Decrease Of Air Density Research Articles

Experimental Study of Hot-Sphere Anemometer Response in Stratospheric Environment.

Accurate wind speed measurement in low-pressure conditions is crucial for the thermal performance validation and attitude control of stratospheric aircraft. As air density decreases, traditional wind speed measurement systems based on principles such as dynamic pressure, heat transfer, ultrasound, and particle velocimetry face significant challenges when applied in low-pressure environments, often failing to achieve the required measurement accuracy. This paper presents the development of a wind speed simulation system based on a rotation method designed to operate in low-pressure conditions, utilizing a space environment simulation chamber in conjunction with a high-precision turntable. The system was employed to conduct response tests on a constant heat flow thermal sphere anemometer within a stratospheric pressure range of 1 kPa to 30 kPa. The experimental results revealed that at extremely low Reynolds numbers, the probe signal exhibited increasing nonlinearity, significantly affecting the response curve at pressures below 15 kPa. While the sensitivity of the hot-sphere probe remained relatively stable at wind speeds above 5 m/s, it decreased nonlinearly as the pressure dropped when wind speeds fell below 5 m/s. Furthermore, this paper analyzes the impact of various interpolation methods on wind speed conversion errors, providing valuable data to support the future development and validation of stratospheric aircraft.

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.

An Integrated Quantitative Method of Risk Analysis and Decision Making for Safety Manipulation of a Forest Firefighting Aircraft by Using Physical Models of Multi-Hazard Factors

Although firefighting aircrafts are effective for fighting forest fires, they are affected by a variety of risks related to forest fires during flight operations such as thermal radiation, temperature rise, decrease in air density, and changes in updraft aerodynamics. However, quantifying these influences poses a challenge. Our research reveals that safety standards predominantly hinge on technical indicators like flight height, speed, and angle of attack, which makes it possible to quantify the above effects. A general method framework for analysing firefighting flight safety criteria was constructed in this thesis. Using relevant physical models, such as heat radiation, temperature, air density, and updraft in a forest fire environment, safety criteria with an analytical form were established. The corresponding safety constraints of each criterion were calculated quantitatively, and the most stringent constraint was determined based on multiple factors to obtain a comprehensive safety constraint boundary composed of the critical altitude, stall speed, and critical angle of attack. Finally, the effectiveness of the method is verified in a simulation case. The research results show that the constrained boundary calculation method proposed in this study can provide a scientific basis for the formulation of technical specifications for forest aviation fire safety and aviation fire task planning.

TEMPERATURE OF THE COMPRESSOR SUCTION AIR AND ITS INFLUENCE ON THE EFFICIENT OPERATION OF THE COMPRESSOR UNIT

The climatic conditions of Uzbekistan are characterized by relatively long summers with air temperature of 40-45 0C and higher, which is the reason of significant heating of air suctioned by compressor. Increase in temperature and corresponding decrease inair density contributes to 8-10% decrease in compressor unit productivity, leading to significant economic losses in the process of compressed air production. By means of artificial cooling of suction air at the inlet to the compressor unit it is possible to increase the energy efficiency of operation of the mine reciprocating compressor unit.The effectiveness of artificial air temperature reduction depends on the amount of temperature reduction and the type of plant drive, as well as on the purpose -toreduce the specific electric energy consumption for compression or to increase the capacity of the reciprocating compressor.

Computational investigation of combined solar chimney power plant with gas power plant in different working conditions

Numerous studies have recently focused on enhancing the efficiency of solar chimney power plants (SCPP) and increasing their output power during periods of limited solar radiation. One such study proposes a novel solution: combining an SCPP with a gas power plant to create a hybrid power plant that generates power consistently, day and night. The system involves burying pipes underground and channeling the hot gas from the gas power plant through them, rather than releasing it into the atmosphere. This process increases the temperature of the soil beneath the canopy, which in turn raises the air temperature and the velocity of the air. The resulting decrease in air density leads to an increase in output power. Our results show that the performance of solar chimney of soil ground with buried pipe is about 30% higher than sand domain.

