Mechanism Of Flow Instability Research Articles

On the evolution of magnetohydrodynamic flow instability in shock-accelerated light bubble

The study investigates the evolution of flow instabilities in a magnetohydrodynamic (MHD) environment involving a shock-accelerated light cylindrical bubble. Numerical simulations were conducted using a cylindrical helium (He) bubble accelerated by a shock wave in nitrogen (N2) gas at various magnetic field strengths. The results highlight the impact of magnetic fields on flow morphology, vorticity generation, and enstrophy. The interaction between incident shock waves and the gas bubble revealed significant differences in flow patterns and interface features when magnetic fields were applied. Key findings include the quantification of shock trajectories and detailed visualizations of the evolving flow structure. The study provides insights into the dynamics of shock–bubble interactions under MHD conditions, contributing to the broader understanding of flow instability mechanisms in such complex environments.

Investigation of Reynolds number effects on flow stability of a transonic compressor using a dynamic mode decomposition method

With the continuous increase in aircraft flight altitude, low Reynolds number effects in high-altitude environments significantly impact the stability of compressor operation. In this study, dynamic mode decomposition (DMD) of the flow field at various time instances near stall conditions in a transonic compressor was performed to investigate the influence of Reynolds number (Re) effects on critical flow characteristics and instability mechanisms. The results indicate that under different Reynolds number index (RNI) conditions near stall conditions, the frequency of tip leakage flow varies. Under high RNI condition, the influence of tip leakage flow is concentrated mainly from the leading edge to the mid-chord. The stall mode is primarily caused by the interaction of shock with the Tip Leakage Vortex, resulting in the breakdown of the vortex. The development of vortex structures inside the passage leads to a delay in the flow field response to blade passing. Under low RNI condition, the tip clearance leakage flow is stronger, with a relatively reduced influence from the leading edge to the mid-chord and an increased impact from the mid-chord to the trailing edge. The main cause of the stall mode is the circumferential movement of vortex structures, causing secondary leakage over adjacent blade tip clearances. The blockage formed by vortex structures within the passage is weaker, and the flow field response to blade passing remains consistent with the blade passing frequency. However, as stall develops further, the flow field response significantly decreases.

Effect of double bypass conditions on the thermodynamic characteristics and internal flow mechanisms in a variable core cycle compression system

The performance of variable cycle core compression system (VCCCS) is crucial for achieving mode transition in variable cycle engine (VCE). The double bypass matching characteristics and internal flow mechanisms of the VCCCS under various conditions are investigated in this study. The results indicate that, in the low bypass ratio (LBR) mode, Under the near choke or design point conditions of external bypass, internal bypass throttling causes the excessive blockage of low-energy fluid near the suction surface of high-pressure compressor (HPC) second stator, which leading the flow instability in VCCCS. Under the near stall condition of external bypass, internal bypass throttling causes the CDFS to reach the stall boundary firstly. The flow instability is triggered by the interaction between tip leakage flow and shock waves in CDFS rotor tip. Following mode transition, the CDFS exhibits lower flow and load, resulting in changes in the matching state of HPC due to the strong coupling effects of upstream components, thereby altering the matching characteristics and flow instability mechanisms of the VCCCS. The impact of different bypass conditions on VCCCS performance is elucidated, further establishing the association between bypass exit meridian velocity and VCCCS performance, which is helpful to select key design parameters.

Thermal-hydraulic phenomena and heat removal performance of a passive containment cooling system according to exit loss coefficient

The natural circulation system has been widely studied for use in various applications because of its inherent advantage. However, it has a key weakness called flow instability that makes the system unstable. Through massive previous research, the mechanisms of flow instability were analyzed, but there was an ambiguous aspect related to the effect of experimental parameters on the phenomenon. Particularly, there has been no report on the heat transfer performance of the system when flow instability phenomena were present. In this study, thermal-hydraulic phenomena of a two-phase natural circulation system that functions as a passive containment cooling system (PCCS) was investigated according to experimental parameters, namely, the temperature boundary (120–158 °C) and exit loss coefficient (0–34.5) under atmospheric pressure conditions. The experimental results showed five different flow types in the loop. The flow modes that occurred by the interaction between flashing and boiling were classified by referring to the mass flow rate, void fraction, and visualization data. The system was more unstable when the temperature boundary conditions increased, but it was more stable when the exit loss coefficient increased. These results have only been confirmed in our research. The reason for the results is that the flow conditions are located on the boundary between Density Wave Oscillation I and the stable flow region, and that boundary does not have clear criteria. In addition, comparing the heat transfer performance of a system by heat rate can confirm the effect of flow instability on the thermal performance of the passive cooling system. As a result, the high exit loss coefficient stabilizes the system better than the low case and has similar heat removal performance.

