Pneumatic Probes Research Articles

Analysis of The Flow-Field Distorsions Induced by Pneumatic Pressure Probes In Test Bench Experiments On Centrifugal Compressors: Are We Testing Right?

Abstract Experimental testing at the test rig still plays a key role in the development of new centrifugal compressor designs for industrial applications. Although a wide set of different probes is used as per common practice, the overall impact of the probes? dimensions on the stage performance and rangeability is often assumed to be negligible. In this study, we aimed at quantifying the intrusiveness effects of pneumatic pressure probes on the flow-field inside a vaned diffuser using a model stage of an industrial centrifugal compressor, for which different experimental setups were tested at the University of Florence test rig. Performance and rangeability were initially assessed using a conventional set of pneumatic probes inserted in the flow path. Then, comparative analyses were realized through dedicated tests by either removing all probes at the diffuser inlet or introducing only a single pressure probe in the upstream section and varying its angular position in the measuring section. Experiments revealed an impact of upstream probes much higher than expected, with a decrease in efficiency and a substantial reduction of stall margin. Moving from this experimental evidence, accurate 3D CFD simulations of the entire stage were carried out including the actual geometry of the probes for two probes configurations and three operating points. Simulations highlighted the effect probes? wakes on downstream vanes and the induced blockage effect, which both appear in line with experimental evidence. As a handout, a recommendation on the optimal probe positioning is suggested.

Effect of vibratory probe compaction method on bearing capacity of loess investigated via random finite element analysis

Probabilistic analyses using random fields are increasingly performed in geotechnical fields; however, they focus on random fields in natural soils. Comparatively, few studies have been conducted regarding random field variations in improved ground. An innovative technique for treating loess–the pneumatic vibratory probe compaction method is used in this study. The effects of different construction techniques on the spatial variability of improved ground and bearing capacity are investigated by varying the pneumatic injection pressure and treatment interval. To determine the posteriori parameter of the effective friction angle of a loess random field, Bayes' theorem and the transitional Markov chain Monte Carlo algorithm are applied. Subsequently, a random finite element analysis is performed. Based on the results, the maximum increase in bearing capacity and the minimum dispersion are achieved at a jet pressure of 0.6 MPa under a treatment interval of 1.4 m. Furthermore, the probability of failure is reduced to the lowest possible level.

AERODYNAMIC IMPACT OF SECONDARY AIR INJECTION FLOWRATES ON THE MAIN ANNULUS FLOW FIELD FOR A TRANSONIC HIGH-PRESSURE TURBINE STAGE

Abstract In this study, the influence of secondary air blowing on the main annulus flow field of a transonic high-pressure turbine (HPT) was investigated experimentally and numerically. The experimental setup was a single-stage, unshrouded turbine with a blading consistent with modern HPTs. The entire testing campaign was conducted in a full annular, rotating, continuous turbine test rig at the Japan Aerospace Exploration Agency (JAXA), which realized the most faithful matching unrivalled of both the primary and secondary stream similarity parameters to reality. An elaborate secondary air system implemented in the hardware enabled it to mimic all the dominant coolant/purge streams representative of advanced hot sections: the full coverage film-cooling on stator and rotor airfoils, disk wheelspace purge air blown forward and aft of the rotor, and coolant injection through the over-tip casing. Detailed three-dimensional flow field measurements for various secondary air flowrates were performed by traversing a pneumatic thermometric combination probe downstream of the rotor. A complete set of numerical simulations was run concurrently with the testing to determine how well they captured the flow physics, particularly the interaction of the ejected secondary streams with the primary flow. The JAXA in-house code, UPACS, and its best practice settings, based on past verification and validation efforts, were employed and not intentionally tuned to better fit the data.

