Increasing Wind Velocity Research Articles

Wind effects on transition and extension characteristics of the external flame projecting from a compartment with opposing openings

The assisting wind force effect on the transition and extension characteristics of the flame projecting outside the window of a compartment was experimentally investigated. The transition criteria, length, and maximum temperature profile of the external flame were studied. As the wind velocity increases, three states: namely a spill-like plume, horizontally ejected flame and no flame outside the window were identified in the experiments. The Froude number can be used to determine the three states of the external flames, with the critical values separating these stages being 2.3 and 6.4. Two length scales, l1 and l2 are proposed to modify the developed theories without a wind effect. The length scales are used to analyze the length and maximum temperature profile of the external flame. The dimensionless flame lengths are proportional to the 1.5 and 1.2 power of the dimensionless convective heat flow rate for the spill-like plume and horizontally ejected flame respectively. Correlations for the maximum temperature rises of the external flame are established between the dimensionless convective heat flow rate and the length (height) of the plume by taking into account the thermodynamic and dynamic effects of the external wind.

Investigation of sidewall height effect on the burning rate and flame tilt characteristics of pool fire in cross wind

In the current study the combining effect of sidewall height and cross air flow on the mass burning rate, flame height and flame tilt behavior of pool fire has been experimentally investigated. The mass burning rate increases as the cross wind velocity increases. The presence of sidewalls also influences the mass burning rate, as it is increased at lower cross wind velocities and decreased as this velocity further increases. A dimensionless parameter is introduced to illustrate the sidewall height effect on the mass burning rate. The effect of sidewall height on burning rate, flame height, and flame tilt angle of pool fire is further investigated. The flame height is an exponential function of a new dimensionless parameter Fr˜. Based on the experimental results, new empirical correlations are proposed to predict flame height and flame tilt angle α in relation to the combining effects of sidewall height and cross wind.

Tularemia Outbreak and After; Effect of Seasonal Changes

Tularemia is a zoonotic infectious disease caused by Francisella tularensis. In Yozgat, a total of 525 cases were identified between 2010 and 2016. A serious epidemic occurred with a total of 442 cases in 2010 and 2011 and the number of cases decreased in the later years. In our study, we investigated the association of seasonal factors (temperature, humidity, amount of precipitation, wind speed) with the tularemia epidemic which occurred in 2010 and 2011 and with the decrease in the number of cases in the later years. This study included tularemia cases seen in Yozgat and its districts between 2010 and 2016. Tularemia was defined as a microagglutination test (MAT) result of ≥ 1/160 or a 4-fold increase in MAT titer between two tests at least two weeks apart, in the presence of consistent clinical findings. Seasonal factors were recorded. The conformity of data to normal distribution was analyzed using the ShapiroWilk test. The Mann-Whitney U test was used with the results of Monte Carlo simulations to compare differences between two independent groups in terms of quantitative data. It was found that tularemia cases are more frequently seen in the spring and winter. Meteorological data showed that wind force was statistically significantly higher in the epidemic years than in the other years (p< 0.05). No statistically significant difference was found between mean air temperature, amount of precipitation, and humidity (p> 0.05). Our study found that wind velocity was significantly higher in the epidemic years than in the other years (p< 0.05) and this increase in wind velocity may have caused an increase in tick population and distribution. We believe that, rather than causing direct transmission of tularemia to humans, the increased tick population plays a key role in the maintenance of the life cycle of tularemia by causing transmission to rodents and domestic animals.

MP03-18 DO WEATHER PARAMETERS AFFECT THE INCIDENCE OF RENAL COLIC IN A PREDOMINANTLY WARM COUNTRY? A MULTICENTER ECOLOGICAL STUDY

INTRODUCTION AND OBJECTIVE:The etiology of kidney stones is multi-factorial, with observed geographic and seasonal differences affecting the rate of stone formation. Multiple studies have reported ...

