Showing papers on "Dynamic pressure published in 2022"

Towards traceable dynamic pressure calibration using a shock tube with an optical probe for accurate phase determination

Abstract: In this paper, we introduce a robust method for dynamic characterization of pressure measuring systems used in time-varying pressure applications. The dynamic response of the pressure measuring systems in terms of sensitivity and phase as a function of frequency at various amplitudes of the measurand can be provided. The shock tube which is the candidate primary standard for dynamic pressure calibration at the National Laboratory for pressure, Sweden, was used to realize the dynamic pressure. The shock tube setup used in this study can realize reference pressure with amplitudes up to 1.7 MPa in the frequency range from below a kilohertz up to a megahertz. The amplitude of the realized step pressure was calculated using the Rankine–Hugoniot step relations. In addition, the accurate time of arrival of the generated shock at the device under test (DUT) was measured using an optical probe based on shadowgraphy. The optical detector has a response time in nanosecond time scale which is several orders of magnitude faster than the response time of any pressure measuring system. Hereby, the latency between physical stimuli and response of the DUT can be measured. By the knowledge of the amplitude and the accurate time of arrival of the reference step pressure, the transfer function of the DUT can be calculated and presented in Bode diagrams of sensitivity and phase response versus frequency. The uncertainty in sensitivity and phase measurements was estimated. The information provided by this work is useful for developing reliable models of dynamic pressure measuring system and provide accurate information about their dynamic response. That in turn will contribute to establish a traceability chain for dynamic pressure calibration.

Study of dynamic debris impact load on flexible debris-resisting barriers and the dynamic pressure coefficient

Abstract: The use of steel flexible barriers to mitigate landslide risk on natural hillsides is becoming common in the last decade in Hong Kong. The current design approach for this kind of barrier structure involves the adoption of the hydrodynamic load model to predict dynamic impact forces, followed by non-linear structural analyses of flexible barriers using numerical programs based on the pseudo-static method. From local guidelines, the dynamic pressure coefficient is taken as 2.0. This empirically considers the effect of impacts from boulders up to 2.0m in diameter. With a view to rationalising the design approach, a series of physical impact tests and numerical analyses was conducted to investigate the dynamic impact on flexible barriers and the resulting barrier response. The tests involved up to 9m³ of debris resisted by a 1.5m high steel barrier, conducted at the 28m long flume facility at the Kadoorie Centre, Hong Kong. Numerical modelling using computer programs LS-DYNA and NIDA-MNN was conducted to analyse the dynamic response. The study aims to evaluate the dynamic pressure coefficient and to verify the current design approach. Results indicate that a coefficient of 1.0 is in general appropriate for design purposes for debris comprising primarily water and fine-grained particles.

Experimental Investigation on the Impact of Dam-Break Induced Surges on a Vertical Wall

Abstract: This paper presents the results of an experimental investigation on the impact of dam-break-induced surges on a vertical wall. The instantaneous surge height and dynamic pressure on a vertical wall were measured for surges with different reservoir depths of H = 200 mm, 250 mm, and 300 mm. The time-histories of horizontal pressure on the wall were measured using the miniaturized pressure transducers, and the surge heights were recorded with an ultrasonic sensor. The relationships between dynamic pressure and surge height on the vertical wall and during the impact were obtained from recorded raw data. The experimental results highlighted detailed processes on the variation of impact pressure during the surge propagation, impact on the wall, runup, falling, and breakup of the turbulent flow. The time-histories of surge height and dynamic pressure were analyzed, and the results were compared with the hydrostatic pressure on the wall to study wave breaking mechanism of tsunami waves on the wall. Dynamic pressures at the impact instant were found to be approximately three times the corresponding static pressure in the bed, in good agreement with previous research Moreover, the maximum surge runup heights on the wall were between 2.1 and 2.3 times the corresponding initial reservoir depths. The vertical distributions of impact pressure were divided into two hydrodynamic regimes. Based on the impact duration, the first regime occurred less than 0.1 s after the impact with highly non-linear pressure distributions, and the second regime showed a semi-hydrostatic pressure distribution from 0.5 s to 0.7 s. The results presented in this study are suitable for the design of coastal infrastructures and can be used to validate numerical models.

