Turbulence Intensity Measurements Research Articles

Wind Speed Shear Exponent: Effects of Sea Surface Roughness in Terms of Spectral Bandwidth

Abstract This note presents results on the wind speed shear exponent demonstrating the effects of the sea surface roughness in terms of the spectral bandwidth of ocean surface waves. The wind speed shear exponent is obtained by combining the logarithmic mean wind speed profile and the power law mean wind speed profile containing the sea surface roughness as a parameter, as used by Viselli et al. (2022, “LiDAR Measurements of Wind Shear Exponents and Turbulence Intensity Offshore the Northeast United States,” ASME J. Offshore Mech. Arct. Eng., 144(4), p. 042001). In the present article, the sea surface roughness is given in terms of the spectral bandwidth as presented by Zhao and Li (2024, “Dependence of Drag Coefficient on the Spectral Width of Ocean Waves,” J. Oceanogr., 80(2), pp. 129–143). Examples of results representing realistic wave conditions are provided. The results should be useful demonstrating how the wind speed shear exponent can be estimated using the spectral bandwidth, which is a frequently used parameter to characterize wave conditions.

Near-Ground wind field characteristics of tracking photovoltaic systems based on field measurements

The study conducts field measurements at a tracking photovoltaic power station in Zhongwei City, Ningxia Hui Autonomous Region, investigating near-ground incoming wind characteristics, spatial coherence, and their impact on the flow field of the tracking photovoltaic system. Actual measurements indicate a low dispersion degree in the roughness index of this area, with an average roughness index of α = 0.1228, which is consistent with the characteristics of open land and desert areas. The incoming wind speed profile largely complies with European wind load specifications, with turbulence intensity measured at different heights exceeding other wind load specifications, primarily due to increased sand movement contributing to turbulence in desert areas. Additionally, this study proposes calculation formulas for measured turbulence intensity, integration scale, and gust factor, offering valuable insights into the incoming wind field characteristics in this region. Furthermore, the investigation into spatial coherence and decay parameters revealed the superior performance of the Krenk model in high frequency bands and over long distances. Lastly, the tracking photovoltaic array induces noticeable shading effects, altering flow field characteristics significantly, with a diminished impact on wind flow velocity as the tilt angle of the photovoltaic panel decreases. These studies serve as a valuable reference for gaining a deeper understanding of wind field characteristics, wind load calculation, and the optimal design of tracking photovoltaic systems.

An evaluation of different measurement strategies to measure wind turbine near wake flow with small multicopter UAS

Wind turbine wake flow, especially in the near wake, that is up to one rotor diameter D downstream, is subject to interaction between tip vortices and ambient turbulence. These interactions are important to understand wake decay, but most difficult to measure with common instrumentation. Small uncrewed aerial systems (UAS) can help to measure at such locations where no masts can be installed. We contrast two measurement strategies, the hover flight with multiple UAS and cross-section flights with single UAS. We show that both strategies have advantages; the cross-section flights provide a full picture of the width and wind speed deficit across the rotor diameter whereas multi-UAS hover flights can provide more reliable turbulence intensity and turbulent flux measurements at specific locations. With both strategies, tip vortices can be detected and qualified to characterize the state of wake decay at different positions. A fit to the vortex models Lamb-Oseen and Burnham-Hallock allows to estimate circulation and core radius of the vortices. For best characterization of the wake, we recommend to combine the hover and cross-section flight strategies in future.

Optimization of Reynolds stress model coefficients at multiple discrete flow regions for three-dimensional realizations of fractal-generated turbulence

