Time-averaged Pressure Research Articles

Impact of cross-sectional area ratio on time-averaged pressure drop induced by jet pump for thermoacoustic engine

Gedeon streaming, a time-averaged mass flow circulating throughout the loop configuration in the oscillating flow, can considerably deteriorate the thermal efficiency of traveling-wave thermoacoustic engine. Jet pump is characterized by a tapered channel with different inlet and outlet areas. It can produce a time-averaged pressure drop to suppress Gedeon streaming. In this study, the suppression mechanism of the jet pump in oscillatory flow is investigated, and the emphasis is put on the effect of cross-sectional area ratio on the performance of jet pumps with different taper angles. An experimental apparatus has been built to measure the time-averaged pressure induced by the jet pump. When the taper angle ranges from 3° to 9°, the time-averaged pressure drop and working efficiency can be improved by increasing cross-sectional area ratio, and the change of taper angle has little effect on the performance of jet pumps. However, as the taper angle increases beyond 9°, the performance of jet pump with a large cross-sectional area ratio degrades considerably. In addition, the time-averaged pressure drops induced by the jet pumps with different cross-sectional area ratios are similar, and the taper angle becomes more dominant for jet pump’s performance.

Shock Train Unsteadiness Characteristics, Oblique-to-Normal Transition, and Three-Dimensional Leading Shock Structure

The structure and unsteadiness characteristics of a shock train in a constant-area ducted flow are studied experimentally as a function of duct back pressure, which is mechanically controlled by a valve. Increasing the back pressure pushes the shock train upstream where the approach conditions (including Mach number and boundary-layer momentum thickness) are different, as these quantities vary along the duct length. Despite nominally constant boundary conditions during a run, the shock train fluctuates about its time-averaged position. Schlieren imaging reveals that the unsteadiness characteristics, including the fluctuation amplitude and frequency content, are independent of back pressure. However, changes in the Mach stem length and shock angles demonstrate that the leading shock structure transitions from oblique to normal as back pressure increases. Time-averaged pressure profiles show that the shock train length decreases and the pressure rise across the shock train increases during this process, but these quantities are nominally constant when normalized by the approach conditions. Finally, stereo particle image velocimetry is used to study the three-dimensional structure of a normal leading shock. The velocity fields show a large separation region on the side-wall of the duct and a degree of axisymmetry that indicates a nominally conical shock structure.

Numerical simulation of catalytic upgrading of biomass pyrolysis vapours in a FCC riser

Catalytic upgrading of biomass pyrolysis vapours is a potential method for the production of hydrocarbon fuel intermediates. This work attempts to study the catalytic upgrading of pyrolysis vapours in a pilot scale FCC riser in terms of hydrodynamics, residence time distribution (RTD) and chemical reactions by CFD simulation. NREL's Davison Circulating Riser (DCR) reactor was used for this investigation. CFD simulation was performed using 2-D Eulerian–Eulerian method which is computationally less demanding than the alternative Euler-Lagrangian method. First, the hydrodynamic model of the riser reactor was validated with the experimental results. A single study of time-averaged solid volume fraction and pressure drop data was used for the validation. The validated hydrodynamic model was extended to simulate hydrodynamic behaviours and catalyst RTD in the Davison Circulating Riser (DCR) reactor. Furthermore, the effects on catalyst RTD were investigated for optimising catalyst performance by varying gas and catalyst flow rates. Finally, the catalytic upgrading of pyrolysis vapours in the DCR riser was attempted for the first time by coupling CFD model with kinetics. A kinetic model for pyrolysis vapours upgrading using a lumping kinetic approach was implemented to quantify the yields of products. Five lumping components, including aromatic hydrocarbons, coke, non–condensable gas, aqueous fraction, and non–volatile heavy compounds (residue) were considered. It was found that the yield of lumping components obtained from the present kinetic model is very low. Thus, the further research needs to be carried out in the area of the kinetic model development to improve the yield prediction.