Dynamic simulation model for three-wheel air-cycle refrigeration systems in civil aircrafts

Abstract: Dynamic simulation model of air-cycle refrigeration systems in civil aircrafts is essential for revealing the operation mechanism during flight process. In the present study, a dynamic model of three-wheel air-cycle refrigeration system was developed. A near-logarithm heat transfer temperature difference function is utilized to improve the stability of the heat transfer solution. A dynamic solution method based on continuity equation and theorem of momentum was presented as the framework of the dynamic mass transfer solution. A pressure-flow decoupling method is presented to solve the dynamic pressure in the high-pressure zone, resolving the absence of key pressure parameters. The model has been validated based on experimental data, with a pack discharge temperature deviation of 0.05K. Dynamic simulations have been conducted with actual flight data to obtain transient performance under airborne condition. In the takeoff and landing phase, the drastic change in the environment results in low discharge temperature, endangering the condenser with icing risk, which can be avoided by enabling the TCV. In the cruise phase, the discharge temperature slightly exceeds the upper limit for a couple of minutes. The optimization by slightly extending the length of heat exchanger channels succeeded in eliminating the excessive discharge temperature with minimal side effects.

Bioinspired dynamic soaring simulation system with distributed pressure sensors

Abstract: Inspired by the albatross, this paper presents the construction of a dynamic soaring simulation system with distributed pressure sensors. The advantage of our system lies in harvesting energy from the wind shear layer and estimating the wind information using a pressure-based sensor system. Specifically, the dynamic soaring simulation system contains an offline training stage and an online estimation and control stage. In the offline training stage, computational fluid dynamics simulations are conducted and used as the data source. A surrogate model is established to correlate the local flow conditions and the surface pressure at optimal sensor positions. In the online estimation and control stage, through sensing the pressure information, the real-time wind velocity and wind gradient are estimated by the surrogate model trained in the offline stage. Moreover, wind information is adopted in the simulation of dynamic soaring control. In this study, the simulation system was applied to linear and circular path-following tasks. It was found that the dynamic soaring simulation system with distributed pressure sensors provides an acceptable estimation of wind velocity and wind gradient with a certain time delay caused by numerical differentiation.

Evaluating the Utility of Pressure Scanners for Unsteady Pressure Measurements in Wind Tunnel Characterization of the Space Launch System

Abstract: In many aerodynamic measurement applications, the ability to make time-accurate measurements with pressure scanners provides practical advantages over making the same measurements directly using flush-mounted transducers. However, the pneumatic distortion due to the tubing between the sensing module and surface port limits the usefulness of such measurements to averaged, steady data only. This issue has restricted the application of pressure scanners for unsteady pressure measurements in the wind tunnel and flight-testing applications. The Wiener-filtered inverse system response model has been proven effective in reconstructing complex unsteady pressure signals acquired remotely using pressure scanners. The unparalleled long-term thermal stability, flexibility and robustness that pressure scanners provide in wind-tunnel and flight-testing applications, combined with an ability to reconstruct the unsteady components of the measured pressure signals, could enable their use in modern applications involving dynamic flow fields and highly separated flows. This work evaluated the feasibility of using pressure scanning systems for time-resolved pressure measurements in the NASA Langley 14- by 22-Foot Subsonic Wind Tunnel. Results demonstrated good agreement between the reference transducers and reconstructed pressure scanner measurements up to frequencies of approximately 500 Hz.

Numerical investigation of the influence of aerothermoelastic dynamic response on the performance of the three-dimensional hypersonic inlet

Abstract: The influence of aerothermoelastic dynamic response on the performance of the three-dimensional hypersonic inlet is investigated in this paper. A dynamic aerothermoelastic analysis framework is developed. The reliability of the framework is verified. The effects of aerodynamic heating on the dynamic response, the effects of the aerothermoelastic dynamic response of the inlet on the flow field structure, and the performance parameters are studied. The results indicate that the static deformation of the leading edge structure is large while the vibration amplitude is small. Meanwhile, the vibration amplitude of the trailing edge structure is larger. The aerothermoelastic dynamic response changes the shock wave structure near the exit, strengthens the shock wave intensity, increases the length of the separated region, and changes the flow field of the exit. Simultaneously, the flow field structure also experiences obvious dynamic changes at different moments. The dynamic response increases the time-averaged flow coefficient, reduces the time-averaged total pressure recovery coefficient, and improves the time-averaged reverse pressure ratio. At the same time, the dynamic response leads to the fluctuation of performance parameters, especially the large fluctuation range of the reverse pressure ratio at the exit.

