Pressure Overshoot Research Articles

Survey of Ventilator Waveform Interpretation Among ICU Professionals.

The interpretation of ventilator waveforms is essential for effective and safe mechanical ventilation but requires specialized training and expertise. This study aimed to investigate the ability of ICU professionals to interpret ventilator waveforms, identify areas requiring further education and training, and explore the factors influencing their interpretation skills. We conducted an international online anonymous survey of ICU professionals (physicians, nurses, and respiratory therapists [RTs]), with ≥ 1 y of experience working in the ICU. The survey consisted of demographic information and 15 multiple-choice questions related to ventilator waveforms. Results were compared between professions using descriptive statistics, and logistic regression (expressed as odds ratios [ORs; 95% CI]) was performed to identify factors associated with high performance, which was defined by a threshold of 60% correct answers. A total of 1,832 professionals from 31 countries or regions completed the survey; 53% of respondents answered ≥ 60% of the questions correctly. The 3 questions with the most correct responses were related to waveforms that demonstrated condensation (90%), pressure overshoot (79%), and bronchospasm (75%). Conversely, the 3 questions with the fewest correct responses were waveforms that demonstrated early cycle leading to double trigger (43%), severe under assistance (flow starvation) (37%), and early/reverse trigger (31%). Factors significantly associated with ≥ 60% correct answers included years of ICU working experience (≥ 10 y, OR 1.6 [1.2-2.0], P < .001), profession (RT, OR 2.8 [2.1-3.7], P < .001), highest degree earned (graduate, OR 1.7 [1.3-2.2], P < .001), workplace (teaching hospital, OR 1.4 [1.1-1.7], P = .008), and prior ventilator waveforms training (OR 1.7 [1.3-2.2], P < .001). Slightly over half respondents correctly identified ≥ 60% of waveforms demonstrating patient-ventilator discordance. High performance was associated with ≥ 10 years of ICU working experience, RT profession, graduate degree, working in a teaching hospital, and prior ventilator waveforms training. Some discordances were poorly recognized across all groups of surveyed professionals.

The 10Hz dynamic response of a fluid-filled pressure monitoring system is a novel alternative to the fast flush test and indicative of unacceptable systolic pressure overshoot.

The standard method for qualitatively evaluating the dynamic response is to see if the gain of the amplitude spectrum curve approaches 1 (input signal = output signal) over the frequency band of the blood pressure waveform. In a previous report, Watanabe reported that Gardner's natural frequency and damping coefficient, which are widely used as evaluation methods, do not reflect the dynamic response of the circuit. Therefore, new parameters for evaluating the dynamic response of pressure monitoring circuits were desired. In this study, arterial pressure catheters with length of 30, 60, 150, and 210 cm were prepared, and a blood pressure wave calibrator, two pressure monitors with analog output and a personal computer were used to analyze blood pressure monitoring circuits. All data collection and analytical processes were performed using step response analysis program. The gain at 10 Hz was close to 1 and the systolic blood pressure difference was small in the short circuits (30 cm, 60 cm), and the gain at 10 Hz was 1.3-1.5 in the 150 cm circuit and over 1.7 in the 210 cm circuit. The difference in systolic blood pressure increased in proportion to the length of the circuit. It could also be inferred that the gain at 10 Hz should be less than 1.2 to meet a clinically acceptable blood pressure difference. In conclusion, the gain at 10 Hz is sufficiently useful as an indicator to determine the correct systolic blood pressure.