The quantification of global turbulence statistical moments generated by grid turbulators is crucial for the enhancement of conjugate heat transfer in industrial thermo-fluid systems. As such, there is a need for precise, low-cost alternatives to numerically model three-dimensional flow dynamics of fractal-generated turbulence (FGT) behind multilength-scale square fractal grids (SFGs), in contrast to previously-reported direct numerical simulations. In this study, a numerical framework consisting of multiple applications of the Reynolds stress model (RSM), each employing its own distinct set of optimized coefficient values, is developed by segregating an FGT flow domain into its production and decay regions with Nelder-Mead optimization on key coefficients then performed independently for each region. The flow fields predicted by such RSM framework achieved overall disparities below 3% and 13% w.r.t. reported experimental measurements of mean velocity and turbulence intensity, respectively, considering the evolution in the flow domain along the streamwise, vertical, and spanwise directions. This is therefore the first documentation of any RANS-turbulence model being validated for mean velocity and turbulence intensity predictions of FGT in all three-dimensions. Thereafter, this proposed RSM framework is generalized to predict industry-relevant turbulence statistical moments of four additional FGT flows. The predicted centerline-statistics are verified against reported experiments, and the findings potentially enable realizations of FGT induced by arbitrary SFGs without relying on a posteriori validation while eliminating further reliance on the Nelder-Mead optimization algorithm on a case-by-case basis. The findings indicate a potential to apply the model coefficients as continuous functions of space to simulate the entire FGT domain. Overall, the accurate and numerically sustainable realizations of FGT in 3D provide valuable insights to engineer potent fluid-solid heat transfer via passive turbulence management within HVAC systems.

Turbulence generated by dust dispersion in the standard 1 m3 vessel

The standard 1 m3 vessel is an apparatus recommended for an assessment of dust explosion indices by ISO, European and American Standards. However the definition of the vessel construction given in the Standards leaves some room when designing it. That may lead to significantly different results obtained in vessels built in different laboratories even when all of them meet the requirements of the Standards. One of key parameters that should be controlled in the tests is turbulence. Several authors reported measurements of turbulence intensity in the 1 m3 vessel. However, all of those results were obtained for pure air dispersed from the dust dispersion system. The paper presents results of turbulence measurements performed in the 1 m3 vessel built and used at Experimental Mine Barbara of Central Mining Institute, Poland. In previous measurements transient flow velocity in the vessel was generated by dust injection from the dust dispersion system. For the measurement the Bi-Directional Velocity Probe developed by McCaffrey and Heskestad ((McCaffrey B.J. (1976)) was used. The construction of the probe was modified to improve its performance in the dusty conditions. The tests were performed for several nominal dust concentrations of two dusts. From the measurements the root-mean-square of instantaneous velocity (u'rms) was calculated. The results were compared with the results obtained for pure air in the dust dispersion system. The presence of dust modifies turbulence in the vessel. Its intensity is reduced and the flow development is delayed.

Experimental investigation of subsonic and transonic flows through a linear turbine cascade

Experimental investigations of high subsonic and transonic flows through a linear cascade consists of VKI LS-59 blades have been carried out. Emphasis was put on analysis of the flow characteristics at the cascade exit. Experiments reported the static pressure measurements on blade surface, flow field survey downstream the cascade by means of Particle Image Velocimetry (PIV) and visualization by means of the Schlieren method. The turbulent intensity measurements have been performed at the cascade inlet to provide inlet conditions for numerical studies. The measurements have been carried out at two isentropic Mach numbers: M2,is=0.777 (high subsonic) and M2,is=0.975 (transonic). The corresponding Reynolds numbers based on the chord length and isentropic downstream velocity were equal to Re2,is=6.21⋅105 and Re2,is=6.82⋅105, respectively. The numerical simulations with Transition SST model have been performed to complement experiments and to verify applicability of data for testing and development of turbulence models. The RANS-based transition model reproduced correct isentropic Mach number profiles on the blade surface but underpredicted the turbulent mixing in the wake flow.

Design and characterizing of blower wind tunnel using experimental and numerical simulation

A new subsonic blower wind tunnel design has been studied both numerically and experimentally; it is also referred to as “blower” wind tunnel. This paper is initially aimed to address each sequential stage of the wind tunnel design process. Rather than applying the standard method of modelling solely the flow in the test section, a large-scale CFD model of the whole wind tunnel was employed. The loss of every constituent element was calculated and then all the losses are added up to determine the power needed for the wind tunnel operation which is used as “intake fan” boundary conditions in the CFD model. Then, flow uniformity and turbulent intensity measurements in an empty test section using a pitot static tube and hot wire anemometer (HWA) were introduced to validate the CFD results. The results showed that flow quality was significantly affected by flow conditioners (uniformity devices) (honeycomb and mesh screens) in the settling chamber and wide-angle diffuser. Investigations were also conducted to evaluate the flow deficit in the wake area behind a convex hump model using both HWA and particle image velocimetry PIV. This was additional experimental tests carried out to validate the suitability of the wind tunnel designed for aerodynamic research.