New Technology of Pressure Relief Control in Soft Coal Roadways with Deep, Violent Mining and Large Deformation: A Key Study

Abstract: Previous studies have shown that the influence of deep dynamic pressure on the surrounding rock control of a coal roadway is one of the difficulties in mine roadway support. Based on the investigation of the headgate 11231 in a coal mine, this study analyzes the damage characteristics of coal roadway surrounding rock affected by deep dynamic pressure, expounds on the difficulties of controlling the roadway surrounding rock, and creatively proposes a cooperative control technology of external anchor–internal unloading for regulating large deformation of roadways. The vertical stress distribution and transfer law of surrounding rock with different hole-making depths, spacing, and lengths after roadway excavation were simulated and studied, and an appropriate parameter range of hole-making space in the stage without dynamic pressure influence was obtained. Considering the influence of mining dynamic pressure, the surrounding rock pressure relief effect of each optimized hole-making parameter was analyzed. In addition, the optimal hole-making parameters (the hole-making depth, spacing, and length were 8 m, 3.2 m, and 3 m, respectively) that can effectively reduce the high stress of roadway shallow surrounding rock in two stages (without and with dynamic pressure) and ensure integrity of the shallow surrounding rock were obtained. The actual field application shows that the new technology can reduce the higher rib deformation by approximately 850 mm and achieve a good surrounding rock control effect. The research and practice show that the pressure relief control for soft coal roadways with deep, violent mining and large deformation has achieved success, providing technical support for the maintenance of the same type of roadway.

Flutter Analysis of the Benchmark Supercritical Wing at Moderate Angles of Attack

Abstract: The paper presents flutter analyses of the Benchmark Supercritical Wing, at moderate angles of attack, performed as part of the Third Aeroelastic Prediction Workshop. Aeroelastic simulations of the pitch and plunge spring-suspended wing were performed using the EZAir flow solver at an ambient Mach number of 0.8, angles of attack ranging from one to five degrees, and various dynamic pressure values. Flutter onset was detected and compared with experimental data, where available. The focus of the study was threefold: 1) Predicting flutter in a computationally efficient manner by fitting a linear dynamic model to responses at pre-flutter conditions and extrapolating a stability parameter, 2) Studying the angle of attack effect on flutter onset and mechanism at this transonic Mach number, and 3) Studying the possible relation between shock buffet and flutter, and the fluid-structure interaction mechanism. Simulations indicate that as the angle of attack increases, shock buffet occurs, the flutter-onset dynamic pressure decreases significantly, and the flutter mechanism changes from two degrees of freedom to single-degree-of-freedom pitch oscillations.

A Two‐Spacecraft Study of Mars' Induced Magnetosphere's Response to Upstream Conditions

Abstract: This is a two-spacecraft study, in which we investigate the effects of the upstream solar wind conditions on the Martian induced magnetosphere and upper ionosphere. We use Mars Express (MEX) magnetic field magnitude data together with interplanetary magnetic field (IMF), solar wind density, and velocity measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, from November 2014 to November 2018. We compare simultaneous observations of the magnetic field magnitude in the induced magnetosphere of Mars (|B|IM) with the IMF magnitude (|B|IMF), and we examine variations in the ratio |B|IM/|B|IMF with solar wind dynamic pressure, speed and density. We find that the |B|IM/|B|IMF ratio in the induced magnetosphere generally decreases with increased dynamic pressure and that a more structured interaction is seen when comparing induced fields to the instantaneous IMF, where reductions in the relative fields at the magnetic pile up boundary (MPB) are more evident than in the field strength itself, along with enhancements in the immediate vicinity of the optical shadow of Mars. We interpret these results as evidence that while the induced magnetosphere is indeed compressed and induced field strengths are higher during periods of high dynamic pressure, a relatively larger amount of magnetic flux threads the region compared to that available from the unperturbed IMF during low dynamic pressure intervals.