Modal stability analysis of the density-stratified plane Couette–Poiseuille flow

Shear and density stratification strongly affect the flow mechanism of the different atmospheric and ocean flows. In this paper, we investigate the stability characteristics of plane Couette–Poiseuille (CP) flow with stable density stratification in the vertical direction. A modal stability analysis is carried out to examine the exponentially growing instability of stratified plane CP flow under different controlling parameters. The domain of the flow is periodic in streamwise and vertical directions. The stability problem is solved numerically using the spectral collocation method. The present analysis is carried out for Reynolds number Re=104 with different speeds of moving wall and different strengths of stratification. The results show that the mass diffusivity impact on the flow instability mechanism is almost negligible beyond the Schmidt number Sc≥20. The three-dimensional mode is generally the most unstable mode for density-stratified CP flow. However, the most unstable mode in unstratified CP flow is always two-dimensional. In contrast to unstratified CP flow, the density-stratified CP flow is unstable even moving wall velocity exceeds 70% of the center velocity of the plane Poiseuille flow component. It is also observed that the moving wall velocity and density stratification simultaneously affect the stability of the flow, which shows the importance of the shear and stratification in the flow.

The comparative transient prediction on hydrodynamic characteristics and flow field properties of pump-jets with accelerating and decelerating ducts

Pump-jet holds a pivotal position in various marine applications, underscoring the need for comprehending their transient behavior for the purpose of design enhancement and performance refinement. This paper employs Reynolds-averaged Navier–Stokes equations method in conjunction with Detached Eddy Simulation model. The study delves into the ramifications of accelerating and decelerating ducts, distinguished by camber f and attack angles α, on transient hydrodynamic characteristics. The hydrodynamic characteristics are investigated numerically, after the validation of the numerical methodology by comparing simulation outcomes against experimental results. Subsequently, the study delves into propulsion characteristics, followed by an exploration of time-domain and frequency-domain data transformed through fast Fourier transform to analyze thrust fluctuations and pulsating pressures. Additionally, a detailed examination of pressure distribution and velocity field is provided, aiming to dissect the mechanisms through the variations in f and α influence the flow field. Findings suggest that the outlet velocity of accelerating ducts significantly surpasses the inlet velocity, a behavior contrasted by decelerating ducts. Notably, the patterns of accelerating and decelerating ducts resulting from alterations in f exhibit consistent characteristics with those brought about by changes in α. However, several opposite characteristics surface in transient flow field due to the distinct modifications in the duct profile. Furthermore, by considering vorticity magnitude distribution and vortices, a comparative analysis elucidates the effects of varying f and α on rotor and stator trailing vortices. This contributes to understanding the flow instability mechanism under differing duct configurations. It is evident that changes in f and α exert significant influence on both performance and flow field.

Dynamic mode characteristics of flow instabilities in a single-stage compressor under different throttling processes

To investigate the influence of throttling processes on dynamic characteristics of compressor stability, the rotating stall development of National Aeronautics and Space Administration Stage 35 was simulated with full-annulus Unsteady Reynolds-Averaged Navier–Stokes under different throttling processes. The numerical methods were verified. By combining Dynamic Mode Decomposition and flow field evolution research, the flow structures and dynamic characteristics of “critical mass flow” under different throttling processes were deeply studied; the flow mechanism of flow instabilities under different throttling processes was explored. It is found that the “critical mass flow” corresponds to the beginning of a rapid decrease in mass flow, mainly characterized by shock forward movement and a larger range of spillage flow. Around “critical mass flow,” if the throttle is still tightening, it presents stall pattern 2; otherwise, it presents stall pattern 1. During the pre-stall, both patterns are dominated by tip clearance vortex (TCV)-shock interference. Stall inception disturbance is generated from TCV-shock interference; pattern 1 presents a single disturbance, while pattern 2 presents multiple disturbances. Subsequently, the TCV-shock interference gradually weakens. The single stall disturbance of pattern 1 gradually develops and stabilizes. The multiple stall disturbances in pattern 2 undergo processes including fusion and disappearance, ultimately developing into a single stall cell. During the stable stall, the throttling processes have no significant impact on the speed of the stall cell, and the flow in the un-stalled region is basically consistent with the speedline. However, the tighter the throttle is, the larger the stalled region, and the weaker the flow capacity of the un-stalled region.

