Longitudinal Wind Speed Research Articles

Water spray flow rate effect on smoke temperature distribution under the ceiling in tunnel fires with longitudinal ventilation

A series of fire tests with various water spray flow rates were conducted in a small-scale longitudinal ventilated tunnel to investigate the influence of flow rates of a water spray system and different longitudinal wind speed on maximum smoke temperature and longitudinal smoke temperature distribution. Then, the test data for the case without the water spray system were compared with previous studies and agreed well with previous model which overestimates smoke temperature of the cases with the water spray. Results show that the maximum smoke temperature decreases and the longitudinal smoke temperature decays faster with the increase of water spray flow rate. Thus an improved model for maximum smoke temperature is proposed by introducing a modified coefficient λrepresenting the water spray flow rate effect. It was found that longitudinal smoke temperature decays exponentially and the decay coefficient increases with increasing water spray flow rate. Therefore considering the effect of water spray flow rate, a modified coefficient Kdown is introduced into the exponential model to predict the longitudinal smoke temperature distribution.

Influence of mechanical smoke exhaust on smoke spread in underground tunnel

The model of a tunnel in Beijing is established, and the smoke reflux, the smoke reflux length and the influence of longitudinal wind speed on temperature distribution of the tunnel vault are studied using numerical simulation method. The length of the tunnel is 150 m, the cross section is circular, the height of the tunnel is 6.3 m and the width is 6 m. The simulation results show that the smoke reflux length of the subway tunnel fire decreases with the increase of the longitudinal positive pressure wind speed, and the reflux length decreases linearly with the increase of wind speed when the reflux length is more than 10 m. The gradient of the reflux length decreases with the increase of the wind speed when the distance from the fire source decreases. The temperature curve of tunnel vault is consistent. Under the same fire source heat release rate, the flue gas temperature decreases with the increase of ventilation wind speed, and the distance between the highest temperature of the ceiling and the fire source decreased with the increase of the longitudinal ventilation wind speed.

Study on the Distribution of Fire Temperature Field of L-type Cable Corridor through Numerical Simulation

Abstract As is known to all, the cable corridor is one of the most important projects in China. In this paper, the fire temperature field distribution of L-type corridor under the condition of different fire source location height is studied through numerical simulation. When the heat release rate of the ignition source is 250 kW and longitudinal wind speed is fixed 0.5 meters per second, the temperature changing rule of the inflection point of L-type corridor is discussed. Furthermore, the temperature prediction formula is established based on the height of the ignition source at different stages according to the fire situation. Combined with the results of these studies, the paper shows that there is obvious smoke accumulation effect in L-type cable corridor.

Simulation analysis on the influence of smoke flow in special section tunnel under mechanical ventilation

In this study, a special section tunnel model was established by using FDS (Fire Dynamics Simulator). In the condition of mechanical ventilation, studied the effect of the model for exhaust velocity interval and curvature, slope on the smoke flow. Finally, the longitudinal wind speed of 3m/s is determined, and the results show that the curvature and slope of the tunnel have no effect on the smoke flow.

Maximum temperature beneath the ceiling in tunnel fires with combination of ceiling mechanical smoke extraction and longitudinal ventilation

This paper experimentally investigated the maximum temperature of smoke flow under the ceiling with the combined effect of ceiling mechanical exhaust system and longitudinal ventilation. Experiments were carried out in a tunnel model with dimensions of 66m×1.5m×1.3m (length×width×height). The longitudinal ventilation wind speed was set by 0–1.2m/s, while the ceiling extraction velocity was 0–2.2m/s with the fire heat release rate of 30–50kW. Smoke temperature beneath the tunnel ceiling was measured by K-type thermocouples. The experimental results showed that the ceiling mechanical exhaust system will affect the smoke control, due to the interactions between induced ambient air flow near the ceiling mechanical exhaust vent and longitudinal ventilation. The actual longitudinal air flow velocity would decrease with the ceiling extraction velocity increased, when the fire source was placed downstream of the ceiling extraction vent. The maximum smoke temperature beneath the tunnel ceiling decreased linearly with the ceiling extraction velocity without longitudinal ventilation. A modified model was put forward to predict the maximum temperature of smoke flow beneath the ceiling with combined effect of ceiling single point extraction and longitudinal ventilation in tunnel fires.

