Instantaneous Pressure Measurements Research Articles

Optical investigation of ammonia rich combustion based on methanol jet ignition by means of an ignition chamber

Ammonia, as a carbon-free alternative fuel, has attracted a lot of attention. However, ammonia has slow laminar burning velocity and high ignition energy and NOx emissions. The ignition chamber has been proven to greatly enhance ignition energy. Methanol, as a low-carbon liquid fuel with a low evaporation temperature (64.5 °C), is easy to store and transport and has the potential to become a good jet ignition fuel in the ignition chamber (pre-chamber). In addition, chemical reaction kinetics analysis of ammonia demonstrated that there are few NOx emissions when the equivalent ratio is higher than 1.2. In this study, the ignition chamber fueled with methanol was used to investigate the jet flow, jet ignition, and combustion process of rich ammonia using visualization experiments and instantaneous pressure measurement. The research results showed that the ignition chamber fueled with methanol improved the jet ignition and combustion of ammonia compared to the ignition chamber fueled with ammonia. Experimental studies of energy substitution ratios of methanol from 1% to 4% showed that a 2% energy substitution ratio achieved better jet ignition performance. Comparing with the stoichiometric combustion of ammonia, the combustion performance deteriorated with the increase of ammonia rich equivalent ratio. A slightly richer equivalent ratio of 1.1 tended to be a good choice for jet ignition of ammonia. The difference in channel diameter between the ignition chamber and the main chamber had large effects on the performance of jet ignition ammonia. The 3 mm channel diameter achieved the highest ammonia-rich combustion speed under the rich equivalent ratios of 1.1 and 1.2 in the main chamber, compared to the diameters of 4.5 mm and 6 mm.

Effect of aortic curvature on bioprosthetic aortic valve performance

Transvalvular pressure gradient (ΔP) after aortic valve replacement is an important surrogate of aortic bioprostheses performance. Invasive ΔP is often measured after transcatheter aortic valve replacement to exclude patient-prosthetic mismatch. However, invasive aortic pressures are usually recorded in the pressure recovery (PR) zone downstream of the valve, potentially resulting in ΔP underestimation compared to noninvasive measurements. PR was extensively studied in straight ascending aortas. However, the impact of various aortic arch configurations on ΔP has not been explored. PR was assessed in a pulse duplicating simulator at various cardiac conditions of cardiac output, heart rates and pressures. Three different aortic geometries with identical root dimensions but with different aortic arches were used: (1) curvature 1, (2) curvature 2, and (3) straight aortic models. Instantaneous pressure and peak ΔP measurements were recorded incrementally along the models for each cardiac condition. The models with aortic arches produced two distinct PR zones (after the valve and after the aortic arch), whereas the model without an aortic arch produced only one PR zone (after the valve). The trend of the pressure and ΔP curves for each model was independent of the cardiac condition used, but the individually measured pressure magnitudes did change with different conditions. In this study, we illustrated the differences in PR between distinct aortic curvatures and straight aorta. PR affects pressure and ΔP measurements. These effects are clear when recording aortic pressures by catheterization and echocardiography.

Sweeping jet control of flow around a circular cylinder

An experimental investigation was conducted to examine the control effectiveness and mechanism of sweeping jets in the control of vortex shedding from a circular cylinder. Wind tunnel experiments were performed at a Reynolds number of 3.2 × 104. Two rows of sweeping jet actuators were arranged symmetrically at positions 70° clockwise and counterclockwise from the front stagnation point. Five operating conditions with different momentum coefficients were tested. Particle image velocimetry was used to measure the detailed flow structures of the uncontrolled and controlled cylinders. With increasing jet strength, the control performance improved non-monotonously. With a relatively small momentum coefficient of less than 0.0086, the sweeping jets enlarged the recirculation bubble in the wake of the cylinder. However, with larger momentum coefficients, the sweeping jets reduced the size of the recirculation bubble by modifying the wake shear layer and pushing the vortex shedding toward the centerline. When the momentum coefficient was increased to 0.2147, sweeping jet control achieved a 73 % decrease in turbulence kinetic energy and a 68 % decrease in the normalized Reynolds shear stress compared with the uncontrolled case. The control effectiveness was similar can be observed at different spanwise planes. Instantaneous pressure measurement showed that with sweeping jet control, the amplitudes of the fluctuating force acting on the cylinder caused by unsteady vortex shedding were reduced by 94 % compared with the uncontrolled case. Proper orthogonal decomposition analysis showed that when the momentum coefficient was 0.2147, a novel flow pattern occurred in which one vortex grew larger while the other shrank in a relatively steady wake region.

