◽  
William J. Shaw ◽  
Branko Kosovic ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Complex Terrain ◽  
Wrf Model ◽  
Turbulence Kinetic Energy ◽  
Spatiotemporal Variability ◽  
Grid Spacing ◽  
Model Framework ◽  
Production Term ◽  
Budget Equation ◽  
Shear Production

AbstractThe assumption of subgrid-scale (SGS) horizontal homogeneity within a model grid cell, which forms the basis of SGS turbulence closures used by mesoscale models, becomes increasingly tenuous as grid spacing is reduced to a few kilometers or less, such as in many emerging high-resolution applications. Herein, the turbulence kinetic energy (TKE) budget equation is used to study the spatiotemporal variability in two types of terrain—complex [Columbia Basin Wind Energy Study (CBWES) site, northeastern Oregon] and flat [Scaled Wind Farm Technology (SWiFT) site, west Texas]—using the Weather Research and Forecasting (WRF) Model. In each case, six nested domains [three domains each for mesoscale and large-eddy simulation (LES)] are used to downscale the horizontal grid spacing from ~10 km to ~10 m using the WRF Model framework. The model output was used to calculate the values of the TKE budget terms in vertical and horizontal planes as well as the averages of grid cells contained in the four quadrants of the LES domain. The budget terms calculated along the planes and the mean profile of budget terms show larger spatial variability at the CBWES site than at the SWiFT site. The contribution of the horizontal derivative of the shear production term to the total shear production was found to be ≈45% and ≈15% at the CBWES and SWiFT sites, respectively, indicating that the horizontal derivatives applied in the budget equation should not be ignored in mesoscale model parameterizations, especially for cases with complex terrain with <10-km scale.

scholarly journals Measuring Turbulent Kinetic Energy Dissipation at a Wavy Sea Surface

2015 ◽  
Vol 32 (8) ◽  
pp. 1498-1514 ◽  
Author(s):  
Peter Sutherland ◽  
W. Kendall Melville
Keyword(s):  
Surface Wave ◽  
Energy Dissipation ◽  
Kinetic Energy ◽  
Wave Field ◽  
Turbulent Kinetic Energy ◽  
Velocity Fields ◽  
Sea Surface ◽  
Stereo Pair ◽  
Near Surface ◽  
Surface Wave Field

AbstractWave breaking is thought to be the dominant mechanism for energy loss by the surface wave field. Breaking results in energetic and highly turbulent velocity fields, concentrated within approximately one wave height of the surface. To make meaningful estimates of wave energy dissipation in the upper ocean, it is then necessary to make accurate measurements of turbulent kinetic energy (TKE) dissipation very near the surface. However, the surface wave field makes measurements of turbulence at the air–sea interface challenging since the energy spectrum contains energy from both waves and turbulence over the same range of wavenumbers and frequencies. Furthermore, wave orbital velocities can advect the turbulent wake of instrumentation into the sampling volume of the instrument. In this work a new technique for measuring TKE dissipation at the sea surface that overcomes these difficulties is presented. Using a stereo pair of longwave infrared cameras, it is possible to reconstruct the surface displacement and velocity fields. The vorticity of that velocity field can then be considered to be representative of the rotational turbulence and not the irrotational wave orbital velocities. The turbulent kinetic energy dissipation rate can then be calculated by comparing the vorticity spectrum to a universal spectrum. Average surface TKE dissipation calculated in this manner was found to be consistent with near-surface values from the literature, and time-dependent dissipation was found to depend on breaking.

scholarly journals Fuzzy Performance between Surface Fitting and Energy Distribution in Turbulence Runner

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Zhongwei Liang ◽  
Xiaochu Liu ◽  
Bangyan Ye ◽  
Richard Kars Brauwer
Keyword(s):  
Kinetic Energy ◽  
Energy Distribution ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Surface Fitting ◽  
Turbulence Kinetic Energy ◽  
Kinetic Energy Distribution ◽  
Turbulence Energy ◽  
Fuzzy Evaluation ◽  
Performance Results

Because the application of surface fitting algorithms exerts a considerable fuzzy influence on the mathematical features of kinetic energy distribution, their relation mechanism in different external conditional parameters must be quantitatively analyzed. Through determining the kinetic energy value of each selected representative position coordinate point by calculating kinetic energy parameters, several typical algorithms of complicated surface fitting are applied for constructing microkinetic energy distribution surface models in the objective turbulence runner with those obtained kinetic energy values. On the base of calculating the newly proposed mathematical features, we construct fuzzy evaluation data sequence and present a new three-dimensional fuzzy quantitative evaluation method; then the value change tendencies of kinetic energy distribution surface features can be clearly quantified, and the fuzzy performance mechanism discipline between the performance results of surface fitting algorithms, the spatial features of turbulence kinetic energy distribution surface, and their respective environmental parameter conditions can be quantitatively analyzed in detail, which results in the acquirement of final conclusions concerning the inherent turbulence kinetic energy distribution performance mechanism and its mathematical relation. A further turbulence energy quantitative study can be ensured.

Predictions of Turbulent Flow in a Turbine Stator/Rotor Passage

1998 ◽  
Author(s):  
R. S. Amano ◽  
B. Song ◽  
S. Sitarama ◽  
B. Lin
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Isotropic Turbulence ◽  
Numerical Study ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Turbulence Kinetic Energy ◽  
Wall Region ◽  
Staggered Grids ◽  
Turbine Stator

Numerical study on a three-dimensional turbulent flow in a turbine stator/rotor passage is presented in this paper. The standard k-ε model was used for the first phase of the turbulence computations. The computations were further extended by employing the full Reynolds-stress closure model (RSM). The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The governing equations in a generalized curvilinear coordinate system are discretized by using the SIMPLEC method with non-staggered grids. The oscillations in pressure and velocity due to non-staggered grids are eliminated by using a special interpolation method. The predicted midspan pressure coefficients using the k-ε model and the RSM are compared with the experimental data. It was shown that the present results obtained by using either model are fairly reasonable. Computations were then extended to cover the entire blade-to-blade flow passage, and the three-dimensional effects on pressure and turbulence kinetic energy were evaluated. It was observed that the two turbulence models predict different results for the turbulence kinetic energy. This variation was identified as being related to some non-isotropic turbulence occurring near the blade surface due to the severe acceleration of the flow. It was thus proven that the models based on the RSM give more realistic predictions for highly turbulent cascade flow computations than a Boussinesq viscosity model.

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