Performance Of Centrifugal Compressor Research Articles

Experimental Study on Effects of Adjustable Vaned Diffusers on Impeller Backside Cavity of Centrifugal Compressor in CAES

The impeller backside cavity (IBC) is a unique structure of centrifugal compressor in compressed air energy storage (CAES) systems, which affects the aerodynamic performance of centrifugal compressor, and the angle change of the downstream coupled adjustable vaned diffusers (AVDs) will affect the flow field inside the cavity and compressor performance. This paper relies on the closed test facility of the high-power intercooling compressor to measure static pressure and static temperature at different radii on the static wall of the IBC. The coupling relationship between the IBC and compressor under variable operating conditions is analyzed, and the influence of AVDs on the internal flow in IBC is studied. The results show that static pressure and static temperature rise along the direction of increasing radius, but static temperature drops near the coupling between the impeller outlet and the cavity inlet. Under AVDs’ design angle, static pressure and static temperature at each point, static pressure loss and static temperature loss in the direction of decreasing radius all increase as the flow decreases. Under variable AVDs’ angles, static pressure and static temperature will change differently, and respective loss will also be different.

Roles of recirculating bubble on the performance of centrifugal compressors

Research works over the years have identified a recirculating bubble locating at impeller shroud in centrifugal compressor operating under off-design conditions. However, its roles on compressor performance have been traditionally oversimplified. In this paper, the characteristics of the recirculating bubble and the full extent of its impact on compressor performance are analyzed through a well-validated three-dimensional numerical simulation. The simulation results show that the bubble is initiated within the impeller passage and stretches gradually in both streamwise and spanwise directions with decreasing flowrates. During this process, it continues to reshape the effective area and flow conditions at the impeller inlet through its effects of blockage, preheating, and preswirl. The evolution of the recirculating bubble can be divided into two phases depending on whether the center of the recirculating bubble passes beyond the impeller inlet. In the initial phase, the blockage rapidly increases and helps to alleviate the impeller incidence and the relevant losses of the active flow. Meanwhile, the negative effects of preheating and preswirl remain relatively low. In the secondary phase, the upstream propagation of the recirculating bubble speeds up and reinforces its negative effects of preheating and preswirl. The fact that the positive and negative effects are not synchronous implies different roles that the bubble plays in the two phases. A model is established to characterize the effects of the recirculating bubble. A combination of the model and a single-zone meanline method is then employed to quantitatively assess the roles of the recirculating bubble by comparing the compressor performance with and without the bubble. The results show that in the initial phase, the recirculating bubble acted as a positive role in suppressing the incidence loss, the tip clearance loss, and the blade loading loss, leading to higher compressor efficiency. However, in the secondary phase, the negative effects overwhelmed the positive effects, which deteriorated the efficiency. The implications of the two-phase evolution of the recirculating bubble on centrifugal compressor design and flow control are also discussed.

CENTRIFUGAL COMPRESSOR PERFORMANCE MAPS TREATMENT FOR INTERNAL COMBUSTION ENGINES OPERATING CYCLE SIMULATION

Simulation of the supercharged internal combustion engines operation cycle is impossible without correct estimation of the supercharger operating parameters. Standard approach is to use specially prepared performance maps of compressor and turbine of the turbocharger, which are based on the experimental (or manufacturer’s) raw data. Centrifugal compressor performance maps interpolation, extrapolation and treatment provides challenging requirements as it is important to get correct simulation under such special conditions as compressor choke, rotating stall and pumping surge. At the same time it’s important to obtain the fast and stable calculations of the engine’s operating cycle. Blitz-PRO – online internal combustion engines operating cycle simulation service – offers supercharger performance maps preprocessing and implementation. It provides three different modes of compressor surge consideration during calculations: 1) full-scale surge mode using Moore-Greitzer approach; 2) mild surge mode with flexible adjustment; 3) “stable” mode, when the surge is neglected and the compressor constant-speed lines are extended from the rotating stall point to the lower mass flow region with the hyperbolic equation. Using the MAN 8G70ME-E engine 12140 kW, 82 rpm operating point as an example, the calculation results are compared for three modes of compressor surge consideration. The “stable” mode provides the fastest and the most stable calculations, while the calculations under the full-scale surge mode could generate the numerical (nonphysical) instability of calculations, which are caused by the high sensitivity of the two-stroke engines to the gas exchange processes as it is shown. The mild surge mode provides fast and stable enough calculation with the surge consideration ability, which could be assumed as the best solution for the given example. The researcher should choose between provided three modes of the centrifugal compressor surge consideration according to the calculations tasks, preferring “stable” mode for initial model setup and mild surge mode for the surge probability check, while the accurate compressor surge simulation needs further development.

