Turbulence velocity spectra and intensities in the inflow of a turbine rotor

2019 ◽  
Vol 870 ◽  
Author(s):  
I. A. Milne ◽  
J. M. R. Graham
Keyword(s):  
Flow Field ◽  
Direct Interaction ◽  
Turbine Rotor ◽  
Small Scale ◽  
Length Scale ◽  
Velocity Measurements ◽  
Tidal Turbine ◽  
Turbulence Velocity ◽  
Scale Turbulence ◽  
Velocity Spectra

The changes in spectra and intensities of the streamwise component of turbulent velocity are calculated in the inflow of a turbine rotor. The flow is initially calculated in the limit when the turbulence is of small scale compared with the rotor diameter. Rapid distortion theory (RDT), Batchelor & Proudman (Q. J. Mech. Appl. Maths, vol. 7 (1), 1954, pp. 83–103) (BP), for small-scale turbulence is combined with the effect of the fluctuating potential flow field on the turbulence caused by the direct interaction of the incident turbulence with the rotor as a sheet of resistance. A second computation is then carried out for turbulence of larger length scale. The results of the calculations are compared with velocity measurements in the inflow of both a commercial wind turbine and a tidal turbine rotor.

scholarly journals Experimental Study of Flow Field Characteristics in Tidal Stream Turbine Arrays

2016 ◽  
Author(s):  
Martin Nuernberg ◽  
Longbin Tao
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Water Channel ◽  
Experimental Studies ◽  
Energy Resource ◽  
Small Scale ◽  
Large Set ◽  
Flow Field Characteristics ◽  
Tidal Turbine ◽  
Turbine Arrays

Tidal currents at many locations around the world have great potential to be used as a large scale renewable energy resource in the future. For large tidal turbine arrays to be commercially viable, the interactions of large devices operating in a confined operating environment need to be understood to optimise the layout of arrays to maximise electricity generation. This study presents results from a comprehensive experimental investigation of the flow field characteristics within tidal turbine arrays across a number of array layout configurations and current velocities. Up to four small scale turbines were placed in a circulating water channel to investigate the effects of changing array configuration and wake interaction on the flow velocity and turbulence characteristics in small array layouts. Detailed account of the resulting flow field characteristics has been taken by particle image velocimetry measurements at a number of locations within the wake of the array thus providing a large set of instantaneous flow recordings for further analysis of flow features and wake characteristics. Results are shown for experimental studies of single, three and four turbine arrays and some preliminary comparison between experimental measurements and numerical results are made.

Recirculating Flow and Turbulence in a Low Aspect Ratio Dump Combustor

2005 ◽  
Author(s):  
S. Karmakar ◽  
A. Kushari
Keyword(s):  
Flow Field ◽  
Turbulent Flows ◽  
Large Scale ◽  
Pressure Sensors ◽  
Sudden Expansion ◽  
Small Scale ◽  
Recirculating Flow ◽  
Dump Combustor ◽  
Frequency Fluctuations ◽  
Scale Turbulence

Re-circulating flows are established in dump combustors at the dump plane due to the sudden expansion. However, given enough length, the separated flow at the dump plane attaches itself inside the combustor and a fully developed, non-circulating, attached flow field is established. But, if the length of the combustor is less than the free-stream reattachment length, then the flow does not re-attach inside the combustor. Instead, a portion of the flow is reflected from the exit section, causing stronger re-circulation that modifies the flow structure inside the combustor. This paper describes an experimental study of turbulent flow field inside a dump combustor for a range of flow Reynolds numbers. The focus of this effort is to study the interaction between the flow re-circulation and the large-scale turbulence. Detailed measurements of the wall pressure transients were taken using strain-gage pressure sensors. The fluctuating component of the pressure was isolated and analyzed. The signals were analyzed using FFT, Auto-Correlation and Cross-correlation to distinguish the re-circulating flow and the large-scale turbulence. The re-circulating flow, identified by low frequency fluctuations in pressure (∼ 0.5 Hz), was seen to be strongest inside the combustor almost half way through the combustor length. At the same time, the large-scale turbulence intensity (identified by high frequency fluctuations in the range of 460 Hz) level is seen to be lower inside the combustor than in the incoming pipe. This can be attributed to the turbulence cascading due to the re-circulating flow, which increases the small-scale energy and reduces the large-scale energy. These results show turbulence modulation due to re-circulating flow and can have far reaching applications in swirling turbulent flows.