New Insights into Abnormal Combustion Phenomena Induced by Diesel Spray-Wall Impingement under Engine-Relevant Conditions

High altitude and low temperature is the common extreme environment for internal combustion engines. Under such operating conditions, heavy-duty diesel engines often suffer from serious abnormal combustion, such as knocking combustion, which results in piston crown breakdown and cylinder head erosion. Spray-wall impingement and pool fires are considered potential causes; however, the detailed mechanism remains poorly understood owing to the lack of research data. In this study, for the first time, the destructive abnormal combustion induced by diesel spray-wall impingement was identified using an optical rapid compression machine under engine-relevant conditions at high altitudes. Combining instantaneous pressure and temperature measurements with simultaneously recorded high-speed photography gives useful insights into understanding the detailed combustion processes. The experimental results show that depending on the extent of diesel spray-wall impingement, supersonic detonation-like reaction fronts featuring bright luminosity can be observed. The propagation of these reaction fronts in-cylinder results in severe pressure oscillations with an amplitude approaching hundreds of atmospheres, which is like the super-knock events in boosted direct-injection spark-ignition engines. Further parametric analysis indicates that the interplay between the diffusion combustion controlled by diesel spray and the premixed combustion dominated by attached film evaporation results in the formation of abnormal combustion. Destructive reaction fronts tend to occur at a prolonged ignition delay time, which facilitates the mixing between diesel evaporation and hot air.

Experimental testing on the influence of shaft rotary lip seal misalignment for a marine hydro-kinetic turbine

Tidal energy has received considerable attention over the past decade due to its predictability and high power density. The research in the tidal turbine area has concentrated primarily on the improvement of the energy conversion efficiency. In contrast, the testing of the tidal turbine’s mechanical components has received less attention. In particular, the reliable operation of rotary seals is crucial to prevent water ingress into mechanical and electrical components. This paper outlines an experimental test campaign to investigate the effect of shaft misalignment. Both instantaneous temperature and pressure measurements were recorded from two rotary seals. It was shown the temperature inside the aligned seal increased until the seal chamber pressure became equal with the inlet water pressure. The wear on the lip seal rings was examined and the difference found to be between 3.28% and 19.61%. Inspection of the seal liners, showed the presence of strong wiping effects for the misaligned seal with maximum track width differences of between 52.94% and 97.60% being noted. The misaligned seal liner experienced wider wear tracks but were not as deep as the aligned seal with differences of between 37.55% and 103.13% being recorded.

Development of Continuous Blood Pressure Measurement System Using Photoplethysmograph and Pulse Transit Time

It is not only a problem for old age anyone. So, blood pressure is the one provides importance information with vital signs about cardiovascular health using oscillometric method. Unfortunately, this method required inflation and following deflation of the cuff. This method only gives instantaneous blood pressure and continuous measurement is not available. It is not available to the patients that required long term monitoring. To overcome this problem, the development of Continuous Non-Invasive Blood Pressure (NIBP) algorithm based on Pulse Transit Time (PTT) using two channel Photoplethysmograph (PPG) is proposed in this study. PPG is a non-invasive device for detecting blood volume changes can be affected by various physiological factors, analysis of the PPG signal can provide sufficient information on the human health condition; more specifically their cardio-vascular related performance. Literatures show that the PTT has linear relationship with blood pressure. Nevertheless, the determination of the model structure, order and real-time implementation to offer a continuous measurement of the PTT still remains challenging tasks in this area. PTT can be as index to monitor cardiovascular disease. In this project, dynamic model based on pulse transit time will be proposed to continuously monitor blood pressure by using PPG signals. Different kind of resolutions in microcontroller combined with PPG sensor will be used as well. MATLAB software is also been applied for PTT calculation based on two PPG sensors. PPG is method for detect blood volume changes with optical source transmitter send from one end and received the signal from another by receiver through body tissue as medium. MATLAB functions as Digital Signal Processing (DSP) for signals received in computer. Linear Regression technique and Fung's algorithm are applied to obtain the best fit line for all the points in order to systolic and diastolic blood pressure measurement. The results showed that the algorithm based on pulse transit time has been developed for the assessment of blood pressure and justify patient’ condition with 86.34% and 88.20% accuracy. Finally, this technique is a simple, user friendly and operator independent PPG system suitable for long term and wearable blood pressure monitor.