Effects of ambient wind on thermal smoke exhaust from a shaft in tunnels with natural ventilation

Abstract This study investigated the influence of ambient wind above the shaft opening on natural ventilation effectiveness in a tunnel by Large Eddy Simulation (LES), which is now widely applied to study the turbulent flow. The smoke movement characteristics were studied in detail, with systematically varying the ambient wind speed above the shaft opening and the longitudinal wind speed in the tunnel. The key heat and flow parameters inside and outside the tunnel and shaft, such as dispersion of smoke, temperature distribution, velocity vector field and mass flow rate of smoke exhausted by the shaft were investigated accordingly. The Reynolds number of the wind is in the range of 0.3–1 × 106 with velocity of 1–3 m/s and the Reynolds number of the smoke flowing in the tunnel and shaft is in the range of 0.1–1.7 × 106 with velocity of 1–5 m/s. The ambient wind above the shaft was found to have two opposite effects on the smoke exhaust from the shaft, namely a negative effect which restricts the smoke exhaust due to the perpendicular direction between the ambient wind and the originally vertical flowing smoke, and a positive effect which induces a negative pressure, in favour of accelerating the smoke exhaust. Moreover, both of these two effects will increase with increasing ambient wind speed above the shaft and they will compete each other simultaneously. The results will provide a theory support to guide the safe evacuation and smoke control in tunnels.

Analysis of wind coherence in the longitudinal direction using turbine mounted lidar

The use of lidar for wind turbine control relies on the hypothesis that the wind coherence in the longitudinal direction is sufficient to derive useful information from wind measurements at upstream locations. We examined wind coherence using measurements of longitudinal wind speed obtained using a forward facing pulsed turbine mounted lidar over three sites. The effect of different atmospheric conditions was evaluated. We found that the coherence decay parameter increases together with turbulence intensity, while the parameter defining the coherence at 0Hz increases with integral length-scale. A correction was applied for artificial coherence decrease due to lidar measurement effects. Results display encouraging similarities with a computational study carried out based on Large Eddy Simulation.

Spatial correlation of atmospheric wind at scales relevant for large scale wind turbines

Wind measurements a short distance upstream of a wind turbine can provide input for a feedforward wind turbine controller. Since the turbulent wind field will be different at the point/plane of measurement and the rotor plane the degree of correlation between wind speed at two points in space both in the longitudinal and lateral direction should be evaluated. This study uses a 2D array of mast mounted anemometers to evaluate cross-correlation of longitudinal wind speed. The degree of correlation is found to increase with height and decrease with atmospheric stability. The correlation is furthermore considerably larger for longitudinal separation than for lateral separation. The integral length scale of turbulence is also considered.

Discussion on Disaster Prevention and Rescue Measures in Underwater Interchange Tunnel

On the basis of fire case, fire experiments analysis, the paper had made the key to underwater interchange parameters of fire scenario, and the variation of heat release rate influenced by underwater interchange cross-sectional and longitudinal wind speed. Based on the actual status of tunnel fire and technique level of operation, established the system of fire prevention safety grades in underwater interchange and corresponding fire safety facilities. By contrasting the required safe evacuation time(TRSET) for personnel in underwater interchange tunnel and available safe evacuation time(TASET), the study draws the appropriate distance between the emergency connection access in underwater interchange.

Characterization of wind velocities in the upstream induction zone of a wind turbine using scanning continuous-wave lidars

