| 1. |
- Al Sam, A., et al.
(författare)
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An Investigation of Wind Farm Power Production for Various Atmospheric Boundary Layer Heights
- 2017
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Ingår i: Journal of Energy Resources Technology. - : ASME International. - 0195-0738 .- 1528-8994. ; 139:5
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Tidskriftsartikel (refereegranskat)abstract
- The dependency of the atmospheric boundary layer (ABL) characteristics on the ABL's height is investigated by using large eddy simulations (LES). The impacts of ABL's height on the wind turbine (WT) power production are also investigated by simulating two subsequent wind turbines using the actuator line method (ALM). The results show that, for the same driving pressure forces and aerodynamic roughness height, the wind velocity is higher at deeper ABL, while the wind shear and the wind veer are not affected by the depth. Moreover, the turbulence intensity, kinetic energy, and kinematic shear stress increase with the ABL's height. Higher power production and power coefficient are obtained from turbines operating at deeper ABL.
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| 2. |
- Al Sam, Ali, et al.
(författare)
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The Influence of Sea Waves on Offshore Wind Turbine Aerodynamics
- 2015
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Ingår i: Journal of Energy Resources Technology. - : ASME International. - 1528-8994 .- 0195-0738. ; 137:5
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Tidskriftsartikel (refereegranskat)abstract
- The impacts of swells on the atmospheric boundary layer (ABL) flows and by this on the standalone offshore wind turbine (WT) performance are investigated by using large eddy simulations (LES) and actuator-line techniques. At high swell to wind speed ratio, the swell-induced stress reduces the total wind stress resulting in higher wind velocity, less wind shear, and lower turbulence intensity level. These effects increase by increasing swell to wind speed ratio (C/U) and/or swell steepness. Moreover, for the same hub-height wind speed (U-hub), the presence of swells increases the turbine power extraction rate by about 3% and 8.4% for C/U-hub = 1.53 and 2.17, respectively.
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| 3. |
- Alsam, A., et al.
(författare)
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Wind-Wave Interaction Effects on a Wind Farm Power Production
- 2017
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Ingår i: Journal of Energy Resources Technology. - : ASME International. - 0195-0738 .- 1528-8994. ; 139:5
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Tidskriftsartikel (refereegranskat)abstract
- In the current study, the effects of the nonlocally generated long sea surface waves (swells) on the power production of a 2 × 2 wind farm are investigated by using large-eddy simulations (LES) and actuator-line method (ALM). The short sea waves are modeled as a roughness height, while the wave-induced stress accounting for swell effects is added as an external source term to the momentum equations. The results show that the marine atmospheric boundary layers (MABLs) obtained in this study have similar characteristics as the MABLs observed during the swell conditions by many other studies. The current results indicate also that swells have significant impacts on the MABL. As a consequence of these changes in the MABL, swells moving faster than the wind and aligned with the local wind direction increase the power extraction rate.
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| 4. |
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| 5. |
- Benti, Gudeta Berhanu, et al.
(författare)
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Numerical and experimental study on the dynamic bearing properties of a four-pad and eight-pad tilting pad journal bearings in a vertical rotor
- 2022
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Ingår i: Journal of energy resources technology. - : American Society of Mechanical Engineers (ASME). - 0195-0738 .- 1528-8994. ; 144:1
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the dynamics of tilting pad journal bearings with four and eight pads are studied and compared experimentally and numerically. The experiments are performed on a rigid vertical rotor supported by two identical bearings. Two sets of experiments are carried out under similar test setup. One set is performed on a rigid rotor with two four-pad bearings, while the other is on a rigid rotor with two eight-pad bearings. The dynamic properties of the two bearing types are compared with each other by studying the unbalance response of the system at different rotor speeds. Numerically, the test rig is modeled as a rigid rotor and the bearing coefficients are calculated based on Navier-Stokes equation. A nonlinear bearing model is developed and used in the steady state response simulation. The measured and simulated displacement and force orbits show similar patterns for both bearing types. Compared to the measurement, the simulated mean value and range (peak-to-peak amplitude) of the bearing force deviate with a maximum of 16 % and 38 %, respectively. It is concluded that, unlike the eight-pad TPJB, the four-pad TPJB excite the system at the third and fifth-order frequencies, which are due to the number of pads, and the amplitudes of these frequencies increase with the rotor speed.
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| 6. |
- Domaschuk, L., et al.
(författare)
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Creep of frozen sand under isotropic and deviatoric components of stress
- 1985
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Ingår i: Journal of energy resources technology. - : ASME International. - 0195-0738 .- 1528-8994. ; 107:2, s. 199-203
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Tidskriftsartikel (refereegranskat)abstract
- The creep behavior of frozen soil is being studied by examining its response to changes in the mean normal stress and changes in the deviatoric components of stress, using separate tests.^The two response components will then be coupled to provide a model for a general stress state.^The paper contains the results of three triaxial compression creep tests on frozen sand (T=-3 C) in which the samples were subjected to changes in the deviatoric components of stress only. Stepwise stress increases were applied for periods up to 1700 hr during which volumetric and axial strains were measured. The samples underwent attenuating creep when subjected to low stress levels and accelerating creep when subjected to higher stress levels, with no indication of a significantly long period of steady-state creep.The samples underwent volume reduction when the axial strains were attenuating and dilated when the axial strain rates began to accelerate.
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| 7. |
- Du, Wei, et al.
