Longitudinal Turbulence Research Articles

Three-dimensional distortion of free-stream turbulence with the leading-edge stagnation point of an elongated bluff body

The paper focuses on studying the unsteadiness, three-dimensionality, and distortion of free-stream turbulence approaching the stagnation point of an elongated bluff body. This aerodynamic problem is complicated because of the combination of blocking, distortion, and three-dimensional (3D) effects. Using the spectral tensor concept, a closed-form solution of the three-dimensional transfer function (3D AAF) of the fluctuating pressure at the stagnation point is proposed. The 3D AAF provides us with an appropriate way to quantitatively study these effects on the unsteady behavior of fluctuating pressures. Our experimental results indicate that the fluctuating pressure at low wavenumbers can be predicted by Bernoulli's equation. The 3D effect becomes more prominent for smaller-scale turbulence, resulting in a more correlated fluctuating pressure in a spanwise direction and a faster decay of pressure spectra at high wavenumbers. By contrast, the distortion plays a more important role in determining this rapid “roll-off” of the stagnation fluctuating pressure spectra. This tendency becomes more prominent with the increase in Lu/D, where Lu is the longitudinal turbulence scale, and D is the leading-edge body dimension. The possible physical interpretation for the unsteady behavior of fluctuating pressures at the stagnation point is discussed.

Turbulence correlation between moving trains and anemometer towers: Theoretical analysis, field measurements and simulation

A precise command of railway operations according to the measured instantaneous wind speed on an anemometer tower along a railway line is the development trend, whose challenges lie in the unknown transfer relation(s) between wind speed fluctuations on a moving train and an anemometer tower, i.e. the turbulence correlation between them. To address this issue, in the current work, the cross-correlation functions of wind speed fluctuations at the moving train and anemometer tower are derived, and an empirical formula of the coherence functions is obtained. The turbulence correlation is inversely related to the separation distance from the anemometer tower to the line, and there is little correlation when this distance is longer than double the longitudinal turbulence length scale. Field measurements of wind characteristics were carried out on an anemometer tower and a moving vehicle, and the turbulence correlation and its expression were validated. Three methods are proposed and compared to evaluate the instantaneous wind speed at the anemometer tower and moving train with this correlation. The methods based on the cross-spectral density and coherence function can accurately simulate the correlation, and the latter performance is slightly better (its simulation of the frequency domain correlation is 52.9% better than the former); the method based on solely independent and identically distributed random phases cannot fully simulate the correlation. From this, the effects of the correlation on train operations are studied and analysed in detail. Our analysis shows that neglecting this correlation leads to conservative estimates: wind speed differences between the anemometer tower and the moving train are at least 18.1% greater, and the safety and economic assessments of train operations in crosswinds are underestimated by at least 32.0%. Considering the correlation can reduce the (excess) safety risk/margin and is an inevitable development of adapting to the detailed assessment of the crosswind stability of vehicles. The quantitative description and simulation of the correlation presented in this work point to the critical importance of wind speed monitoring systems for the detailed crosswind assessment, and provide a theoretical basis for further research work on the crosswind stability of vehicles under true/realistic turbulent flow wind.

Effects of turbulence intensity and integral length scale on wind-induced vibrations of a three-dimensional aeroelastic square cylinder

Despite a wealth of prior research on the effects of free-stream turbulence (FST) on the aerodynamics of square cylinders, there is limited knowledge about their aeroelasticity such as characteristics of wind-induced vibrations that vary with the FST properties. This paper focuses on the investigation of the effects of FST properties including longitudinal turbulence intensity and integral length scale on the wind-induced vibrations of a three-dimensional (3D) aeroelastic square cylinder with an aspect ratio of 10 (a super-tall building model). Through wind tunnel testing, displacements of the aeroelastic model are measured in smooth flow and four turbulent flows to experimentally investigate its characteristics of fluid-solid interaction, including along- and across-wind vibrations, especially vortex-induced vibration and galloping. The effects of the turbulence intensity with a higher-level than previous studies are also investigated. The results show that the root-mean-square (RMS) displacements of the along-wind responses increase with the increase of turbulence intensity and are not affected by integral length scale. For the across-wind responses, in the non-lock-in region, the RMS displacements generally increase with the increase of turbulence intensity. In the lock-in region, the RMS displacements remain unchanged with the increase of turbulence intensity, while increase with the increase of integral length scale. This paper aims to improve the comprehension of the effects of FST on the wind-induced vibrations of 3D square cylinders and to furnish valuable insights for the wind-resistant design of slender structures, such as supertall buildings.