Progress on Transonic Flutter and Shock Buffet Computations in Support of the Third Aeroelastic Prediction Workshop

Abstract: This paper reports on the progress of the NASA Langley team contributions to the third Aeroelastic Prediction Workshop’s (AePW-3) High Angle Working Group (HAWG). The primary objectives of HAWG is to predict the fluter dynamic pressure of the NASA Benchmark Supercritical Wing (BSCW) configuration at Mach 0.8 and 5� angle of attack. The secondary objective is to determine if a shock-buffet onset is present at or near that flow condition. The computational results are obtained using FUN3D, an unstructured grid Reynolds-averaged Navier-Stokes solver developed at the NASA Langley Research Center. The preliminary analysis results show a computationally-obtained flutter dynamic pressure of approximately 120 psf. Initial results describing unforced BSCW unsteady flow environment at flutter condition are also presented.

Chaos Analysis of Single-Stage Spur Gear System Considering Backlash Fractal

Abstract: Abstract Purpose Considering the time-varying pressure angle and dynamic clearance, the effects of rotational speed, tooth surface friction, and tooth surface morphology on the system’s dynamic response are studied. Method An improved gear nonlinear model is proposed, which considered nonlinear factors such as time-varying pressure angle, position angle, tooth surface morphology, and tooth surface friction. The time-varying dynamic backlash is deduced, and the nonlinear dynamic equation of the gear is established. The nonlinear dynamic response of the gear system is obtained based on Runge–Kutta method. Results The influence of the rotational speed and tooth surface friction on single-stage spur gear system response is analyzed through the analysis of the bifurcation diagram, the three-dimensional spectrum diagram, the proportion of the meshing state, and the largest dynamic meshing force (LDMF). Dynamic response differences between the three different model are compared. In addition, by changing the tooth surface roughness and fractal dimension, the influence of tooth surface morphology on the dynamic response of the system is studied. Conclusion Compared with the traditional model, when the dynamic center distance and dynamic pressure angle are considered, the system response may enter a chaotic state earlier. When the tooth surface friction is further considered, the chaotic state of the system response is suppressed. At the same time, the velocity of the dynamic transmission error is significantly reduced, and the fluctuation amplitude of the dynamic pressure angle is increased. The value of LDMF rose overall. The stability of the system response decreases with the increase of tooth surface roughness and fractal dimension. Compared with the fractal dimension, the tooth surface roughness has a more obvious effect on the dynamic response of the system.

Immediate Impact of Solar Wind Dynamic Pressure Pulses on Whistler‐Mode Chorus Waves in the Inner Magnetosphere

Abstract: Solar wind-magnetosphere coupling is a key link of the space weather chain. There have been increasing reports of solar wind dynamic pressure pulses influencing the whistler-mode chorus wave growth in the inner magnetosphere, but the response conditions and mechanisms of chorus growth remain under debate. Here we present a statistical study of the immediate impact of solar wind dynamic pressure pulses on inner magnetospheric chorus waves using Van Allen Probes data from 2012 to 2019. A stronger pulse is found to have a greater likelihood to change the chorus amplitude particularly on the dayside. Positive pulses can significantly enhance chorus amplitudes, while negative ones result in a weakening in chorus amplitudes. As supported by direct observations, these pulses alter the linear growth of waves by modifying energetic electron distributions; in contrast, geomagnetic field modeling indicates no significant changes in the geomagnetic field inhomogeneity controlling the nonlinear growth threshold of waves.

Formation Mechanisms of the Molecular Ion Polar Plume and Its Contribution to Ion Escape From Mars

