scholarly journals Performance of Turbulence Models in Simulating Wind Loads on Photovoltaics Modules

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3290 ◽  
Author(s):  
Mireille B. Tadie Fogaing ◽  
Arman Hemmati ◽  
Carlos F. Lange ◽  
Brian A. Fleck
Keyword(s):  
Energy Transport ◽  
Turbulence Models ◽  
Wind Loads ◽  
Turbulence Energy ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Velocity Gradients ◽  
Large Pressure ◽  
The Mean ◽  
Recirculation Length

The performance of five conventional turbulence models, commonly used in the wind industry, are examined in predicting the complex wake of an infinite span thin normal flat plate with large pressure gradients at Reynolds number of 1200. This body represents a large array of Photovoltaics modules, where two edges of the plate dominate the flow. This study provided a benchmark for capabilities of conventional turbulence models that are commonly used for wind forecasting in the wind energy industry. The results obtained from Reynolds Averaged Navier-Stokes (RANS) k - ε , Reynolds Normalization Group (RNG) k - ε , RANS k - ω Shear Stress Transport (SST) and Reynolds Stress Model (RSM) were compared with existing Direct Numerical Simulations (DNS). The mean flow features and unsteady wake characteristics were used as testing criteria amongst these models. All turbulence models over-predicted the mean recirculation length and under-predicted the mean drag coefficient. The major differences between numerical results in predicting the mean recirculation length, mean drag and velocity gradients, leading to deficits in turbulence kinetic energy production and diffusion, hint at major difficulties in modeling velocity gradients and thus turbulence energy transport terms, by traditional turbulence models. Unsteadiness of flow physics and nature of eddy viscosity approximations are potential reasons. This hints at the deficiencies of these models to predict complex flows with large pressure gradients, which are commonly observed in wind and solar farms. The under-prediction of wind loads on PV modules and over-estimation of the recirculation length behind them significantly affects the efficiency and operational feasibility of solar energy systems.

Differential stress modelling of turbulent flows in model reciprocating engines

1997 ◽  
Vol 211 (1) ◽  
pp. 59-77 ◽  
Author(s):  
C. J. Lea ◽  
A. P. Watkins
Keyword(s):  
Experimental Data ◽  
Turbulent Flows ◽  
Turbulence Intensity ◽  
Laser Doppler Anemometry ◽  
Turbulence Models ◽  
Apparent Difference ◽  
Mean Flow ◽  
Differential Stress ◽  
Reciprocating Engines ◽  
The Mean

A study is made here of the application of a differential stress model (DSM) of turbulence to flows in two model reciprocating engines. For the first time this study includes compressive effects. An assessment between DSM and k-ɛ results is made comparing with laser Doppler anemometry experimental data of the mean flow and turbulence intensity levels during intake and compression strokes. A well-established two-dimensional finite-volume computer code is employed. Two discretization schemes are used, namely the HYBRID scheme and the QUICK scheme. The latter is found to be essential if differentiation is to be made between the turbulence models. During the intake stroke the DSM results are, in general, similar to the k-ɛ results in comparison to the experimental data, except for the turbulence levels, which the DSM seriously underpredicts. This is in contrast to a parallel set of calculations of steady in-flow, which showed significant gains from using the DSM, particularly at the turbulence field level. The increased number of grid lines employed in those calculations contribute to this apparent difference between steady and unsteady flows, but cycle- to-cycle variations are more likely to be the primary cause, resulting in too high levels of turbulence intensity being measured. However, during the compression stroke the DSM returns vastly superior results to the k-ɛ model at both the mean flow and turbulence intensity levels. This is because the DSM generates an anisotropic shear stress field during the early stages of compression that suppresses the main vortical structure, in line with the experimental data.