Optimizing the Control of the Hydraulic Driving System for the Power Shift Gearbox of a Cotton Picker Based on Dual Working Conditions

In response to the issues of slow dynamic response, uneven shifting, and strong jolting during the starting and shifting operations of the cotton picker, we established a model for automatic power shifting control. We proposed optimization strategies using the Statechart logic control method and BP neural network control method. Different control effects were analyzed concerning pressure, flow rate, motor speed, vehicle speed, impact degree, and slip-grinding work. The results showed that the Statechart logic control method increased the response time of the flow rate by 46.67% during the starting process, with a good linear characteristic during the variation. It reduced the impact during starting and shifting by 38.57% and 67%, and the sliding friction power during starting and shifting by 51.95% and 33.33% respectively. The BP neural network control method reduced the pressure overshoot during starting and shifting by 25% and 30.77%, respectively, demonstrating better robustness. The pump, motor speed, and vehicle speed showed smooth growth after starting and shifting, with faster vehicle speed response during the starting process. Additionally, the vehicle speed overshoot during shifting significantly decreased, ensuring overall performance that meets the operational requirements of the cotton picker. This finding holds practical significance for the advancement of control strategy optimization and the development of the control system for the powershift gearbox in cotton pickers.

Cardiovascular responses to mild perinatal asphyxia in growth-restricted preterm lambs.

Growth-restricted neonates have worse outcomes after perinatal asphyxia, with more severe metabolic acidosis than appropriately grown neonates. The cardiovascular physiology associated with fetal growth restriction (FGR) may alter their response to asphyxia. However, research on asphyxia in FGR is limited. Here we compared cardiovascular hemodynamics in preterm FGR and control lambs during mild perinatal asphyxia. We induced FGR in one twin at 89 days gestation (term 148 days), while the other served as a control. At 126 days gestation, lambs were instrumented to allow arterial blood pressure and regional blood flow recording, and then mild perinatal asphyxia was induced by umbilical cord clamping, and resuscitation followed neonatal guidelines. FGR lambs maintained carotid blood flow (CBF) for 7 min, while control lambs rapidly decreased CBF (P < 0.05). Fewer growth-restricted lambs needed chest compressions for return of spontaneous circulation (ROSC) (17 vs. 83%, P = 0.02). The extent of blood pressure overshoot after ROSC was similar, but it took longer for MAP to return to baseline in FGR lambs (18.83 ± 0.00 vs. 47.67 ± 0.00 min, P = 0.003). Growth-restricted lambs had higher CBF after ROSC (P < 0.05) and displayed CBF overshoot, unlike control lambs (P < 0.03). In conclusion, preterm growth-restricted lambs show resilience during perinatal asphyxia based on prolonged CBF maintenance and reduced need for chest compressions during resuscitation. However, CBF overshoot after ROSC may increase the risk of cerebrovascular injury in FGR.NEW & NOTEWORTHY Preterm growth-restricted lambs maintain carotid blood flow for longer than control lambs during asphyxia and have a lower requirement for chest compressions than control lambs during resuscitation. Preterm growth-restricted, but not control, lambs displayed an overshoot in carotid blood flow following return of spontaneous circulation.

The effect of imposed resistance in neonatal resuscitators on pressure stability and peak flows: a bench test.

The importance of neonatal resuscitator resistance is currently unknown. In this study we investigated peak flows and pressure stability resulting from differences in imposed resistance during positive pressure ventilation(PPV) and simulated spontaneous breathing (SSB) between the r-PAP, low-resistance resuscitator, and Neopuff™, high-resistance resuscitator. In a bench test, 20 inflations during PPV and 20 breaths during SSB were analysed on breath-by-breath basis to determine peak flow and pressure stability using the Neopuff™ with bias gas flow of 8, 12 or 15 L/min and the r-PAP with total gas flow of 15 L/min. Imposed resistance of the Neopuff™ was significantly reduced when the bias gas flow was increased from 8 to 15 L/min, which resulted in higher peak flows during PPV and SSB. Peak flows in the r-PAP were, however, significantly higher and fluctuations in CPAP during SSB were significantly smaller in the r-PAP compared to the Neopuff™ for all bias gas flow levels. During PPV, a pressure overshoot of 3.2 cmH2O was observed in the r-PAP. The r-PAP seemed to have a lower resistance than the Neopuff™ even when bias gas flows were increased. This resulted in more stable CPAP pressures with higher peak flows when using the r-PAP. The traditional T-piece system (Neopuff™) has a higher imposed resistance compared to a new neonatal resuscitator (r-PAP). This study shows that reducing imposed resistance leads to smaller CPAP fluctuations and higher inspiratory and expiratory peak flows. High peak flows might negatively affect lung function and/or cause lung injury in preterm infants at birth. This study will form the rationale for further studies investigating these effects. A possible compromise might be to use the traditional T-piece system with a higher bias gas flow (12 L/min), thereby reducing the imposed resistance and generating more stable PEEP/CPAP pressures, while limiting potentially harmful peak flows.