REVIEW ON COOLING METHOD OF GAS TURBINE POWER PLANT

In order to increase output power and thermal efficiency, the temperature going into a gas turbine is much higher than the point at which the material would melt. In order to protect the airfoil of a gas turbine from hot gas and, as a result, extend the blade's life, new internal and film cooling arrangements must be developed immediately. When the incoming air is heated, the gas turbine's output rises proportionately as well. The power output of a gas turbine is determined by the amount of mass flowing through it. Because of this, electricity generation decreases on warm days due to a decrease in air density. It takes a 1% rise in air temperature to reduce power production by 1%. The purpose of this research is to discuss current strategies for cooling incoming air to gas turbines. Mechanical chillers, evaporative coolers, and fogging methods have all been examined. This study focuses primarily on the fogging inlet air cooling system. There are many ways to cool the air going into the engine, but the high-pressure intake fogging method has become more popular over the past ten years because it costs less and makes a big difference in power.

Simulation Study of Fuel Concentration Field in Common-rail Diesel Engine Combustion Chamber under Plateau Environment

China has the largest plateau in the world, with an average altitude of 2000m-4500m. Due to the decrease of atmospheric pressure and temperature, the decrease of air density and the decrease of water boiling point, resulting in a decrease in power, economy, low temperature starting and cooling, soot emissions and other performance, soot emissions increase, the diesel engine can not accord with the requirements of plateau areas in the plateau area. Fuel concentration field of diesel engine has important influence on its dynamics, economy and emissions. The paper uses numerical simulation to study the fuel concentration field of combustion chamber in the plateau environment of CA6DL2-35E3R common-rail diesel engine. The results show that altitude has great impact on fuel concentration field of combustion chamber, and fuel concentration field increases with the increase of altitude, and compared with high speed condition, more fuel is distributed at the bottom and top of the combustion chamber under low speed condition.

Effect of Channel Size on Air-Cooling Performance in Interior Permanent Magnet Motor Driving Aviation Fans at High Altitude

Abstract To enhance worldwide environmental conditions, the air transport industry must drastically reduce carbon dioxide emissions. Electrification of aircraft propulsion systems is one way to meet this demand. In particular, the focus is on obtaining single-aisle aircraft with partial turbo-electric propulsion and approximately 150 passenger seats by the 2030s. To develop a single-aisle aircraft with partial turbo-electric propulsion, an air-cooled interior permanent magnet (IPM) motor with an output of 2 MW is desired. One of the most difficult problems in air cooling is that air-cooling performance decreases with increasing altitude because the air density decreases. To investigate the effect of altitude on air-cooling performance in the IPM motor, the authors formulated mathematical system equations to describe heat transfer inside the target air-cooled IPM motor, and mathematical analytical solutions were obtained. The most severe condition is the top-of-climb condition. For this condition, a designer should choose cooling air mass flow rates that keep the temperature of the permanent magnets below the maximum temperature limit of 100 °C and the temperature of the coils below the maximum temperature limit of 250 °C. Here, the sizes of the air-cooling channels strongly affect air cooling with the IPM motor. In this paper, the authors briefly review the mathematical formulations and their solutions, investigate the effect of channel size on air-cooling performance in an IPM motor, and explore the optimum configuration and settings for the air cooling channels.

Atmospheric Effects and Precursors of Rainfall over the Swiss Plateau

In this study, we investigate the characteristics of atmospheric parameters before, during, and after rain events in Bern, Switzerland. Ground-based microwave radiometer data of the TROpospheric WAter RAdiometer (TROWARA) with a time resolution of 7 s, observations of a weather station, and the composite analysis method are used to derive the temporal evolution of rain events and to identify possible rainfall precursors during a 10-year period (1199 available rain events). A rainfall climatology is developed using parameters integrated water vapor (IWV), integrated liquid water (ILW), rain rate, infrared brightness temperature (TIR), temperature, pressure, relative humidity, wind speed, and air density. It was found that the IWV is reduced by about 2.2 mm at the end of rain compared to the beginning. IWV and TIR rapidly increase to a peak at the onset of the rainfall. Precursors of rainfall are that the temperature reaches its maximum around 30 to 60 min before rain, while the pressure and relative humidity are minimal. IWV fluctuates the most before rain (obtained with a 10 min bandpass). In 60% of rain events, the air density decreases 2 to 6 h before the onset of rain. The seasonality and the duration of rain events as well as the diurnal cycle of atmospheric parameters are also considered. Thus, a prediction of rainfall is possible with a true detection rate of 60% by using the air density as a precursor. Further improvements in the nowcasting of rainfall are possible by using a combination of various atmospheric parameters which are monitored by a weather station and a ground-based microwave radiometer.