Time-averaged pressure drop induced by a jet pump in oscillatory flow

Gedeon streaming is known to considerably deteriorate the thermal efficiency of a traveling-wave thermoacoustic engine with looped configuration. The time-average pressure drop induced by a jet pump can efficiently suppress the Gedeon streaming. In this study, such suppression mechanism of the jet pump is investigated, and the emphasis is put on the effects of the dimensionless rounding, the taper angle, and the cross-sectional area ratio. An experimental apparatus has been set up to measure the time-averaged pressure drop induced by the jet pumps in oscillatory flow. Controlled experiments and characterization reveal the time-averaged pressure drop and working efficiency increase with a rise in dimensionless rounding when it is less than 0.15. For jet pumps with the fixed opening areas, the taper angle in the range from 3° to 9° is capable of producing a larger time-averaged pressure drop with a higher working efficiency, and the change of taper angle has little effect on the performance. However, performance degradation is observed as the taper angle increases beyond 9°. Moreover, when the taper angle ranges from 3° to 9°, the time-averaged pressure drop and working efficiency can be improved by increasing the cross-sectional area ratio.

Turbulent velocity and pressure fluctuations in gas turbine combustor exit flows

This paper presents the results of two test programmes using novel instrumentation to characterise the pressure and turbulent velocity fields in gas-turbine combustor exit flows. The probes are uncooled, therefore a fast-insertion traverse system is employed to prevent thermal degradation of the instrumentation in these severely hostile high-temperature environments. High-bandwidth ultra-miniature pressure transducers are used to measure unsteady total pressure, whilst a Pitot tube is employed to measure time-averaged total pressure. The probes are 4 mm in diameter with a measurement bandwidth of the order of 100 kHz. In the first test programme, the probes are used to characterise the streamwise turbulent velocity field approximately two axial chords downstream of an uncooled single-stage turbine in a turbojet engine. Established data reduction methods and calibration against a hot-wire are used to obtain turbulent velocity fluctuations from unsteady total pressure measurements. Comprehensive turbulence results are presented including time-histories, power spectra, intensities, and lengthscales obtained at four-engine conditions and at two radial and two circumferential measurement locations. In the second test programme the probes are demonstrated in an industrial combustor rig, featuring a can combustor with swirler nozzle and no dilution holes, at temperatures up to 1500 K. Static pressure fluctuations are obtained up to 100 kHz, and some typical combustor spectral features are identified.

Investigations of Compressible Turbulent Flow in a High-Head Francis Turbine

Dynamic stability of the high-head Francis turbines is one of the challenging problems. Unsteady rotor–stator interaction (RSI) develops dynamic stresses and leads to crack in the blades. In a high-head turbine, vaneless space is small and the amplitudes of RSI frequencies are very high. Credible estimation of the amplitudes is vital for the runner design. The current study is aimed to investigate the amplitudes of RSI frequencies considering a compressible flow. The hydro-acoustic phenomenon is dominating the turbines, and the compressibility effect should be accounted for accurate estimation of the pressure amplitudes. Unsteady pressure measurements were performed in the turbine during the best efficiency point (BEP) and part load (PL) operations. The pressure data were used to validate the numerical model. The compressible flow simulations showed 0.5–3% improvement in the time-averaged pressure and the amplitudes over incompressible flow. The maximum numerical errors in the vaneless space and runner were 6% and 10%, respectively. Numerical errors in the instantaneous pressure amplitudes at the vaneless space, runner, and draft tube were ±1.6%, ±0.9%, and ±1.8%, respectively. In the draft tube, the incompressible flow study showed the pressure amplitudes up to eight times smaller than those of the compressible. Unexpectedly, the strong effect of RSI was seen in the upper and lower labyrinth seals, which was absent for the incompressible flow.

