Research On Rotating Stall Process Of Marine Gas Turbine Compressor At Low Rotating Speed

Rotating stall has always been one of the most important problems for gas turbine engine compressors.Especially for marine gas turbines,which require a wide range of variable operating conditions,the problem of low engine stability is particularly important.Marine engines require low pressure compressors with high surge margin and efficiency at low and medium speeds.Rotating stalls are often a precursor to compressor performance degradation and surge,thus revealing the rotational stall process in the low speed range of the compressor.Mastering the causes and characteristics of flow instability has important basic research value for achieving high stability design and expansion measures of compressors in low working conditions.In this paper,the first stage of the subsonic compressor of the marine gas turbine in the compressor laboratory of Harbin Engineering University is taken as the research object.Combined with the SST turbulence model and the Reynolds average unsteady method(URANS)numerical simulation method,the compressors at low and medium speeds are studied.The stall mechanism of the channel model was analyzed and verified on a 1.5-stage compressor test rig.The research content of this paper mainly includes the following aspects:Firstly,under the condition of 50%rotation speed of the compressor,the calculation of the non-constant constant value of the whole channel is carried out.The analysis of the parameters such as flow rate and wall static pressure during the whole stall process shows that the compressor stall process can be divided into four stages under medium speed conditions.,respectively,the steady flow phase,the rotational instability phase,the stall precursor phase,and the complete stall phase.The comparative analysis shows that the initial disturbance with certain periodicity first appears in the unstable phase of rotation,which makes the signal of three frequency bands added to the static pressure spectrum of the machine,corresponding to the frequency of occurrence of disturbance in the flow channel(low frequency band),The frequency of the periodic interaction(middle frequency band),the leakage vortex fluctuation,and the fracture frequency(high frequency band)of the radial secondary flow and the leakage vortex that migrate to the tip of the blade.Secondly,revealing the origin and connection of the pressure disturbance in the unstable phase of rotation and the precursor of stall in the low and medium speeds.A detailed analysis of the flow field in the tip region indicates that the pressure disturbance is mainly caused by the fractured vortex and suction surface moving to the radial secondary flow of the tip and the second half of the tip of the blade.The interaction is formed by the tip of the secondary vortex.Moreover,as the throttling increases,the position of the radial secondary flow and the tip leakage vortex moving to the tip of the blade further moves toward the front edge of the suction,and the starting position of the secondary vortex of the tip is further closer to the leakage vortex of the tip.The starting position,so that the tip leakage vortex is completely broken,the flow field structure corresponding to the unstable phase of rotation is destroyed,and the precursor of the sudden tip stall appears.The numerical analysis also shows that the signal amplitude of the mid-top frequency band(1206Hz-1707Hz)of the compressor increases further when entering the stall,and the leading edge overflow and the trailing edge return phenomenon occur simultaneously at the tip clearance.Finally,the low-speed stall process test of the 1.5-stage compressor was carried out.The Kulite high-frequency dynamic pressure sensor and the high-frequency data acquisition system were used to measure and collect the tip pressure during the stall of the compressor.The fast Fourier transform(FFT)was used.The filtering technique is used to process the pressure signal.The analysis shows that the initial propagation velocity of the stall is about 72.48%of the rotational speed,and the stall velocity of the stall is about 52.34%of the rotational speed after the complete stall.From the stall disturbance to the compression.The machine experienced a total of 10 laps before and after the complete stall,and the disturbance spanned 2-3 pitches at the top of the blade.The characteristic frequency corresponding to each stage is found by spectrum analysis,that is,the mid-frequency characteristic frequency of 48.92%BPF in the unstable phase of rotation,and the 15-150 Hz low-frequency frequency band which gradually increases in the stall process.Through the compressor level test,the steady flow field characteristics between the stages in the stall process are obtained,and the static pressure distribution cloud map of the blade tip in the stall process is given according to the pressure signal collected by the dynamic pressure sensor.The results of this paper show that the spectral characteristics of the tip pressure signal in the stall process exhibit different characteristics at each stage.The tip vortex is the origin of the stall process and the key flow phenomenon of the stall,starting from the diameter of the suction surface of the blade.The secondary flow plays an important role in the stall process.