Abstract: We investigated the formation mechanism of a molecular ion plume and its contribution to ion escape based on Mars Atmosphere and Volatile EvolutioN (MAVEN) observations from November 2014 to October 2019 and numerical models. Here, we report a CO2+-rich plume event and a statistical study of the molecular ion plume. MAVEN observed a CO2+-rich plume event, in which the maximum CO2+ escape flux is approximately 4.2 × 106 cm−2s−1, on 28 August 2015 under strong solar wind dynamic pressure conditions. A numerical simulation using strong solar wind dynamic pressure conditions from the event suggested that the molecular ion plume is formed by deep penetration of the solar wind-induced electric field, which is caused by strong solar wind dynamic pressure. A statistical study showed that CO2+ plume events tend to be observed under high solar wind dynamic pressure and strong electric field conditions. This tendency is consistent with the formation mechanism of the molecular ion plume suggested by the event study. The O2+ plume does not show the same tendency. This is because O2+ ions are abundant in the high-altitude ionosphere, and O2+ plumes can be formed even under weak solar wind conditions. The subsolar crustal magnetic fields tend to prevent the formation of the molecular ion plume by shielding the ionosphere from the solar wind. The escape rate ratio is approximately 45:53:3 during the whole statistical survey period, suggesting that a molecular ion plume from the ionosphere is a non negligible ion escape channel from Mars.

Pressure and velocity variation in remote-controlled plane using cfd analysis

Abstract: Aircraft are significant because they transport people and commodities through a wide range of terrains in a short amount of time. Newton's third law states that thrust is created by fly motors due to the response powers provided by fume gases. In this paper, computational fluid dynamics (CFD) analysis of an aeroplane is used to create an ideal design. Prior to the time-consuming production of aircraft, qualitative and quantitative wing characterisation gives important information for verifying wing choices and design. Each wing was independently subjected to CFD study at various velocities. Each wing's lift, drag, pressure, and velocity were measured, and a comparison analysis revealed how little adjustments to the wing's pressure, drag, velocity lift may have a significant impact. Each wing's lift, drag, pressure, and velocity were measured, and a comparison analysis revealed how small adjustments to the wing's overall flow characteristics improved the overall flow characteristics.

FTLE and Surface-Pressure Signature of Dynamic Flow Reattachment During Delta-Wing Axial Acceleration

Abstract: An experimental investigation was conducted on the aerodynamics of an NACA0012 airfoil wing with triangular planform geometry undergoing steady and axial accelerations at as a model of an unmanned combat air vehicles encountering unsteady environments at pre- and poststall angles of attack (Marzanek, M., and Rival, D., “Separation Mechanics of Non-Slender Delta Wings During Streamwise Gusts,” Journal of Fluids and Structures, Vol. 90, Oct. 2019, pp. 286–296.). Ensemble-averaged flowfields, forces, moments, and surface-pressure distributions were measured in the Optical Towing Tank for Energetics Research facility at Queen’s University. To characterize the evolution of the flowfield coherent structures around a wing under axial gusts or accelerations, a Lagrangian flowfield analysis including the finite-time Lyapunov exponent (FTLE) was conducted. Results indicate that axial acceleration can induce a dynamic flow reattachment at the poststall angle of attack, and clear FTLE ridges extend from the wing surface and travel down the chord as reattachment progresses. A distinct signature in the surface-pressure distribution tracks closely with the location where the FTLE ridges meet the wing. The timing of how this surface-pressure distribution moves aft is shown to correlate with the relatively large-scale fluctuation in the pitching moment. The current work reveals the correlation between FTLE and surface pressure, which further hints at a potential approach of dynamic estimation by using Lagrangian coherent structures.

Investigation on Dynamic Pressure Characteristics Induced by an Internal Solitary Wave in a Two-layer Fluid of Finite Depth

Abstract: In this paper, the dynamic pressure characteristics induced by an internal solitary wave (ISW) in a two-layer fluid of finite depth are studied. A method for detecting ISWs by dynamic pressure is proposed. First, an accurate controllable ISW numerical flume is established based on the applicability conditions of three kinds of ISW theories. Then the relationship between the maximum dynamic pressure and the amplitude of the ISW under four density stratifications is studied. The results show that the dynamic pressure variation induced by the ISW is synchronous with that of interface displacement. Under the same density stratification, the maximum dynamic pressure has a strong linear relationship with the corresponding amplitude. Furthermore, the nonlinear error is less than 7 %, and the relationship is not affected by the ocean structure. According to the above characteristics of dynamic pressure, a series of dynamic pressure measurement experiments were carried out in a large internal wave flume (IWF) using a very low frequency (VLF) piezoelectric sensor. The experimental results show that the dynamic pressure measurement results are in good agreement with the numerical simulation results. Last, the Miyata-Choi-Camassa (MCC) theory is used to invert the measured maximum dynamic pressure to the amplitude of ISW, and compared with the measured amplitude, the maximum error is less than 6 %, which verifies the feasibility of the inversion method of ISW amplitude by using dynamic pressure measurement proposed in this paper, and provides a new method and idea for detecting ISW at sea in the future.