Capability Assessment of Five Different RANS-Based Turbulence Models to Simulate the Various Regions of Slot Turbulent Impingement Jet Flow

2017 ◽  
Author(s):  
Mahmoud Charmiyan ◽  
Ahmed-Reza Azimian ◽  
Ebrahim Shirani ◽  
Fethi Aloui
Keyword(s):  
Experimental Data ◽  
Turbulence Models ◽  
Jet Flows ◽  
Two Dimensional ◽  
Mean Flow ◽  
Impingement Jet ◽  
Image Velocimetry ◽  
The Mean ◽  
Bottom To Top ◽  
Plate Distance

In this paper, impingement of a turbulent rectangular flow to a fixed wall is investigated. The jet flows from bottom-to-top and the output jet Reynolds is 16000. The nozzle-to-plate distance is equal to 10 (H/e = 10). Five turbulence models, including k-ε, RNG k-ε, k-ω SST, RSM and v2f model have been used for two-dimensional numerical simulation of the turbulent flow. Because of the complexities of the impingement flow, such as curved streamlines, flow separation, normal strains and sudden deceleration in different areas, different turbulence models are proposed to simulate different regions of the flow. To investigate the capability of these turbulence models in simulating different regions of the impinging jet, the mean flow velocity field and turbulent kinetic energy are extracted and compared with the experimental data of a two-dimensional particle image velocimetry (PIV). The calculated error of these five turbulence models was presented for the various flow regions, while it have not been clearly investigated earlier. Results indicate the highest conformity of the v2f model with the experimental data at the jet centerline. However, this model does not predict well the flow at the shear layer and wall-jet areas. RSM Gibson and Lander model has the highest conformity with the experimental data in these regions.

scholarly journals The Development of the Mean Flow and Turbulence Structure in an Annular S-Shaped Duct

1994 ◽  
Author(s):  
K. M. Britchford ◽  
J. F. Carrotte ◽  
S. J. Stevens ◽  
J. J. McGuirk
Keyword(s):  
Reynolds Stress ◽  
Laser Doppler Anemometry ◽  
Reynolds Shear Stress ◽  
Turbulence Models ◽  
Test Facility ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Mean Velocity ◽  
Curvature Effects ◽  
The Mean

This paper describes an investigation of the mean and fluctuating flow field within an annular S-shaped duct which is representative of that used to connect the compressor spools of aircraft gas turbine engines. Data was obtained from a fully annular test facility using a 3-component Laser Doppler Anemometry (LDA) system. The measurements indicate that development of the flow within the duct is complex and significantly influenced by the combined effects of streamwise pressure gradients and flow curvature. In addition CFD predictions of the flow, using both the k-ε and Reynolds stress transport equation turbulence models, are compared with the experimental data. Whereas curvature effects are not described properly by the k-ε model, such effects are captured more accurately by the Reynolds stress model leading to a better prediction of the Reynolds shear stress distribution. This, in turn, leads to a more accurate prediction of the mean velocity profiles, as reflected by the boundary layer shape parameters, particularly in the critical regions of the duct where flow separation is most likely to occur.

Organized structures in a reattaching separated flow field

1984 ◽  
Vol 143 ◽  
pp. 413-427 ◽  
Author(s):  
T. R. Troutt ◽  
B. Scheelke ◽  
T. R. Norman
Keyword(s):  
Vortex Dynamics ◽  
Large Scale ◽  
Mixing Layer ◽  
Separated Flow ◽  
Turbulence Energy ◽  
Hot Wire ◽  
Mean Flow ◽  
Large Scale Vortex ◽  
The Mean ◽  
Important Time

Spanwise structures in a two-dimensional reattaching separated flow were studied using multisensor hot-wire anemometry techniques. The results of these measurements strongly support the existence and importance of large-scale vortices in both the separated and reattached regions of this flow. Upstream of reattachment, vortex pairings are indicated and the spanwise structures attain correlation scales closely comparable to previously measured mixing-layer vortices. These large-scale vortices retain their organization far downstream of the reattachment region. However, pairing interactions appear to be strongly inhibited in this region. It is suggested that large-scale vortex dynamics are primarily responsible for some of the important time-averaged features of this flow. Notably, the reduction of turbulence energy in the reattachment region and the slow transition of the mean flow downstream of reattachment are attributed to effects associated with these vortices.

scholarly journals Compressible turbulent channel flows: DNS results and modelling