Effectiveness evaluation of extrapolation to frequency response of hydrophone sensitivity for measuring instantaneous acoustic pressure of diagnostic ultrasound

Precise measurement techniques of instantaneous acoustic pressure using the frequency response of hydrophone sensitivity have been investigated to evaluate the safety of diagnostic ultrasound. This technique requires the frequency range of sensitivities broader than bandwidth of the ultrasound. But available frequency range of sensitivities on a calibration certificate is limited. Extrapolation to the frequency range of certificated sensitivities might be an effective approach; however, the effectiveness of such extrapolation has not been sufficiently studied. In this paper, we propose a quantitative method for evaluating the effectiveness of such extrapolation, which is characterized by showing the narrowest frequency range of certificated hydrophone sensitivities necessary for precise measurement of instantaneous acoustic pressure in diagnostic ultrasound. The evaluation results showed that the extrapolation was generally effective for precise measurement using the certificated hydrophone sensitivity with a narrower frequency range than the bandwidth of the measured ultrasound.

Active flow control in an axial compressor for stability improvement: on the effect of flow control on stall inception

In this paper, the effect of an active flow control system on the onset mechanisms of rotating stall in an axial compressor is experimentally investigated. A particular emphasis is thus given on the flow patterns present in the tip region right before stall and how they evolve when active flow control is applied. The mechanisms involved during stall formation without control are carefully assessed and compared to the literature. To this purpose, the development of the first instability into rotating stall is discussed by monitoring its speed inside the compressor. This analysis also relies on instantaneous pressure measurements at the casing of the compressor.

Comparison of various instantaneous pulmonary arterial wedge pressure measurements with prognostic validation

Abstract Background Current recommendations on the diagnosis of pulmonary hypertension due to left heart disease (PH-LHD) emphasize the need for standardization of pulmonary arterial wedge pressure (PAWP) measurement. Instead of mean PAWP values instantaneous mid-A wave pressures or, in case of atrial fibrillation (AF), measurement 130–160 ms after the QRS onset is recommended. Recently, PAWP at the QRS onset has also been proposed. Our aim was to compare the various instantaneous PAWP measurements and assess the prognostic value of the derived diastolic pressure gradients (DPG) in heart failure (HF) patients. Methods and results PAWP and pulmonary arterial pressure (PAP) tracings of 116 patients with PH-LHD were manually analyzed offline. PAWP was measured in 4 different ways: 1. mean value [PAWPM]; 2.mid-A wave value in sinus, and at 10 ms intervals 130–160 ms following QRS onset in AF [PAWPR]; 3. at the onset of the QRS complex [PAWPQRS]; 4. pre C-wave point value [PAWPC]. The pre C-wave point was chosen as a reference for truly end-diastolic pressures. The corresponding DPGM, DPGR, DPGQRS and DPGC were calculated. The patients were followed for 17 (8–27) months and the prognostic value of the various DPG measurements for predicting all-cause mortality was assessed. The pre C-wave point was identifiable in 35 patients (30%); on average it occurred 171 ms after the QRS-onset whereas the A wave-onset and A-wave peak happened on average 62 and 149 ms after the QRS-onset, respectively. All three instantaneous PAWP measurements gave significantly lower values than PAWPM [19.3 (15.4–25.0)]. PAWPR did not differ from PAWPC [18.1 mmHg (14–22) vs. 19.2 mmHg (13–22.8), p=0.9], whereas PAWPQRS was lower [15.8 mmHg (12.2–19.9), p<0.001]. Accordingly, all instantaneous DPG measurements were higher than DPGM, yielding lower prevalence of negative DPG (29%, 17% and 45%, for DPGR, DPGQRS and DPGM, respectively). In AF (n=30), DPGR values at 130–140–150–160 ms demonstrated increasing scatter and progressively overestimated DPGQRS. For prognostic assessment, in case of both DPGQRS and DPGR, 6 mmHg was identified as a best cut-off value for predicting all-cause mortality, at which both indices provided superior prognostic information than DPGM [DPGR: HR 2.7; CI 1.1–6.9, p=0.029; DPGQRS: HR 2.6; CI 1.1–6.4, p=0.037, high-risk cases 17 for both; DPGM: HR 2.8; CI 1.0–7.6, p=0.045, high-risk cases 10]. Conclusions PAWP measured at the mid-A wave provides a reliable assessment of the end-diastolic PAWP in sinus rhythm. On the other hand, ECG-gated measurements yield more robust evaluation of PAWP in AF. Finally, both approaches carry significant and similar prognostic information in PH-LHD. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): AIN was supported by the János Bolyai Scholarship of the Hungarian Academy of Sciences