Experimental study of flow control on tip leakage flow in variable geometry linear turbine cascades with different pivot layouts

Variable geometry turbines are essential for adjusting operational conditions in industrial gas turbines and variable cycle engines. These adjustments necessitate partial gaps at both ends of the variable guide vanes to alter the turning angle, consequently introducing an aerodynamic performance penalty. Moreover, the pivot layout profoundly influences aerodynamic losses. Research on turbine cascades that considers various partial gap layouts is limited, particularly in terms of experimental studies, which are rarely conducted. This study aims to diminish aerodynamic losses and augment the efficiency of gas turbines by examining the impact of pivot layouts on partial gap clearance and secondary flow. It further investigates the effectiveness of flow control strategies at the blade tip across different pivot configurations within a variable geometry turbine cascade, utilizing pneumatic probe scanning and surface oil flow visualization techniques. The results reveal that employing a cavity at the tip can significantly reduce aerodynamic losses in schemes both with and without a pivot, achieving maximum loss reductions of 15.8% and 3.7%, respectively. Additionally, a narrower squealer width can further decrease these losses. However, with a pivot located at the tip, the resulting separation flow and wake vortex become predominant sources of losses. The presence of the pivot weakens the tip leakage flow rate and the intensity of the tip leakage vortex (TLV), thus diminishing the effectiveness of cavity tip flow control. The cavity moderates TLV and enhances the interaction between TLV and the wake vortex, leading to increased aerodynamic losses.

Study on the influence of pneumatic probe on the wake flow field of transonic turbine cascade

Study on the influence of pneumatic probe on the wake flow field of transonic turbine cascade

Experimental investigation of secondary flow losses in a variable geometry linear turbine cascade with winglet tip

Variable geometry turbines (VGT) hold a crucial role in gas turbines and variable cycle engines (VCE) by allowing adjustments to different operational conditions. In order to realize the adjustable function of the VGT stator blade, there will be partial gap structure at both ends of the stator blade, which will lead to partial leakage flow and serious secondary flow loss at the blade end that cannot be ignored, especially in a large angle adjustment range. At present, there are few researches on turbine cascades considering the real partial gap structure and winglet tip, and the numerical simulation calculation is mainly used, while the in-depth study using wind tunnel test is rarely seen. Therefore, this study attempts to analyze the internal flow characteristics of variable geometry turbine cascade by using five-hole pneumatic probe scanning and surface oil flow visualization, and discusses the mechanism of controlling partial clearance leakage flow and reducing secondary flow loss in the cascade by using winglet tip flow control technology. The winglet offset distance and the change of the relationship between the pivot and the clearance position on the flow field and flow loss is studied experimentally for the first time. The results show that the influence mechanism of winglet tip applied in VGT partial gap is quite different from that of typical blade tip clearance application, and more consideration should be given to the influence of pivot structure. Reasonable parameter selection can achieve a maximum loss reduction of 13.4 % and 20.2 % with and without pivot, respectively, while the unreasonable flow control scheme may lead to the loss or even increase with pivot. The interaction between the new secondary flow structure induced by pivot in the gap and other gap leakage flows is analyzed to explore the new mechanism of using winglet tip to reduce the loss of gap leakage flow.

Clinical Performance Comparison of Ultrahigh-speed Dual Pneumatic Vitrectomy Probes: Is Faster and Smaller Better?

Various vitrectomy probes are currently being used commercially, and there are ongoing efforts toward developing probes with higher cutting rates and smaller gauges. This study aimed to compare the efficiency and safety of various commercially available small gauge ultrahigh-speed dual pneumatic vitrectomy probes. We retrospectively analyzed the medical records of patients and recorded intraoperative videos while they underwent microincision three-port vitrectomy surgery for idiopathic epiretinal membrane at Soonchunhyang University Seoul Hospital. The patients were categorized into four groups based on the vitrectomy probe used during surgery: 23-7500 (UltraVit 23-gauge 7,500 cuts per minute [CPM]), 23-7500 (UltraVit 25-gauge 7,500 CPM), 25-10K (Advanced UltraVit 25-gauge 10,000 CPM), and 27-10K (Advanced UltraVit 27-gauge 10,000 CPM). In total, 82 eyes from 82 patients were included in this work, with 16, 11, 26, and 29 eyes in groups 23-7500, 25-7500, 25-10K, and 27-10K, respectively. The corresponding vitrectomy times were 295.56 ± 53.55, 293.09 ± 50.28, 299.92 ± 59.42, and 349.38 ± 67.23 seconds, respectively. There was a significant difference in the vitrectomy time between the groups (p = 0.004). The mean number of sutures was 3, 3, 2.96, and 0.83, respectively. In the 23-7500 group, there was one case of iatrogenic retinal break, while in the 27-10K group, there was one case of postoperative hypotony. Although advancements have been made in the 27-gauge vitrectomy probe, it still takes more vitrectomy time than it does when using the 23- and 25-gauge probes. However, the delay was within an average of 1 minute, and considering the significantly reduced need for sutures, there is a substantial benefit in terms of postoperative discomfort. Therefore, when choosing a probe for epiretinal membrane surgery among the four options, it is reasonable to select the 27-gauge probe according to the surgeon's preference.

