Changes In Air Density Research Articles

Numerical simulation investigation on aerodynamic characteristics of rotor in plateau environment

To investigate the impact of high-altitude environments on helicopter rotor aerodynamic characteristics, this study developed a computational model that integrates CFD, BP neural networks, and the free wake method. The accuracy of the model was validated through wind tunnel experiments and comparisons with CFD results. Using this model, the effects of altitude and temperature at high altitudes on rotor aerodynamic characteristics during hover and forward flight were studied. The results indicate that with constant temperature, rotor thrust significantly decreases as altitude increases, primarily due to reduced air density. As altitude rises with unchanged temperature, the decrease in air density directly affects the lift and thrust generated by the rotor, leading to a decline in hover performance. Furthermore, the study found that rotor aerodynamic coefficients do not vary significantly across different altitudes. Further analysis suggests this stability is due to the high Reynolds number in the calculated state. In the high Reynolds number range, changes in Reynolds number have minimal impact on aerodynamic coefficients, resulting in relatively stable aerodynamic performance across varying altitudes. At a constant altitude, lower temperatures lead to slight increases in rotor thrust and torque, while the thrust coefficient and power coefficient remain almost unaffected. This phenomenon is attributed to changes in air density and viscosity caused by the lower temperatures. The increase in air density positively impacts thrust and torque, while the reduction in air viscosity decreases the rotor's surface frictional resistance. This partially offsets the increase in lift and drag caused by the higher air density, leading to negligible changes in thrust and power coefficients.

Experimental and Numerical Study of Air Flow Reversal Induced by Fire in an Inclined Mine Working

Effective fire prevention in mine workings and tunnels requires a thorough theoretical analysis of the heat and mass transfer processes within these structures. This involves using established models to calculate non-isothermal air flow dynamics in long tunnels and mine workings. While the ventilation of tunnels has been extensively studied, significant challenges persist regarding mine ventilation systems, particularly due to their complex and branched topology. This study aimed to address these challenges and gaps in mine ventilation. We designed a laboratory bench to simulate an inclined mine working with a heat source (fire) and validated a mathematical model of heat and mass transfer in such settings. Using experimental measurements, we verified the model’s accuracy. It is important to note that our experimental and theoretical analyses focused solely on the thermal effects of a fire, without considering the release of harmful impurities. Using the validated model, we conducted multiparameter simulations to identify the conditions leading to the formation of a thermal slug in an inclined mine working and the subsequent reversal of air flow. The simulation data enabled us to determine the dependency of the critical heat release rate on the aerodynamic parameters of the mine working. Additionally, we evaluated the changes in average air density within a mine working at the critical heat release rate. These findings are crucial for the further development of a network-based method to analyze air flow stability in mine ventilation networks during fires.

Turkey vultures tune their airspeed to changing air density.

Animals must tune their physical performance to changing environmental conditions, and the breadth of environmental tolerance may contribute to delineating the geographic range of a species. A common environmental challenge that flying animals face is the reduction of air density at high elevation and the reduction in the effectiveness of lift production that accompanies it. As a species, turkey vultures (Cathartes aura) inhabit a >3000 m elevation range, and fly considerably higher, necessitating that they accommodate for a 27% change in air density (0.890 to 1.227 kg m-3) through behavior, physiology or biomechanics. We predicted that birds flying at high elevation would maintain aerodynamic lift performance behaviorally via higher flight speeds, rather than increases in power output or local phenotypic adaptation. We used three-dimensional videography to track turkey vultures flying at three elevations, and data supported the hypothesized negative relationship between median airspeed and air density. Additionally, neither the ratio of horizontal speed to sinking speed nor flapping behavior varied with air density.