Experimental identification of longitudinal and vertical lift aerodynamic admittance functions of thin sections

Previous studies of two-dimensional (2D) aerodynamic admittance function (AAF) identification methods have basically ignored the effects of different turbulence components, which may lead to unpredictable errors for practical engineering applications. This paper presents pressure measurement experiments on thin sections with a geometric ratio of 1:50 in various turbulent fields. Based on the three-dimensional (3D) two-wavenumber theoretical analytical framework, the two-wavenumber coherence function is obtained by fitting the measured spanwise root-coherence function at the effective spacing with an empirical model. A new method is proposed, assuming that the ratio relationship between the lift AAFs due to longitudinal and vertical turbulence components of the measured model section satisfies its corresponding theoretical solution ratio relationship. The 2D lift AAFs of the airfoil section induced by different turbulence components are identified following the proposed identification framework. Consistent with the previous research, force correlation is significantly larger than turbulence correlation, and the traditional 3D one-wavenumber AAFs obtained are different in different turbulent fields. The separated 2D lift AAFs demonstrate that the contributions of u- and w- turbulence to the buffeting lift force are significantly different, and are more precise, according to the ratio between the Horlock function and Sears function. Then, the method is successfully extended to estimate the AAFs with respect to the u- and w-turbulence components of a streamlined box girder section, further validating the applicability of the identification method to the streamlined box girder. Furthermore, comparing the separated 2D lift AAFs under different turbulence fields reveals their independence from turbulence characteristics.

Turbulence characteristics of non-spherical isolated particles with different flatness on a rough bed surface

The transport of non-spherical particles on bed is significantly influenced by flow dynamics and particle shape. To study the impact of changes in the flatness of isolated bed particles on the surrounding flow characteristics, we prefabricated three isovolumetric particles with varying levels of flatness and analyzed the flow field around them using two-dimensional particle image velocimetry measurement methods. The results show that the presence of the particles significantly alters the turbulence parameters of the surrounding flow. Specifically, the influence extends up to 1D upstream of the particles, 0.5D above the particle tops, and throughout most of the downstream region, where D represents the equivalent particle diameter. The particles cause a reduction in Reynolds stress and turbulent kinetic energy in the near-bed upstream region, with a more pronounced effect observed for particles with lower flatness. Increased particle flatness is associated with a smaller difference in the longitudinal time-averaged velocity between upstream and downstream regions. In the wake region, particle flatness shows a negative correlation with Reynolds stress, longitudinal turbulence intensity, and turbulent kinetic energy, with this effect being more pronounced closer to the particles. Quadrant analysis indicates that ejection (Q2) and sweep (Q4) quadrant events remain dominant in the presence of particles, while particle flatness positively correlates with the frequency of outward (Q1) and inward (Q3) events in the wake region and negatively correlates with the frequency of Q2 and Q4 events. This study enhances our understanding of particle-fluid interactions, particularly the response relationship between non-spherical particles and turbulent mechanisms.