The effects of balance board on the balance parameters in five children with spastic cerebral palsy.

This study evaluated the effects of an instrumented balance board on the balance parameters in children with spastic cerebral palsy by carrying out a pilot single-group pre-post clinical trial. Five children aged 5 to 15 years with spastic diplegia and a Gross Motor Function Classification System level of I or II were included. All participants attended 20 sessions with an instrumented balance board, 45 minutes per session, 3 times a week for 7 weeks. The main outcome measures included the center of pressure excursion, velocity, and overshoot during quiet standing with open and closed eyes. The assessments were performed in the mediolateral and anteroposterior directions at pre- and one week post-intervention. Non-parametric tests showed that the excursion did not change significantly except in the mediolateral direction with eyes closed (p < 0.05). The velocity of the center of pressure improved in both directions and eye conditions (p < 0.05). Also, the maximum velocity decreased with eyes open (mediolateral, anteroposterior, and total) (p < 0.05), while the change was not significant with the eyes closed. The overshoot measurements did not change significantly. It is recommended to consider balance board training for improving balance parameters in children with cerebral palsy.

Analysis of Pressure Impact Characteristics of a Hydraulic Position Servo System Based on Series Servo Valves

As one of the causes of system vibration and noise, pressure impact is always undesired. Analysis of pressure impact characteristics of a hydraulic position servo system based on a two-stage series servo valve is carried out to reduce the system impact. The influence of factors such as system flow rate, additional servo valve opening gain, external load, and system overflow pressure on the system pressure impact is analyzed. The results show that the series servo valve scheme can bring down the peak impact pressure at the inlet of the hydraulic cylinder by 8%~11% when the system flow rate or overflow pressure is low to a certain extent. In most other cases, the suppression effect of the impact peak pressure is unapparent. The impact pressure overshoot is always decreased accompanied by an easier trend to overflow for the system. At last, another new idea of application promotion with higher reliability and adaptability is proposed.

Soil hydraulic conductivity in the state of nonequilibrium

AbstractHydraulic nonequilibrium in soil during water infiltration and drainage is a well‐known phenomenon. During infiltration, water initially invades easily accessible pores before it slowly redistributes towards some state of energetic minimum. In analogy, during drainage, easily drainable pores are emptied more rapidly than those blocked by bottlenecks. The consequence is that the water content is lagging behind the water potential and both state variables do not follow a unique water retention curve as typically assumed when applying Richards equation. Current models that account for nonequilibrium allow for the required decoupling of water content and water potential; however, they do not consider the consequences for the hydraulic conductivity. In this contribution, we present a physically based approach to estimate hydraulic conductivity during nonequilibrium, which depends on both water content and water potential during nonequilibrium conditions. This approach of a dynamic hydraulic conductivity function is demonstrated for an infiltration process into relatively dry soil and for a stepwise drainage and rewetting with decreasing and increasing water fluxes (i.e., multistep flux experiment). The new approach reproduces well‐known phenomena such as pressure overshoot and preferential flow across infiltration fronts using a unified concept for hydraulic conductivity. This was not possible with existing models assuming some fixed unsaturated conductivity function depending on either water content or water potential.