Rapid distortion of turbulence into an open turbine rotor

2017 ◽  
Vol 825 ◽  
pp. 764-794 ◽  
Author(s):  
J. M. R. Graham
Keyword(s):  
Isotropic Turbulence ◽  
Strain Analysis ◽  
Turbine Rotor ◽  
Small Scale ◽  
Mean Flow ◽  
Mean Velocity ◽  
Actuator Disc ◽  
Tidal Turbine ◽  
Tidal Stream ◽  
The Mean

Rapid distortion of turbulence (RDT) theory is applied to homogeneous, isotropic turbulence incident on a horizontal axis turbine rotor such as a wind turbine or tidal-stream turbine. The mean flow field of the rotor which distorts the turbulence is represented by the commonly used axisymmetric actuator disc model due to Betz and Joukowski. The fluctuating streamwise component of the turbulence distorted by this field is calculated at the actuator disc plane. Turbulence velocity intensities and spectra are evaluated for general ratios of turbulence integral length scale to the rotor diameter, including the small-scale limit for which the original homogeneous strain analysis of Batchelor and Proudman may be applied. The distortion of the mean velocity profile of an incident rotor wake which may be considered a zero frequency disturbance relevant to wind and tidal turbine operation in large arrays is also analysed by the same method, treating it as a deterministic disturbance in the incident flow.

Effects of Trailing Edge Alterations on the Performance of a Small-Scale, Low-Solidity Tidal Turbine Blade Designed for Less Energetic Flows

2019 ◽  
Author(s):  
Job Immanuel Encarnacion ◽  
Gavin Lavery ◽  
Stephanie Ordoñez-Sanchez ◽  
Cameron Johnstone
Keyword(s):  
Turbine Rotor ◽  
Small Scale ◽  
Minimum Thickness ◽  
Ansys Fluent ◽  
The Best Approximation ◽  
Simulated Performance ◽  
Physical Testing ◽  
Tidal Turbine ◽  
Lift And Drag ◽  
The Ideal

Abstract Computer simulations aid in the design of any device. However, physical testing is still needed to validate these simulations and problems may arise if fabrication limits are not incorporated. This study was undertaken to quantify the losses in a low-solidity turbine rotor designed for less energetic flow. The blade was tested at a scale of 1m resulting in a blade length of 219mm. A 0.5mm minimum thickness fabrication limit was worked with by shifting all the points of the upper surface of the blade sections by 0.5mm at the 219mm scale introducing a huge distortion in each of the blade sections. Lift and drag characteristics of the distorted aerofoil are obtained via ANSYS Fluent and served as the corrected inputs for the BEM characterisation. It was found that the BEM predicts a reduced performance similar to the physical testing although it still over predicts the performance of the turbine. However, there is an agreement on the trend of the simulated performance and the physical testing in addition to the reduction of the variation between the two. Additional aerofoil alterations are studied to inform on future experimental designs. It was then found that out of the altered cases, shifting the upper surface by the required minimum thickness resulted in the best approximation of the simulated performance. This is far from acceptable as the variation between the ideal computer simulated case is too large to just incorporate corrections. Thus, an analysis is carried out using a 400mm scaled blade, thereby decreasing the distortion on each blade section. The results of the analysis show good agreement with the ideal section and minimal reduction in performance at about 5% less than the ideal.