РЕЗУЛЬТАТЫ ИССЛЕДОВАНИЯ ПНЕВМОПЛОТНОСТИ ЦИЛИНДРОПОРШНЕВОЙ ГРУППЫ ДИЗЕЛЬНОГО ДВИГАТЕЛЯ

Reducing the leakproofness of the working volume of the cylinder due to wear of the cylinder piston group or other reasons leads to interruptions in the engine work. (Research purpose) The research purpose is in studying the dependence of the pneumatic leakproofness of the cylinder-piston group of a diesel engine on the position of the piston and the pressure of the air supplied to the cylinder. (Materials and methods) When diagnosing the cylinder-piston group, various devices are used, including pneumatic testers. This test method does not provide reliable information about the reasons for the decrease in air density and since the engine cylinders wear out unevenly, the diagnostic process must be performed at different positions of the piston. (Results and discussion) During the study of pneumatic tightness, it was found that the leakproofness of the worn cylinder-piston group in the zone of the upper dead center at the minimum pressure of the supplied air was 12.8 percent lower than in the rest of the cylinder. With an increase in pressure, the difference in leakproofness decreased to 6.3 percent. Authors confirmed the hypothesis of the dependence of the leakproofness of the worn cylinder-piston group on the position of the piston, which allows us to more accurately determine the cause of the violation of the leakproofness of the cylinder. The low pressure of the supplied air shows a greater informative value of the measurement due to a wider change in the air density in the upper dead center zone compared to the middle part of the cylinder and a smaller change in the density of the air flowing through the gaps of the cylinder-piston group. (Conclusions) In order to increase the degree of accuracy of testing the pneumatic density of the cylinder-piston group, measurements must be carried out several times at different pressures of the supplied air.

Flow and Noise Characteristics of Centrifugal Fan in Low Pressure Environment

The influence of low-pressure environment on centrifugal fan’s flow and noise characteristics was studied experimentally and numerically. A testbed was established to conduct the experimental test on the performance of a centrifugal fan, and the characteristic curve and power consumption curve of the fan under different pressure were obtained. Then the simulation model of the centrifugal fan was established, which was used to simulate the working process of centrifugal fan under different negative pressures. The results showed that the total pressure and static pressure of the fan decrease with the decrease of the ambient pressure. The total and static pressures of the fan under 60 kPa pressure condition decreased by 42.3% and 38.3%, respectively, compared with those of fan under the normal pressure. The main reason for this phenomenon is that the decrease of the environmental pressure leads to the decrease of air density. Besides, with the drop of environmental pressure, the sound pressure and sound power of the fan noise decreases.

Моделювання процесу витрат повітря у камері пневмомарзана ротаційного висікального модуля

Equipment for the manufacture of cardboard products is constantly being improved. New sections for die cutting are being designed. As well as devices for carrying out technological processes of die-cutting and cutting down of cardboard products. The tendency to improve the rotational method of trimming and die cutting of sheet materials is increasing. The main problem in the design of die cutting equipment is the quality of the processes performed.The advantages of the rotary die cutting sections include high productivity. Therefore, improving this process is very important. This article deals with the technological process of cutting in the knife-counter—knife zone. The problem of the interaction of cutting actuators is considered. The use of pneumatic systems greatly simplifies the die cutting process.An advantage of the pneumatic die cutting module is that it can be integrated into the transport system. This combination of conveyor and rotary module allows for curved separation of cardboard sweep.The aim of this study is to simulate the technological parameters of the process of cutting cardboard reamers in a pneumatic system. The calculation was carried out by computer aided design.Accordingly, in the working area of die cutting of the pneumatic system, the air pressure changes. Therefore, temperature parameters of air are important parameters. As previous studies have shown, air temperature can affect the performance of the rotary die cutting module. With increasing temperature, the required air flow rate increases to maintain the required working pressure. This is directly related to a decrease in air density with increasing temperature.Improving the geometry of the nozzle of a pneumatic system is an important study. A partial drop in pressure in the working areas of the die cutting can lead to a decrease in the quality of material processing.The basis of the work is research on the influence of air flow and its temperature variables as a characteristic working fluid. Additional studies carried out using the SolidWorks computer-aided design system show the dependence of the air volumetric flow rate on its variable temperature in the working area of the pneumatic rotary die cutting section.