Test–retest reliability of the Tekscan® F-Scan® 7 in-shoe plantar pressure system during treadmill walking in healthy recreationally active individuals

In-shoe plantar pressure systems are commonly used in clinical and research settings to assess foot function during functional tasks. Recently, Tekscan® has updated their F-Scan® in-shoe plantar pressure system; however, this system’s test–retest reliability has not been established. Therefore, the purpose of this study was to determine the test–retest reliability of the F-Scan® 7 system in recreationally active individuals during treadmill walking. Seventeen healthy adults completed 2 sessions of treadmill walking. For each session, participants were fitted for shoes and pressure insoles and walked on a treadmill at a self-selected pace for 30 s. Following the sessions, the test–retest reliability peak pressure, pressure time integral, average pressure and pressure contact area over 4 regions of the foot (heel, mid-foot, forefoot and toes) was assessed by calculating intraclass coefficients (ICC 2,k) and coefficient of variation percentage (CoV%). Pressure contact area consistently had the highest ICCs and lowest CoV% (ICCs: 0.91–0.98; CoV%: 2.7–7.8%). Whereas, the forefoot and toe regions had the highest ICCs for all 4 measures (ICCs: 0.83–0.98; CoV%: 3.1–13.4%). During treadmill walking in healthy recreationally active individuals, the reliability of the new Tekscan F-Scan® ranged from poor to high and was dependent on the measure and region of the foot.

Pressure, temperature, and three-component velocity fields by filtered Rayleigh scattering velocimetry.

The filtered Rayleigh scattering (FRS) technique, extended by the method of frequency scanning, is a powerful tool to characterize thermodynamic, as well as aerodynamic, properties of technical flows. In this Letter, we report on the first application of an FRS velocimeter, which is capable of acquiring time-averaged planar pressure, temperature, and three-component velocity distributions simultaneously. The method is validated by characterizing the near-field, as well as the far-field, of a turbulent jet.

Impact of achieved blood pressure on renal function decline and first stroke in hypertensive patients with chronic kidney disease.

The effect of achieved blood pressure (BP) on first stroke and renal function decline among hypertensive patients with mild to moderate chronic kidney disease (CKD) is still uncertain. In total, 3230 hypertensive patients with estimated glomerular filtration rate 30-60 mL/min/1.73m2 and/or proteinuria were included in the present analyses. Eligible participants were randomly assigned to a daily treatment of a combined enalapril 10 mg and folic acid 0.8 mg tablet or an enalapril 10 mg tablet alone. Participants were followed up every 3 months. The study outcomes included first stroke and the progression of CKD. The median antihypertensive treatment duration was 4.7 years. Compared with participants with a time-averaged on-treatment systolic blood pressure (SBP) of 135 to ≤140 mmHg, the incidence of total first stroke [1.7% versus 3.3%; hazard ratio (HR), 0.51; 95% confidence interval (CI): 0.26-0.99] and ischemic stroke (1.3% versus 2.8%; HR, 0.46; 95% CI: 0.22-0.98) decreased significantly in those with a time-averaged SBP of ≤135 mmHg. Furthermore, a time-averaged diastolic blood pressure (DBP) of ≤80 mmHg, compared with a time-averaged DBP level of 80 to ≤90 mmHg, was significantly related to a decreased risk of hemorrhagic stroke (0.2% versus 0.9%; HR, 0.18; 95% CI: 0.04-0.80). However, compared with participants with a time-averaged SBP of 135 to ≤140 mmHg, a lower but non-significant trend of CKD progression was found in those with a time-averaged SBP of ≤130 mmHg. A BP treatment level of ≤135/80 mmHg, compared with a BP treatment level of 135-140/80-90 mmHg, could lead to a decreased risk of first stroke in hypertensive patients with mild-to-moderate CKD.

Characteristics of aeration in the flow downstream of a radial gate with a sudden fall-expansion aerator in a discharge tunnel

Abstract The mechanisms of cavitation damage in flood releasing tunnels remain unclear. In this study a series of physical experiments and numerical calculations were conducted to investigate the flow pattern, pressure distribution and cavitation downstream of a sudden fall-expansion aerator in a discharge tunnel. When the radial gate was partly open, the bottom cavity length reduced drastically, the lateral cavity disappeared, and the flow cavitation index near the sidewalls was less than 0.2. The pressure on the floor and sidewalls can be divided into four regimes: the cavity regime, the impact regime, the reflective regime and the stable regime. The time-average pressure is subject to a unimodal distribution when the gate is fully open, whereas a bimodal distribution is presented when the gate is partly open. The negative pressure regime presented an elliptic shape. Cavitation erosion occurred easily on lateral expansion sidewalls in the tunnel with the radial gate partly open.