Investigation of turbulence and interfacial exchange features of the gap area within the fully developed Shallow-Submerged canopy flow

The flow patterns within a longitudinal gap area formed by discontinuous distributions of submerged canopy, as well as the momentum and mass exchange characteristics between the gap area and the overlying free-flow, were studied using high-resolution Large Eddy Simulation (LES). The gap area is located within the fully developed region of submerged canopy flow. The simulations considered four aspect ratios of the gap area, L/h (ranging from 1 to 4), where L and h represent the span of the gap area and the height of the canopy, respectively, and two canopy densities, ϕ = 0.08 and 0.15. Results indicate that recirculation vortices appear only at ϕ = 0.15 and penetrate the downstream canopy patches to varying extents, with the distance of invasion decreasing as L/h increases. Influenced by the recirculation vortices, the bed shear stress in the downstream part of the gap area and the initial section of the downstream canopy patch is significantly increased compared to the fully developed region of the upstream canopy patch. Within the parameter range covered, vertical penetration of the mixing layer into the gap area always occurs, consistently falling into the shear layer growth regime, with significant enhancement of turbulence within the gap area even at L/h = 1. The high momentum entrainment elevates longitudinal velocity and turbulence intensity in the upper corner regions of the downstream canopy patch’s leading edge, combined with localized increases in bed shear stress, potentially destabilizing plants at the forefront of the downstream canopy patch. Although the total momentum exchange across the interface between the gap area and the upper free-flow layer is approximately independent of L/h, larger canopy densities lead to stronger momentum transport, and turbulent transport always dominates. Mass exchange generally increases with L/h, with more efficient vertical mass exchange in ϕ = 0.15 cases at L/h = 3 and 4.

Heat transfer enhancement mechanics of different micro-disturbing structures for transcritical hydrocarbon fuel using 3-D secondary flow intensity analysis

Heat transfer enhancement based upon micro-disturbing structures becomes increasingly important for thermal protection of air-breathing propulsion systems. To explore the influence mechanism of different structures on heat transfer in regenerative cooling channels of scramjet engines, flow structures and heat transfer of supercritical-pressure n-Decane in mini-channels with dimple and micro-rib arrays are numerically investigated. Results indicate effective heat transfer enhancement inside the channels depends more on efficient transverse turbulence disturbance rather than longitudinal or perpendicular turbulence disturbance. Severe thermal stratification generates strong shear layers in channels, where transverse secondary flows bring much intenser flow mixing than longitudinal secondary flows, especially in transcritical temperature region where the best heat transfer enhancement is obtained. With same characteristic dimensions, longitudinal micro-disturbing structures like dimples have lower flow resistance, but transverse micro-disturbing structures like micro-ribs achieve stronger heat transfer enhancement. Besides, the performance of micro-ribs is much more sensitive to the dimensional change. Therefore, micro-ribs have larger working excursion for enhancing performance factor than dimples. With optimal structure parameters: hr = e = 0.3 mm, pr = 3 mm, hd = 0.225 mm, dd = 1.5 mm, overall performance factor in micro-ribbed channel is 1.14 times of that in dimpled channel. Those conclusions provide effective support for optimization design for the regenerative cooling structures.

Scaling effects on peak wind load estimation for low-rise buildings: An experimental and analytical study