Turbulence Intensity Measurement in the Test Section of Shiraz Wind Tunnel Using Hot Wire Anemometry

Turbulence Intensity Measurement in the Test Section of Shiraz Wind Tunnel Using Hot Wire Anemometry

Energetic bounds on gyrokinetic instabilities. Part 3. Generalized free energy

Free energy, widely used as a measure of turbulence intensity in weakly collisional plasmas, has been recently found to be a suitable basis to describe both linear and nonlinear growth in a wide class gyrokinetic systems. The simplicity afforded by this approach is accompanied by some drawbacks, notably the lack of any explicit treatment of wave–particle effects, which makes the theory unable to describe things like stability thresholds or dependence on the geometry of the background magnetic field. As a step toward overcoming these limitations, we propose an extension of the theory based on a generalization of the free energy. With this, it is demonstrated that resonance effects are recovered, and the bounds on growth are significantly reduced. The simplicity and efficient computation of the associated ‘optimal’ growth rates makes the theory potentially applicable to stellarator optimization.

Towards improving passengers safety and comfort based on turbulence tests in aerodynamic tunnel

First, the article outlines the elements of an ongoing research project, aiming to demonstrate that the basic ICAO standard EDR (Eddy Dissipation Rate) index of atmospheric turbulence intensity, defined as the cubic root of the turbulence energy per unit time and mass, can be measured and calculated in Wind Tunnel (WT) according to the basic Kolmogorov concept. This involves showing that EDR index calculated in WT, taking a sufficient number of velocity measuring points, can be an objective measure of turbulence intensity, independent of the body immersed in the fluid. Secondly, it is shown that these measurements are accompanied by intermediate active vibration control tests. For this purpose, a Turbulence Generator was built and installed in the WT and an intelligent wing model with implemented LQG active control was introduced in the WT. These two procedures, complementary in substance, aim to demonstrate the consistency of the flight approach based on the objectivity of this ICAO standard EDR index and the vibration reduction methodology in a turbulent atmospheric environment.

Development, evaluation, and implementation of building downwash and plume rise enhancements in AERMOD

ABSTRACT Recent research has pointed out many reasons why the building downwash formulation in AERMOD needs to be updated due to: overly simplified equations for building wake development; equations that do not account for porous or streamlined structures; a discontinuity in the streamline equation; and over predictions when compared to field observations for buildings with a large footprint. Because of these issues, a research study was initiated in late 2016 with an overall objective of improving the building downwash algorithms in PRIME. The research study involved the use of wind tunnel modeling to develop a database of wind speed and turbulence intensity measurements downwind of various rectangular solids and streamlined (i.e., tanks and towers) structures. Based on those measurements, new equations (PRIME2) were developed to better describe the turbulence increase and velocity deficit in building wakes for these structure types. The PRIME2 building wake equations for turbulence intensity increase and velocity deficit were shown to agree better with wind tunnel observations than the current PRIME equations in AERMOD. The new equations were documented in a journal article and were added to AERMOD’s PRIME subroutine. A new version of AERMOD was then compiled with the new enhanced turbulence and wind speed equations (PRIME2) for evaluation. The key feature of the PRIME2 equations is that building wake enhanced turbulence decays rapidly back to ambient levels above the top of the building versus the current PRIME theory that has constant enhanced turbulence extending up to the height of the wake. This paper provides details on the implementation of the PRIME2 code into AERMOD, PRIME plume rise enhancements, the field databases used to evaluate PRIME2, and the evaluation of PRIME2 against three field databases. The paper shows that AERMOD with the PRIME2 building downwash equations and other enhancements provides the overall best agreement with field observations. Implications: While AERMOD/PRIME is supposed to provide accurate and unbiased estimates (within a factor of two), recent research has identified several problems with the current building downwash theory in AERMOD and comparisons against field observations have shown significant under and overpredictions. One major problem is that the current theory has the wake effect extending well above the top of the building while new research shows that the wake effect decays rapidly above the top of the building. This could lead AERMOD to underpredict or overpredict ground-level concentrations. Based on recent wind tunnel tests, a new building downwash theory has been developed and documented in a Journal article. This theory has been added to the PRIME building downwash algorithm in AERMOD and is currently included as an Alpha option in AERMOD. This paper evaluates that new theory against field observations and demonstrates that the updated theory provides better agreement with field observations than the current AERMOD. This paper points out that research and development of model building downwash improvements should be an ongoing process to help ensure a “sustainable” future where these improvements can ultimately provide a model with unbiased performance and thereby allow for responsible industrial development. This study has shown that improvements can be made in a rather quick manner and be included as Alpha options in EPA model updates. The next challenge is to transition these options from Alpha to Beta options and then finally to a default status.