On the Variation of Cup Anemometer Performance Due to Changes in the Air Density

In the present paper, the effect of air density variations on cup anemometer performance is analyzed. The effect on the sensor’s performance is mainly due to the difference between the altitude at which the cup anemometer is working and the altitude at which this instrument was calibrated. Data from the available literature are thoroughly analyzed, focusing on explaining the coupled effect of the air temperature on both the rotor’s friction torque and the air density (that is, related to the aerodynamic torque on the rotor). As a result, the effect of air density variation at constant temperature (that is, leaving aside any variation of friction forces at the anemometer rotor shaft) on the sensor transfer function (i.e., on the calibration constants) is evaluated. The analysis carried out revealed a trend change in the variation with air density of the transfer function of the cup anemometer. For densities greater than 0.65, the calibration constants of the instrument have a variation with density that must necessarily change suddenly as the start-up speed, represented by the calibration constant B, becomes zero around this value of air density. To highlight the relevance of the present research, some estimations of the effect of wind speed measurement errors associated with air density changes on the Annual Energy Production (AEP) of wind turbines are included. A 1.5% decrease in the AEP forecast at air density corresponding to 2917 m above sea level is estimated for 3000–4500 kW wind turbines.

Exploring influence of air density deviation on power production of wind energy conversion system: Study on correction method

Thousands of wind turbines are already installed, providing renewable energy to meet the growing energy demand of consumers. This article investigates the effect of air density deviation, which depends on weather conditions, on power production of operational wind turbines, and examines strategy to mitigate this effect. Throughout the year, the air density in the area where the wind turbines are installed experiences continuous variations. It affects the annual power production of the wind turbine. Therefore, it is essential to discover a method that can reduce the effect of air density changes on power production of the wind turbine without adding extra extender blade. The effect of air density deviation on parameter of the wind turbines is investigated using four years measurement data (with a 10-minute interval) as well as simulation data. To reduce air density effect, the pitch angle and torque gain are readjusted rather than setting it constant based on the air density value. The analysis and simulation study were conducted in Matlab/Simulink® software. The results revealed that the suggested correction in pitch angle and torque gain according air density effectively alleviated the effect of air density variations, and the power production of the wind turbine was increased.

Theoretical Calculation and Experimental Verification of Wind-Driven Rain Aerodynamic Forces on the Bridge Main Beam

Regarding the issue of changes in the aerodynamic force of the bridge main beam under the action of wind-driven rain, this article explores the changes in air density caused by rainfall, the calculation theory of raindrop impact force and its simplified mass-weighted equivalent method (MWEM), and the calculation method of water accumulation thickness on the surface of the main beam. The calculation shows that the changes in air density caused by rainfall can be ignored, and the error of the MWEM increases with the increase in rainfall intensity; however, even at a rainfall intensity of 709 mm/h, the deviations in the MWEM value of the horizontal and vertical raindrop impact force is only about +5% and −4%, respectively. Then, based on the above analysis, a calculation model for the aerodynamic three-component forces of the main beam caused by rainfall under the action of wind-driven rain is provided. Finally, taking two typical main beam sections as an example, static three-component force tests are carried out on the main beam model under different rainfall intensities. The experimental results show that the drag coefficient variations obtained through the MWEM are in good agreement with experimental data, which proves the correctness of the theoretical model of the raindrop impact force. But for the lift and torque coefficient, the differences between theoretical and experimental values are much more significant than the drag coefficient, and it increases with the increase in rain intensity. It can be seen that the surface ponding model and influence of rainfall intensity need to be further explored. In summary, the theoretical calculation method for the additional aerodynamic force of wind-driven rain on the main beam proposed in this article is convenient and practical, and it can provide a certain reference for the rapid safety assessment of bridges under extreme meteorological conditions.

Peculiarities of the Calculations of the Gas Turbine Cooling Systems

Gas turbine cooling systems have the branched networks of various channels whose hydraulic and heat exchange capabilities define the air flow required for the cooling of turbine parts and, thus, directly influence the efficiency of gas turbines. Cooling system elements are, in particular, the throttles, diaphragms, seals, openings that act as regulating parts or elements to maintain pressure in the system. As a rule, the channels of this type have a significant pressure drop, and therefore during the calculations it is necessary to very carefully consider a change in air density along the channel. Therefore, we present in this paper the method developed by the authors for determining the hydraulic resistance in the openings, and the data obtained by it perfectly agree with the experimental data. It is shown how to take into account the effect of the air compressibility on the coefficient of hydraulic resistance in the cooling channels that allows for the use of the numerous experimental dependencies for the coefficients of hydraulic resistance of incompressible liquids. A method of calculating hydraulic resistances of the openings by defragmenting their total hydraulic resistance into separate components has been proposed. A generalized dependence was established for the hydraulic resistance of the discharge openings in the discs and in the mounting gaps between the shanks of the blades and the discs, taking into account the transverse air flows.