1995 ◽  
Vol 305 ◽  
pp. 185-218 ◽  
Author(s):  
P. G. Huang ◽  
G. N. Coleman ◽  
P. Bradshaw
Keyword(s):  
Turbulent Flows ◽  
Pressure Fluctuations ◽  
Channel Flows ◽  
Compressible Turbulence ◽  
Turbulent Shear ◽  
Turbulence Energy ◽  
Mean Flow ◽  
Reynolds Analogy ◽  
The Mean ◽  
Compressibility Effects

The present paper addresses some topical issues in modelling compressible turbulent shear flows. The work is based on direct numerical simulation (DNS) of two supersonic fully developed channel flows between very cold isothermal walls. Detailed decomposition and analysis of terms appearing in the mean momentum and energy equations are presented. The simulation results are used to provide insights into differences between conventional Reynolds and Favre averaging of the mean-flow and turbulent quantities. Study of the turbulence energy budget for the two cases shows that compressibility effects due to turbulent density and pressure fluctuations are insignificant. In particular, the dilatational dissipation and the mean product of the pressure and dilatation fluctuations are very small, contrary to the results of simulations for sheared homogeneous compressible turbulence and to recent proposals for models for general compressible turbulent flows. This provides a possible explanation of why the Van Driest density-weighted transformation (which ignores any true turbulent compressibility effects) is so successful in correlating compressible boundary-layer data. Finally, it is found that the DNS data do not support the strong Reynolds analogy. A more general representation of the analogy is analysed and shown to match the DNS data very well.

scholarly journals Three-Dimensional Navier-Stokes Computation of Turbine Nozzle Flow With Advanced Turbulence Models

1995 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Reynolds Stress ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Nozzle Flow ◽  
Stress Model ◽  
Mean Flow ◽  
The Mean ◽  
Algebraic Reynolds Stress Model

A three-dimensional Navier-Stokes procedure has been used to compute the three-dimensional viscous flow through the turbine nozzle passage of a single stage turbine. A low Reynolds number k-ε model and a zonal k-ε/ARSM (algebraic Reynolds stress model) are utilized for turbulence closure. The algebraic Reynolds stress model is used only in the endwall region to represent the anisotropy of turbulence. A four-stage Runge-Kutta scheme is used for time-integration of both the mean-flow and the turbulence transport equations. For the turbine nozzle flow, comprehensive comparisons between the predictions and the experimental data obtained at Penn State show that most features of the vortex-dominated endwall flow, as well as nozzle wake structure, have been captured well by the numerical procedure. An assessment of the performance of the turbulence models has been carried out The two models are found to provide similar predictions for the mean flow parameters, although slight improvement in the prediction of some secondary flow quantities has been obtained by the ARSM model.

Scaling of adverse-pressure-gradient turbulent boundary layers

1992 ◽  
Vol 238 ◽  
pp. 699-722 ◽  
Author(s):  
P. A. Durbin ◽  
S. E. Belcher
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Wall Layer ◽  
Small Range ◽  
Surface Shear Stress ◽  
Pressure Gradients ◽  
Mean Flow ◽  
The Mean

An asymptotic analysis is developed for turbulent boundary layers in strong adverse pressure gradients. It is found that the boundary layer divides into three distinguishable regions: these are the wall layer, the wake layer and a transition layer. This structure has two key differences from the zero-pressure-gradient boundary layer: the wall layer is not exponentially thinner than the wake; and the wake has a large velocity deficit, and cannot be linearized. The mean velocity profile has a y½ behaviour in the overlap layer between the wall and transition regions.The analysis is done in the context of eddy viscosity closure modelling. It is found that k-ε-type models are suitable to the wall region, and have a power-law solution in the y½ layer. The outer-region scaling precludes the usual ε-equation. The Clauser, constant-viscosity model is used in that region. An asymptotic expansion of the mean flow and matching between the three regions is carried out in order to determine the relation between skin friction and pressure gradient. Numerical calculations are done for self-similar flow. It is found that the surface shear stress is a double-valued function of the pressure gradient in a small range of pressure gradients.