Effects of number of inlet guide vanes on the aerodynamic performance of a centrifugal compressor

Variable inlet guide vanes (VIGVs) are widely used for flow throttling and also extending the operating range of centrifugal compressors. Although there are several studies on the effects of adding IGVs on the performance curve of the compressors, none of them have focused on the number of vanes. In the current study, high-fidelity three-dimensional numerical simulations are carried out to analyze the effects of adding VIGVs with different number of vanes on the aerodynamic performance of a single-stage centrifugal compressor. The selected compressor prototype is a high flowrate single-stage compressor equipped with a vaned diffuser, designed and fabricated by Siemens. Computational fluid dynamic simulations are performed for three different number of guide vanes at three IGV inclination angles of 0, −30 and +45 degrees. The numerical results are validated by comparing the pressure-rise curves with the available experimental data of the compressor data sheet, where a good agreement was achieved. Results show that at the fully-open condition, the number of vanes does not have considerable effect on the performance curve of the compressor. However, as the IGV inclination angle increases, the number of inlet vanes plays a considerable role in the compressor efficiency. For example, at IGV inclination angle of +45 degree, increasing the number of vanes from 7 to 11 can increase the compressor maximum efficiency up to 5 points. Numerical results showed that increasing the number of inlet guide vanes imposes a higher pressure drop in the inlet passage of the compressor while generating a more uniform velocity distribution at the suction surface of the impeller. Due to the existence of several counteracting effects, an optimum number of inlet guide vanes can be found.

Centrifugal Compressor Polytropic Performance—Improved Rapid Calculation Results—Cubic Polynomial Methods

This paper presents a new improved approach to calculation of polytropic performance of centrifugal compressors. This rapid solution technique is based upon a constant efficiency, temperature-entropy polytropic path represented by cubic polynomials. New thermodynamic path slope constraints have been developed that yield highly accurate results while requiring fewer computing resources and reducing computing elapsed time. Applying this thermodynamically sound cubic polynomial model would improve accuracy and shorten compressor performance test duration at a vendor’s shop. A broad range of example case results verify the accuracy and ease of use of the method. The example cases confirm the cubic polynomial methods result in lower calculation uncertainty than other methods.

Effects of Inlet Guide Vanes on the Performance and Stability of an Aeronautical Centrifugal Compressor

Abstract A research centrifugal compressor stage designed and built by Safran Helicopter Engines is tested at three inlet guide vanes (IGV) stagger angles. The compressor stage includes four blade rows: axial inlet guide vanes, a backswept splittered impeller, a splittered vaned radial diffuser (RD), and axial outlet guide vanes (OGVs). The methodology for calculating the performance is detailed, including the consideration of humidity in order to minimize errors related in particular to operating atmospheric conditions. The shift of the surge line toward lower mass flow rate as the IGV stagger angle increases highly depends on the rotation speed. The surge line shift is very small at low rotation speeds, whereas it significantly increases at high rotation speeds. A first-order stability analysis of the impeller and diffuser sub-components shows that the diffuser (resp. impeller) is the first unstable component at low (resp. high) rotation speeds. This situation is unaltered by increasing the IGV stagger angle. At low rotation speeds below a given mass flow rate, rotating instabilities (RI) at the impeller inlet are detected at zero IGV stagger angle. Their occurrence is conditioned by the relative flow angle at the tip of the leading edge of the impeller. As the IGV stagger angle increases, the mass flow decreases to maintain a given inlet flow angle. Therefore, the onset of the rotating instabilities is delayed toward lower mass flow rates. At high rotation speeds, the absolute flow angle at the diffuser inlet near surge decreases as the IGV stagger angle increases. As a result, the flow is highly alternate over two adjacent channels of the radial diffuser beyond the surge line at IGV stagger angle of 0 deg.