Calculation of Thermodynamic Wetness Loss in Steam Turbines Using Computational Fluid Dynamics Simulation

Abstract In the paper, the behavior of wet steam flow is described in three different steam turbines. The first one is the 1100 MW turbine in the nuclear power plant with the pressurized water reactor. The second one is the 660 MW turbine in the fossil fuel power plant with ultrasupercritical steam parameters at the turbine inlet. The last turbine has a nominal output of 34 MW and operates in the municipal waste-to-energy plant. However, this turbine can often also operate even at 2 MW or higher. In all three turbines in the last stage area passages are made for an optical probe to measure steam wetness and primary droplets size, and for a pneumatic probe to determine the pressures, velocities and flow directions. Based on experimentally obtained data, analyses of thermodynamic wetness loss for all three turbines are performed using numerical flow simulations considering equilibrium and nonequilibrium steam. The condensation model that includes the nucleation rate and droplet growth velocity used in ansyscfx is calibrated based on experimentally obtained data. It is evident that the obtained loss patterns depend fundamentally on the turbine type and operating parameters.

Alcon Constellation® Vision System

Alcon Constellation® is the most widely used vitreo-retinal surgical systems in the world, providing up-to-date technology for vitreoretinal surgery. This system has many innovative features. These features provide the ability to use high-speed, small-diameter and dual pneumatic vitrectomy probe systems, to give the surgeon the chance to intervene in the forward and backward movement speeds of the guillotine, to control the intraocular pressure sensitively during the operation, to have an internal endolaser, and to automate the intraocular gas mixture at the desired rate. The aim of the vitrectomy surgeon is to bring the retinal tissue to a normal anatomical position by cleaning it from other tissues without creating an iatrogenic tear. The first and most important condition for the surgeon to fulfill this task and to minimize the tissue healing problems that may occurs after surgery is the safe, efficient and rapid removal of vitreous from the eye and retinal tissue. The Alcon Constellation® system is the most up-to-date vitreoretinal surgical device platform available today, enabling the vitreo-retinal surgeon to consistently achieve these goals.

Pneumatic-Probe Measurement Errors Caused by Fluctuating Flow Angles

Pneumatic probes such as five-hole probes (5HP) can conveniently measure three-dimensional flow angles, plus total and static pressure. In most applications, transducers are connected using pneumatic tubes, allowing the probe head to be highly miniaturized and robust. However, such “steady” probes are often used in unsteady flows, where they measure a pneumatically averaged flowfield that can differ from the time mean. To better understand these pneumatic averaging effects, an analytical framework is constructed using a quasi-steady model. Total and static pressure coefficients have a symmetric response to both positive and negative incidence. When incidence fluctuates, there is therefore a bias in the pneumatic average. These errors are evident in a shedding wake experiment, where a 5HP overestimates total pressure loss by up to 44% compared to a Kiel probe. These effects can be predicted by coupling an unsteady Reynolds-averaged Navier–Stokes calculation with the quasi-steady model. By predicting pneumatic averaging errors, the quasi-steady model can be used to obtain like-for-like validation of calculations against experimental data. Measurement data can also be corrected, provided that flow angle fluctuations can be measured or estimated. This approach can be readily used to postcorrect the large body of historical data likely to have been corrupted by pneumatic-averaging errors.