The Effect of Surface Modification on Heat Transfer of Heat Exchanger

This study mainly discussed the influence of different surface properties,namely an unmodified copper fin surface and a modified hydrophobic fin surface, on the heat transfer effect of heat exchangers with air velocity ranging from 0.5 m/s to 2.5 m/s and relative humidity of 60% and 90%. The researchers established the following conclusions based on the experiment results. The heat transfer and water removal rates of the two heat exchangers increased with an increase in wind velocity. When the inlet air velocity was increased from 0.5 to 2.5 m/s, the heat transfer and water removal rates of both heat exchangers were increased by approximately 90%.Under similar air velocity conditions, heat exchangers with hydrophobic surfaces constantly removed the condensed water droplets, thereby preventing the water droplets from causing surface thermal resistance. As a result, the condensation heat transfer effect of hydrophobic surfaces was greater than that of unmodified copper surfaces. Compared with heat exchangers with unmodified copper fin surfaces, heat exchangers with hydrophobic surfaces exhibited a 5.56% higher heat transfer efficiency.

Experimental and Theoretical Studies of Wet Snow Accumulation on Inclined Cylindrical Surfaces

Wet snow accumulation on bridge cables and its shedding due to external phenomena such as rise in temperature, wind, and gravity is a serious threat to the safety of cars and pedestrians crossing the bridge. Commonly the accumulated snow on bridge cables is removed by external means such as mechanical removal or heat treatment which are expensive, time-consuming, and high-risk processes and are conducted based on little or no information available regarding the actual size and shape of the accumulated snow. In addition, cleaning of cables using the mechanical methods can potentially lead to erosion of cable materials when applied over years, resulting in enhanced surface roughness and potentially increased wet snow/ice accumulation during future precipitation events, and sometimes might require replacement of cable stays, which is an extremely costly and complicated task. Optimizing the number of mechanical cleaning procedures such as chain release through predicting the shape and thickness of the accumulated snow on the cable stays reduces the cost, time, and risk associated with the process. In this study, wet snow accumulation on torsionally rigid inclined cylinders of high-density polyethylene (HDPE) has been studied experimentally and numerically. A 2-D numerical model has been developed utilizing weather data to predict the thickness and the shape of the accumulated wet snow on inclined cylindrical surfaces. Outdoor experiments were also conducted to measure the density and thickness of accumulated snow, while monitoring the weather data real time. Overall, snow density was found to be linearly increasing with an increase in wind velocity, during snow precipitation. The maximum thickness and shape of the accumulated snow on cables obtained from the numerical model were found to be in good agreement with the outdoor experimental data. This work aims to provide a mean for prediction of snow accumulation on surfaces for optimizing the efficiency of the costly and high-risk snow removal procedures.

Correlations for fire-wind enhancement flow characteristics based on LES simulations

Unraveling the physics of fire-wind interaction has long been a subject of interest. Among all the physics involved, enhancement of wind by fire deserves great attention due to its potential effects on building structures downstream of the fire source in bushfire attack events. Predominantly, two contributing factors determine the extent to which wind is enhanced by fire: freestream wind velocity and fire intensity. This study employs Large-Eddy Simulation (LES) to fundamentally investigate the combined effects of freestream wind velocity and fire intensity on fire-wind enhancement. An added module was implemented to an open-source transient fire solver in order to analyze the effects of freestream wind velocity and fire intensity based on the analysis of interactions between momentum and fire-induced buoyancy forces. Simulations are performed for parametric combinations of wind velocity and fire intensity. The LES results demonstrate that the normalized maximum wind enhancement increases with a reduction of freestream wind velocity and an increase in fire intensity. The non-dimensional Froude number, Fr, and normalized fire intensity, I*, were employed to quantify the effects of freestream wind velocity and fire intensity, respectively. A correlation was developed to determine the maximum wind enhancement as a function of Fr and I*. The location corresponding to maximum wind enhancement occurs further downstream of the fire source as freestream wind velocity or fire intensity increases. A correlation based on the Fr number and I* was developed for the location at which maximum wind enhancement occurs. Furthermore, the concept of wind enhancement plume line was defined as a line along which the local wind enhancement occurs at a given longitudinal location downstream of the fire source, for which a correlation was also developed. Moreover, a gradual decaying trend is observed in wind enhancement after reaching a peak along the wind enhancement plume line in all simulation scenarios for which a correlation was also developed as a function normalized longitudinal direction.