Interface Shearing Promoted Plastic Flow Instability of Nanolaminated Composites

Nanocrystalline laminated composites (NLCs) with alternating phases exhibit exceptional mechanical properties, thermal stability, and resistance to radiation damage and shock. However, inherent plastic flow instability poses a persistent challenge, independent of loading direction. This study explores the mechanisms of buckling and kinking in soft-hard and soft-soft NLCs under compression loading, attributing plastic deformation to dislocation slips and interface shearing/sliding. Despite these merits, plastic flow instability remains a challenge in NLCs under compression, irrespective of loading direction. This study focuses on elucidating the mechanisms of plastic flow instability, particularly buckling and kinking, observed in soft-hard and soft-soft NLCs. A mesoscale crystal plasticity model integrating the interfacial shear (IS) and confined layer slip (CLS) mechanisms is developed. In soft-soft Cu-Nb multilayers, the model reveals that easy interface sliding promotes plastic strain in the interface, inducing strain softening by lowering interface shear resistance. Conversely, the contribution of interface shear to plastic deformation diminishes with increasing Cu/Nb layer thickness, reducing the likelihood of strain softening. For soft-hard Al-Al2Cu eutectics, easier interface shear intensifies plastic deformation in Al layers but suppresses it in Al2Cu layers, triggering structural instability in the latter. The critical strain for bulking in the same thick Al2Cu layer decreases with increasing Al layer thickness. In summary, lowering interface resistance will promote compression instability of NLCs, while thickening soft layer will retard the occurrence of compression instability regardless of soft-soft or soft-hard NLCs.

Numerical analysis of accelerating and decelerating ducts modified by camber on the unsteady flow field of pump-jet

Utilizing the Reynolds-averaged Navier-Stokes equations method in conjunction with Detached Eddy Simulation model, this paper investigates effects of duct camber (f) on transient hydrodynamic characteristics, particularly propulsion performance and flow field behavior. The research begins by validating the numerical methodology through experimental and numerical assessments of propeller VP1304 and a pump-jet operating under mooring conditions. The exploration commences with examining propulsion characteristics, followed by analyzing time-domain and frequency-domain data, wherein thrust fluctuations and pulsating pressures are scrutinized via fast Fourier transform (FFT). The pressure distribution and velocity field are subsequently presented to unveil the mechanisms triggered by variations in f. Comparative findings highlight that in cases of pump-jets with lower camber, the outlet velocity exceeds the inlet velocity, a trend contrary to scenarios involving higher f values. Additionally, by analyzing vorticity magnitude distribution and vortices, this study attains comparative insights into the effects of accelerating and decelerating ducts on rotor and stator trailing vortices, offering a window into the flow instability mechanism amidst diverse duct configurations. The results showcased to demonstrate the substantial impact of f variation on hydrodynamic properties. This comprehensive investigation yields practical guidance for the optimal design of pump-jets, potentially informing future design endeavours.

Experimental Research on Flow Instability Mechanism of a Highly Loaded Axial Compressor

Abstract The performance and stable operating range of compressors are critical for the efficient operation of various turbomachinery systems. To reveal the flow instability mechanism of a high-speed and high-loaded compressor, a systematic experimental study on a 1.5-stage high-loaded compressor was conducted in this paper. First, the aerodynamic design and aerodynamic performance evaluation of the compressor were carried out. At 100% corrected speed, the measured choked flowrate, peak efficiency, and stall margin were 4.59 kg/s, 87.1% and 17.5%, respectively. Second, the flow instability mechanism of the highly loaded compressor at different corrected speeds was clarified through the experiments. At 50% corrected speed, the compressor rotor developed from a spike-wave stall precursor to a rotating stall; at 70% corrected speed, the compressor developed directly from a spike-wave precursor to surge; at 90% corrected speed, the compressor has undergone the process of modal wave precursor, spike-wave precursor, and surge. Further, at 70% and 90% corrected speed, a classic surge occurred with surge frequencies of 11.91 Hz and 9.59 Hz, respectively. Through the analysis of short-time power spectrum maximum amplitude, the warning time for the surge was 6.7 ms and 15.6 ms, respectively. Finally, as the compressor throttles to stall/surge conditions, the degree of fluctuation of the autocorrelation coefficient and cross-correlation coefficient increases.