DYNAMIC MODEL OF THE DURATION OF GASEOUS ENVIRONMENT PUMPING FROM A LIMITED VOLUME

An analytical equation for the duration of air pumping from a limited volume has been developed. The equation of the mechanical energy of air movement takes into account the law of mass conservation for a gas in a controlled volume, the work of the energy of air movement and the work to overcome air friction. Gaseous medium is Newtonian. The duration of pumping (filling) the limited volume of the pneumatic chamber with air was calculated by comparing the mass flow per second and the increase in mass, as a differential of the change in air density. The mathematical model enables the simulation of air pumping time depending on pressure, as a density parameter and at different Mach numbers in the subsonic range. The K1* proportionality coefficient, which characterizes the ratio of the dynamic force of gas mass displacement to the static pressure relative to the diameter of the air pipeline, is proposed as a criterion for evaluating the dynamics of the flow. It should be noted that the analytical dependence works for Newtonian media and Mach numbers of M < 1, the gas flow is caused by the pressure difference, the gas itself is limited by a chamber space characterized by a volume as design parameter of structure.

Current and future wind energy resources in the North Sea according to CMIP6

Abstract. We explore the changes in wind energy resources in northern Europe using output from historical to mid-21st century CMIP6 simulations and the high-emission SSP5-8.5 scenario. This study improves upon many assumptions made in the past. First, we interpolate the winds to hub height using model-level raw data; second, we use a large ensemble of CMIP6 models; third, we consider the possible wake effects on the annual energy production of a large wind farm cluster proposed for the North Sea. The common practice of extrapolating 10 m wind speeds to turbine height using the power law with a constant shear exponent is often a poor approximation of the actual turbine-height wind speed. This approximation can exaggerate the future changes in wind resources and ignore possible surface roughness and atmospheric stability changes. The evaluation of the wind climatologies in the CMIP6 models over the North Sea for the historical period shows good correspondence with measurements from tall masts and three reanalysis data points for 16 of the 18 models. Some of the models run at relatively high spatial resolution are as good as the reanalyses at representing the wind climate in this region. Our results show that annual mean wind speed and wind resources in northern Europe are not particularly affected by climate change in 2031–2050 relative to 1995–2014, according to a subset of 16 models in the CMIP6 collection. However, the seasonal distribution of these resources is significantly altered. Most models agree on reductions in the future wind in summer in a band that extends from the British Isles to the Baltic Sea and on increases in winter in the southern Baltic Sea. The energy production calculations show that summer energy production in a planned large wind farm cluster in the North Sea could be reduced by a median of 6.9 % during 2031–2050 when taking into account the wind farm wakes (that accounts for −0.7 %) and the changes in air density (that account for −0.9 %).

Measurement of airborne ultrasound using laser Doppler vibrometry

The speed of light in air is dependent on the air's instantaneous density. Since air density is modulated by sound, sound in the air can be observed and measured using optical methods. One such optical method is Laser Doppler Vibrometry (LDV). Most commonly, LDVs measure the mechanical velocity of a surface. However, by placing a rigid reflector beneath a sound beam in air, it is possible to measure the time rate-of-change of optical refractive index and thus to measure dynamic changes in air density, or sound. In prior demonstrations, this method has been used to visualize sound fields in the audible frequency range and ultrasonic range underwater. Here, we present the first measurements of high-intensity airborne ultrasound beams in the frequency range spanning 100 kHz–300 kHz. We observe accumulated distortion, wave steepening, and weak shock formation as high intensity sound beams propagate. LDV measurements are compared against numerical simulations of the sound field. Advantages of the LDV technique are discussed, and we also attempt to quantify limitations of the technique which include spatial averaging of the measurand along and normal to the optical beam path.