Gas temperature rise and flame length induced by two buoyancy-controlled propane burners aligned parallel to the cross wind

This paper investigates the gas temperature rise and flame length of buoyant turbulent diffusion flames under cross wind, which does exist in fuel leakage fire accidents. Two identical propane burners with the same heat release rate were employed as fire sources. The burner spacing, heat release rate and cross wind velocity were changed. The results show that with the increase of the cross wind velocity, the gas temperatures in downwind region are strongly increased, resulting in a strong heat transfer to nearby energy loads. On the other hand, the non-monotonic trend of the flame length is caused by the cross wind effect. In addition, a segmented function predicting the flame length under cross wind is developed for merging and non-merging flames, which involves the heat release rate, burner spacing, pool size and cross wind velocity. The findings of this work have potential practical applications for optimal arrangements of energy loads, which allow predictions to be made regarding the possible threat and the establishment of the necessary safety distance to prevent the damage of multiple fires.

Vertical Wind Effect on Slope and Shape Parameters of Gamma Drop Size Distribution

AbstractApproximate equations for slope Λ and shape μ parameters of the gamma raindrop size distribution (DSD) are derived from theoretical considerations on the basis of the reflectivity-weighted mean terminal velocity VT and Doppler spectral width σp of the raindrop echoes. These approximate equations are then corrected to reduce the error by using the long-term ground-based disdrometer measurements. We applied these equations on the VHF-radar measurements (i.e., reflectivity-weighted mean fall velocity and Doppler spectral width) to estimate μ and Λ aloft. The effects of the vertical wind velocity on the VHF radar-estimated μ–Λ and σp–VT values are investigated. The result shows that there is a tendency for the μ and Λ values to increase with an increase of the upward wind velocity. In addition, the terminal velocity and the spread of the DSD estimated from the precipitation echoes are strongly related to the vertical air velocity. The stronger the upward vertical air velocity is, the larger the terminal velocity and the smaller the spread of the DSD will be. The dependence of the estimated μ and Λ values on the vertical wind velocity is very likely caused by the updraft that can support and carry away the smaller raindrops in the original drop size distribution in the radar volume. Consequently, the DSDs aloft are truncated and the corresponding μ and Λ values estimated from the radar returns tend to be larger. To confirm this assertion, we intentionally truncate disdrometer-measured DSDs at small drop size end and calculate corresponding μ and Λ values. The results show that the distribution patterns of the μ–Λ scatter diagrams of the truncated DSDs bear strong resemblance to those of the radar observations, both of which are very different from those obtained on the ground.

Aerodynamic noise evaluation for Aeolian tone and acoustical insulating plate by similarity law

The objective of this research is to assess aerodynamic noise sources and the wind velocity conversion of the similarity law in an increasing wind velocity. We measured the aerodynamic noise that radiates from cylinders with and without periodic holes and a pantograph model with and without a sound insulating plate in a low-noise high-speed wind tunnel. The noise level of the cylinders was in proportion to the sixth power of wind velocity because the cylinders acted as a dipole sound source. The effect of noise reduction caused by the change in flow structure, that is, the periodic holes, also continued. However, the second peak noise radiating from the cylinder was in proportion to the sum of the sixth power and the eighth power of wind velocity and was underestimated by wind velocity conversion based on a dipole sound source. The noise level of the pantograph model with the sound insulating plate was in proportion to lower than the sixth power of wind velocity in contrast to the pantograph model itself. This is because the noise reduction effect of the sound insulating plate had a frequency characteristic. In this research, when increasing the wind velocity, the dominant pantograph noise frequency region shifted to a higher level, and the dominant noise level began to be affected by the noise reduction of the sound insulating plate. This caused the reduction effect of the sound insulating plate to be underestimated by 2.5 dB due to the noise level conversion of wind velocity. To solve this problem, the plate’s theoretical reduced noise level, which was calculated by using the Fresnel number, was subtracted from the estimated noise level of the pantograph itself. This lead to pantograph noise with the sound insulating plate being estimated within a 0.8-dB difference.