Development of a noninvasive instantaneous blood pressure measurement device based on volume-compensation method and study of its control algorithm

An instantaneous blood pressure measurement device based on volume compensation was developed, and a measurement control method was tested and improved on the device. The device consists of a cylindrical finger cuff, a compact proportional solenoid valve, an air pump and a hardware circuit. Finger cuff contains a pair of led and photo-diode. The hardware circuit consists of a feedback controls circuit and a signal processing circuit based on a microprocessor controller. A neural network predictive controller is proposed to replace the traditional PID controller for experiments. Simulation and experiments show that the neural network predictive controller has better control effect than the traditional PID controller.

Repeatability of High-Pressure Measurement in a Diesel Engine Test Bed.

This paper addresses the issue of metrological accuracy of instantaneous in-cylinder pressure measurement in a diesel engine test bed. In studies, the central unit has been the single-cylinder AVL 5402 engine. The pressure measurement was performed with a sensor designed for thermodynamic analysis, and the results were related to the crank angle, where two rotations corresponding to the four-stroke working cycle were denoted as angles between −360° and +360°. The novelty of this paper is the proposition of how to perform a type A uncertainty estimation of the in-cylinder pressure measurement and to assess its repeatability. It was demonstrated that repeatability of the measurement during the ignition process was difficult to estimate because of the phenomena that cannot ensure the repeatability conditions. To solve the problem, two methods were proposed. In one method, the pressure was measured in the subsequent cycles immediately after the ignition was turned off, and in another method, the engine was driven by a starter. The latter method provided maximal pressure values much lower than during usual tests. The obtained repeatability of measured pressure was %EV = 0.4%, which proved high capability of the evaluated measurement system.

Numerical and experimental studies on the aerodynamics of a 5:1 rectangular cylinder at angles of attack

The aerodynamic behavior of a 5:1 rectangular cylinder at angles of attack (AoA) up to 15° is investigated based on Three-dimensional Large-Eddy Simulations (3D LES) and instantaneous pressure measurements. The numerical results indicate that the separated flow is highly sensitive to AoA and involves two patterns: (i) the flow reattaches to the bottom surface and the length reduces as AoA increases, (ii) the separation bubble around the top surface grows with AoA and does not reattach as AoA≥4°. The relationships between flow topology and the pressure statistics are obtained numerically by addressing their distributions in different flow regimes. With respect to these relationships, the differences between the separated-reattached and fully separated flows are determined. On the basis of these relationships, the influence of AoA on the mean, fluctuation, phase difference and, chordwise and spanwise correlations of pressures are studied experimentally. There is a close correspondence between each parameter and the length of the separation bubble, which involves different fluid phenomena in the chordwise and spanwise directions. Furthermore, a weak low-frequency flapping motion is observed in the separation bubble at large AoAs when the main vortex center behind the tail corner. Finally, the influences of AoA on the unsteady and spanwise features of the total forces are analyzed.

Reprint of: Stochastic modeling of a freely rotating disk facing a uniform flow

The fluid–structure interaction between a thin circular disk and its turbulent wake is investigated experimentally and described with a low-order stochastic model. The disk faces a uniform flow at Reynolds number Re=133 000 and can rotate around one of its diameters. It is equipped with instantaneous pressure measurements to give the aerodynamic loading: moments and center of pressure of the front and base sides. When the disk is fixed and aligned, symmetry-breaking vortex shedding is observed and all orientations are visited with equal probability, yielding axisymmetric long-term statistics. Very-low-frequency antisymmetric modes as recently observed by Rigas et al. (2014) are not observed unless the disk shape is modified into that of a bullet, showing the importance of the separation angle. It suggests that these modes are linearly stable for the disk while they are unstable for the bullet shape. When the disk is fixed and inclined, the base center of pressure (CoP) shifts preferentially towards one side of the rotation axis. Finally, when the disk is free to rotate, the front moment is proportional to the disk inclination (aerodynamic stiffness), while the base moment is well correlated with the disk inclination. From these observations, a low-order model is derived that couples (i) the CoP, forced stochastically by the turbulent flow, and (ii) the disk inclination, as a linear harmonic oscillator forced by the base moment. The model captures well the main statistic and dynamic features observed experimentally. One difference lies in the distribution of the disk inclination (which features exponential tails in the measurements but is Gaussian in the model), suggesting a possible refinement with non-linearities or time delays. The model is expected to capture coupled dynamics in other systems involving turbulent wakes behind freely rotating bluff bodies.