(författare)
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Film Cooling in the Cutback for Trailing Edge With Different Incident Angles
- 2023
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Ingår i: Journal of Energy Resources Technology, Transactions of the ASME. - : ASME International. - 0195-0738. ; 145:5
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Tidskriftsartikel (refereegranskat)abstract
- The cutback film cooling was important to decrease the trailing edge temperature and prolong the working life of gas turbines. Many investigations concerning cutback film cooling have already been done. However, only a few papers involve the influence of incident angle on the film cooling effectiveness (η) at the trailing region. In this work, detached eddy simulation (DES) is applied to calculate the η near the cutback region for different incident angles. Five different incident angles (0 deg, 5 deg, 10 deg, 15 deg, and 20 deg) and three blowing ratios (0.2, 0.8, and 1.25) are considered. The flow structure, temperature distribution, and η characteristics are analyzed in detail. Results imply that the incident angle changes the flow structure notably. As the incident angle increases, the separation region is suppressed, but the η was changed nonlinearly. At the low blowing ratio, the incident angle mainly affects the η near the slot. However, the incident angle changes the η downstream of the slot exit under a high blowing ratio. When the blowing ratio becomes large, the η near the centerline becomes larger.
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| 8. |
- Emami, Mohsen D., et al.
(författare)
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Effect of operational parameters on combustion and emissions in an industrial gas turbine combustor
- 2019
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Ingår i: Journal of Energy Resources Technology. - : ASME International. - 0195-0738 .- 1528-8994. ; 141:1
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Tidskriftsartikel (refereegranskat)abstract
- Enhancing a combustion system requires increased combustion efficiency, fuel savings, and reduction of combustion emissions. In this paper, the combustion of CH4 in the combustor of an industrial gas turbine is studied and NO and CO formation/emission is simulated numerically. The objective of the current work is to investigate the influence of combustive parameters and varying the percentage of distributed air flow rate via burning, recirculation, and dilution zone on the reactive flow characteristics, NOx and CO emissions. The governing equations of mass, momentum, energy, turbulence quantities Renormalized group (RNG) (k-ε), mixture fraction and its variance are solved by the finite volume method. The formation and emission of NOx is numerically simulated in a postprocessing fashion, due to the low concentration of the pollutants as compared to the main combustion species. The present work focuses on different physical mechanisms of NOx formation. The thermal-NOx and prompt-NOx mechanism are considered for modeling the NOx source term in the transport equation. Results show that in a gaseous-fueled combustor, the thermal NOx is the dominant mechanism for NOx formation. Particularly, the simulation provides more insight into the correlation between the maximum combustor temperature, exhaust average temperatures, and the thermal NO concentration. Results indicate that the exhaust temperature and NOx concentration decrease while the excess air factor increases. Moreover, results demonstrate that as the combustion air temperature increases, the combustor temperature increases and the thermal NOx concentration increases dramatically. Furthermore, results demonstrate that the NO concentration at the combustor exit is at maximum value in a swirl angle of 55 deg and a gradual rise in the NOx concentration is detected as the combustion fuel temperature increases. In addition, results demonstrate that the air distribution of the first case at laboratory conditions is optimal where the mass fractions of NO and CO are minimum.
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| 9. |
- Hyvärinen, Ann, et al.
(författare)
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Effects From Complex Terrain on Wind-Turbine Performance
- 2017
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Ingår i: Journal of energy resources technology. - : ASME Press. - 0195-0738 .- 1528-8994. ; 139:5
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Tidskriftsartikel (refereegranskat)abstract
- In this work, experimental measurements are made to study wind turbines over complex terrains and in presence of the atmospheric boundary layer. Thrust and power coefficients for single and multiple turbines are measured when introducing sinusoidal hills and spires inducing an artificial atmospheric boundary layer. Additionally, wake interaction effects are studied, and inflow velocity profiles are characterized using hot-wire anemometry. The results indicate that the introduced hills have a positive impact on the wind-turbine performance and that wake-interaction effects are significantly reduced during turbulent inflow conditions.
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| 10. |
- Jagodzińska, Katarzyna, 1990-, et al.
(författare)
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Torrefaction of Agricultural Residues: Effect of Temperature and Residence Time on the Process Products Properties
- 2020
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Ingår i: Journal of energy resources technology. - : ASME Press. - 0195-0738 .- 1528-8994. ; 142:7, s. 070908-1-070908-8
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Tidskriftsartikel (refereegranskat)abstract
- To date, few studies on the potential utilization of agricultural residue torrefaction products have been performed. Thus, torrefaction product characterization aimed at its potential utilization was performed. Wheat–barley straw pellets and wheat–rye chaff were used in the study. The impact of the torrefaction temperature (280–320 °C) on polycyclic aromatic hydrocarbons (PAHs) content in the biochar and noncondensable gas (noncondensables) composition was investigated. The impact of the torrefaction time (30–75 min) on the composition of the condensable volatiles (condensables) and their toxicity were also studied. The torrefaction process was performed in a batch-scale reactor. The PAH contents were measured using high-performance liquid chromatography (HPLC), and the noncondensables composition was measured online using a gas analyzer and then gas chromatograph with flame ionization detector (GC-FID). The condensables composition and main compound quantification were determined and quantified using gas chromatography–mass spectrometry (GC/MS). Three toxicity tests, for saltwater bacteria (Microtox® bioassay), freshwater crustaceans (Daphtoxkit F magna®), and vascular plants (Lemna sp. growth inhibition test), were performed for the condensables. The PAHs content in the biochar, regardless of the torrefaction temperature, allows them to be used in agriculture. The produced torgas shall be co-combusted with full-caloric fuel because of its low calorific value. Toxic compounds (furans and phenols) were identified in the condensable samples, and regardless of the processing time, the condensables were classified as highly toxic. Therefore, they can be used either as pesticides or as an anaerobic digestion substrate after their detoxification.
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