Kombination von Radial- und Seitenkanalstufen für Turboverdichter

Unsteady gas pressure oscillations occur at impeller outlet and diffuser of radial and side channel compressors, engendered by the blades grid of the impeller. They have effect beyond the limits of inlet and outlet. If a radial stage is coupled to a side channel stage, then the unsteady gas pressure oscillations of the side channel stage have an effect inside the radial stage affecting flow and characteristic curve. Because of that, the radial stages unstable characteristics and the limit of rotating stall can be moved to lower volume flows or completely suppressed by connecting a side channel stage before or behind it. Therefore the permissible range of operation of combined compressor stages can be extended compared with a radial compressor stage. Moving the limit of rotating stall of the radial compressor stage and lower the gas pressure oscillations caused by Rotating Stall as a result of the side channel stages unsteady gas pressure oscillations will be proved experimental. As a criterion for Rotating Stall in radial compressor stages also the proportion between RMS of gas pressure oscillations and the total pressure increase in the radial compressor stage can be used.     

Kopplung von Gasdruckschwingungen in Radialverdichtern

Unsteady flow processes occur in centrifugal compressors, especially noticeable in passing region between impeller flow and reposing diffusers like return bend or radial diffuser. This unsteady flow causes gas pressure oscillations of considerable extent. If the unsteady flow generates two or more gas pressure oscillations, which result of different arousals with different frequencies, interconnection of gas pressure oscillations occur, leading into new vibration occurrences and side bands at base frequency in frequency spectrum. If frequencies and magnitude of pressure oscillation amplitudes of single oscillations with sinusoidal oscillation progression are known, the resulting gas pressure oscillation progression of interconnected gas pressure oscillations can be calculated and also experimental proven.     

Gasdruckschwingungsverteilung im Meridianschnitt von Seitenkanalverdichtern

The blade pass and the turbulent eddy flow in unsteady pressure field of the side channel cause heavy gas pressure oscillation in the side channel with negative concomitant phenomenons, mechanical vibration stimulus of the compressors casing and noise emission from the compressor. The gas pressure oscillation isn´t homogeneous distributed in the side channel, but it shows a topology with considerable gradients in profile of the side channel at α_K = constant with more intense dependence in circumferential direction. Gas pressure oscillation can be characterized by RMS, peak value of gas pressure oscillation and amplitude value of gas pressure oscillation at blade rotation frequency as main stimulating frequency. In this report experimental results of gas pressure oscillation of a side channel compressor are presented.     

Druckschwingungen in Seitenkanalpumpen

By the turbulent vortex forced by the impeller, strong high-frequency pressure oscillations occur in the side channel. These pressure oscillations result from the temporal modification of the vortex structure and the specific impulse flow transportation in the side channel. They are visible due to the high-frequency character neither at integral static pressures not in the characteristic lines of the pumps. However, they add essentially to the energy transfer to the pumped fluid and to the increase of the static pressure in the side channel. The dynamic pressure oscillations in the side channel with the characteristic exciter frequency by the blade revolution frequency are transmitted to the pump case and a part of it is emitted as effective acoustic pressure to the environment. The blade revolution frequency is by far recognizable as exciter frequency in the pressure oscillations, in the mechanical case oscillation and as effective acoustic pressure in the raised amplitude parts. The pressure oscillations refer to the unsteady flow in side channel pumps.     

Druckschwingungsverteilung im Seitenkanal von Verdichtern

Distribution of the pressure oszillations in the side channel of compressors The investigation of the unsteady pressure field in side channel machines with high pressure coefficients of ψ_n = 3,5 to 34 gives a better understanding of the unsteady turbulent vorticity flow in the impeller and the side channel and also of the energy transfer. The impeller with high number of blades generates a turbulent vorticity flow, which exists over the entire side channel. The specific momentum causes pressure oscillations of p(t) = 250 Pa to 9,0 kPa also in the entire side channel which lead to an increase of the static pressure in the circumference of the side channel. The oscillation of the pressure is exited by the blade passage frequency and the frequency of the turbulent vorticity flow, with the lower frequencies having priority to the energy transfer. It also leads to dissipation losses limiting the efficiency and causing a heat up of the gas.     