A flow field around a cylindrical probe in proximity to stator blades and its effect on the measurements

In multistage axial compressors of gas turbine engines, there is a need for a detailed understanding of the flow field in between the blade rows, which could be obtained by spanwise traversing. This requires a pneumatic probe to be immersed into the flow path between the blade rows, where the space is limited. Therefore, the probe will affect the flow field around it and in the blade channel, and the probe readings will be affected by that flow field. As a result, these probe readings cannot be translated to flow parameters based on just the freestream calibration characteristics, obtained in the idealized wind tunnel. In our paper, we provide a computational analysis of the flow field around the cylindrical probe in a constrained inter-blade-row environment at different circumferential locations and flow conditions both upstream and downstream of the stator blade row. It is shown that the flow angle measurement error can reach up to five degrees in the mid-pitch locations compared to undistorted flow, and dynamic head measurements can be up to 30% away from the actual mean values of the flow. These deviations are shown to be caused by flow field interaction inside the blade channel and, as a result, measured values, obtained during industrial compressor testing, could be corrected accordingly. The universal correction procedure is proposed for further use in the industry

Experimental and Numerical Studies of the Aerodynamics of Stationary Two-Shaft Gas Turbine Exhaust System

In this study, the aerodynamic performance of the exhaust system of a two-shaft gas turbine was investigated experimentally and numerically. The investigation focused on the system “Turbine Stage-Diffuser—Collector Box” and aimed to examine the impact of inlet conditions and geometry particularities on the efficiency of the exhaust system. The experiments were conducted on the Test Ring ET4 (Experimental Turbine-4) at the Peter the Great St.Petersburg Polytechnic University, which was equipped with a special diversion channel to examine the non-axisymmetric outlet of the exhaust duct. The collector box was designed to rotate by 180 degrees around the turbine axis to investigate its impact on the system’s performance. Flow traversing parameters were measured with the five-channel pneumatic pressure probes, and numerical simulations were performed with CFX 15.0. The RANS (Reynolds-averaged Navier–Stokes) equations were closed with the SST (k-ω) turbulence model (Shear Stress Transport model). The study concluded that the RANS SST model predicts the flow in the diffuser before the struts accurately. However, downstream the struts, the CFD (Computer fluid dynamic) results over-predicted the exhaust diffuser pressure recovery coefficient by 14% due to the complex vortex structure of the turbulent flow, which the Averaged Navier–Stokes equations did not resolve. The study highlights the importance of considering the last stage of the turbine, diffuser, and collector box as an integrated system when investigating the aerodynamics of exhaust ducts. The study also emphasizes the impact of geometry and inlet conditions on the exhaust diffuser’s performance and efficiency. The results of this study can be used to optimize the design of the exhaust system of two-shaft gas turbines and improve their thermal efficiency. The integrated approach of combining experimental and numerical methods can provide a detailed and reliable flow picture and can be used for future research in this area.

Experimental Study of Oxygen Depletion Effects on Soot Morphology and Nanostructure in Coflow Diffusion Aviation Fuel (RP-3) Flames

Oxygen concentration is a significant factor affecting soot formation and oxidation. However, there are few studies that have focused on the morphology and nanostructure characteristics of soot in aviation kerosene, oxygen-depleted combustion flames. In the present paper, five coflow flames under initial oxygen volume concentrations of 18.5%, 19%, 20%, 21%, and 23.5% were studied. The pneumatic probe sampling method and high-resolution transmission electron microscopy (HRTEM) analysis were conducted to quantify the morphology and nanostructure parameters, and laser extinction (LE) was applied to determine the soot volume fraction. Among the cases of different oxidizer oxygen concentrations (23.5% to 18.5%), the change in soot volume fraction was quantified, and the degree of graphitization of soot particles, i.e., the maturity, were compared. The results show that the peak value of soot volume fraction of the flames increased by 0.73 ppm as the oxygen concentration increased from 21% to 23.5%, and decreased by 1.25 ppm as the oxygen concentration decreased from 21% to 18.5%. When the oxygen concentration decreased from 23.5% to 18.5%, the soot primary particle diameter at the same dimensionless height decreased and then increased, which was attributed to the competition between the changes in the residence time and the growth rate of the soot particles. The quantitative analysis results of the soot nanostructure suggested that reduced oxygen concentration inhibited the graphitization process of carbon lattices and decreased the maturity and oxidation resistance of soot. When the oxygen concentration decreased from 23.5% to 18.5% at the same dimensionless height, the mean fringe length decreased by an average of 0.18 nm, and the mean value of fringe tortuosity and spacing increased by an average of 0.053 and 0.035 nm.