Discussion: “LiDAR Measurements of Wind Shear Exponents and Turbulence Intensity Offshore the Northeast United States” (Viselli, A., Faessler, N., and Filippelli, M., 2022, ASME J. Offshore Mech. Arct. Eng., 144(4), p. 042001)

Abstract The work by Viselli et al. (Viselli, A., Faessler, N., and Filippelli, M., 2022, “LiDAR Measurements of Wind Shear Exponents and Turbulence Intensity Offshore the Northeast United States,” ASME J. Offshore Mech. Arct. Eng., 144(4), p. 042001) presents results on wind shear exponents and turbulence intensity obtained from the analysis of field data collected offshore the Northeast United States. This discussion is focused on the wind shear exponent that is obtained by combining the logarithmic mean wind speed profile and the power law mean wind speed profile, containing the sea surface roughness as a parameter. Here, the sea surface roughness is specified using three formulae given in terms of significant wave height and spectral wave steepness. The discussion points out how the sea surface roughness can be included in future applications of the authors' analysis method.

Influence of Road Types on Transiting Test for Aerodynamic Coefficient Measurements Using Passive Wind Generated by a Moving Vehicle

A transiting test using vehicle-driving passive wind is a novel experimental technique to perform aerodynamic tests, proposed by the authors. However, this low-cost, short-cycle, and symmetrical test method can be influenced by many factors. In this paper, a comparative study on the influence of road types on a transiting test of aerodynamic coefficient measurements is presented. The tests were carried out on three different roads (expressway, viaduct highway, and tunnel highway); for each road type, structure models with and without end plates were investigated. For all the road types, measured turbulence intensity (around 4%) was similar to that of the wind tunnel test under the following conditions: 3 °C temperature, 42% humidity, 0.28 m/s natural wind speed, vehicle driving in a straight line with stable speed, and no traffic flow. All the tests were conducted under the above conditions. To deal with the interference components in the original data signals obtained from a viaduct highway and tunnel highway, a low-pass filter with a 1 Hz cutoff frequency was used. With wind attack angles changing, the tendency of the aerodynamic coefficients of the test model in the transiting test showed satisfactory consistency with that of the wind tunnel test; and the results exhibited fine repeatability. Regarding the drag coefficients, the test model with end plates was in good agreement with those from the wind tunnel test. Compared with the wind tunnel test, the results of expressway showed the best consistency, considering turbulence intensity, pavement surface roughness, and other factors. Thus, the transiting test in future research should be conducted on the expressway, with end plates installed on both ends of the structure model.

In-Flame And In-Cylinder Flow/Turbulence Measurements Near The Glow Plug Using Flame Image Velocimetry And Particle Image Velocimetry In An Optical Compression-Ignition Engine