侧壁式压水室离心泵小流量非稳态旋转失速特性

用数值计算方法研究具有特殊结构的侧壁式压水室离心泵,分析小流量工况时模型泵的非稳态旋转失速特性,用快速傅里叶变换(FFT)获得压力脉动信号的频谱特征。结果表明,小流量工况时模型泵的扬程曲线呈驼峰状,压水室不同位置处压力分布不均;受叶轮旋转产生的非稳态作用影响,叶轮不同叶片流道内流动结构差异较大。不同流量下,叶轮内部分离涡结构诱发的激励频率各异,0.4ФN工况时模型泵压力脉动频谱图出现0.5fR及高次谐波频率,压力脉动最大幅值出现于4fR频率处;0.2ФN流量时非定常流动结构会诱发0.18fR及高次谐波频率;0.05ФN流量时压力脉动频谱图同时出现0.1fR、0.28fR两种激励频率。旋转失速现象出现时,频谱图中叶频处压力脉动幅值不再起主导作用。     

Modelling of the non-reactive deposits impact on centrifugal compressor aerothermo dynamic performance

The centrifugal compressor blockage is considered an important issue in compressor operation and one of the main causes of machine failure. This is normally initiated by the presence of deposits with the process gas yielding to reduce the effective flow area, increase the frictional losses and distort the pressure distribution profile. The influences of flow blockage cover the thermodynamic, aerodynamic and rotordynamic performance parameters of centrifugal compressor as will be investigated further in this study. Accordingly, this paper introduces a novel approach to model the impact of non-reactive deposits flow on the centrifugal compressor aerothermodynamics performance. The developed set of empirical equations in this study provides a new way to derive the equivalent compressor performance map at various degrees of fouling with a consideration of gas properties and stage efficiency variation and without a prior knowledge of the detailed geometrical features. In order to emphasize the validity of the new method, it has been tested with two operating cases and the obtained results were compared with the internal inspection findings from the stage overhauling process. Besides, this approach has been proven to be valid for the modelling of flow blockage effect at the suction side, compressor internals and downstream equipment. Furthermore, a new methodology has been established to assess the possibility of deposits accumulation in the gas path of the compression system based on the operational data of the discharge parameters.     

Isotropie der turbulenten Wirbelströmung in Seitenkanalverdichtern

The impeller with a high number of blades causes a turbulent vorticity flow in the side channel, which is the reason for the specific impuls flow and the energy transfer in the side channel. High frequency pressure oscillations were caused according to the changes of the vorticity structure in the side channel. The dissipation loses are the reason for the heat up of the gas during the compression. According to the transported gas mass flow the turbulent vorticity flow is superposed from the average flow velocity of the gas. They depend from the peripheral speed of the impeller and the size of the compressor. The superposition of the turbulent vorticity flow and the average flow velocity cause the question of the isotrope of the turbulent vorticity flow in the side channel for the working area of the compressor. Experimental results from side channel compressors will give an answer to this.     

Geschwindigkeit der Expansionsströmung am Unterbrecheraustritt von Seitenkanalverdichtern

The expansion flow of this breaker mass flow of side channel compressors decisively influences the intake flow of the gas mass flow in the side channel and so affects the energy transfer and the increase of pressure in the front area of the side channel. This causes a decrease of pressure and losses in this area. By taking measurements of the dynamic pressure fluctuations in the side channel it could be shown that in this area of the side channel the greatest pressure oscillations and with that the highest root main square of the dynamic pressure oscillation occure which finally lead to vortex formation with great losses of pressure. For this reason a decrease of pressure in the inlet area of the side channel is caused which leads to reduction of the increase of pressure. Suggestions for the improvement of the contour of the inlet of the side channel with less decrease of pressure and density are made.     