Influence of geometric, kinematic, gas-dynamic parameters on rotor dynamic state taking into account gas dynamic flow in labyrinth seals clearances

Abstract: The present work details a new approach to the study of GTU rotor vibrations, based on the solution of a related dynamic problem for the «gas – dynamic flow – deformable structure» sys-tem. The modern tendency to increase an aggregates power with a simultaneous decrease stiffness results in new phenomenons that affected a rotor vibration state. The compressor rotor model with a labyrinth seal is considered. ANSYS software product is used. The calculations were carried out on a high-performance computer complex PNRPU. The performed calculations showed a qualitative and quantitative effect of a gas-dynamic gap on the rotor dynamics. A 2FSI calculations series was performed to study the influence of geometric, kinematic and gas-dynamic parameters on the rotor dynamic state. A pressure fluctuations spectral analysis in the gas-dynamic gap and displacements has been carried out. The obtained spectrograms pro-cessing it possible to plot amplitudes and frequencies dependences of resonant pressure oscil-lations over an initial pressure in the gas-dynamic gap. It was found that the initial pressure in a gas-dynamic gap has the greatest influence. A rotor and gas oscillations resonant frequency was found, which corresponds to a change in the shaft axis spatial position. The «gas – struc-ture» system resonant frequencies were obtained for models differing in mass and stiffness. A decrease in an elasticity modulus of the structure led to a decrease in the maximum pressure fluctuations amplitude, while a decrease in mass led to its increase. For the base model and the model with lower rigidity, the resonant pressure oscillations frequency depends on the initial pressure value according to a law close to linear, while for the model with a lower mass, the dependence has a pronounced non-linear character.

Ranking the drivers of the Martian bow shock location: a statistical analysis of Mars Atmosphere and Volatile EvolutioN and Mars Express observations

Abstract: <p>The Martian interaction with the solar wind leads to the formation of a bow shock upstream of the planet. The shock dynamics appears complex, due to the combined influence of external (solar photons, solar wind plasma and fields) and internal (crustal magnetic fields, ionized atmosphere) drivers. The extreme ultraviolet fluxes and magnetosonic mach number are known major drivers of the shock location, while the influence of other possible drivers is less constrained or unknown such as crustal magnetic fields or the solar wind dynamic pressure and the Interplanetary Magnetic Field (IMF) intensity and orientation.</p><p>We analyze and rank the influence of the main drivers of the Martian shock location, based on published datasets from Mars Express and Mars Atmosphere Volatile EvolutioN missions and on several methods such as the Akaike Information Criterion, Least Absolute Shrinkage Selection Operator regression, and partial correlations. We include here the influence of the crustal fields, extreme ultraviolet fluxes, magnetosonic mach number, solar wind dynamic pressure and various Interplanetary Magnetic Field parameters (intensity and orientation angles).</p><p>We conclude that the major drivers of the shock location are extreme ultraviolet fluxes and magnetosonic mach number, while crustal fields and solar wind dynamic pressure are secondary drivers at a similar level. The IMF orientation also plays a significant role, with larger distances for perpendicular shocks rather than parallel shocks.</p>

Robust Sliding Mode Control for Hypersonic Cruise Missile Using Dynamic Pressure Feedback

Abstract: Hypersonic Cruise Missile (HCM) generally adopts the air-breathing scramjet engine as the propulsion, which needs strict conditions of the missile flight dynamic pressure. It is crucial to satisfy the dynamic pressure conditions for scramjet powering on when the aerodynamic drag or thrust is deviated during the standard trajectory command tracking. In this paper, a novel robust control system is presented that the autopilot of HCM adopts the dynamic pressure directly as feedback variable to track the command. To ensure the accurate tracking of dynamic pressure and the stability of attitude, a four-dimensional model of HCM including dynamic pressure and normal overload is deducted. Meanwhile, to deal with the unmodeled dynamics and the external disturbances, a sliding mode controller is designed to guarantee the stability and robustness. The stability analysis of the overall system under the proposed control method is investigated via the Lyapunov theorem. Simulation results show that the proposed controller can ensure good tracing performance of the HCM while existing deviations of aerodynamic drag or thrust, unmodeled dynamics and external disturbances.