The connection between the spectrum of turbulent scales and the skin-friction statistics in channel flow at

2019 ◽  
Vol 871 ◽  
pp. 22-51 ◽  
Author(s):  
Lionel Agostini ◽  
Michael Leschziner
Keyword(s):  
Skin Friction ◽  
Channel Flow ◽  
Large Scale ◽  
Direct Interaction ◽  
Conditional Probability Density ◽  
Small Scale ◽  
Shear Stresses ◽  
Mode Decomposition ◽  
Small Scales ◽  
Scale Turbulence

Data from a direct numerical simulation for channel flow at a friction Reynolds number of 1000 are analysed to derive statistical properties that offer insight into the mechanisms by which large-scale structures in the log-law region affect the small-scale turbulence field close to the wall and the statistical skin-friction properties. The data comprise full-volume velocity fields at 150 time levels separated by 50 wall-scaled viscous time units. The scales are separated into wavelength bands by means of the ‘empirical mode decomposition’, of which the two lowest modes are considered to represent the small scales and three upper modes to represent the large scales. Joint and conditional probability density functions are then derived for various scale-specific statistics, with particular emphasis placed on the streamwise and shear stresses conditional on the large-scale fluctuations of the skin friction, generally referred to as ‘footprinting’. Statistics for the small-scale stresses, conditional on the footprints, allow the amplification and attenuation of the small-scale skin friction, generally referred to as ‘modulation’, to be quantified in dependence on the footprints. The analysis leads to the conclusion that modulation does not reflect a direct interaction between small scales and large scales, but arises from variations in shear-induced production that arise from corresponding changes in the conditional velocity profile. This causal relationship also explains the wall-normal change in sign in the correlation between large scales and small scales at a wall-scaled wall distance of approximately 100. The effects of different scales on the skin friction are investigated by means of two identities that describe the relationship between the shear-stress components and the skin friction, one identity based on integral momentum and the other on energy production/dissipation. The two identities yield significant differences in the balance of scale-specific contributions, and the origins of these differences are discussed.

Similarity of dissipation and enstrophy in particle-induced small-scale turbulence

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Zhuo Wang ◽  
Kun Luo ◽  
Junhua Tan ◽  
Dong Li ◽  
Jianren Fan
Keyword(s):  
Small Scale ◽  
Scale Turbulence

scholarly journals Quantification of Measurement and Model Effects in Monopile Foundation Scour Protection Experiments

2021 ◽  
Vol 9 (6) ◽  
pp. 585
Author(s):  
Minghao Wu ◽  
Leen De Vos ◽  
Carlos Emilio Arboleda Chavez ◽  
Vasiliki Stratigaki ◽  
Maximilian Streicher ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Flow Field ◽  
Three Dimensional ◽  
Small Scale ◽  
Maximum Wave Height ◽  
Chaotic Flow ◽  
The Mean ◽  
Scour Protection ◽  
Damage Number ◽  
Measurement Effects

The present work introduces an analysis of the measurement and model effects that exist in monopile scour protection experiments with repeated small scale tests. The damage erosion is calculated using the three dimensional global damage number S3D and subarea damage number S3D,i. Results show that the standard deviation of the global damage number σ(S3D)=0.257 and is approximately 20% of the mean S3D, and the standard deviation of the subarea damage number σ(S3D,i)=0.42 which can be up to 33% of the mean S3D. The irreproducible maximum wave height, chaotic flow field and non-repeatable armour layer construction are regarded as the main reasons for the occurrence of strong model effects. The measurement effects are limited to σ(S3D)=0.039 and σ(S3D,i)=0.083, which are minor compared to the model effects.

scholarly journals Role of large-scale advection and small-scale turbulence on vertical migration of gyrotactic swimmers

2019 ◽  
Vol 4 (12) ◽  
Author(s):  
C. Marchioli ◽  
H. Bhatia ◽  
G. Sardina ◽  
L. Brandt ◽  
A. Soldati
Keyword(s):  
Vertical Migration ◽  
Large Scale ◽  
Small Scale ◽  
Scale Turbulence
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