Stochastic modeling of a freely rotating disk facing a uniform flow

The fluid–structure interaction between a thin circular disk and its turbulent wake is investigated experimentally and described with a low-order stochastic model. The disk faces a uniform flow at Reynolds number Re=133 000 and can rotate around one of its diameters. It is equipped with instantaneous pressure measurements to give the aerodynamic loading: moments and center of pressure of the front and base sides. When the disk is fixed and aligned, symmetry-breaking vortex shedding is observed and all orientations are visited with equal probability, yielding axisymmetric long-term statistics. Very-low-frequency antisymmetric modes as recently observed by Rigas et al. (2014) are not observed unless the disk shape is modified into that of a bullet, showing the importance of the separation angle. It suggests that these modes are linearly stable for the disk while they are unstable for the bullet shape. When the disk is fixed and inclined, the base center of pressure (CoP) shifts preferentially towards one side of the rotation axis. Finally, when the disk is free to rotate, the front moment is proportional to the disk inclination (aerodynamic stiffness), while the base moment is well correlated with the disk inclination. From these observations, a low-order model is derived that couples (i) the CoP, forced stochastically by the turbulent flow, and (ii) the disk inclination, as a linear harmonic oscillator forced by the base moment. The model captures well the main statistic and dynamic features observed experimentally. One difference lies in the distribution of the disk inclination (which features exponential tails in the measurements but is Gaussian in the model), suggesting a possible refinement with non-linearities or time delays. The model is expected to capture coupled dynamics in other systems involving turbulent wakes behind freely rotating bluff bodies.

Validation of a NOx estimation methodology based on the analysis of in-cylinder pressure trace

Internal combustion engines control systems are evolving rapidly in order to meet the most recent emissions standards: this process requires a deep knowledge of how the combustion process takes place, since heat-release control is crucial to manage the trade-off between engine-out emissions and best suit the tailpipe aftertreatment system operating point.Nitrogen oxides (NOx) have currently become a critical pollutant emission that needs to be limited in compression-ignited engines. Since a selective catalytic reduction (SCR) system is present in several applications, engine-out NOx concentration is a fundamental parameter to be evaluated.This work shows how an estimation of NOx concentration can be deduced from instantaneous in-cylinder pressure measurement and some of the parameters, related to the intake charge, currently available on electronic control units (ECU). A prediction model, based on Zeldovich mechanisms and Arrhenius rate of combustion is proposed, which exploits as main contributions: rate of heat release and adiabatic flame temperature. An experimental campaign (DOE) has been carried out on a diesel engine, varying the main engine control parameters, to tune the model in steady-state operating point. The predictive capability is then evaluated by feeding the model with a validation dataset in both steady state and transient condition. Finally, model response to measure uncertainties is discussed.

Flow around a slotted circular cylinder at various angles of attack

We experimentally investigated the flow characteristics around a circular cylinder with a slot at different angles of attack. The experimental campaign was performed in a wind tunnel at the Reynolds number of Re = 2.67 × 104. The cylindrical test model was manufactured with a slot at the slot width S = 0.075 D (D is the diameter of the cylinder). The angle of attack α was varied from 0° to 90°. In addition to measuring the pressure distributions around the cylinder surface, a digital particle image velocimetry (PIV) system was employed to quantify the wake flow characteristics behind the baseline cylinder (i.e., baseline case of the cylinder without slot) and slotted cylinder at various angles of attack. Measurement results suggested that at low angles of attack, the passive jet flow generated by the slot would work as an effective control scheme to modify the wake flow characteristics and contribute to reducing the drag and suppressing the fluctuating lift. The flip-flop phenomenon was also identified and discussed with the slot at 0° angle of attack. As the angle of attack α became 45°, the effects of the slot were found to be minimal. When the angle of attack α of the slot approached 90°, the self-organized boundary layer suction and blowing were realized. As a result, the flow separations on both sides of the test model were found to be notably delayed, the wake width behind the slotted cylinder was decreased and the vortex formation length was greatly shrunk, in comparison with the baseline case. Instantaneous pressure measurement results revealed that the pressure difference between the two slot ends and the periodically fluctuating pressure distributions would cause the alternative boundary layer suction and blowing at α = 90°.