Though scaling effects on estimation of peak wind loads are extensively documented in the literature, there is a lack of systematic comparison of such scaling effects across different model scales tested in wind tunnels. Moreover, the limited studies on large-scale physical models accepted the inadequacy of simulating the large turbulent eddies rather than addressing the missing low-frequency turbulence simulation inherent in such large-scale testing. This study provides an in-depth comparison of estimates of peak wind loads obtained using a range of experimental scaled models (1:100 and 1:6 model scales) of the Wind Engineering Research Field Laboratory (WERFL) building while applying a Partial Turbulence Simulation (PTS) methodology to incorporate the effects of turbulence. Large-scale wind tunnel testing of structures provides the advantage of achieving an improved Reynolds number (Re) similarity, more accurate geometric similarity, and enhanced resolution of flow details such as corner vortices, than is possible with the use of smaller model scales. However, as the model scale increases, achieving turbulence similarity becomes challenging due to limitations in simulating the low-frequency turbulent eddies in the wind tunnel. The PTS method has been used in the recent past to account for the low-frequency turbulence effects in the peak wind load estimation. The method is referred to as 1DPTS when considering longitudinal turbulence components only and 2DPTS when considering both longitudinal and lateral turbulence components in the analysis. The computationally intensive 2DPTS can be further simplified by using a weighted average method as described in this paper as “weighted average PTS.” The current study explores the effect of scaling on peak wind load estimation by using the 1DPTS, 2DPTS, and weighted average PTS methods. Results from the multi-scale experimental tests demonstrate that using larger model scales and compensating for the low-frequency turbulence deficit in the post-test analysis significantly improve the agreement with the prototype data owing to the simulation of a higher Reynolds number. Furthermore, comparing the results of the proposed weighted average method with full-scale data reveals its potential as a substitute for the original 2DPTS method, offering enhanced accuracy, particularly at the roof corner for oblique wind directions. While the effects of Re are well known, the findings of this study explore its impact in conjunction with the application of the PTS methods on peak Cp estimation across five different model scales with Re ranging from 3.65 × 104 to 2.43 × 106, the latter being closest to the full-scale (field) Re. The findings provide new insights into how large-scale physical model testing in high Re flows, supported by analytical PTS-based compensation, can enhance the accuracy of peak wind load estimations for critical scenarios including cornering winds that generate conical vortices.

Effects of turbulence integral length scales on aerodynamic characteristics and displacement responses of a square prism

This paper investigates the influence of the inflow turbulence integral length scales on the aerodynamic forces on a surface-mounted finite-length square prism and its displacement responses by computational fluid dynamics simulations. Four turbulent inflow conditions with the same mean wind speed and turbulence intensity but different longitudinal and transverse turbulence integral length scales are generated for the simulations. First, the wind pressures and forces on a rigid square prism model and the shear layer characteristics are simulated by large eddy simulations. The simulation results show that the mean characteristics of the wind pressures and shear layers are not sensitive to the turbulence integral length scales. However, the root mean square (RMS) wind pressures on side faces and RMS across-wind forces are increased with the longitudinal turbulence integral length scale, and the mechanism is analyzed by the proper orthogonal decomposition. Second, the displacement responses at the mean wind speed of vortex-induced resonance are computed based on an aeroelastic square prism model by fluid–solid interaction simulations. The RMS displacements of the model are observed to be more sensitive to the transverse turbulence integral length scale rather than the longitudinal turbulence integral length scale. Finally, the influence of the turbulence integral length scales on the Reynolds stresses around the square prism is presented and discussed.

Onsite measurements of pedestrian-level wind and preliminary assessment of effects of turbulence characteristics on human body convective heat transfer

Wind is an important factor affecting outdoor thermal comfort in urban environment, but its turbulence characteristics at the pedestrian level and effects on convective heat transfer (hc) from a human body remain poorly understood. Previous studies were only conducted in wind tunnels with low turbulence intensity, small turbulence integral length scale, and fixed prevailing wind direction. To address this knowledge gap, this field study was conceived to monitor the pedestrian level wind in actual outdoor settings and to measure the hc of a thermal manikin at the same time. The results show that both longitudinal and lateral turbulence intensity significantly enhance whole body hc. It remains to be examined whether the small-scale wind direction variation can be included in the lateral turbulence intensity or vice versa. The integral length scale found at the two sites were larger than a typical manikin dimension, and the whole body hc peaked when these two scales were comparable. As the first major field study to quantify convection heat loss of a thermal manikin exposed to real-life urban boundary layer wind, it is demonstrated crucial to consider realistic turbulence characteristics in the field when evaluating hc over a human body for urban microclimate design.