Investigation of the dynamic stability of pressure regulators when taking into account the inertial forces of the hydraulic fluid flow

Abstract: The dynamic stability of pressure regulators in hydraulic systems of technological machines is considered, in which additional hydrodynamic forces arise in unsteady modes. The magnitude of these hydrodynamic forces is determined mainly by the first derivative of the flow rate through the throttle slot of the regulator in time. Experimental studies of pressure regulators have shown that hydrodynamic forces, depending on the switching scheme and the design dimensions of these devices, can affect their stability in various ways.

The Influence of Extreme Levels of the Solar Wind Dynamic Pressure on the Structure of Nightside Auroral Precipitation

Abstract: Abstract The data from the DMSP spacecraft were used to study the characteristics of ion and electron precipitation in the nightside sector of the auroral zone during magnetically quiet periods at extreme values of the solar wind dynamic pressure ( Psw ). It was shown that the ion pressure at the isotropy boundary (IB) increases with Psw and can reach a level of 4–6 nPa at Psw = 20–22 nPa. The latitude profiles of the ion pressure obtained at different levels of Psw indicate that the increase in Psw is accompanied by an expansion of the ion precipitation region and a shift of the IB to lower latitudes. At 〈 Psw 〉 = 0.5 nPa, the IB latitude is ~70.4° CGL, while at 〈 Psw 〉 = 16.3 nPa, it shifts toward the equator to ~64.6° CGL. As the Psw level decreases, the energy fluxes of precipitating electrons decrease significantly. At Psw < ~ 2.0 nPa, auroras in the region of the auroral oval can be considered subvisual. At extremely low values of dynamic pressure, Psw = ~ 0.2 nPa, it becomes very problematic to identify the zone of electron and ion precipitation.

Study on dynamic characteristics of a combined air pressure reducing valve

Abstract: Aiming at a kind of combined high pressure reducing ratio air pressure reducing valve with two stages in series, computational fluid dynamics (CFD) method is used to study the flow field characteristics of the pressure reducing valve. For different pressure reducing states, the dynamic characteristics of the pressure reducing valve are studied through unsteady simulation, and the variation law of characteristic parameters with time in typical processes such as starting, pressurization and decompression is analyzed. The results show that the variation law of the parameters such as pressure of the chamber and flow rate of valve is different in different pressure reducing states and working processes, but the flow field of the pressure reducing valve has reasonable aerodynamic damping characteristics, which can achieve stable operation in the regulation process in a large range of pressure reducing ratio, and has good dynamic characteristics.

Numerical simulation research on the correlation between bicycle drag and dynamic pressure

Abstract: Competitive cycling is one of the most popular sports in the world. In order to study the correlation between the drag and dynamic pressure field distribution of competitive cyclists at different velocity, the SST k-ω model was used for CFD numerical simulation in this work. The dynamic pressure field around the cyclist's system is analyzed, and the key monitoring points are set up and the dynamic pressure change trend at different velocity and the change trend of the steadystate dynamic pressure difference of the monitoring points are calculated. The results show that the variation trend of the dynamic pressure difference at different velocity is highly consistent with the variation trend of the drag coefficient, indicating that the dynamic pressure difference is an important source of drag.

Novel secondary standard for calibration of dynamic pressure sensors

Abstract: Abstract Recent research activities in dynamic pressure metrology have been mainly focusing on the development of primary standards like the shock tube or drop-weight apparatus to establish traceability to SI. However, these calibration facilities require a high level of expertise leading to elaborate and time-consuming calibrations. The development of secondary calibrators, based on the reference sensor principle, offering efficient and cost-effective calibrations is essential to meet the needs for industry and to disseminate the dynamic pressure quantity to a wide end-user community. This paper reports a novel secondary calibrator for dynamic pressure measurements up to 300 bar with an expanded uncertainty of about 3.0 %. A heating option enable calibrations at elevated temperatures up to 200 °C making it an ideal solution for convenient calibrations of dynamic pressure transducers used for measurement in internal combustion engine applications.