Aircraft Takeoff Performance in a Changing Climate for Canadian Airports

Temperature and wind are major meteorological factors that affect the takeoff and landing performance of aircraft. Warmer temperatures and the associated decrease in air density in future climate, and changes to crosswind and tailwind, can potentially impact aircraft performance. This study evaluates projected changes to aircraft takeoff performance, in terms of weight restriction days and strong tailwind and crosswind occurrences, for 13 major airports across Canada, for three categories of aircraft used for long-, medium- and short-haul flights. To this end, two five-member ensembles of transient climate change simulations performed with a regional climate model, for Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios, respectively, are analyzed. Results suggest that the projected increases in weight restriction days associated with the increases in daily maximum temperatures vary with aircraft category and airfield location, with larger increases noted for airfields in the south central regions of Canada. Although avoiding takeoff during the warmest period of the day could be a potential solution, analysis focused on the warmest and coolest periods of the day suggests more weight restriction hours even during the coolest period of the day, for these airfields. Though RCP8.5 in general suggests larger changes to weight restriction hours compared to RCP4.5, the differences between the two scenarios are more prominent for the coolest part of the day, as projected changes to daily minimum temperatures occur at a much faster rate for RCP8.5 compared to RCP4.5, and also due to the higher increases in daily minimum temperatures compared to maximum temperatures. Both increases and decreases to crosswind and tailwind are projected, which suggest the need for detailed case studies, especially for those airfields that suggest increases. This study provides useful preliminary insights related to aircraft performance in a warmer climate, which will be beneficial to the aviation sector in developing additional analysis and to support climate change adaptation-related decision-making.

Evaluating The Performance of Solar Chimney Power Plant

Growing global energy demand has become worrying due to the fluctuating fossil fuel prices, the damage caused by the use of conventional fuels as the toxic emissions and global warming. Therefore, dependence on alternative and sustainable sources has become a pressing topic. In this paper will review the performance of solar chimney power plant, the parameters that affect on the performance, conversion efficiency and power output for a different collection of prototypes. During this study there are found that power output of the solar chimney power plant is directly proportional to increase of the height of the chimney, specifically when the solar chimney is sloped where the performances is better as well as the conversion efficiency. While increasing the diameter of collector will provide a big heating area which cause a decrease of air density due to rise in the air temperature under the solar collector which lead to increase the flow of driving force and the mass flow rate that causes an increase in the power output. Pressure drop is an important factor for identifying the maximum power output when the solar radiation is a constant which effect on thermodynamic properties. Therefore, the efficiency will increase with increasing the optimal proportion of pressure drop.

Directional Absorption of Parameterized Mountain Waves and Its Influence on the Wave Momentum Transport in the Northern Hemisphere

AbstractThe directional absorption of mountain waves in the Northern Hemisphere is assessed by examination of horizontal wind rotation using the 2.5° × 2.5° European Centre for Medium‐Range Weather Forecasts ERA‐Interim reanalysis between 2011 and 2016. In the deep layer of troposphere and stratosphere, the horizontal wind rotates by more than 120° all over the Northern Hemisphere primary mountainous areas, with the rotation mainly occurring in the troposphere (stratosphere) of lower (middle to high) latitudes. The rotation of tropospheric wind increases markedly in summer over the Tibetan Plateau and Iranian Plateau, due to the influence of Asian summer monsoonal circulation. The influence of directional absorption of mountain waves on the mountain wave momentum transport is also studied using a new parameterization scheme of orographic gravity wave drag (OGWD) which accounts for the effect of directional wind shear. Owing to the directional absorption, the wave momentum flux is attenuated by more than 50% in the troposphere of lower latitudes, producing considerable orographic gravity wave lift which is normal to the mean wind. Compared with the OGWD produced in traditional schemes assuming a unidirectional wind profile, the OGWD in the new scheme is suppressed in the lower stratosphere but enhanced in the upper stratosphere and lower mesosphere. This is because the directional absorption of mountain waves in the troposphere reduces the wave amplitude in the stratosphere. Consequently, mountain waves are prone to break at higher altitudes, which favors the production of stronger OGWD given the decrease of air density with height.