Assessing vertical diffusion in a stratified lake using a three‐dimensional hydrodynamic model

AbstractVertical turbulent diffusivity (Kz), which can be estimated from water temperature, is a key factor in the evolution of water quality in lentic waters. In this study, we analysed the capability of a three‐dimensional hydrodynamic model (EFDC) to capture water temperature and vertical diffusivity in Lake Arendsee in the Northern German plain. Of particular interest to us is to evaluate the model performance for capturing the diffusion minimum within the metalimnion and analyse the response of the metalimnetic Kz to meteorological forcing, namely changing wind speed and warming. The comparison confirmed that the calibrated model could reproduce both stratification dynamics and vertical diffusion profiles in the lake. The model was also shown to be able to capture the duration and vertical extent of the metalimnetic diffusion minimum. The scenario results illustrate that, compared to air temperature, wind velocity appeared to be the more influential meteorological variable on the vertical exchange within the metalimnion. While increasing wind velocities mostly affected the minimum values of Kz in the metalimnion and thus led to intensified vertical exchange, the reduction of wind velocity mostly affected the depth of minimal Kz, but not its absolute value.

Investigation of the relationship between dust storm index, climatic parameters, and normalized difference vegetation index using the ridge regression method in arid regions of Central Iran

Wind erosion is a serious environmental issue caused by the interaction between various climatic and terrestrial factors. Using the ridge regression (RR) method, the present study aimed to investigate the relationship between these parameters and dust storm index (DSI) in arid regions of Central Iran during 2000–2014. The removal area of soil particles in the dustiest season was further detected via sand and dust roses. The results showed that the highest activity of wind erosion occurred in spring (DSI > 1). The RR analysis indicated that only the air temperature changes had a significant positive effect on DSI variations during the first period (β = +0.38; p < .05). For the second period, decreased precipitation and increased wind velocity were identified as the most important factors influencing the DSI variations. The estimated regression coefficients concerning precipitation and wind speed at 95% confidence level were (−1.02) and (+0.51), respectively. Based on the R2 value, 27% of the DSI changes could be explained by the air temperature variations in the first period. However, approximately 50% of the DSI variations were explained by the rainfall and wind speed changes in the second period. These results illustrate the effective application of RR to elucidate the relationship of climatic and terrestrial factors with DSI. It was further observed that the removal area of soil particles in the northeastern, southeastern, and western parts of Central Iran was easterly, northerly, and westerly, respectively.

Quantification of driving factors on NDVI in oasis-desert ecotone using geographical detector method

Within oasis-desert ecotone regions, the normalized difference vegetation index (NDVI) is an important parameter for evaluating the growth of vegetation. An accurate quantitative study between NDVI and environmental and anthropogenic factors is critical for understand the driving factors of vegetation growth in oasis-desert ecotone. In 2016, four periods Landsat 8 OLI_TIRS images, relevant climatological parameters data (air temperature, air relative humidity, wind velocity and accumulated temperature), land cover type data and soil data were selected as proxies. In order to quantify the explanatory power for NDVI spatial and temporal distribution in the southern edge of Dunhuang City and northern side of the Mingsha Mountain, the geographical detector model was used to explain the potential influences of factors versus the spatial distribution of NDVI, and each explanatory variable’s relative importance can be calculated. The factor detector results disclose that the spatial distribution of NDVI is primarily dominated by land cover type. The risk detector results show that, high NDVI region is located within woodland. The mean value of NDVI displays an increase and then decrease trend with air temperature increase. With the increase of wind velocity and decrease of air relative humidity, the NDVI value shows a decrease trend. The interactive q values between the two factors are higher than any q value of separated factors. Results also indicate that the strongest interactive effects of NDVI are different in distinct seasons. Consequently, anthropogenic activity is more important than environmental factors on NDVI in oasis-desert ecotone. We also demonstrate that air relative humidity rather than air temperature have played a greater role in NDVI spatial distribution.