Effects of deformability of RBCs on their dynamics and blood flow passing through a stenosed microvessel: an immersed boundary-lattice Boltzmann approach

In this paper, the motion of high deformable (healthy) and low deformable (sick) red blood cells in a microvessel with and without stenosis is simulated using a combined lattice Boltzmann-immersed boundary method. The RBC is considered as neo-Hookean elastic membrane with bending resistance. The motion and deformation of the RBC under different values of the Reynolds number are evaluated. In addition, the variations of blood flow resistance and time-averaged pressure due to the motion and deformation of the RBC are assessed. It was found that a healthy RBC moves faster than a sick one. The apparent viscosity and blood flow resistance are greater for the case involving the sick RBC. Blood pressure at the presence of stenosis and low deformable RBC increases, which is thought of as the reason of many serious diseases including cardiovascular diseases. As the Re number increases, the RBC deforms further and moves easier and faster through the stenosis. The results of this study were compared to the available experimental and numerical results, and good agreements were observed.

Droplet squeezing through a narrow constriction: Minimum impulse and critical velocity

Models of a droplet passing through narrow constrictions have wide applications in science and engineering. In this paper, we report our findings on the minimum impulse (momentum change) of pushing a droplet through a narrow circular constriction. The existence of this minimum impulse is mathematically derived and numerically verified. The minimum impulse happens at a critical velocity when the time-averaged Young-Laplace pressure balances the total minor pressure loss in the constriction. Finally, numerical simulations are conducted to verify these concepts. These results could be relevant to problems of energy optimization and studies of chemical and biomedical systems.

Sensitivity Analysis and Accuracy of a CFD-TFM Approach to Bubbling Bed Using Pressure Drop Fluctuations.

Based upon the two fluid model (TFM) theory, a CFD model was implemented to investigate a cold multiphase-fluidized bubbling bed reactor. The key variable used to characterize the fluid dynamic of the experimental system, and compare it to model predictions, was the time-pressure drop induced by the bubble motion across the bed. This time signal was then processed to obtain the power spectral density (PSD) distribution of pressure fluctuations. As an important aspect of this work, the effect of the sampling time scale on the empirical power spectral density (PSD) was investigated. A time scale of 40 s was found to be a good compromise ensuring both simulation performance and numerical validation consistency. The CFD model was first numerically verified by mesh refinement process, after what it was used to investigate the sensitivity with regards to minimum fluidization velocity (as a calibration point for drag law), restitution coefficient, and solid pressure term while assessing his accuracy in matching the empirical PSD. The 2D model provided a fair match with the empirical time-averaged pressure drop, the relating fluctuations amplitude, and the signal’s energy computed as integral of the PSD. A 3D version of the TFM was also used and it improved the match with the empirical PSD in the very first part of the frequency spectrum.

Status of noise pollution in urban area of Dharan Sub- Metropolitan City and Inaruwa Municipality of Sunsari District, Nepal

The environmental noise level measurement in Dharan and Inaruwa cities of eastern Nepal were conducted and compared with the ambient noise standards provided by Government of Nepal. The noise pollution assessment was performed in autumn and winter seasons by the indicator average day time sound pressure level (Ld, during 7.00 to 22.00 hrs) and average night time sound pressure level (Ln, during 22.00 to 7.00 hrs). The Ld and Ln values at the commercial, silence and residential zones of Dharan were 78 to 82 and 72 to 73, 65 to 73 and 60 to 70, 65 to 76 and 62 to 64 dB(A) in autumn and 78 to 79 and 72 to 76, 64 to 71 and 58 to 68, 63 to 74 and 60 to 62 dB(A) in winter, respectively whereas for Inaruwa, measurement were 75 to 77 and 73 to 75, 59 and 57, 67 and 60 dB(A) in autumn and 66 to 70 and 63 to 68, 55 and 53, 65 and 58 dB(A) in winter, respectively. The results showed that noise levels exceeded the standard value at most of the sites.