Energy transfer mechanism during ethanol evaporation with external tangential temperature gradient under low pressure environment

For the purpose of revealing the energy-transfer process during ethanol evaporation under low pressure environment, experimental measurement and numerical simulation are adopted for ethanol evaporation at different liquid depths and external radial temperature differences in annular pools. The results show that two thermocapillary vortexes appear below the liquid–vapor interface. Most of the latent heat of vaporization is from the liquid phase, but little from the gas phase. With the increase of liquid layer depth, the steady axisymmetric flow will transform into three-dimensional time-dependent convection. The mechanism of flow instability should be attributed to the variation lag of velocity behind the variation of flow resistance. The critical vapor pressure of flow destabilization depends on radial temperature difference and liquid layer depth. Furthermore, the magnitude of temperature discontinuity across the liquid–vapor interface is the largest near the hot inner cylinder. With the increase of the liquid layer depth, the temperature discontinuity decreases.

Radius ratio dependency of the instability of fully compressible convection in rapidly rotating spherical shells

Based on the fully compressible Navier–Stokes equations, the linear stability of thermal convection in rapidly rotating spherical shells of various radius ratios $\eta$ is studied for a wide range of Taylor number $Ta$, Prandtl number $Pr$ and the number of density scale height $N_\rho$. Besides the classical inertial mode and columnar mode, which are widely studied by the Boussinesq approximation and anelastic approximation, the quasi-geostrophic compressible mode is also identified in a wide range of $N_\rho$ and $Pr$ for all $\eta$ considered, and this mode mainly occurs in the convection with relatively small $Pr$ and large $N_\rho$. The instability processes are classified into five categories. In general, for the specified wavenumber $m$, the parameter space ($Pr, N_\rho$) of the fifth category, in which the base state loses stability via the quasi-geostrophic compressible mode and remains unstable, shrinks as $\eta$ increases. The asymptotic scaling behaviours of the critical Rayleigh numbers $Ra_c$ and corresponding wavenumbers $m_c$ to $Ta$ are found at different $\eta$ for the same instability mode. As $\eta$ increases, the flow stability is strengthened. Furthermore, the linearized perturbation equations and Reynolds–Orr equation are employed to quantitatively analyse the mechanical mechanisms and flow instability mechanisms of different modes. In the quasi-geostrophic compressible mode, the time-derivative term of disturbance density in the continuity equation and the diffusion term of disturbance temperature in the energy equation are found to be critical, while in the columnar and inertial modes, they can generally be ignored. Because the time-derivative term of the disturbance density in the continuity equation cannot be ignored, the anelastic approximation fails to capture the instability mode in the small-$Pr$ and large-$N_\rho$ system, where convection onset is dominated by the quasi-geostrophic compressible mode. However, all the modes are primarily governed by the balance between the Coriolis force and the pressure gradient, based on the momentum equation. Physically, the most important difference between the quasi-geostrophic compressible mode and the columnar mode is the role played by the disturbance pressure. The disturbance pressure performs negative work for the former mode, which appears to stabilize the flow, while it destabilizes the flow for the latter mode. As $\eta$ increases, in the former mode the relative work performed by the disturbance pressure increases and in the latter mode decreases.

Numerical Study of the Improvement in Stability and Performance by Use of a Partial Vaned Diffuser for a Centrifugal Compressor Stage

The influence of different diffuser configurations on the flow stability and aerodynamic performance of a centrifugal compressor stage with a mass flow coefficient of 0.196 is numerically investigated. Research results show that the performance of a traditional full-height vaned diffuser (TVD) deteriorates rapidly, and a shroud-side partial vaned diffuser (SVD) displays better adaptability in off-design conditions. SVD can suppress the development of vortices generating at the diffuser leading-edge. Therefore, it can reduce the flow loss inside the stage and improve the flow stability of the stage at low mass flow rates. The unsteady analysis for TVD and SVD shows that the stall cell propagates at about 35.7% of impeller rotational speed in the semi-vaneless space and diffuser passages. Furthermore, the internal flow in TVD and SVD is studied by employing the proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) methods. The flow loss and instability mechanism in the stage are consequently revealed more comprehensively.