Numerical study on the effect of blade surface deterioration by erosion on the performance of a large wind turbine

As the demand for the development of onshore wind farms in areas with low wind speeds and large offshore wind farms increases, the size of the wind turbine and its rotor has also increased rapidly. An increase in the rotor diameter implies an increase in the relative wind velocity (with respect to each cross section in the radial direction of the blade) near the tip region of the blade. This in return accelerates the surface damage caused by the erosion of the leading edge, thereby increasing the frequency of maintenance and lowering competitiveness in the cost of energy. In this study, computational fluid dynamics (CFD) analysis was performed to analyze the correlation between the leading-edge erosion damage and output performance of the blade. CFD simulations were performed using a tip airfoil (NACA 64_618) and a full-scale wind turbine (NREL 5 MW) based on the state of erosion of discarded blades considering approximately 12 years of maintenance-free operation. The irregular erosion at the airfoil leading edge results in premature stall phenomena and reduces the aerodynamic efficiency. Thus, the accurate analysis of the flow separation point and flow change is necessary. Therefore, three-dimensional transient CFD analysis was performed to consider the complex flow generated on the blade surface. The erosion at the leading edge reduced the airfoil lift by up to 23% and drag by 100%, reducing the aerodynamic efficiency, which in effect reduced annual energy production by up to 4%.

Experimental investigation on pyramid solar still with single and double collector cover—Comparative study

AbstractSun radiation is the heat energy source for solar still. That should be utilized maximum for increasing the evaporative rate at the top surface of the brine. The pyramid shape solar still (PSSS) can receive solar input radiation from all four directions. In this research, the top layer of conventional pyramid shape solar still (CPSSS) is covered with air‐packed cover and analysed the effect in the modified still after air packed in between the two glasses, finally, that result is compared with the CPSSS. The air inside the two glasses will be receiving maximum radiation and retain in it. It can be used as top side insulation and which can ensure the maximum insulation for heat energy inside the PSSS. The CPSSS and air‐packed pyramid shape solar still (APPSSS) were fabricated and experimented. The experiments were conducted at an ambient condition of the Chennai, Tamil Nadu (12.9416°N, 80.2362°E). The CPSSS gives good yield at evening when an increase in wind velocity. The APPSSS gives a lower performance as compared to the CPSSS due to the air‐packed cover.

Numerical Investigation of A Novel Single-Pass All-Glass Receiver for Parabolic Trough Collector

ABSTRACT A novel single-pass all-glass parabolic trough receiver (SPAG-PTR) that has a potential to improve the reliability of the parabolic trough collector was developed. Both heat losses with/without the ends insulation and thermal efficiency of the SPAG-PTR were numerically investigated and the bellows on the ends of the receiver were optimized. The results show that the three waves bellow SPAG-PTR with the ends insulation has a lower heat loss up to 10.5 W/m in the temperature of 540 K, which is about 15% less than the ends without insulation case. In addition, the results from the steady-state heat transfer model shows that the heat loss increases with the increase of vacuum pressure, wind velocity, and temperature. Thermal efficiency of this kind of SPAG-PTR is about 0.62 ~ 0.72 in the temperature range of 540 ~ 330 K. Furthermore, the thermal stress and heat loss of the receiver was simulated, the optimal structure with two waves of each bellow were obtained, which could decrease the heat loss about 2%~2.5% than the three waves-bellow type. All these results show that this optimized SPAG receiver is promising in the medium-low temperature solar thermal utilizations.

Fluidization behavior monitoring of phosphogypsum in cyclone separator using electrical capacitance tomography

The fluidized behavior and the concentration distribution of phosphogypsum in the cyclone separator are studied and analyzed using twin-plane electrical capacitance tomography. Particle concentration is relatively low in the central region of the cyclone separator, and the concentration near the side wall of the cyclone separator is relatively high. With the increase in wind velocity, the radial particle concentration decreases, and the separation efficiency increases first and then decreases. Finally, regression analysis is used to fit the radial concentration distribution data of phosphogypsum. The analysis results are helpful to improve the cyclone structure and separation efficiency and to optimize the size of the cyclone separator.