Ultraslim pneumatic lithoclast probe through single channel with dormia trapping the stone versus laser uerterolithotripsy in the treatment of ureteric stones; multicenter study

Ultraslim pneumatic lithoclast probe through single channel with dormia trapping the stone versus laser uerterolithotripsy in the treatment of ureteric stones; multicenter study

Design and Demodulation of a Fiber-Optic Fabry-Perot Sensor Applied in a High- Frequency Pneumatic System

This study proposes a high-frequency pneumatic system and demodulation method based on polydimethylsiloxane (PDMS) film-embedded fiber-optic Fabry-Perot sensor to meet the conflicting requirements of small sizes and wide frequency-response range not achieved by conventional pneumatic probes. The high modulus of elasticity of PDMS films provides the potential for an upper limit of a pneumatic frequency response up to 20 kHz, and the new demodulation algorithm, based on the ability of the F-P cavity to return to its initial length from the maximum cavity length change, is utilized to analyze its variation. The process of recovering F-P cavity corresponds with the sparse part of the signal, which takes advantage of the unique characteristics of interference fringes in this part. Moreover, the relationship between the relative change of the F-P cavity length and pneumatic pressure, as well as the relationship between the duration of the relative change of the F-P cavity length and the frequency are analyzed comprehensively. The rationality of the proposed demodulation scheme is verified from the angle-error analyses. These analyses could be helpful for integrated and high-frequency response pneumatic detection.

The Interaction of Main Stream Flow and Cavity Flows in Turbine Center Frames and Turbine Vane Frames

Abstract This paper focuses on the interaction between the last high-pressure turbine (HPT) stage purge flows and the intermediate turbine duct (ITD) in modern turbofan engines. Two state-of-the-art ITD concepts are analyzed in this work: the turbine center frame (TCF), which is supported by symmetric aerodynamic strut fairings and generally adopted in conventional dual-spool engines; the turbine vane frame (TVF), which features turning struts and splitters and is typical of geared turbofan engines. The measurement campaigns for both setups are carried out in the transonic test turbine facility (TTTF) at Graz University of Technology. The test vehicles consist of an HPT stage, the ITD (TCF or TVF), and the first low-pressure turbine (LPT) vane or blade row. The same HPT stage is used for both ducts, to enable consistent, engine-representative inlet conditions between the two solutions. All the HPT stator–rotor cavities are supplied with purge flows by a secondary air system, with independent mass flow and temperature control for each purge line. Five-hole probe data are acquired at the inlet and outlet sections of the ITDs, to characterize the aerodynamic flow field entering and leaving the duct. In addition to the pneumatic probe tests, seed gas concentration measurements are performed in the same planes, to track down the cavity air in the mainstream and investigate its postegress behavior. Finally, detailed post-test computational fluid dynamics (CFD) results are presented to get additional insight into the flow phenomena developing through the strut passage.

Experimental Study on the Aerodynamic Characteristics of Blades at the Last Stage of a Steam Turbine at Off-Design Conditions

Experimental investigations have been carried out on the flow characteristics of the last stage long blades operating under off-design conditions. A model turbine test rig similar to a small power station was applied. The last stage blades with a scaling factor of 1 : 4.8 was used for pneumatic experiments. The rotor blade height was 375 mm, and the rotation speed was set to 7200 rpm. Five volumetric flow coefficients were utilized, corresponding to φ =0.61, 0.77, 0.92, 1.02, and 1.15. Pneumatic probes were used to focus on measuring pressures and swirl angles. The variation of different pneumatic parameters along the span and circumferential direction was investigated. The change patterns of the three-dimensional aerodynamic characteristics of the last stage blades during the off-design conditions were revealed. Results indicated that there was a high correlation between the variation of pneumatic parameters and different off-design conditions. In particular, the large meridional expansion angle at the tip led to abrupt changes in the inlet parameters, and the overlap even occupied by 17% blade height. Due to the influence of the exhaust hood, the circumferential static pressure-unevenness was up to 77.8% at the last stage outlet.