The present study implements two diagnostic methods based on tracking of seeded olive oil droplets (PIV: particle image velocimetry) and pattern changes detected in high-speed flame movies (FIV: flame image velocimetry) in a small-bore optical diesel engine. For each measurement, a total of 100 engine cycles are recorded and processed to address the inherent cyclic variations. The ensemble-averaged flow fields and turbulence intensity distribution extracted from individual cycles via the spatial filtering method are discussed with a particular interest in the influence of glow plug on flow and turbulence, i.e. rigid body and fluid interaction. The PIV results show a swirl flow structure forms and rotates with its centre shifted towards the exhaust side, leading to an asymmetric swirl structure. By comparing a PIV laser plane tilted towards the glow plug and a 10 mm horizontal plane below the cylinder head with no glow flow-plug interaction, it is observed that the flow-plug interaction causes the flow winding around the plug tip to generate complex flow structures and new vortices downstream of the plug. The tilted plane and 10-mm plane show similar bulk flow magnitude distribution patterns; however, the flow-plug interaction generates high turbulence in the tilted plane right downstream of the plug tip where new vortices form, which lasts for a few crank angles. The spatially averaged flow magnitude and turbulence intensity are measured higher in the 10-mm plane where there is no flow-plug interaction, suggesting the increased turbulence is a localised behaviour. The flame-plug interaction is also investigated during the combustion event using the FIV method. The level of flame-plug interaction is adjusted by changing the inter-jet spacing angle of two nozzle holes with one case showing high interaction and the other displaying low interaction. From the FIV measurements, the most significant effect of the flame-plug interaction is observed as the further penetration of the wall bounced flame for the high interaction case. This is due to the glow plug as a rigid body blocking the swirl flow and promoting the flame penetration back towards the centre of the combustion chamber upon the piston-bowl wall impingement. The measured turbulence intensity is also higher thanks to the enhanced wall bounced flame in addition to more significant flame-plug interaction at the interface.

CFD assessment of wind energy potential for generic high-rise buildings in close proximity: Impact of building arrangement and height

High-rise building complexes are of great importance for enabling sustainable urban development in large parts of the world. Earlier studies have indicated that high wind speed regions can be present along the passage between two high-rise buildings as well as above the roofs. At such locations, urban wind energy could be harvested by installing wind turbines between and/or above the roof of the buildings. However, the available wind energy potential around an array of generic high-rise buildings in close proximity has not yet been assessed for different building configurations. This paper conducts a detailed evaluation of the impacts of the building arrangement and height for a 2 × 2 array with a building height-to-street width ratio of 30 on the mean wind velocity and the wind energy potential along the passages between both upstream and downstream buildings as well as on their roofs. The following parameters are analyzed: (i) the passage width between the two upstream buildings (w), (ii) the streamwise distance between the upstream and downstream buildings (d), and (iii) the height difference between the upstream and downstream buildings (ΔH). The 3D steady Reynolds-averaged Navier-Stokes (RANS) equations are solved using the Reynolds stress model (RSM) turbulence model for closure. The CFD results are validated using wind-tunnel measurements of mean wind speed and turbulence intensity performed for the same building array. The results show elevated wind power density along the upstream passages for small w (=0.15B), high d (=0.6B), and equal building height (ΔH = 0). In contrast, comparatively high values of w, small d, and ΔH < 0 yield high wind power densities between the downstream buildings. Among the different wind turbine types considered, horizontally-mounted vertical axis wind turbines seem the most promising option for wind energy harvesting between the buildings.

Validation of near‐shore wind measurements using a dual scanning light detection and ranging system

AbstractThis paper reports results from a 2‐month validation campaign of near‐shore wind measurements taken by a dual scanning light detection and ranging (LiDAR) system at a coastal site in Japan. A meteorological mast and a vertical profiling LiDAR device were deployed at an offshore research station approximately 1.5 km from the coast. Offshore winds at heights of 66, 120, and 180 m above sea level were observed by the scanning LiDAR system. Comparisons with a sonic anemometer found that the radial velocities had a coefficient of determination of more than 0.99 without unreasonable bias. The accuracy of 10‐min mean wind speeds and directions was then evaluated. The 10‐min values from the dual scanning LiDAR system were accurate enough to satisfy the acceptance criteria used for floating LiDAR systems. In addition, the vertical velocity and direction profiles from the dual scanning LiDAR system were compared with those from a vertical profiling LiDAR device. The performance of turbulence intensity (TI) measurements was also evaluated. Although the TIs from the dual scanning LiDAR system were slightly lower than those from the sonic anemometer, they were equivalent to those from the cup anemometers. This investigation concluded that the near‐shore wind measurements using the dual scanning LiDAR system are beneficial for reducing near‐shore wind measurement costs, because the system can measure not only 10‐min wind speed and direction, but also parameters associated with assessing site‐specific conditions without installing offshore meteorological masts.