Atmospheric turbulence strength distribution along a propagation path probed by longitudinally structured optical beams

Atmospheric turbulence can cause critical problems in many applications. To effectively avoid or mitigate turbulence, knowledge of turbulence strength at various distances could be of immense value. Due to light-matter interaction, optical beams can probe longitudinal turbulence changes. Unfortunately, previous approaches tended to be limited to relatively short distances or large transceivers. Here, we explore turbulence probing utilizing multiple sequentially transmitted longitudinally structured beams. Each beam is composed of Bessel-Gaussian ({{{{{{rm{BG}}}}}}}_{{{{{{mathcal{l}}}}}}{{=}}0,{k}_{z}}) modes with different {k}_{z} values such that a distance-varying beam width is produced, which results in a distance- and turbulence-dependent modal coupling to {{{{{mathcal{l}}}}}}{{{{{mathscr{ne }}}}}}0 orders. Our simulation shows that this approach has relatively uniform and low errors (<0.3 dB) over a 10-km path with up to 30-dB turbulence-structure-constant variation. We experimentally demonstrate this approach for two emulated turbulence regions (~15-dB variation) with <0.8-dB errors. Compared to previous techniques, our approach can potentially probe longer distances or require smaller transceivers.

A Numerical-Experimental Framework to Separate the Effects of Different Turbulence Components on the Buffeting Forces of Bluff-body Structures

In conventional buffeting analyses of flexible civil engineering structures, the differences between the effects of longitudinal (u-) and vertical (w-) turbulence components were usually ignored. This assumption could cause unpredictable errors and needs to be refined. To improve the accuracy of buffeting analyses, this paper proposes a framework combining Computational Fluid Dynamics simulation and wind tunnel test to analyze the buffeting forces considering the differences between turbulence components. First, the Aerodynamic Admittance Functions (AAFs) with respect to u- and w- turbulence are numerically evaluated. Next, the total buffeting forces are experimentally measured. Finally, the numerical and experimental results are combined following a theoretical scheme to separate the effects of u- and w-turbulence. Results show that u- and w- turbulence have different contributions to the buffeting forces, directly indicating the inaccuracy of the conventional assumption. In the turbulence field investigated, the buffeting lift force at zero angle of attack (AoA) are all contributed from the w-turbulence, while the contribution from u-turbulence increase as AoA increases. This numerical-experimental framework overcomes the limitations of the conventional method by quantitatively describing the different contributions of u- and w- turbulence.

Reynolds stress modeling of supercritical narrow channel flows using OpenFOAM: Secondary currents and turbulent flow characteristics

In this study, the full Launder, Reece and Rodi pressure-strain model, and nonlinear boundary damping functions were incorporated in OpenFOAM® to simulate the turbulence-driven secondary currents in supercritical narrow channel flows, such as in sediment bypass tunnels. Five simulations were performed under uniform flow conditions covering Froude numbers from 1.69 to 2.56 and aspect ratios (channel width to flow depth) ar from 0.9 to 1.91 to investigate the formation of secondary currents and their impacts on longitudinal velocity, turbulence characteristics, and bed shear stress distribution. The numerical results of the maximum longitudinal velocity and the average shear velocity show marginal deviations, of less than 2.6%, from two-dimensional experimental results acquired under decelerating flow conditions. However, some differences are observed for the secondary currents and for the vertical turbulence intensity and Reynolds shear stress in the outer flow region, especially for cases with higher flow nonuniformity (that can influence the surface perturbation) whose influence is missing in the numerical model. No intermediate vortex is observed for ar = 1.91. However, it develops for lower ar and detaches from the free surface vortex when ar ≤ 1.05. Such vortex bulges the longitudinal velocity contour lines inward and the zone of higher longitudinal velocity narrows and deepens with a decrease in ar. The decrement reduces the magnitude of the normalized maximum secondary velocity. It also affects the bottom vortex which alters the bed shear stress distribution.