Study on Obtaining Real Power Curve of Wind Turbines Using SCADA Data

The key problem to be solved in the process of wind turbine (WT) operation and maintenance is to obtain the wind turbine performance accurately. The power curve is an important indicator to evaluate the performance of wind turbines. How to model and obtain the power curve of wind turbines has always been one of the hot topics in research. This paper proposes a novel idea to get the actual power curve of wind turbines. Firstly, the basic data preprocessing algorithm is designed to process the zero value and null value in the original supervisory control and data acquisition (SCADA) data. The moving average filtering (MAF) method is employed to deal with the wind speed, the purpose of which is to consider the comprehensive result of wind on the wind turbine power in a certain period. According to the momentum theory of the ideal wind turbine and combined with the characteristics of the anemometer installation position, the deviation between the measured wind speed and the actual wind speed is approximately corrected. Here, the influence of dynamic changes in air density is also considered. Then, the Gaussian fitting algorithm is used to fit the wind-power curve. The characteristics of the power curve before and after wind speed correction are compared and analyzed. At the same time, the influence of the parameter uncertainty on the reliability of the power curve is considered and investigated. Finally, the characteristics of the power curves of four wind turbines are compared and analyzed. The research results show that among these power curves, WT3 and WT4 are the closest, WT2 is the next, and WT1 has the farthest deviation from the others. The research work provides a valuable basis for on-site performance evaluation, overhaul, and maintenance of wind turbines.

Mathematical modeling of greenhouse-livestock complex heated by solar and bioenergy sources

The article develops a mathematical model of the heat supply system of the greenhouse complex, taking into account the free heat flow in the animals, solar energy, heat energy stored in heat accumulators and developed through the program MATLAB / Simulink. In the development of a mathematical model of the heat supply system of the greenhouse complex, a block diagram of the equation in the program MATLAB / Simulink was developed, without taking into account the change in air density and specific heat capacity with temperature. According to the graphic results obtained for the daily value of solar radiation 500 W/m2, outside air temperature, -6 °C in Karshi, the air temperature inside the greenhouse rises to 22 °C, water tank battery temperature to 13 °C, underground heat accumulator temperature to 17 °C. can be seen. while the amount of total solar radiation was 300 W/m2, this figure was found to be 14 °C, 9 °C, and 12 °C.

Statistical Approaches to Optimize QACT Frequency During Proton Therapy: A Single Institution Study

<h3>Purpose/Objective(s)</h3> Patients treated with proton beam therapy (PBT) undergo routine quality assurance CT (QACT) scans during their course of treatment, which determines whether the initial plan remains accurate for the whole course of treatment or needs to be re-planned based on the findings on their QACTs. The objective of this study is to optimize and reduce the QACT frequency, while maintaining the treatment quality. The benefits of reducing QACT frequency include reducing imaging dose and optimizing use of patient time and staff resources. <h3>Materials/Methods</h3> We performed a retrospective IRB-approved single-institution review of all patients of three anatomical sites (e.g., Brain, Prostate and Head and Neck [HN]), who were treated with PBT between July 2019 and July 2020. The number of patients treated for these three sites, number of QACTs performed, number of patients re-planned and number of re-plans are listed in the table. For each anatomic site, the QACT and re-planning pattern were analyzed to find the optimal frequency of QACTs needed. <h3>Results</h3> <b>Brain</b>: Out of 204 QACTs, 6 (2.9 %) were used for adaptive planning. One patient was re-planned twice. It was found that 3 out of 5 patients were re-planned due to weight loss or anatomical changes. All revision plans were delivered within 7-12 fractions of the treatment. One QACT per patient at the beginning of the second week of the treatment was proposed for the brain patients. <b>Prostate</b>: Out of 236 QACTs, 3 (3.6 %) were used for adaptive planning. All three revision plans were delivered within 17-29 fractions of their treatments. Hence, one QACT per patient during the middle of the treatment course was proposed for this group. <b>HN</b>: Out of 97 patients, 32 (33 %) underwent adaptive planning on their QACTs. A total of 37 revision plans were made on 437 QACTs, where 8.5% QACTs were used for adaptive planning. Out of 32 patients re-planned, 26 of them were due to either weight loss or anatomy change and/or tumor shrinkage, 4 patients were due to need for a new mask and the remainder due to air density changes within sinuses. The average time between a QACT and the revision plan delivery was five days. Bi-weekly QACTs were proposed for the HN patients. We found no adaptive planning occurred in the last week of treatment. <h3>Conclusion</h3> The above newly proposed quality assurance CT (QACT) patterns for these three anatomical sites are the optimal patterns, while maintaining the treatment quality. Following this analysis, we have adopted a new paradigm with decreased routine QACTs in these disease sites. To mitigate any risks due to the proposed QACT patterns, increasing the cone beam CT (CBCT) frequency during treatment is recommended.