Effects of aeroelasticity on the performance of hypersonic inlet

Effects of the aeroelasticity on the performance of the hypersonic inlet have been investigated numerically in this study. The aeroelasticity has been simulated using the coupled computational fluid dynamics/computational structural dynamics method, which is solved by the in-house code. The unsteady Reynolds-averaged Navier–Stokes equations have been solved in the computational fluid dynamics simulation, and the modal method has been adopted in the computational structural dynamics simulation. Two cases have been utilized to validate the numerical method. Finally, the aeroelasticity has been simulated for inlet plate with different thicknesses. The effects of aeroelasticity on performance parameters and flow structure have been discussed in detail. The results show that the generalized displacements present the “beat” phenomenon in the time domain. The power spectral density of the generalized displacements implies that the aeroelastic instability is mainly caused by the coupling between the fourth- and fifth-order modes. The time-average flow rate coefficient and pressure rise ratio increase relative to the initial value, while the total pressure recovery coefficient decreases. The fluctuation amplitude of the flow rate coefficient is small, while that of the total pressure recovery coefficient and pressure rise ratio are relatively large. Besides, the phases of the three performance parameters are greatly different. Furthermore, the aeroelasticity has significant effect on the shock wave structure especially at the exit of the inlet.

Effect of taper angle on the performance of jet pumps for a loop-structured thermoacoustic engine

Gedeon streaming, which circulates throughout the loop configuration with a time-averaged manner in the oscillating flow, can considerably deteriorate the efficiency of traveling-wave thermoacoustic engine. A jet pump is characterized by a tapered channel with different opening areas, which can produce a time-averaged pressure drop to suppress Gedeon streaming. Three jet pumps with different taper angles, i.e., 5°, 9°, 15°, are studied. Following Iguchi's hypothesis, the turbulent oscillating flow can be considered as a steady flow. The flow structures though the jet pumps are numerically simulated. Meanwhile, an experimental apparatus has been built to measure the performance of jet pump operating in the turbulent oscillating flow. The results show that the simulation is in a good agreement with the experiment data for the jet pumps with small taper angles. For the jet pump with 15° taper angle, the simulation results match well with the experiment data when the velocity at small opening of jet pump is higher than 50 m/s. However, when the velocity is lower, the simulation results deviate from the experiment data considerably, which can be attributed to the flow separation in the diverging direction operated differently in the steady flow and oscillating flow at lower velocity.

Optimal Systolic Blood Pressure Levels for Primary Prevention of Stroke in General Hypertensive Adults: Findings From the CSPPT (China Stroke Primary Prevention Trial).

We aimed to investigate the relationship of time-averaged on-treatment systolic blood pressure (SBP) with the risk of first stroke in the CSPPT (China Stroke Primary Prevention Trial). A post hoc analysis was conducted using data from 17 720 hypertensive adults without cardiovascular disease, diabetes mellitus, and renal function decline from the CSPPT, a randomized double-blind controlled trial. The primary outcome was first stroke. Over a median follow-up duration of 4.5 years, the association between averaged on-treatment SBP and risk for first stoke followed a U-shape curve, with increased risk above and below the reference range of 120 to 130 mm Hg. Compared with participants with time-averaged on-treatment SBP at 120 to 130 mm Hg (mean, 126.2 mm Hg), the risk of first stroke was not only increased in participants with SBP at 130 to 135 mm Hg (mean, 132.6 mm Hg; 1.5% versus 0.8%; hazard ratio, 1.63; 95% confidence interval, 1.01-2.63) or 135 to 140 mm Hg (mean, 137.5 mm Hg; 1.9% versus 0.8%; hazard ratio, 1.85; 95% confidence interval, 1.17-2.93), but also increased in participants with SBP <120 mm Hg (mean, 116.7 mm Hg; 3.1% versus 0.8%; hazard ratio, 4.37; 95% confidence interval, 2.10-9.07). Similar results were found in various subgroups stratified by age, sex, and treatment group. Furthermore, lower diastolic blood pressure was associated with lower risk of stroke, with a plateau at a time-average on-treatment diastolic blood pressure <80 mm Hg. In conclusion, among adults with hypertension and without a history of stroke or myocardial infarction, diabetes mellitus, or renal function decline, a lower SBP goal of 120 to 130 mm Hg, as compared with a target SBP of 130 to 140 mm Hg or <120 mm Hg, resulted in the lowest risk of first stroke.