Variation Characteristics of the Wind Field in a Typical Thunderstorm Event in Beijing

The understanding of wind field characteristics during thunderstorms is key to structural design for resistance to thunderstorms. In this paper, the directional thunderstorm wind model is adopted to analyze the characteristics of vertical variations of the wind field in a typical thunderstorm event in the Beijing urban area, based on the measured data. First, the longitudinal and lateral fluctuating wind speed components were decoupled and the change of direction was obtained. Then, variation of the wind speed, wind direction, turbulence intensity, turbulence integral length scale, and gust factor with the height and time were studied. The measured thunderstorm wind spectrum and the coherence function of horizontal longitudinal reduced turbulent fluctuations were analyzed and compared with empirical models. The results showed that the wind speed profile presented an obvious “nose shape” near the peak wind speed. The longitudinal turbulence integral scale was larger than the lateral one. The Von Karman spectrum is relatively effective in fitting the thunderstorm wind spectrum. Compared with synoptic winds, the gust factor during the pass of thunderstorm wind is larger, so it seems necessary to consider the influence of thunderstorm wind in engineering design.

Combining active and passive wind tunnel tests to determine the aerodynamic admittances of a bridge girder

In conventional buffeting analyses for long-span bridges, the aerodynamic admittance functions (AAF) with respect to the longitudinal (u-) and vertical (w-) turbulence components are usually assumed to be equivalent. This assumption could cause unpredictable errors due to complicated turbulence-structure interactions. This study proposes an experimental method to determine the u- and w- AAFs in the framework of three-dimensional buffeting theory. First, passive wind tunnel test is conducted to measure necessary aerodynamic parameters. Next, the turbulence characterized only by u-velocity fluctuations is generated in a multi-fan active-controlled wind tunnel to reproduce the u-velocity component in the passive wind tunnel test. The aim is to identify the u-AAF separately. Finally, the w-AAF is evaluated by combining the parameters measured in the active and passive wind tunnel tests. For a streamlined bridge girder, results show significant discrepancies between the u-AAF and w-AAF. The derivation degrees depend on the frequency and the angle of attack (AoA). This indicates the inaccuracy of the conventionally invoked assumption. In detail, the w-AAF is higher than the u-AAF at low frequencies, whereas the relationship reverses at higher frequencies. The proposed method is also applicable for other bluff-body structures, it is useful for improving the accuracy of buffeting analyses.

Heat transfer and performance enhancement investigation of novel plate heat exchanger

• Enhancement of heat transfer and performance have been investigated for a novel PHE. • The effect of changing depth and surface of ripple on performance and heat exchange has been studied. • The results showed that the effect of longitudinal turbulence on Nu number is greater than the transverse ones. • The improvement of Nu number and Performance by improving transverse turbulence was 13% and 8%, respectively. • The improvement of Nu number and Performance by improving the longitudinal turbulence was 52% and 36%, respectively. • Comparing the enhanced performance of NPHE with those of other types in the literature shows an improvement of up to 37%. In this paper, the enhancement of heat transfer and performance have been investigated numerically for a novel plate heat exchanger. The effect of changing the shape of the hyperbolic tangent function and the dimensions of the plate profile on the flow properties have been studied numerically by ANSYS Fluent 16.0. The results show that the transverse disturbances of fluid movement increase the heat transfer, as the heat transfer is enhanced by increasing the concavity of the hyperbolic tangent function. Moreover, as the corrugation depth of the plate increases, the heat transfer increases. As a result, it was found that the effect of the longitudinal turbulence in the direction of flow on the heat transfer is greater than the effect of the transverse turbulence. By comparing the results with those of the novel plate heat exchanger, it was shown that the heat transfer and performance have been enhanced on average by 13% and 8%, respectively when using the hyperbolic tangent function “y = tanh(x)”, while they have been enhanced on average by 52% and 36% respectively at the corrugation depth of 2.5 mm. Further, when comparing the enhanced performance of the novel plate heat exchanger with those of other plate geometries, the enhanced performance showed an improvement of up to 37% over its nearest competitor.