As a wind turbine generates power, induced velocities, lower than the freestream velocity, will be present upstream of the turbine due to perturbation of the flow by the rotor. In this study, the upstream induction zone of a 225 kW horizontal axis Vestas V27 wind turbine located at the Danish Technical University's Risø campus is investigated using a scanning Light Detection and Ranging (lidar) system. Three short-range continuous-wave “WindScanner” lidars are positioned in the field around the V27 turbine allowing detection of all three components of the wind velocity vectors within the induction zone. The time-averaged mean wind speeds at different locations in the upstream induction zone are measured by scanning a horizontal plane at hub height and a vertical plane centered at the middle of the rotor extending roughly 1.5 rotor diameters (D) upstream of the rotor. Turbulence statistics in the induction zone are studied by more rapidly scanning along individual lines perpendicular to the rotor at different radial distances from the hub. The mean velocity measurements reveal that the longitudinal velocity reductions become greater closer to the rotor plane and closer to the center of the rotor. Velocity deficits of 1%–3% of the freestream value were observed 1 D upstream of the rotor, increasing at the rotor plane to 7.4% near the edge of the rotor and 18% near the center of the rotor while the turbine was operating with a high estimated mechanical coefficient of power (CP) of 0.56 yielding an estimated axial induction factor of 0.25. The velocity reductions relative to the freestream velocity become smaller when the turbine's coefficient of power decreases; for a low CP of 0.16 resulting in an estimated induction factor of 0.04, the velocity deficits are ∼1% of the freestream value 1 D upstream of the rotor and only 6% at the rotor plane near the center of the rotor. Additionally, the mean radial wind speeds were found to increase close to the edge of the rotor disk indicating an expansion of the incoming flow around the rotor. Radial velocity magnitudes at the edge of the rotor disk of approximately 9% and 3% of the freestream longitudinal wind speed were measured for the abovementioned high and low CP values, respectively. Turbulence statistics, calculated using 2.5-min time series, suggest that the standard deviation of the longitudinal wind component decreases close to the rotor, while the standard deviation of the radial wind component appears to increase. When the turbine was operating with a high CP of 0.54 resulting in an estimated induction factor of 0.22, standard deviation decreases of up to 22% of the estimated freestream value and increases of up to 46% were observed for the longitudinal and radial components, respectively, near the center of the rotor.

Wind turbine drive train dynamic characterization using vibration and torque signals

Dynamic analysis of wind turbine drive train subjected to stochastic aerodynamic loads is carried out in the present study. The longitudinal wind speed at the turbine site normally consists of a mean value superimposed with ramp, gust and turbulence components. In the present study, the aerodynamic torque is obtained by considering wind speed parameters of a typical wind turbine site. The dynamic model accounts for time varying gear mesh stiffness, bearing elasticity and torsional shaft stiffness. The dynamic analysis is done with stochastic aerodynamic loads and the vibration responses are obtained in time and frequency domains. It is observed that the entire spectral content of the vibration signals is confined to low frequency region, whereas higher frequencies are hidden. In order to capture the hidden frequency information from vibration signals, the wavelet decomposition technique is used. The dynamic analysis using torque signals is also discussed. The present study shows that, from the internal resistive torque all the characteristic frequencies can be clearly observed.

Large‐eddy simulation of stable boundary layer turbulence and estimation of associated wind turbine loads

ABSTRACTStochastic simulation of turbulent inflow fields commonly used in wind turbine load computations is unable to account for contrasting states of atmospheric stability. Flow fields in the stable boundary layer, for instance, have characteristics such as enhanced wind speed and directional shear; these effects can influence loads on utility‐scale wind turbines. To investigate these influences, we use large‐eddy simulation (LES) to generate an extensive database of high‐resolution ( ∼ 10 m), four‐dimensional turbulent flow fields. Key atmospheric conditions (e.g., geostrophic wind) and surface conditions (e.g., aerodynamic roughness length) are systematically varied to generate a diverse range of physically realizable atmospheric stabilities. We show that turbine‐scale variables (e.g., hub height wind speed, standard deviation of the longitudinal wind speed, wind speed shear, wind directional shear and Richardson number) are strongly interrelated. Thus, we strongly advocate that these variables should not be prescribed as independent degrees of freedom in any synthetic turbulent inflow generator but rather that any turbulence generation procedure should be able to bring about realistic sets of such physically realizable sets of turbine‐scale flow variables. We demonstrate the utility of our LES‐generated database in estimation of loads on a 5‐MW wind turbine model. More importantly, we identify specific turbine‐scale flow variables that are responsible for large turbine loads—e.g., wind speed shear is found to have a greater influence on out‐of‐plane blade bending moments for the turbine studied compared with its influence on other loads such as the tower‐top yaw moment and the fore‐aft tower base moment.Overall, our study suggests that LES may be effectively used to model inflow fields, to study characteristics of flow fields under various atmospheric stability conditions and to assess turbine loads for conditions that are not typically examined in design standards. Copyright © 2013 John Wiley & Sons, Ltd.