Wind Turbine Systematic Wake to Wake Analysis: Quantification of Turbulence and Statistical Analysis for Optimal Wind Farm Design

Through this work, we have analyzed wake to wake interactions between horizontal axis wind turbines located in line to each other. We have quantified wake interactions based on hot wire anemometric data and statistical correlations using a model wind farm fabricated inside a wind tunnel. The results of these measurements show that a high level of turbulent kinetic energy is generated at the region of intersection between rotor and stator wakes. Numerical models of wake interactions of wind turbines under varying turbulent inflow conditions using the actuator line technique and EllipSys3D Navier-Stokes solver were carried out to resolve dynamics of wake interactions. Our results showed good agreement with field measurements of wake deficit and turbulence intensity for inline and eccentric turbine arrangements.

Comparative study on the wind characteristics of tunnel–bridge and tunnel–flat ground infrastructures on high-speed railway

The difference in natural wind characteristics of the tunnel–bridge (TB) and tunnel–flat ground (TF) infrastructure may result in varied aerodynamic behaviours of the high-speed railway train (HSRT). Hence, continuous natural wind sampling is conducted on typical TB and TF sites by using three ultrasonic and one three-cup anemometers. The mean and fluctuating wind characteristics of the two sites are compared and discussed in detail based on field measurement data. The main results can be concluded as follows: Firstly, the prevailing wind direction on the TB site is perpendicular to the running direction of the HSRT due to the occlusion effect, whereas the mean direction on the TF site is easily deflected by the near-ground vegetations and other obstacles. Secondly, the turbulence intensities of the TF site are larger than those of the TB site, and the lognormal distribution is applicable for describing the probability distribution of measured turbulence intensity on the two sites. Thirdly, the von Kármán spectrum accurately depicts the wind energy distribution of the TB and TF sites in the frequency domain, whereas the empirical spectrum adopted by the specification show inferior accuracy. Lastly, the coherence distance of the TB site is considerably longer than that of the TF site. The coherence distance of u and v components of the TB site is seven times longer than a train body (approximately 25 m), and that of u component of the TF site is shorter than two times of a train body.

Field Study of Turbulence Intensity measurement by Nacelle Mounted Lidar (NML)

In this paper, Nacelle Mounted LiDAR (NML) was used to study Turbulence Intensity (TI) by dataset from three measurement campaigns, using two approaches: the white box test and the black box test. The white box test was to compare TI LOS using each Line Of Sight, while the black box test was to compare TI Hub using all LOS by relative reconstruction algorithm at wind turbine hub height. The result of white box test showed that the correlation coefficient of TI LOS varied from 0.923 to 0.955 and the slope varied from 0.978 to 1.030. The result of black box test showed that the correlation coefficient of TI Hub is 0.8337∼0.8924 and the slope is 0.904∼0.935. This study provided some promising results to wind energy community, which could be the evidence base for the further investigation for the temporal-spatial turbulence structure in low Atmospheric Boundary Layer.

Reynolds number dependence of inner peak turbulence intensity in pipe flow

Streamwise turbulence statistics in the range from Reτ = 990 to Reτ = 20 750 at the High Reynolds Number Actual Flow Facility at the National Metrology Institute of Japan are presented, specifically focusing on the Reynolds number dependence of the inner peak turbulence intensity. Velocity measurements are conducted using laser Doppler velocimetry (LDV), taking account of problems specific to this method, with the aim of providing reliable experimental results. The control volume and the fringe pattern of LDV, both of which influence turbulence statistics, are directly measured using a rotary wire device, and they are used to correct the measured turbulence intensity using methods developed in this study. The present results for mean velocity and turbulence intensity profiles agree well with direct numerical simulation data. The inner peak turbulence intensity in this pipe experiment increases with the increasing Reynolds number. It is found that the Reynolds number dependence of the inner peak up to Reτ = 20 750 is very similar to that in a turbulent boundary layer (TBL). The slope of the outer logarithmic region in the turbulence intensity profile is twice the slope obtained from the relation between the inner peak and the Reynolds number. This relation is also consistent with that for TBL flow.