Numerical investigation of unsteady cavitating turbulent flows around a three-dimensional hydrofoil using stress-blended eddy simulation

The mechanism of flow instability, which involves complex gas–liquid interactions and multiscale vortical structures, is one of the hot research areas in cavitating flow. The role of turbulence modeling is crucial in the numerical investigation of unsteady flow characteristics. Although large-eddy simulation (LES) has been used as a reliable numerical method, it is computationally costly. In this work, we used a hybrid Reynolds-averaged Navier–Stokes (RANS) and LES model, that is, stress-blended eddy simulation (SBES), to improve the prediction capability for the cloud cavitating flow. Our hybrid approach introduces a shielding function to integrate the RANS model with the LES applied only regionally, such as to large-scale separated flow regions. The results showed that the periodic shedding of cavity growth, break off, and collapse around a three-dimensional Clark-Y hydrofoil was reproduced in accordance with experimental observations. The lift/drag coefficients, streamwise velocity profiles, and cavity patterns obtained by the SBES model were in better agreement with the experimental data than those obtained by the modified RANS model. The re-entrant jet dynamics responsible for the break off of the attached cavity were discussed. Further analysis of vorticity transportation indicated that the stretching and dilatation terms dominated the development of vorticity around the hydrofoil. In conclusion, the SBES model can be used to predict cavitating turbulent flows in practical engineering applications.

Single-phase density wave oscillation -A new mechanism of flow instability in inverted U-type steam generator

Flow reversal under low mass flow conditions is harmful to the performance of inverted U-type steam generator (UTSG) and existing research attributes the phenomenon to be flow excursion instability. In this paper, a new mechanism of flow instability that could also induce flow reversal, namely single-phase density wave oscillation (DWO), was analyzed based on numerical methods. As a primary study, the analysis was done in parallel channels consisted of two identical inverted U-type tubes. It was found that for UTSG at low mass flow conditions, the compressibility of single-phase flow would be a key factor to trigger the positive feedback of mass flow-temperature-pressure drop in DWO. Single-phase DWO should result in premature of flow reversal compared to that caused by flow excursion (FE), and analysis showed that it could occur only if the primary side temperature difference and average temperature of UTSG were both large enough, and for large-scale UTSG DWO would disappear due to the increase of total pressure drop. Parameter effects on single-phase DWO in UTSG were also carefully studied and it was found that the trends could be well explained by the variation of system compressibility.

Unsteady RANS simulation of fluid dynamic and heat transfer in an oblique self-oscillating fluidic oscillator array

Impinging jet played an important role in cooling technology. The steady-state jet could be transformed into an oscillatory one based on the intrinsic flow instability mechanisms by using self-oscillating fluidic oscillators. In this paper, a high-performance microchannel heat exchanger based on a fluidic oscillator array was presented. The fluidic oscillators were tilted at an angle of 30° above the impinging surface to extend the influence area of the jets. The unsteady RANS turbulence models were adopted to study the fluid dynamic and heat transfer performance of the jet array. The time-resolved pressure field and velocity field were calculated to show that the parallel oscillators would produce three modes, including co-directional oscillation, reverse oscillation, and irregular oscillation, under synchronous and asynchronous output phases. The sweeping jets improved the heat removal performance by increasing the average Nusselt number and enlarging the influence range on the external flow field. The heat removal performance of the sweeping jets was almost equivalent under different oscillation modes.

Numerical investigation on flow instabilities in low-pressure steam turbine last stage under different low-load conditions

The modern power generation system requires steam turbines operating at flexible operating points, and flow instabilities readily occur in the low-pressure (LP) last stage under low-load conditions, which may cause failure of the last stage moving blades. Some studies have shown that within this operating range, a shift of the operating point may lead to flow instabilities. Numerical simulation has gradually developed into a popular method for such researches, but it is expensive for a complex model, which has to be balanced between efficiency and accuracy. This work is divided into three parts: Firstly, one of the low-load conditions is selected to provide both URANS model and the Scale-Adaptive Simulation (SAS) model. The results of the two models are compared to evaluate specific flow phenomena; Secondly, through calculations of different low-load conditions, the flow structure and propagation characteristics of instabilities in the last stage are obtained; Finally, flow analysis is applied to explain the formation mechanism of flow instabilities in LP steam turbines. The results show that, the introduction of SAS model increases the randomness of flow over time, but does not fundamentally change the flow instabilities. Flow instabilities take different forms at different flow rate, from rotating instability to rotating stall. The formation of flow instabilities is related to the radial flow in the cascade passages.