Study on the Influencing Factors of the Response Characteristics of the Slide Valve-Type Direct-Acting Relief Valve with External Orifice

The slide valve-type direct-acting relief valve with external orifice (SVTDARVWEO) is widely used in hydraulic systems, and its response characteristics are influenced by key factors. It is of great significance to carry out research on the influencing factors of the response characteristics of the SVTDARVWEO. The working principle of the SVTDARVWEO is analyzed in the present study. The simulation model of the SVTDARVWEO is established using AMESim. The influence of the orifice diameter, viscosity coefficient, valve element mass, spring stiffness, oil seal length, and valve element diameter on the response characteristics of the SVTDARVWEO is studied. The results show that: (1) The smaller the orifice diameter is, the smaller the oscillation frequency, amplitude and maximum overshoot of pressure, flowrate, displacement and velocity are. (2) When the viscosity coefficient is 50 N/(m/s), 55 N/(m/s) and 60 N/(m/s), the pressure, flowrate, displacement and velocity oscillate periodically, but the amplitude of the oscillation decreases gradually, and the oscillation frequency is 250 Hz. When the viscosity coefficient is 60 N/(m/s), the pressure, flowrate, displacement and velocity will reach their respective stable values earlier. (3) When the valve element mass is 0.01 kg, 0.015 kg and 0.02 kg, the pressure, flowrate, displacement and velocity oscillate periodically, but the amplitude of oscillation decreases gradually. When the valve element mass is 0.01 kg, the pressure, flowrate, displacement and velocity will reach the stable value earlier. (4) The smaller the spring stiffness is, the greater the maximum overshoot of pressure, flowrate, displacement and velocity is, and the higher the number of oscillations to reach the stable value are, in addition to more time being required. (5) With the increase in oil seal length, the maximum overshoot of pressure and velocity, stability value of displacement also increase correspondingly. (6) With the increase in the valve element diameter, the stable value of pressure decreases, and the oscillation frequency of pressure, flowrate, displacement and velocity increase, but the oscillation amplitude decreases.

Performance Assessment of Hydraulic Micro Relief Valve

Directly operated relief valves often exhibit abnormal or unstable behavior resulting in noise, premature wear, degraded performance, and failure. In this work, an investigation is carried out to assess the role of the hydraulic damper on the poppet element. The article reports the details of the investigation approach, integrating specific experimental tests with lumped-parameter modelling.Starting from a reference layout, the hydraulic behavior of different damper configurations is characterized (ranging from undamped to strongly damped poppets), for pressure and flow-rate conditions typically encountered in micro-hydraulic power packs. Depending on the damper design, the poppet operation ranges from unacceptability (due to noise) to fine-tuned response. The investigation give the chance to highlight how the damper layout impacts on the valve behaviour, in terms of pressure overshoot and settling time and provides the necessary information for relief valve design, modelling and analysis.

Research on Acceleration Performance Optimization of Large Inertia Hydraulic Actuator Based on Main Valve Input Shaping

In order to optimize the acceleration performance of a large inertia hydraulic actuator, this paper proposes a main valve input shaping control strategy, which makes the valve flow supply match the load-control demand by adjusting the main valve flow growth rate. Taking a load-independent flow distribution system as the research object, and aiming at the problems of large pressure overshoot, excessive overflow and oscillation tendency during the actuator acceleration process, this paper divides the acceleration process into the pressure build-up condition, the inertia-acceleration condition and the stable-flow regulation condition according to the change characteristics of the actuator driving pressure, and divides the main valve control signal into five stages to design the valve flow growth rate, thereby smoothing the driving pressure fluctuations by adjusting the actuator inertial load and mitigating the pressure release process. Based on the key structure-hydraulic parameters and test data of a 6-ton excavator, a virtual excavator that can accurately simulate the swing action and boom lifting action is built, and the software-in-the-loop test of the input-shaping control algorithm is carried out. The test results indicate that the proposed control strategy can effectively suppress the pressure overshoot, oscillation, and flow overmatching, thereby improving the dynamic stability and energy efficiency of the system.