Estimation of the influences of spatiotemporal variations in air density on wind energy assessment in China based on deep neural network

This study proposes a deep neural network-based wind energy assessment method, aiming to systematically evaluate the effects of the spatiotemporal variations in air density on wind energy assessment in China. On this basis, the spatiotemporal patterns of air density are modelled on a high-spatial-resolution scale (1000 m × 1000 m). The influence of the spatiotemporal distribution characteristics of air density on the wind energy production is quantified, and the spatiotemporal variability of the corresponding wind energy production is estimated. The results demonstrate that changes in air density during the year present typical periodic characteristics. The mean air density value in January is 1.079 kg/m3, the highest throughout the year. The difference in mean air density between cold and warm seasons in the study area shows a decreasing law of higher in the northeast and lower in the southwest. When the elevation is less than 3500 m, it reaches 5.06%. The observed spatiotemporal variability in annual energy production exhibits a distinct seasonal cycle, with the highest production appears in spring (2.968 GWh/yr). The total annual energy production in the cold season is 16.08 GWh/yr, whereas the annual energy production decreases by higher than 23.46% when it comes to the warm season.

Elevational niche-shift migration: Why the degree of elevational change matters for the ecology, evolution, and physiology of migratory birds

Abstract Elevational migration can be defined as roundtrip seasonal movement that involves upward and downward shifts in elevation. These shifts incur physiological challenges that are proportional to the degree of elevational change. Larger shifts in elevation correspond to larger shifts in partial pressure of oxygen, air density, temperature, and ultraviolet (UV) exposure. Although most avian examples of elevational migration involve subtle shifts that would have minimal impacts on physiology, shifts of any magnitude have previously been considered under the broad umbrella of “elevational migration”. Here, we consider extreme seasonal elevational movements (≥2,000 m), sufficient to shift the elevational dimension of the eco-climatic niche. Migratory bird populations typically maintain inter-seasonal stability in the temperature, precipitation, and elevational aspects of their climatic niches, a tendency that likely reflects genetic physiological specialization on environmental conditions such as atmospheric pressure. A shift of ≥2,000 m involves a ≥20% change in air density and oxygen partial pressure, sufficient to incur functionally impactful declines in arterial blood-oxygen saturation and require compensatory shifts in respiratory physiology. We refer to this phenomenon as elevational niche-shift migration (ENSM). In this review, we analyzed &amp;gt;4 million occurrence records to identify 105 populations, representing 92 bird species, that undergo complete or partial ENSM. We identified key ecological and evolutionary questions regarding the causes and consequences of ENSM. Our synthesis reveals that ENSM has evolved independently in at least 29 avian families spanning 10 orders. Nonetheless, ENSM is rare relative to other forms of seasonal migration, consistent with the general tendency of seasonal niche conservatism by migratory species and evolutionarily conserved elevational range limits. For many migratory species and populations, within-species patterns of migratory connectivity are not sufficiently understood to determine ENSM status. ENSM is distinguished by its scale within the broader phenomenon of elevational migration. Critical examination of ENSM illustrates fundamental constraints on the ecology and evolution of migration systems, topographical influences on geographic patterns of migratory connectivity, and the remarkable metabolic flexibility of certain bird species that allows them to occupy disparate elevations across different seasons.

Long-term changes in offshore wind power density and wind turbine capacity factor in the Iberian Peninsula (1900–2010)

This study analysed temporal and spatial changes in offshore wind power density (WPD) and capacity factor (CF) around the Iberian Peninsula during the 20th century by analysing data from ERA20 and ERA5. Both WPD and CF were calculated using reanalysis data considering a wind turbine with a hub height of 90 m and incorporating the effect of air density changes. Since ERA5 assimilates more observations, the data from ERA20 was bias-corrected using quantile matching, with ERA5 reanalysis data as the reference. As both variables are based on wind speed (WS), this variable was also corrected and analysed. The results show that the mean values for WPD, CF, and WS during the 20th century were highest in the Atlantic zone and the Gulf of Lyon and lowest around the Balearic Islands. The results of the assessment of decadal trends using the Theil–Sen estimator show that all indicators increased significantly in the waters of the Iberian Peninsula during the study period (1900–2010). Considering the mean slope over this period, the change over the entire period could amount to 174 Wm-2 for WPD, 8.8% for CF, and 1.1 ms−1 for WS. Based on these changes, offshore wind turbines would have increased their returns by approximately 20% over the 11 decades.