Thin-film evolution and fingering instability of self-rewetting films flowing down an inclined plane

This paper examines the evolution patterns and essential mechanisms of flow instability of a self-rewetting fluid (SRF) coating on an inclined plane. Considering that the self-rewetting liquid has an anomalous surface tension with temperature change, some interesting phenomena will be found and should be explained. Using the thin-film model, the evolution equation of the air–liquid interface is derived, and the thickness of the liquid film is determined by a fourth-order partial differential equation. Taking T0 (temperature corresponding to the minimum of surface tension) as a cutoff point, two representative cases of the nonlinear flow are comprehensively discussed. One is the case of Ti > T0, and the other is Ti < T0 (interfacial temperature Ti). Based on traveling wave solutions, linear stability analysis (LSA) of the small perturbation applied to the initial condition is given, and the results of LSA are confirmed and explained by the numerical simulations. Results show that the inclined angle and the Weber number always stabilize the free surface, while the Marangoni effect and the Biot number play different roles for the two cases. As Ti − T0 varies from a negative value to a positive value, the Marangoni effect switches to the reverse Marangoni effect. With Ti − T0 < 0, the Marangoni effect enhances the fingering instability, while the Marangoni effect makes the flow more stable if Ti − T0 > 0. The Biot number Bi = 1 corresponds to the most unstable state for Ti < T0 and to the most stable state for Ti > T0.

Aeroelastic analysis of an idealized landing gear door in subsonic potential flow

Landing gear doors on aircraft have experienced flutter during preliminary flight testing. While designs vary widely, landing gear doors are typically plate-like structures with a relatively rigid actuator attached to their inside surface. To better understand the aeroelasticity of landing gear doors, this study investigates the aeroelastic stability of an idealized model. The model consists of a hinged plate with an interior constraint approximating the actuator attachment. The plate is subject to uniform flow, and an unsteady vortex lattice model is coupled to the structural model to predict critical flow velocities. The location and footprint area of the internal constraint, along with plate aspect and mass ratios, are varied to investigate a large parameter space. Results reveal that the critical flow speed and instability mechanism are sensitive to the postulated actuator placement. In general, flutter is the dominant mode of instability when the actuator is postulated in the leading quarter of the plate. In other postulated locations, divergence dominates. However, the exact shape and location of the boundary between flutter and divergence is configuration dependent and found to be especially sensitive to changes in aspect ratio.

Experimental investigation of transient characteristics of mild surge and diffuser rotating stall in a centrifugal compressor with vaned diffuser

The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence of flow instability such as stall and surge. The paper experimentally examines the developing process of surge and stall occurring in a centrifugal compressor to advance the understanding on flow mechanism of flow instability. It is found that three types of pressure fluctuation can be observed at low flowrate region. At the critical point, the local stall firstly occurs in some specific diffuser passages and the enlarged local diffuser stall eventually induces the mild surge of compression system indicated by the sinusoidal pressure fluctuation. At lower mass flow rate, the diffuser stall cell begins to circumferentially propagate along the impeller rotating direction at 11% of rotor speed with the existence of mild surge. In comparative analysis of IGV pre-swirl angle on the occurrence of mild surge, the mild surge still occurs at the operating condition when the slope of the characteristic map of test stage is still obviously negative, in which the compression system is supposed to be stable in previous study. And a new suggested criterion for the prediction of mild surge is demonstrated that the occurrence of mild surge depends on the destabi-lization effect of downstream components about diffuser and volute. Combined with the experimental data, the streamwise distribution characteristic of diffuser stall can be used to develop the simplified model of lumped parameters for the analysis on the generation mechanism of the diffuser rotating stall. The quantitative investigation on the relation between the pressure-rise characteristic of subcomponents and the occurrence of mild surge and diffuser rotating stall not only advances the prediction of stability limit but also lays the theoretic foundation for controlling these unsteady behaviors to improve the operating range.