In vitro prediction of the lower/upper-critical biofluid flow choking index and in vivo demonstration of flow choking in the stenosis artery of the animal with air embolism

<i>In vitro</i> prediction of the lower/upper-critical biofluid flow choking index and <i>in vivo</i> demonstration of flow choking in the stenosis artery of the animal with air embolism

Components of aircraft life support systems interact with each other and the user

The life support system in a tactical aircraft provides necessary supplemental oxygen to the aircrew. However, interactions among its various components may generate unexpected breathing loads. We focus here on the interactions between a regulator and breathing mask commonly used together in the U.S. Navy, the CRU-103 regulator and MBU 23/P mask, and some effects of the interactions on the user. The data reported were collected during a larger research effort examining potential physiological and cognitive effects of low regulator inlet pressures. Seventeen participants completed a series of tasks under mild exercise while breathing 40% O2 (balance N2) from an MBU-23/P mask supplied by a CRU-103 regulator with supply pressures 10, 6, 4, and 2 psig (CRU-103 specifications are for inlet pressures from 5 to 120 psig). Variables measured included flow to the mask and pressures at the regulator supply, in the hose to the mask, and in the mask. In addition to restricting inspiratory flow, low inlet pressure to the CRU-103 caused a counterintuitive overshoot in gas delivery pressure at end-inspiration, a mean increase of 1.5 cm H2O between the 10- and 2 psig conditions. The added pressure to the exhalation valve increased the expiratory threshold, the pressure to start expiratory flow, by approximately 2 cm H2O, increasing the effort needed to exhale.

Performance-Matching Optimization Design of Loader-Hydraulic System Based on Hydrodynamics Analysis

The study of the performance of dynamic hydraulic throttling under the condition of stable fluid is of great significance. The effect of a step change in pressure differences on the throttling performance of a hydraulic valve is studied. This paper studies the dynamic and static performance of a hydraulic-valve-outlet throttling-speed regulation system, builds a more accurate mathematical model, considers the linear factors of the flow of hydraulic-valve throttling, analyzes the influence of the step-load change in pressure difference on the stability of the hydraulic-valve movement speed, and constructs a nonlinear mathematical model of the speed-regulation system of the outlet throttling. A pressure sensor is used to measure the change in pressure overshoot, and the effect of a pressure-difference step change on the throttling performance of the hydraulic valve is studied under steady-fluid conditions. The theory is analyzed and verified by experiment, and the parameters of hydraulic components are modified using the dynamic-change rule of the hydraulic valve’s two-chamber pressure.

Transient performance study of high pressure fuel gas supply system for LNG fueled ships

The transient performance of the fuel system is a critical issue for the operation of liquefied natural gas (LNG) fueled ships. In this paper, experiments and simulations of a high pressure fuel gas supply system (HP-FGSS) were conducted to investigate the system transient responses during load variations and environmental disturbances. A prototype of the HP-FGSS was tested at different running loads from 0% to 110% in combination with a MAN high pressure two-stroke dual fuel engine. A dynamic model of the HP-FGSS was developed and validated by the test data. The effects of the operating parameters and equipment sizes on the system performances were simulated and analyzed. The results show that during the load variations from 75% to 100% the fuel gas pressure fluctuation is nearly 10 bar and lasts for 5 min. The HP-FGSS control system has a high robustness to the LNG composition, but the pressure overshoot increases as the methane content decreases. The LNG composition will also affect the steady state value of the gas temperature. The buffer tank volume has a significant impact on the pressure response. The pressure disturbance in the LNG tank induced by violent sloshing will be transmitted to the suction port of the high pressure pump, causing a cavitation risk.