Gasdruckschwingungsverteilung im Arbeitskanal von Seitenkanalverdichtern

The magnitude of energy transfer in side channel compressors depends on intenseness of gas pressure oscillation and transport of specific momentum in the side channel. For analysis of energy transfer from impeller to gas, the static pressure distribution and the intenseness of gas pressure oscillation in meridian profile of the side channel subject to radius and also to axial distance to impellers grid was measured with a high tightness of reading points. In order to plot the intenseness of gas pressure oscillation in meridian profile of the side channel, gas pressure oscillation in side channel has been characterized by RMS, peak value and amplitude value of gas pressure oscillation at blade rotation frequency. The results of gas pressure oscillation and tangential velocity progression in side channel from laser measurement show that the strongest gas pressure oscillations and highest velocities appear in outer region of the impeller and side channel, which refer to intense energy transfer in this region.     

Grenzbereiche von Seitenkanalverdichtern im Vakuumbetrieb

The kinematic viscosity of the gas rapidely rises with decreasing suction pressure in the vacuum region, which leads to a decrease of the reynolds number of the flow in the side channel and to a laminar flow structure which may cause a modification of the side-channel-compressor behavior during the energy transfer. By the reduced density of the gas in the vacuum region of the side channel compressor the mass flow and the transfered specific enthalpy are decreased with constant volume flow. Through that, the specific growth of enthalpy during the compression and during the expansion of the mass flow in the breaker decreases. This leads to a decrease in the growth of the temperature during the compression at the same pressure ratio and the thermal load of the compressor is reduced. The polytropic change of state of the gas during the compression approaches an adiabatic change of state for decreasing suction pressure in the vacuum region. The polytropic change of state of the expansion flow in the breaker approaches the theoretical expected isothermal change of state for decreasing suction pressure, whereby side channel compressors are relieved of thermal load and higher pressure ratios are within reach. So the breaker of the side channel compressor, which causes in pressure operation mode high specific dissipation losses and leads to high polytropic exponents effects in the higher vacuum region thermodynamic advantages of the pressure region.     

Druckverlauf und Gasdruckschwingung im Schaufelkanal von Seitenkanalverdichtern

The pressure in the impeller, in the side channel and in the breaker of a side channel compressor with the polytropic compression and with the polytropic expansion of the breaker mass flow was investigated experimentally, and the occurring shock waves were detected during the expansion of the gas in the breaker. Thereby different pressure flows occur at the four measuring points in blade channel on the blade pressure and suction side of the related radius from r _i /r ₂=0.80 and r _i /r ₂=0.95, which give an indication of the blade channel flow. In addition to the periodic increase in pressure and the gas expansion in the breaker, the superimposed pressure oscillation in the side channel is caused by the blade rotation frequency. This superimposed pressure oscillation can be decomposed by Fourier transformation in the two pressure oscillation components. These phenomena are the reason for the more accurate investigation of the pressure flow in the blade channel during the polytropic compression and expansion of the breaker mass flow. The gradient of the effective values of the gas pressure oscillation in the blade channel leads not only to the operating characteristics of the side channel compressor ??p=f(?,n), but also to the breaker curve characteristic ??p _U =f(?,n).     

Überschallströmung und instationäre Verdichtungsstöße in Seitenkanalverdichtern

For some years it is known that the admission flow into the side of side channel compressors sensitive and thereby disrupt the work of transferring gas to the impeller only to the scope angle of Δα _K =95° begins. The delay of the work transferred to the breaker could exit through the stationary pressure measurement in the side channel in 1999 identified and confirmed repeatedly. The reason, however, could not be found so far. Only the unsteady pressure measurement in the rotating impeller and a strong temporal resolution of the pressure in the breaker and behind the breaker showed unsteady compression shocks immediately after the interrupter input and output. The following contribution shows the experimental results of pressure measurement in rotating impeller. The results were measured by a telemetry system with transmitters and receiving antenna from the rotating impeller in the high-resolution measurement has been transferred. This allowed the foundations for a further optimization of the side channel and transmission of the work to be.     