Accounting for the role of turbulent flow on particle dislodgement via a coupled quadrant analysis of velocity and pressure sequences

Recent studies have demonstrated the importance of duration, in addition to magnitude, of energetic turbulent events on particle dislodgement under threshold of motion conditions. It is therefore proposed here that the use of turbulence sequences, instead of single instantaneous extreme events, is more appropriate for characterizing the role of fluctuating velocities and associated hydrodynamic forces on particle mobility. The validity of the proposed method is examined through the detailed analysis of directly measured velocity and pressure data sets. In an effort to relate the results of the conventional velocity quadrant analysis with the instantaneous pressure measurements, the concept of pressure quadrant analysis is introduced. The coupled sequences of the synchronous velocity and pressure quadrant events allow for a more complete description of the local turbulent flow characteristics, including the prevalent coherent structures, and more clear interpretation of their role on particle mobility. It is concluded here that large-scale sweep structures are capable of generating excessive and persistent force fluctuations which are predominantly responsible for the dynamic process of particle dislodgement. This result supports the impulse criterion as the proper way of accounting for the cumulative effect of coherent structures on particle movement.

Fluid force and symmetry breaking modes of a 3D bluff body with a base cavity

A cavity at the base of the squareback Ahmed model at Re≃4×105 is able to reduce the base suction by 18% and the drag coefficient by 9%, while the flow at the separation remains unaffected. Instantaneous pressure measurements at the body base, fluid force measurements and wake velocity measurements are investigated varying the cavity depth from 0% to 35% of the base height. Due to the reflectional symmetry of the rectangular base, there are two Reflectional Symmetry Breaking (RSB) mirror modes present in the natural wake that switch from one to the other randomly in accordance with the recent findings of Grandemange et al. (2013b). It is shown that these modes exhibit an energetic 3D static vortex system close to the base of the body. A sufficiently deep cavity is able to stabilize the wake toward a symmetry preserved wake, thus suppressing the RSB modes and leading to a weaker elliptical toric recirculation. The stabilization can be modelled with a Langevin equation. The plausible mechanism for drag reduction with the base cavity is based on the interaction of the static 3D vortex system of the RSB modes with the base and their suppression by stabilization. There are some strong evidences that this mechanism may be generalized to axisymmetric bodies with base cavity.

Experimental investigation of flow characteristic of tip leakage flow in an axial flow compressor rotor

Tip leakage flow fields in a small-scale high-speed subsonic axial flow compressor rotor were investigated by virtue of the steady and casing instantaneous pressure measurements over wide stable operating range. Fast Fourier transformation and short time Fourier transformation analyses were conducted to elucidate the flow characteristics at different operating conditions, with an emphasis on extending experimental database to validate the previous and subsequent numerical investigations, which would be crucial to the understanding of the origin of tip flow unsteadiness. The measured quasi-steady flow characteristics agreed well with the flow features of tip leakage flow from previous steady simulations. The unsteady flow characteristic of tip leakage flow was the appearance of rotating instability, which was of varying frequency closely related to tip loading variation. An agreement between the unsteady flow characteristics of tip leakage flow from the current measurements and from the previous unsteady simulations to some extent indicated that further systematical unsteady simulations and a deeper quantitative validation of simulation results should be made so that the origin of rotating instability could be uncovered precisely.

Experimental and Numerical Investigation of Flow Characteristics Near Casing in an Axial Flow Compressor Rotor at Stable and Stall Inception Conditions

Casing instantaneous pressure measurements and full-annulus unsteady simulations were undertaken to analyze flow characteristics near casing at stable and stall inception conditions in an axial flow compressor rotor, and the objective was to establish its linkage with the stall inception process. The measured flow characteristic at near-stall stable operating conditions was the appearance of rotating instability (RI), which attributed to the activity of an unsteady flow with varying frequency. A similar flow characteristic was found in the simulated near-stall stable flow conditions, and detailed analyses of instantaneous flow field indicated the formation and activity of tip secondary vortex could be flow mechanism for the appearance of RI as far as nonuniform tip loading distribution in measurements was concerned. The measured flow characteristic before spike emergence was still the activity of RI. However, it was submerged into flow field accompany by the emergence of spike. The simulated stall inception process was similar to that from measurement, and further analyses of instantaneous flow field established the causal linkage between RI and stall inception process for the test rotor.