Effects of axial gap on aerodynamic force and response of shrouded and unshrouded blade

Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure. Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The resulting aerodynamic forces were interpolated to the finite element (FE) model through surface effect elements prior to conducting forced response calculations. Effects of axial gap on aerodynamic forces were studied. In addition, influence of axial gap on the response of the shrouded blade was compared with that on the response of the unshrouded blade. Results demonstrated that as the axial gap increases, time-averaged pressure on the blade surface changes very little, while the pressure fluctuations decrease significantly. Pressure and aerodynamic forces on the blade surface display periodic variation, and the vane passing frequency component is dominant. Amplitudes of aerodynamic forces decrease with increasing axial gap. Restricted by the shroud, deformation and response of shrouded blade are much lower than those of the unshrouded blade. The response of unshrouded blade shows obvious beat vibration phenomenon, while the response of the shrouded blade does not have this characteristic because the shroud restrains multiple harmonics. Blade response in time domain was converted to frequency domain using fast Fourier transformation (FFT). Results revealed that the axial gap mainly affects the forced harmonic at the vane passing frequency, while the other two harmonics at natural frequency are hardly affected. Amplitudes of the unshrouded blade response decrease as the axial gap increases, while amplitudes of the shrouded blade response change very little in comparison.

Evaluation of Hemodynamics in a Prestressed and Compliant Tapered Femoral Artery Using an Optimization-Based Inverse Algorithm.

The important factors that affect the arterial wall compliance are the tissue properties of the arterial wall, the in vivo pulsatile pressure, and the prestressed condition of the artery. It is necessary to obtain the load-free geometry for determining the physiological level of prestress in the arterial wall. The previously developed optimization-based inverse algorithm was improved to obtain the load-free geometry and the wall prestress of an idealized tapered femoral artery of a dog under varying arterial wall properties. The compliance of the artery was also evaluated over a range of systemic pressures (72.5-140.7 mmHg), associated blood flows, and artery wall properties using the prestressed arterial geometry. The results showed that the computed load-free outer diameter at the inlet of the tapered artery was 6.7%, 9.0%, and 12% smaller than the corresponding in vivo diameter for the 25% softer, baseline, and 25% stiffer arterial wall properties, respectively. In contrast, the variations in the prestressed geometry and circumferential wall prestress were less than 2% for variable arterial wall properties. The computed compliance at the inlet of the prestressed artery for the baseline arterial wall property was 0.34%, 0.19%, and 0.13% diameter change/mmHg for time-averaged pressures of 72.5, 104.1, and 140.7 mmHg, respectively. However, the variation in compliance due to the change in arterial wall property was less than 6%. The load-free and prestressed geometries of the idealized tapered femoral artery were accurately (error within 1.2% of the in vivo geometry) computed under variable arterial wall properties using the modified inverse algorithm. Based on the blood-arterial wall interaction results, the arterial wall compliance was influenced significantly by the change in average pressure. In contrast, the change in arterial wall property did not influence the arterial wall compliance.

Damping insert materials for settling chambers of supersonic wind tunnels

This study describes the application of a novel damping insert material for reducing the flow fluctuations in a tandem nozzle supersonic wind tunnel. This new damping material is composed of multi-layer stainless steel wired meshes. The influences of the multi-layer mesh, such as the quantity of the mesh layer and the installed location in the settling chamber, to the freestream quality have been investigated. A Pitot probe instrumented with a Kulite pressure sensor and a hot-wire probe are employed to monitor the flow fluctuation in the test section of the wind tunnel. Thereafter, a combined modal analysis is applied for the disturbance qualification. Additionally, the transient Mach number in the test section is measured. The disturbance qualification indicates that the multi-layer mesh performs well in providing reduction of vorticity reduction and acoustic fluctuations. Comparable flow quality of the freestream was also obtained using a combination of flexible damping materials. However, the life-span of the new damping materials is much longer. The time transient of the Mach number measured in the test section indicates that the mean flow is rather constant over run time. Furthermore, the time-averaged pressure along the settling chamber is recorded and it shows the distribution of pressure drop by settling chamber inserts.