轴流压气机旋转失速和喘振的非线性反馈控制

旋转失速和喘振是轴流压气机中的两种主要的不稳定工作形式,限制了压气机稳定工作范围。本文中提出了一种新的对旋转失速和喘振的非线性反馈控制策略,即把压升作为反馈信号,来补偿节流阀系数值。研究结果表明,这种控制策略很简单,但是能够消除失速时伴随的迟回效应;也能够增加压气机的喘振裕度。     

Anteil des Schalldruckes an den Gasdruckschwingungen in Seitenkanalverdichtern

Machines and plants operating within the vicinity of people need to be subjected to noise investigation and reduction. This includes the fans, pumps and the compressors. It is known that only a small part of the pneumatic oscillations, which result from turbulence, current exchange or by strong expansion currents are emitted as effective sound pressure and released into the environment. Although there are several mathematical models on the origin and propagation of sound, the audible amount of turbulence and/or pressure oscillation has not been known until now. These ratio values can be determined by parallel measurements of the pneumatic oscillation in a machine and of the effective sound pressure on the acoustic sources in relation to the distance to the acoustic source and the operating parameters of the compressor. The following contribution determines these values for a side‐channel compressor.     

部分失速工况下轴流压气机转子受力特性的研究

首次将轴流压气机的受力特性与工况相结合,分析压气机转子的速度变化和受力特性。首先从理论角度阐述了轴流压气机的失速原理及过程,然后对压气机在正常运行工况和部分失速工况下的受力表达式进行理论推导,通过仿真得出轴流压气机在部分失速工况下的受力特性,最后将仿真结果与理论推导部分相对比。论文通过仿真验证了理论分析的可行性,并得出了失速工况下轴流压气机的速度变化与受力特性,为后续转子的振动分析以及转子的结构优化设计提供有益参考。     

Spezifische Energieverteilung im Kanal von Seitenkanalverdichtern

Distribution of energy in the channel of side channel compressors With dynamic pressure sensors, the total pressure and dynamic pressure share can be measured in any density of the side channel profile. The dynamic progression of gas pressure, which appears as gas pressure oscillation, can be characterized by peak value of gas pressure oscillation, RMS and amplitude value p_A of gas pressure oscillation at blade rotary frequency. Out of it, the regions of intense transport of specific momentum and intense energy transfer in side channel can be ascertained. Out of the distribution of velocity in side channel profil in association with the distribution of pressure, the distribution of specific energy in side channel can be ascertained as well.     

不同湍流模型下旋转叶片气固耦合动力学特性的研究

本文对轴流式压气机内旋转叶片在不同湍流模型的气固耦合作用下的动力特性进行了研究。利用FSI（fluid-structure interaction）的双向顺序耦合算法,采用CFX和ANSYS对压气机内气体和旋转叶片分别计算,并通过迭代求解,获得叶片在气流作用下的动力学响应。为了研究耦合场内对叶片动力特性的影响,本文对某一级转子叶片进行流固耦合计算,由于在模拟流场计算中,不同的湍流模型对计算结果影响较大,采用3种湍流模型：标准κ-ε湍流模型(standard κ-ε)、重正化群κ-ε湍流模型（renormalization group κ-ε,RNG κ-ε）和大涡湍流LES模型（Large eddy simulation）,获得了叶片在瞬态流场变化下的动力特性,并比较了不同湍流模型对计算的影响,为工程上对压气机内转子工作特性的分析提供一个可行的方法。     

Thermodynamic potential of using a counter rotating novel axial impeller to compress water vapor as refrigerant

This paper investigates the thermodynamic potential of using multi-stage variable speed counter rotating axial impellers as part of a water chiller system to compress water vapor (R718) as refrigerant. For this multi-stage compressor a modified cycle with an intercooling strategy is used between stages. Multi-stage compression with flash intercooling results in at least 30% improvement of coefficient of performance (COP) at full load compared to conventional refrigerants like R134a. Novel axial composite impellers, manufactured at extremely low cost, are proposed to take the compression role. To predict this counter rotating axial impeller’s thermodynamic capacity, a numeric CFD approach is taken in the study to generate steady state performance maps; based on the maps it is found that maximum pressure ratio of single counter rotating stage reaches 1.3 with isentropic efficiency around 70%. The aim of this study is to demonstrate that this counter rotating novel axial impeller has the potential to produce a high enough pressure ratio, and with a practical isentropic efficiency, in a multi-stage compressor to compress water vapor as refrigerant.