The probabilistic turbulence profiles of tropical cyclones in open and flat terrain

The fluctuating winds are usually characterized in the frequency domain by the power spectral density (PSD) function and the coherence function, in which the turbulence intensity and turbulence integral scale are key parameters to describe the gust characteristics of turbulent winds. These parameters estimated from tropical cyclone (TC) observations show significant scattering. Starting from a critical review of the state of the art, the Von Karman spectra are chosen for the TC winds. The turbulence intensity and the turbulence integral scale used in wind spectral functions are discussed in detail. By introducing randomness into the empirical models, the probabilistic longitudinal turbulence profiles of TCs are derived from a wide collection of field measurements with open and flat terrain in the literature. Moreover, the probabilistic models of the lateral and vertical turbulence components are obtained by assuming proportionality between these two components and the longitudinal one. The mean and standard deviation of the developed models for TCs are compared with those defined in the seven major wind loading codes worldwide as well as the model given by Solari to testify these models and illustrate their differences to synoptic winds.

Effects of Groin Type and Bed Properties on Flow in Groin Fields: Comparison of Fixed- and Mobile-Bed Experiments

Groin type and vegetation in groin fields directly affect flow field, bank protection, and river evolution. Many studies focus on fixed-bed contexts, but there are few studies on the influence of riverbed changes on hydrodynamic characteristics around groins. In this study, three types of groins are investigated experimentally in fixed and mobile beds in terms of time-averaged flow characteristics, turbulence characteristics, and bed changes. In both fixed- and mobile-bed experiments, vegetation reduced erosion of the groin field and main stream. Compared with the fixed-bed experiment, the velocity in the main stream was decreased in the mobile-bed experiment, and the longitudinal turbulence intensity and lateral momentum exchange were increased. In this study, an improved three-dimensional groin group (upstream wing submerged T-shaped groin group) produced a lower sediment scouring capacity, average scour depth, and entrainment coefficient k than I-shaped and T-shaped groin groups.

Moving Spatial Turbulence Model for High-Fidelity Rotorcraft Maneuvering Simulation

A moving spatial turbulence model is developed for rotorcraft maneuvering simulation under different flight conditions. The recursive algorithms are adopted to model its distributed longitudinal turbulence components, which are correlated with the lateral and vertical axes to form a local spatial turbulence field. The flow field is constrained around the rotorcraft by following its movement, and the corresponding turbulence components are updated at a constant spatial interval. The statistical properties along the longitudinal, lateral, and vertical directions have been validated against the von Kármán theory. A synthetic simulation environment consisting of a flight dynamics model and a pilot model is constructed to demonstrate the effectiveness of the turbulence model. Its performance is validated by comparing the power spectral densities of both rotorcraft responses and pilot controls in turbulence against flight test data. The piloted simulation results on an Approach-to-Hovering task show that the handling qualities ratings are susceptive to the level of turbulence and significantly increase when performing aggressive controls. The simulation also accurately predicts the expected effect of varied aircraft speed, wind speed, turbulence intensity, and stability augmentation system on piloted handling qualities rating for rotorcraft flight in turbulence.

Turbulence characteristics in a weir-orifice-slot combined fishway with an identical layout

A combined fishway containing notched weir, central orifice and vertical slot with an identical layout was designed, and its turbulence characteristics were experimentally studied. An acoustic Doppler velocimetry (ADV) was used to measure three-dimensional velocity. Flow regime, average velocity, turbulence intensity, Reynolds stress, power frequency-spectrum, correlation function, turbulence scale were analysed. The experimental results showed the combined fishway was of remarkable three-dimensional flow structures. Longitudinal velocity exhibited obvious extreme value region on the horizontal plane. Extreme values of longitudinal turbulence intensity were concentrated mainly on the mixing region between weir flow and orifice jet, as well as the vertical slot wall jet region, extreme value region of transverse turbulence intensity occurred on the central plane of orifice jet, and extreme values of vertical turbulence intensity were scattered. Reynolds stress extreme value occurred mainly in the convergent zone of multiple jets. Dominant frequency of power frequency-spectrum was highest for notched weir and lowest for vertical slot. Longitudinal velocity fluctuation exhibited a correlation with time, which was characterised by dominant frequency. Turbulence scales showed eddy structures were related to flow zones.