Mechanism for initial brows-like meso-scale vortex effects on tropical cyclone track

We used a two-dimensional quasi-geostrophic barotropic model simulation to study effects of an initial brows-like meso-scale vortex on tropical cyclone (TC) track. Our results show that the impact of each of the three foundational factors (the environmental current, the asymmetric structure and the asymmetric convection system) on TC track varies with time and the importance of each of the factors is different for the different TC motion time period. They show two kinds of the effects. One is a direct way. The asymmetric outer wind structure and the positive longitudinal wind speed averaged in radial-band (100–300) km in the period of (0–11) h are caused by the introduction of the initial brows-like meso-scale vortex, which results in TC track to turn to the north from the northwest directly. The other is an indirect influence. First, initial TC axisymmetric circulation becomes a non-axisymmetric circulation after the addition of the meso-scale vortex. The initial non-axisymmetric circulation experiences an axisymmetrizational process in the period of (0–11) h. Second, axisymmetrizationed TC horizontal size is enlarged after t=12 h. Third, both the TC asymmetric structure and the TC energy dispersion induced-anticyclone are intensified, which quickens the TC motion and results in the track to turn to the north indirectly. The TC motion is characterized by the unusual track under the direct and the indirect effect. The formation of the unusual track should be attributed to the common effects of three factors, including the environmental flow, the TC asymmetric structure and the asymmetric convection system.

THE ACCURACY OF USING THEULYSSESRESULT OF THE SPATIAL INVARIANCE OF THE RADIAL HELIOSPHERIC FIELD TO COMPUTE THE OPEN SOLAR FLUX

We survey observations of the radial magnetic field in the heliosphere as a function of position, sunspot number, and sunspot cycle phase. We show that most of the differences between pairs of simultaneous observations, normalized using the square of the heliocentric distance and averaged over solar rotations, are consistent with the kinematic effect whereby the radial component of the frozen-in heliospheric field is increased by longitudinal solar wind speed structure. In particular, the survey shows that, as expected, the flux excess effect at high latitudes is almost completely absent during sunspot minimum but is almost the same as within the streamer belt at sunspot maximum. We study the uncertainty inherent in the use of the Ulysses result that the radial field is independent of heliographic latitude in the computation of the total open solar flux: we show that after the kinematic correction for the excess flux effect has been made it causes errors that are smaller than 4.5%, with a most likely value of 2.5%. The importance of this result for understanding temporal evolution of the open solar flux is reviewed.

Improved Wind and Turbulence Measurements Using a Low-Cost 3-D Sonic Anemometer at a Low-Wind Site

A year of data from sonic anemometer and mechanical wind sensors was analyzed and compared at a low-wind site. Results indicate that 15-minute average and peak 1-second wind speeds (u) from the sonic agree well with data derived from a co-located cup anemometer over a wide range of speeds. Wind direction data derived from the sonic also agree closely with those from a wind vane except for very low wind speeds. Values of standard deviation of longitudinal wind speed (σu) and wind direction fluctuations (σø) from the sonic and mechanical sensors agree well for times with u > 2 ms-1 but show significant differences with lower u values. The most significant differences are associated with the standard deviation of vertical wind fluctuations (σw): the co-located vertical propeller anemometer yields values increasingly less than those measured by the sonic anemometer as u decreases from 2.5 approaching 0 ms-1. The combination of u over-estimation and under-estimation of σw from the mechanical sensors at low wind speeds causes considerable underestimation of the standard deviation of vertical wind angle fluctuations (σø), an indicator of vertical dispersion. Calculations of σø from sonic anemometer measurements are typically 5° to 10° greater than from the mechanical sensors when the mechanical instruments indicate that σø < 5° or so. The errors with the propeller anemometer, cup anemometer and wind vane, caused by their inability to respond to higher frequency (smaller scale) turbulent fluctuations, can therefore lead to large (factors of 2 to 10 or more) errors in both the vertical and horizontal dispersion during stable conditions with light winds. The sonic anemometer clearly provides more accurate and reliable wind data than the mechanical wind sensor with u < 2.5 ms-1

Centennial changes in solar activity and the response of galactic cosmic rays

There is a growing consensus that the eleven year-modulation of galactic cosmic rays (GCRs) resulting from solar activity is related to interplanetary propagating diffusive barriers (PDBs). The source of these PDBs is not well understood and numerical models describing GCR modulation simulate their effect by scaling the diffusion tensor to the interplanetary magnetic field strength (IMF). The implications of a century-scale change in solar wind speed and open solar flux, for numerical modelling of GCR modulation and the reconstruction of GCR variations over the last hundred years are discussed. The dominant role of the solar non-axisymmetric magnetic field in both forcing longitudinal solar wind speed fluctuations at solar maximum and in increasing the IMF is discussed in the context of a long-term rise in the open solar magnetic flux.