Integrated adjustable diffuser and its influence on centrifugal compressor performance

Integrated adjustable diffuser and its influence on centrifugal compressor performance

Multistage carbon dioxide compressor efficiency enhancement using waste heat powered absorption chillers

AbstractThe performance of a multistage centrifugal compressor is highly influenced by the ambient conditions, especially during the summer seasons; their capacity shrinks and thus the power requirement for compression will increase. The prime cause of these constraints is the interstage cooling limitations. This study simulates various suction conditions of a multistage compressor on Aspen HYSYS® and suggests its debottlenecking by making the suction temperatures comparable to winter seasons. This is achieved by installing an additional exchanger at the downstream of each interstage cooler, cooling down the gas further by using absorption refrigeration chillers. These chillers are powered up by the waste heat recovered from the exhaust steam coming from the prime mover, steam turbine, of the same compressor. This modification will save a considerable amount of power (663 kW), net savings (Gross Savings – OPEX: 72 289 $/y), and reduce the carbon footprint (954 ton/y) of the overall process.

Experimental Validation of the Aerodynamic Performance of an Innovative Counter-Rotating Centrifugal Compressor

Turbomachinery with double counter-rotating impellers offers more degrees of freedom in the choice of design and control parameters compared to conventional machines. For these innovative machines, the literature review shows that more publications concerning axial type turbomachines are available than centrifugal ones. This work deals with a design and experimental performance analysis, applied to two counter-rotating impellers of a centrifugal compressor “CRCC”. CRCC was designed with a specifically developed tool based on mean-line approach coupled with optimization algorithms and a stream-curvature through-flow method to satisfy the design criteria. This paper presents an experimental validation of the CRCC design tool and its performances against the baseline “SR”, composed of one centrifugal impeller and a volute for which experimental data are available. CRCC numeric simulations are also validated by experimental data. For a fair comparison between CRCC and SR, the same volute is used for both configurations. The CRCC studied here includes a first conventional impeller with an axial inlet and a radial outlet, while the second impeller is parametrically designed and can be considered a rotating bladed diffuser with a radial inlet and outlet. The obtained results show that CRCC can deliver a pressure rise increase of two compared to SR, along with an increase of isentropic efficiency and also validate the design method of this novel layout. The experimental results also show that the speed ratio of CRCC has a positive effect on the surge and shock margin.

Centrifugal Compressor Stall Control by the Application of Engineered Surface Roughness on Diffuser Shroud Using Numerical Simulations.

Downsizing in engine size is pushing the automotive industry to operate compressors at low mass flow rate. However, the operation of turbocharger centrifugal compressor at low mass flow rate leads to fluid flow instabilities such as stall. To reduce flow instability, surface roughness is employed as a passive flow control method. This paper evaluates the effect of surface roughness on a turbocharger centrifugal compressor performance. A realistic validation of SRV2-O compressor stage designed and developed by German Aerospace Center (DLR) is achieved from comparison with the experimental data. In the first part, numerical simulations have been performed from stall to choke to study the overall performance variation at design conditions: 2.55 kg/s mass flow rate and rotational speed of 50,000 rpm. In second part, surface roughness of magnitude range 0–200 μm has been applied on the diffuser shroud to control flow instability. It was found that completely rough regime showed effective quantitative results in controlling stall phenomena, which results in increases of operating range from 16% to 18% and stall margin from 5.62% to 7.98%. Surface roughness as a passive flow control method to reduce flow instability in the diffuser section is the novelty of this research. Keeping in view the effects of surface roughness, it will help the turbocharger manufacturers to reduce the flow instabilities in the compressor with ease and improve the overall performance.

Analytical prediction of Reynolds-number effects on miniaturized centrifugal compressors under off-design conditions

The use of micro-scale centrifugal compressors in closed-loop thermodynamic cycles working with fluids different than air is gaining in importance in novel miniaturized energy systems. Miniaturization implies a decrease in the Reynolds number, which usually entails efficiency drops. The aim of this paper is to study the low-Reynolds-number effects on the performance of micro-scale centrifugal compressors under off-design conditions. Consequently, an analytical prediction method is formulated to characterize the efficiency variations using different working fluids and pressurization factors. A numerical model of a reference micro-scale compressor is developed to assess the degree of agreement between the results obtained by these two methods. The results show the Reynolds-number effects on the whole characteristic map of the reference compressor for air, carbon dioxide, propane and isobutane. These fluids were chosen according to their efficiency increase potential, which is measured by a proposed Reynolds-number-based estimator. Although some divergences have been identified, the agreement between analytical and numerical results can be considered to be globally satisfactory. Efficiency increases in the range of 2–6% points are obtained with slight pressurization factors using air or carbon dioxide. These variations could even achieve a rise of 9 pp in the case of propane and isobutane.