The effects of pressure on X-ray fluorescence analyses: pXRF under high altitude conditions

As altitude increases, air density decreases, and the physics of X-rays being transmitted through air mean that the transmission of low-energy X-rays increases and accordingly the transmission effectiveness of low-atomic weight elements (e.g. Mg, Al, and Si) also increases. Here we assess the performance of pXRF units across a range of pressures.

Femtosecond laser ablation of an aluminum target in air

The dynamics of laser ablation of solid target with ultrashort intense laser pulses is not only fundamentally interesting, but also relevant to a few important applications such as microfabrication, laser propulsion, laser induced breakdown spectroscopy, etc. By use of time-resolved pump-probe shadowgraphic imaging technology, we study the dynamic process of laser ablation of a planar aluminum target in air. The incident laser pulses are from a Ti: sapphire femtosecond laser amplifier system with a duration of 50 fs, central wavelength of 800 nm, pulse energy varying between 4 mJ and 7 mJ. Time-resolved shadowgraphs of material ejection from the aluminum target are recorded at the time delay up to a few nanoseconds after laser irradiation. By changing the distance between the target and the focal point of the incident laser, we obtain the shadowgraphs of the target ejection under different laser spot sizes. When the laser spot size is relatively large say, over 1 mm, the irradiated target surface is ablated in the form of a planar shock. However, when the laser spot size is relatively small, the ejection appears in the form of a hemispherical blast wave. It is found that the hemispherical blast wave well conforms to the Sedov's blast wave theory. When the laser energy is relatively large, it is found that ionization of air has a great effect on laser ablation. Additional small ejections appear as columnar and hemispherical structures near the laser axis, which are superimposed on the large planar shock. These can be attributed to the following processes. Firstly, as the ionization of air occurs near the laser axis, effective heat transfer from air plasma to the aluminium target leads to enhanced target temperature. This leads to the formation of a columnar structure on a picosecond time scale. Secondly, the columnar ejection and air plasma expansion near the laser axis result in the decrease of air density and pressure, which leads to the formation of the hemispherical structure on a nanosecond time scale.

Efecto de la Relación de Compresión en el Rendimiento de Motores de Combustión Interna a diferentes Altitudes

Considering these factors, this study developed analytical-empirical equations to obtain power losses in internal combustion engines (Otto cycle) at a different altitude based on the compression ratio of the engine and on the adiabatic coefficients of air-fuel air and pure air. The decrease in air density with altitude is the most important cause for the power loss of internal combustion engines. However, there are other factors that introduce additional power reduction, and that are not considered in current models available. An expression that not only considers the density of air but also includes the compression ratio of the engine is proposed. Thus, the power loss due to the altitude for an internal combustion engine with a certain power at sea level, is slightly lower at higher compression ratios.

Optimization of Air Cooling Ribs for 1.5MW Wind Rotor Based on CFD

To enhance heat exchange between the rotor and external environment, many ribs are arranged on the cover of the machine. The air cooling condition for 1.5MW wind rotor is evaluated by Computational fluid dynamics(CFD). It is found that the density of the air, the flow velocity and the arrangement of the ribs on the rotor cover is the main factors impacting the air cooling effect of the rotor. Under the same running power, the air cooling condition becomes worse with the decrease of air density and becomes better with the increase of wind speed. To improve the cooling condition of the wind rotor, the arrangement of the ribs on the cover is optimized. The results show that the width ratio of the ribs and channels plays an important role in the heat convection. In all our cases, 0.5 is the best. Considering the manufacture processing, the arrangement of 400 ribs is selected in our optimization.

Effect of altitude on football performance

Altitude will impact football performance through two separate and parallel pathways related to the hypobaric (physical) and hypoxic (physiological) components of terrestrial altitude: (a) the decrease in partial pressure of oxygen reduces maximal oxygen uptake and impairs "aerobic" performance by reducing maximal aerobic power, increasing the relative intensity of any given absolute level of work, and delaying recovery of high-energy phosphates between high-intensity "interval" type efforts; (b) the decrease in air density reduces air resistance which will facilitate high-velocity running, but will also alter drag and lift thereby impairing sensorimotor skills. These effects appear to have their greatest impact very early in the altitude exposure, and their physiological/neurosensory consequences are ameliorated by acclimatization, though the extent of restoration of sea level type performance depends on the absolute magnitude of the competing and living altitudes.