Cardiorespiratory impact of intrathoracic pressure overshoot during artificial carbon dioxide pneumothorax: a randomized controlled study

BackgroundThe aim of this study is to evaluate cardiovascular and respiratory effects of intrathoracic pressure overshoot (higher than insufflation pressure) in patients who underwent thoracoscopic esophagectomy procedures with carbon dioxide (CO2) pneumothorax.MethodsThis prospective research included 200 patients who were scheduled for esophagectomy from August 2016 to July 2020. The patients were randomly divided into the Stryker insufflator (STR) group and the Storz insufflator (STO) group. We recorded the changes of intrathoracic pressure, peak airway pressure, blood pressure, heart rate and central venous pressure (CVP) during artificial pneumothorax. The differences in blood gas analysis, the administration of vasopressors and the recovery time were compared between the two groups.ResultsWe found that during the artificial pneumothorax, intrathoracic pressure overshoot occurred in both the STR group (8.9 mmHg, 38 times per hour) and the STO group (9.8 mmHg, 32 times per hour). The recorded maximum intrathoracic pressures were up to 58 mmHg in the STR group and 51 mmHg in the STO group. The average duration of intrathoracic pressure overshoot was significantly longer in the STR group (5.3 ± 0.86 s) vs. the STO group (1.2 ± 0.31 s, P < 0.01). During intrathoracic pressure overshoot, a greater reduction in systolic blood pressure (SBP) (5.6 mmHg vs. 1.1 mmHg, P < 0.01), a higher elevation in airway peak pressure (4.8 ± 1.17 cmH2O vs. 0.9 ± 0.41 cmH2O, P < 0.01), and a larger increase in CVP (8.2 ± 2.86 cmH2O vs. 4.9 ± 2.35 cmH2O, P < 0.01) were observed in the STR group than in the STO group. Vasopressors were also applied more frequently in the STR group than in the STO group (68% vs. 43%, P < 0.01). The reduction of SBP caused by thoracic pressure overshoot was significantly correlated with the duration of overshoot (R = 0.76). No obvious correlation was found between the SBP reduction and the maximum pressure overshoot.ConclusionsIntrathoracic pressure overshoot can occur during thoracoscopic surgery with artificial CO2 pneumothorax and may lead to cardiovascular adverse effects which highly depends on the duration of the pressure overshoot.Trial registrationClinicaltrials.gov (NCT02330536; December 24, 2014).

Experimental study on the effect of filling ratio on an R141b two-phase thermosyphon loop with a horizontal parallel tube evaporator

A two-phase thermosyphon loop is an ideal heat transfer device to achieve compact and efficient cooling with low energy consumption. In this paper, a two-phase thermosyphon loop with a horizontal parallel tube evaporator for multiple heat source cooling is proposed. The effect of the filling ratio on the transient response of temperature and pressure, heat transfer characteristics, instability issues, as well as flow regimes under different heat loads are investigated experimentally and visually. The filling ratios are divided into three groups according to their unique heat transfer and instability characteristics. The research results show that a too low or too high filling ratio is not conducive to the safe and stable operation of the system. At medium and high filling ratios, temperature and pressure overshoot are prone to occur, threatening the safe operation of the system; geyser boiling is another unstable phenomenon that can be inhibited as the heat load increases. Gravity will lead to uneven distribution of working fluid in the evaporator and further affect the temperature uniformity and heat transfer capability. From the perspective of temperature control performance and heat transfer capability, 30% is the optimal filling ratio in this study, with a minimum thermal resistance of 0.12 ℃ ⋅W-1 and a maximum heat transfer coefficient of 1345.36 W⋅m−2⋅℃−1. This paper provides a basis for designing and applying a two-phase thermosyphon loop for multiple heat source cooling in confined spaces.