Estimation of the influences of air density on wind energy assessment: A case study from China

The distribution characteristics of air density in China were modelled on a high-spatial-resolution scale (4000 m × 4000 m) and the absolute error was calculated by comparing with constant air density. Daily mean air pressure and air temperature time series from 2403 meteorological stations for the period 1998–2018 were used to compute air density at the hub height of a typical wind turbine. The statistical air density distributions were applied in the study area and the influence of elevation on changes in air density was quantified. Mean annual energy production in the study area was estimated using extrapolated parameters of the Weibull distribution and adjusted power curves. Compared with energy production under the assumption of constant air density, the results demonstrate that over 33% of the study area had a mean air density less than 1.000 kg/m3 due to the effect of elevation. Values as low as 0.347 kg/m3 were observed in the Tibetan Plateau. Energy production was underestimated (0.04–1.76%) in the north-east and north when the variability of air density was considered, and wind resources were overestimated by more than 20% in approximately 13.1% of the study area. The results of this study will contribute to identifying suitable locations for developing the wind energy industry. The influence of air density on wind energy production at different elevations can now be quantified, allowing more efficient utilization of wind resources.

Factors influencing strength and direction of natural ventilation pressure in general mines to control mine airing

The article presents three main factors, influencing the strength of natural ventilating pressure in general mines between the shafts: gas emission from mines (air density changes due to the change in concentration of other gases), changes of air parameters taken in by ventilating shafts, and air pressure due to the productivity shifts of the Main Fan Unit (or other devices for positive and negative control of air distribution). According to the experiment data the equations mentioned in other works for calculating natural ventilating pressure in general mines and taking into account the parameters of the air taken in are precise. Applying these formulas basing on the results of hydro meteorological forecast, whose accuracy in the short-term forecast is also high, it is possible predict the operating mode of the system of ventilation.

Calculation of pressure losses during pneumatic transport

A method for calculating pressure losses during pneumatic transport is considered with the aim of choosing the most favorable operating mode, which allows to reduce the consumption of compressed air. It has been established that the generally accepted formulas for calculating pressure losses along the path, calculated as the sum of the pressure losses for pure gas and material, do not explain the fact of the initial decrease in pressure losses with increasing air flow rate, and then their growth. The importance of accounting for changes in air density and air flow velocity along the length of the pipe, as well as the need to take into account the overlap of part of the pipeline section with material in the case of high concentrations, is shown. It is proposed to determine the pressure loss using the Bernoulli equation in integral form, for example, the Gauss method using eight nodes. The applicability of the method for calculating both straight and inclined sections of pipelines is established. The experimental results of studying and analyzing the proposed isothermal model in a vacuum pneumatic transport laboratory installation are presented. An example of calculating the pressure loss for an industrial pneumatic conveying system with a pipe length of 450 m and an inner diameter of 147 mm at various flow rates of the material is shown. Ill. 4. Ref. 21. Tab. 1.

Design and Experimental Test of a Common-path Coherent-dispersion Spectrometer for Exoplanet Searches

A coherent-dispersion spectrometer (CODES) system using the radial velocity (RV) method for exoplanet searches is established in this paper. This spectrometer utilizes a new Sagnac interferometer with common-path and asymmetric designs. Compared with the traditional Michelson interferometer-based spectrometer for exoplanet detection, these designs markedly improve the stability of the optical path difference (OPD) to positional changes in optical elements or air density changes, reducing the need for active cavity stabilization. Furthermore, the asymmetric Sagnac design allows convenient separation of the two complementary outputs. In order to verify the feasibility of the CODES, an optical Doppler shift experiment is constructed in the laboratory. The RV signal was extracted by the phase shifts of the interference fringes produced by the spectrometer. The experimental results show that the obtained retrieved RV is 76.7 m s−1, with an absolute error of 0.3 m s−1 compared to simulated values. And the root mean square error (RMSE) and the standard deviation (STD) are 21.3 m s−1 and 21.4 m s−1, respectively. Error analyses show that the OPD change caused by the temperature variation is the main factor for the RMSE and STD.