Calibration of pneumatic multi-hole probes for transonic turbomachinery flows

The calibration data of a five-hole probe and a six-hole probe designed for measurements in transonic turbomachinery flows are presented. The probes feature a special base pressure hole on the back side to avoid the Mach number insensitivity of pressure probes near Mach number unity. There is only little literature available on the performance of such probes, especially in flows with large radial flow angles. To close this gap, the probes are calibrated for radial flow angles up to 32^circ. A significant influence of this flow angle on the coefficients used for Mach number determination is shown. At large positive flow angles, the relationship between the pressure coefficient using the base pressure and the Mach number is not biunique for the six-hole probe. Therefore, an experimental study of Mach number measurement deviations is performed at the calibration wind tunnel. Different evaluation methods are examined. The sample standard deviation over 210 randomly distributed points is reduced by 66% compared to the same probe design without the base pressure hole. This is achieved using two calibration coefficients for the Mach number simultaneously in a multidimensional interpolation.

A Randomized, Single-Blind Clinical Trial Comparing Robotic-Assisted Fluoroscopic-Guided with Ultrasound-Guided Renal Access for Percutaneous Nephrolithotomy.

We conducted a randomized, single-blind clinical trial comparing the surgical outcomes of robotic-assisted fluoroscopic-guided (RAF group) and ultrasound-guided (US group) renal access in mini-percutaneous nephrolithotomy (PCNL). We recruited patients who underwent mini-PCNL with ureteroscopic assistance for large renal stones between January 2020 and May 2021. Block randomization was performed using online software. Automated needle target with x-ray was used for fluoroscopic-guided renal access in the RAF group. PCNL was performed by residents using a pneumatic lithotripsy system with 16.5Fr/17.5Fr tracts. The primary outcome was single puncture success, and the secondary outcomes were stone-free rate, complication rate, parameters measured during renal access and fluoroscopy time. In total, 71 patients (35 in US group, 36 in RAF group) were enrolled. No difference was seen in the single puncture success rate between the US and RAF groups (34.3% and 50.0%, p=0.2). In 14.3% cases in the US group vs no cases in the RAF group, the resident was unable to obtain access due to difficult targeting (p=0.025). The mean number of needle punctures was significantly fewer, and the median duration of needle puncture was shorter in the RAF group (1.83 vs 2.51 times, p=0.025; 5.5 vs 8.0 minutes, p=0.049, respectively). The stone-free rate at 3 months after surgery was 83.3% and 70.6% in the RAF and US groups, respectively (p=0.26). Multivariate analysis revealed that RAF guidance reduced the mean number of needle punctures by 0.73 times (p=0.021). RAF renal access in mini-PCNL may have further potential applications in this field.

An experimental investigation of soot morphology and nanostructure in high-pressure co-flow laminar methane diffusion flames

Pressure is a significant factor affecting soot formation and oxidation. However, there are only scarce studies in the literature that probe soot samples in high-pressure laminar diffusion flames and then analyze the soot nanostructure quantitatively. In this study, a novel pneumatic probe sampling method was proposed to obtain soot samples in methane co-flow laminar diffusion flames with pressures ranging from 0.2 to 0.8 MPa. Compared with thermophoretic sampling, this method was more suitable for long-time sampling to obtain adequate soot samples in flames with low soot concentration. The soot morphology and nanostructure were analyzed quantitatively by high-resolution transmission electron microscopy (HRTEM). The results show that as the pressure increases, the soot samples at 10, 20, 30, and 40 mm heights above burner (HAB) exhibit larger soot particle size, more ordered nanostructure, longer crystallite fringe, the larger size of poly-aromatic hydrocarbons (PAHs), lower fringe tortuosity, and smaller fringe spacing. In particular, the soot samples at 10 mm HAB showed the largest differences in morphology and nanostructure as the pressure increased. The quantitative analysis results suggested that elevated pressure increased graphitization, maturity, and oxidation resistance of soot, which was most possibly attributed to enhanced soot nucleation and surface growth by pressure.