Cardiac sympathetic innervation in Parkinson\u2019s disease versus multiple system atrophy

PurposeThe aims of this study were to evaluate the diagnostic accuracy of the dual imaging method combining cardiac iodine-123-metaiodobenzylguanidine single-photon emission computed tomography combined with low-dose chest computed tomography compared to routine cardiac scintigraphy, and assess regional differences in tracer distribution and the relationships between imaging and autonomic function in Parkinson’s disease and multiple system atrophy.MethodsA prospective study including 19 Parkinson’s disease and 12 multiple system atrophy patients was performed. Patients underwent clinical evaluation, iodine-123-metaiodobenzylguanidine single-photon emission computed tomography combined with chest computed tomography, planar scintigraphy, and cardiovascular autonomic function tests.ResultsCo-registration of single-photon emission computed tomography and chest computed tomography resulted in three groups with distinct patterns of tracer uptake: homogeneous, non-homogeneously reduced and absent. There was a significant difference in group allocation among patients with multiple system atrophy and Parkinson’s disease (p = 0.001). Most multiple system atrophy patients showed homogeneous uptake, and the majority of Parkinson’s disease patients showed absent cardiac tracer uptake. We identified a pattern of heterogeneous cardiac tracer uptake in both diseases with reductions in the apex and the lateral myocardial wall. Sympathetic dysfunction reflected by a missing blood pressure overshoot during Valsalva manoeuvre correlated with cardiac tracer distribution in Parkinson’s disease patients (p < 0.001).ConclusionsThe diagnostic accuracy of the dual imaging method and routine cardiac scintigraphy were similar. Anatomical tracer allocation provided by the dual imaging method of cardiac iodine-123-metaiodobenzylguanidine single-photon emission computed tomography and chest computed tomography identified a heterogeneous subgroup of Parkinson’s disease and multiple system atrophy patients with reduced cardiac tracer uptake in the apex and the lateral wall. Sympathetic dysfunction correlated with cardiac imaging in Parkinson’s disease patients.

Explosion Impact Strength Evaluation Technology and Safety Measures for Refrigerant Circuit Components.

The demands of heat cycles are increasing in the recent society where high performance of electronics or comfortability of our life are required. In order to use them safely and efficiently, the thermal accidents caused by high speed destruction or explosion have to be avoided. The usage of a pressure relief valve is one of effective measures. For an instance it can safely exhaust high-pressure combustible gas generated as a diesel engine like explodes in an air conditioner compressor. In this study histories of strain and pressure growing process that was referred as diesel explosion process in the compressor were estimated and measured. Then it was found that the pressure reached to a maximum at 4 msec after the valve was opened, due to the heat supply from the combustion gas inside the compressor, and that these phenomena induced the overshoot of valve pressure. These phenomena were estimated by analyses and experiments, it was found that this overpressure caused the delay of functional removement of the valve. Finally, these information were applied to product design, and these knowledges were able to avoid pressure vessel breakage.

Aerothermodynamic characteristics of hypersonic curved compression ramp flows with bistable states

The aerothermodynamic characteristics (including wall friction Cf, pressure pw, and heat flux St) in curved compression ramp (CCR) flows with bistable states are studied numerically and theoretically. Direct numerical simulations of bistable states of separation/attachment induced by variation of the turning angle ϕ, as well as the influence of inflow Mach number and wall temperature on dual-solution interval, are carried out. Distributions of wall friction, pressure and heat flux are analyzed. Further, the emergence of the first and second minima of Cf in the separation bubble is interpreted, which are dominated by the adverse pressure gradient induced by separation and reattachment shock, respectively. The present results and analysis indicate that the reversed-flow singularity of F. T. Smith (Proc. R. Soc. London. A: Math. Phys. Sci. 420, 21–52 (1988)] is less likely to occur in CCR flows. The prediction of pressure peak ppk of separation states confirms the model based on the minimum viscous dissipation theorem [Hu et al., Phys. Fluids 32(10), 101702 (2020)]. While the pressure overshoot pos can be analyzed by shock-polars with pressure match of compression and expansion process. The correlation between heat flux peak and pressure peak of both separation and attachment states is also discussed in terms of the classical power relation.