The Effect of Manufacturing Tolerances on the Performance of Gas Turbine Air System Metering Holes With Chamfered Inlets

2018 ◽  
Author(s):  
Polina Chernukha ◽  
Adrian Spencer ◽  
James A. Colwill
Keyword(s):  
Gas Turbine ◽  
Mass Flow ◽  
Small Deviation ◽  
Pressure Ratio ◽  
Mean Flow ◽  
High Discharge ◽  
Large Pressure ◽  
Flow Through ◽  
Manufacturing Tolerances ◽  
The Mean

The current study represents an experimental and steady-state computational analysis of the mass flow through a single metering orifice with uniform and non-uniform chamfers. Chamfered holes have been used extensively in gas turbine air-systems for the ease of production and their (relatively high) discharge coefficient is insensitive to typical chamfer depth tolerances. This work extends the understanding of chamfer tolerances by investigating non-uniform chamfers due to angular misalignment of the chamfer tool relative to the hole. The range of the deviation angles between the axis of the tool and the axis of the metering orifice was 0–12°. The tests were performed in the pressure ratio range of 1.1...1.48, representing the range between idle and take-off operation points. A 3D CFD analysis of the tests using the Shear-Stress Transport (SST) k–ω model to simulate the mean flow field inside the metering orifice has also been completed. The results showed that at large pressure ratios, representative of the take-off operation point, the metering orifice with non-uniform chamfers showed reduction in mass flow delivery as high as 4%. A threshold in metering holes performance was detected for the tool inclination of 9.5°. At low pressure ratios, for conditions typically representative of idle operation point, a small deviation angle causes mass flow increase across the orifice.

scholarly journals The Influence of Inlet Swirl on the Flow Within an Annular S-Shaped Duct

1996 ◽  
Author(s):  
D. W. Bailey ◽  
J. F. Carrotte
Keyword(s):  
Experimental Investigation ◽  
Streamwise Velocity ◽  
Stagnation Pressure ◽  
Turbine Engines ◽  
Pressure Gradients ◽  
Gas Turbine Engines ◽  
Mean Flow ◽  
Inlet Swirl ◽  
Tangential Momentum ◽  
The Mean

An experimental investigation has been carried out to determine the effects of inlet swirl on the flow field that develops within an annular S-shaped duct. The duct is representative of that used to connect the compressor spools on multi-spool gas turbine engines. By removing the outlet guide vanes from an upstream single stage compressor swirl angles in excess of 30° were generated. Results show that within the S-shaped duct tangential momentum (Wr) is conserved, leading to increasing swirl velocities through the duct as the radius decreases. Furthermore, this component influences the streamwise velocity as pressure gradients are established to ensure the mean flow follows the duct curvature. Consequently in the critical region adjacent to the inner casing, where separation is likely to occur, higher streamwise velocities are observed. Within the duct substantial changes also occur to the turbulence field which results in an increased stagnation pressure loss between duct inlet and exit. Data is also presented showing the increasing swirl angles through the duct which has consequences both for the design of the downstream compressor spool and of any radial struts which may be located within the duct.

Pressure-gradient-dependent logarithmic laws in sink flow turbulent boundary layers

2008 ◽  
Vol 615 ◽  
pp. 445-475 ◽  
Author(s):  
SHIVSAI AJIT DIXIT ◽  
O. N. RAMESH
Keyword(s):  
Differential Equations ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Mean Velocity ◽  
Wide Range ◽  
Gradient Parameter ◽  
The Mean

Experiments were done on sink flow turbulent boundary layers over a wide range of streamwise pressure gradients in order to investigate the effects on the mean velocity profiles. Measurements revealed the existence of non-universal logarithmic laws, in both inner and defect coordinates, even when the mean velocity descriptions departed strongly from the universal logarithmic law (with universal values of the Kármán constant and the inner law intercept). Systematic dependences of slope and intercepts for inner and outer logarithmic laws on the strength of the pressure gradient were observed. A theory based on the method of matched asymptotic expansions was developed in order to explain the experimentally observed variations of log-law constants with the non-dimensional pressure gradient parameter (Δp=(ν/ρU3τ)dp/dx). Towards this end, the system of partial differential equations governing the mean flow was reduced to inner and outer ordinary differential equations in self-preserving form, valid for sink flow conditions. Asymptotic matching of the inner and outer mean velocity expansions, extended to higher orders, clearly revealed the dependence of slope and intercepts on pressure gradient in the logarithmic laws.

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