Detection and analysis of coherent structures in urban turbulence

The continuous wavelet transform provides a suitable tool to visualize the vertical structure of turbulence and to detect coherent structures in turbulent time series. This is demonstrated with a simple example of an artificially ramp structured time series. In this study turbulence data, i.e. the fluctuations of the horizontal wind components u′ and v′, the vertical component w′ and temperature T′, sampled with 20.83 Hz and measured simultaneously at three levels (z/h=1.5, 2.1 and 3.2, with z as the sensor height and h the height of the roughness elements) over an urban canopy in the inner city of Basel, Switzerland, are analyzed. The detection of the coherent structures was performed using the Mexican hat wavelet and the zero-crossing method. The analysis for unstable conditions shows that organized structures (ejection-sweep cycles) cover about 45% of the total run time. A conditional average from a total of 116 detected ejection-sweep sequences during 7 hours was calculated over a time window of 100 seconds. This dominating time scale was derived from peak frequencies of the wavelet spectra as well as from the Fourier spectra. It is shown that the normalized amplitudes of fluctuations of temperature and longitudinal wind speed during the events are largest at the lowest measurement level just above the canopy and decrease with increasing distance from the roughness elements. A comparison of related studies over different non-urban surfaces (mainly forests) shows that the shape of conditionally averaged ejection-sweep sequences is very similar for all canopies, however, the dominating time scale in general increases the rougher the surface is and the higher the roughness elements are.

A phenomenological model for the dynamic response of wind turbines to turbulent wind

To predict the average power output of a wind turbine, a response model is proposed which takes into account: (i) the delayed response to the longitudinal wind speed fluctuations; (ii) a response function of the turbine with arbitrary frequency dependence; (iii) wind fields of arbitrary turbulence intensity. In the limit of low turbulence intensity, the dynamical ansatz as proposed in 1992 by Rosen and Sheinman is reproduced. It is shown, how the response function of the turbine can be obtained from simulation experiments of a specific wind turbine. For two idealized situations the dynamic effect of fluctuating wind is estimated at turbulence intensities 0⩽ I u ⩽0.5. At the special mean wind speed V=8 m/s , the turbine response function is determined from simulation data published by Sheinman and Rosen in 1992 and 1994.

Simultaneous measurements of wind speed profiles at two sites using Doppler sodars

In the wind-resistant design of buildings and structures, it is very important to accurately assess the design wind speed at a particular site, considering the variation in wind speed with terrain roughness. The authors attempt to find a reasonable method for estimating design wind speed for given terrain roughness, through simultaneous wind observations at altitudes up to 420 m at sites with different roughnesses using two sets of Doppler sodars. In this paper, the characteristics of the mean wind speed profiles evaluated for each distinguished wind speed in each wind direction were presented. The longitudinal mean wind speed profiles in the same storms were also compared for two pairs of sites to study the variation in longitudinal mean wind speed as it is affected by inland terrain roughness.

Wind speed profiles measured over ground using Doppler sodars

Abstract In the wind-resistant design of buildings and structures, it is very important to accurately assess the design wind speed at a particular site, considering the variation in wind speed with terrain roughness. In this study, the authors’ group attempts to find a reasonable method for estimating design wind speed for a given terrain roughness, through simultaneous wind observations at altitudes up to 420 m over two sites with different roughnesses using Doppler sodars. Prior to the observations, preliminary measurements were conducted to determine the effect of measurement conditions such as the transmission method, pulse length, power and frequency, on both the data collectable rate and the measured values. The quality of the data obtained under various measuring conditions was studied, and then a proper measuring condition was determined. Then, simultaneous observations of atmospheric boundary layer wind speeds were conducted by Doppler sodars at a “seaside” area and a “suburban” area. The characteristics of the mean wind speed profiles, which were evaluated for each distinguished wind speed level in each wind direction, are presented. The longitudinal mean wind speed profiles in the same storms at the two sites were also compared to study the variation in longitudinal mean wind speed as this is affected by inland terrain roughness