Numerical analysis of wind velocity effects on fire-wind enhancement

Variation in flow characteristics triggered through the fire-wind interface can potentially damage the buildings during bushfires. Fire-wind enhancement which is referred to as the increase of wind velocity, caused by the fire-wind interaction, is one of the destructive phenomena in this regard. In spite of the significance, the underlying mechanism contributing to this phenomenon is still not well understood. This study employs computational fluid dynamic (CFD) simulation to fundamentally investigate the effects of free-stream wind velocity on fire-wind enhancement through analyzing the momentum and buoyancy of fluid. Fire-wind interaction is shown to cause the generation of fire-induced longitudinal negative pressure gradient which results in fire-induced pressure and viscous forces in longitudinal direction. These forces are further found as the prime reason for the distortion of the wind velocity profile. A module is implemented to the FireFOAM solver to calculate and extract these forces quantitatively. The results reveal that under a constant fire intensity, the level of distortion and/or enhancement in the wind velocity profile comparatively reduces with the increase of free-stream wind velocity. A new non-dimensional group (modified Euler number) is introduced to take into account dominant fire-induced forces causing fire-wind enhancement. Richardson number and the modified Euler number are employed to determine the influence of free-stream wind velocity and longitudinal distance from the fire source on wind velocity enhancement. Large-eddy simulation (LES) results indicate that while the level of enhancement generally depends on both Richardson and the modified Euler number, the location of the maximum level of enhancement along the plume centreline coincides with the maximum value of modified Euler number under a constant free-stream wind velocity scenario.

Experimental Investigation of Effect of External Side Wind on Fire Behaviors in a Corridor Connected to a Shaft

High-rise buildings are usually in a windy environment. The motion of fire-induced smoke and fire behaviors may be strongly affected by the external wind forces except by the stack effect. It turns out that wind with different directions and velocities can cause disparity in fire dynamics. Since most previous researches only focused on the cross wind conditions, this work investigated the effect of external side wind from 0 m/s to 1.21 m/s on the air flow behaviors, combustion characteristics of methanol pools and smoke temperature in a 1/6 scaled corridor connected to a 6-floor shaft. A remarkable observation is that the external side wind (parallel to top window, shown in Fig. 1) leads to pressure attenuation inside building and induces air to flow inside through bottom door. Therefore, the smoke spreads faster under the synergic effects of side wind and stack effect. At the steady stage, the supplement air flow velocity increases with wind velocity but remains proportional to 1/3 power of HRR. An equation incorporating the wind effect is proposed to predict the air flow velocity. Results also show that compared to cross wind conditions, the mass loss rates of methanol pools increase at high wind velocities. The wind effect on smoke temperature is obvious in cases with small pools. Here, the temperature first increases to a peak value and then decreases with increased wind velocity. However, the temperature remains the same in cases with large pools within our wind velocity range. The temperature in the shaft is also correlated with mass loss rate and wind velocity. This work shows that external side wind would increase the fire hazard of buildings by contributing to the combustion and spreading of smoke. Thus engineers should consider the effect of side wind carefully when designing smoke control system.

Diurnal and seasonal variations of radon (222Rn) and their dependence on soil moisture and vertical stability of the lower atmosphere at Pune, India

Continuous measurements of the concentration of Radon (222Rn) and its progenies were made with a Radon detector, RTM 2200, at a tropical site, Pune (18° 31′ N, 73° 55′ E, 560 m), India from January to December 2012. Simultaneous measurements of small ions of <1.6 nm diameter were made with a Neutral Air Ion Spectrometer (NAIS). Annually - averaged diurnal variation curves of 222Rn concentration showed a peak (~9.9 Bq m−3) at 0800 Local Time (LT) and a minimum (~5.4 Bq m−3) at 1800 LT. Diurnal variations of 222Rn concentration during winter, post-monsoon, and pre-monsoon seasons were almost similar in shape but with decreasing amplitudes in these seasons. However, during monsoon season, 222Rn concentration was the lowest and remained almost constant throughout the day. Monthly mean value of 222Rn concentration was the highest in December and the lowest in June. Polonium (218Po) concentration did not show any systematic diurnal variation. Results are explained in terms of surface meteorology, soil moisture, soil temperature, vertical wind velocity, local topography and development of atmospheric boundary layer. 222Rn concentration increased with soil moisture content of <16%, rapidly dropped down to dry soil values and then remained almost constant with increasing soil moisture. On the other hand, 222Rn concentration decreased with the increase of upward vertical wind velocity in the atmospheric boundary layer. The diurnal variations of ionization rate, directly estimated from 222Rn measurements, and calculated from ion concentration measurements showed some similarities but differed in their amplitudes. Annual effective dose of 222Rn (~0.075 mSv) as estimated from our measurements at Pune was found below the value prescribed by World Health Organization.