Effects of vaneless region length on the performance of centrifugal compressor with vaned diffuser

Effects of vaneless region length on the performance of a centrifugal compressor with vaned diffuser are studied in this paper. The vaneless region is defined as the space between the impeller outlet and the vaned diffuser inlet. In this work, the studied ratio between the diffuser inlet and impeller outlet is from 1.06 to 1.20. The simulation results show that the variation in the vaneless region has a great impact on the performance of the compressor stage. It is found that the proper extension of vaneless region improves the performance of compressor stage by significantly reducing the separation near shroud and uniformly disturbing flow velocity at impeller outlet and diffuser inlet. Sufficient extension of the vaneless region is necessary to produce beneficial effects, while the excessive extension will instead deteriorate the compressor performance. The mechanism of performance improvement is that reasonable vaneless space length is able to constrain the flow separation and to make the flow more uniform in the diffuser.

Computational Analysis on the Performance of Centrifugal Compressor with Tapered Wall and Rotating Tapered Wall Vaneless Diffuser

Computational Analysis on the Performance of Centrifugal Compressor with Tapered Wall and Rotating Tapered Wall Vaneless Diffuser

Experimental and numerical investigation on the influence of the diffuser blade setting angle on the performance of centrifugal compressor

Setting angle of the front blade row of tandem cascade diffuser was investigated experimentally to understand its influence on the performance of centrifugal compressor. Three diffusers with different setting angles were tested. The change of front blade setting angle mainly alters. The angle of attack (AOA) on the leading edge of front blades, which affects the surge point of the compressor. The throat area of the blade row is also modified, which affect the chock point of the compressor. With the increase of setting angle, performance curves of centrifugal compressor move to large flow rate side, the operation range is increased at the same time. In addition, numerical simulation was used to investigate the flow details on the passage of diffuser blades. Overall, the setting angle of front blade row has a significant influence of the performance of centrifugal compressor.

Effects of hydrogen blending on hydraulic and thermal characteristics of natural gas pipeline and pipe network

Blending a fraction of hydrogen into the natural gas pipeline or urban pipe network is an efficient approach for hydrogen delivery. In this paper, the mathematical model of Hydrogen-Blended Natural Gas (HBNG) transportation is established, and the influences of hydrogen blending on hydraulic and thermal characteristics of natural gas pipeline and pipe network are numerically investigated. The impact of hydrogen blending ratio on the performance of centrifugal compressor and the operating point for joint operation of pipeline and compressor is discussed. Results illustrate that compared with natural gas without hydrogen, the hydrogen blending can reduce the pipeline friction resistance and increase the volume flow rate. However, due to the lower volumetric calorific value of HBNG, the energy flow rate actually decreases under the same transportation condition. Meanwhile, the temperature drop along the pipeline slows down due to the blended hydrogen. The performance degradation of centrifugal compressor occurs with the increasing hydrogen blending ratio, and the operating point for joint operation of pipeline and centrifugal compressor moves to the direction of higher volume flow rate and lower pressure. This study is expected to shed a light on the hydrogen delivery by natural gas pipelines and pipe networks.

Numerical Investigation of a Centrifugal Compressor with a Pre-Compression Wedge Diffuser under High Subsonic Conditions

As the total pressure ratio of centrifugal compressors increases, the diffuser inlet flow becomes highly subsonic or even supersonic, which causes additional shock loss. The shock loss leads the stage performance to drop greatly. Pre-compression is an efficient method for reducing shock loss and improving the stage performance. To study the effect of wedge diffusers with pre-compression blades on centrifugal compressor performance, wedge diffusers with various pre-compression angles, divergence angles and numbers of blades were designed and investigated via a numerical method. As a result, it is found that the compressor stage achieves high peak efficiency when the pre-compression angle ranges from 2.5° to 5.5° and when the divergence angle ranges from 7° to 9°. As the number of blades increases, the total pressure ratio and adiabatic efficiency of the compressor stage increase slightly, whereas the surge margin of the stage decreases.

Novel Simplified Blade Hub Line Optimization of High-Pressure Ratio Centrifugal Compressor Design Using Numerical Simulations

The focus of this research is to numerically investigate the effect of blade hub line variation on the performance (Total pressure-ratio and Isentropic-Efficiency) of centrifugal compressor from stall to choke to study the operating range and stall margin. An optimization technique is carried out in which the meridional profile hub line is modified and compared with the high Mach number SRV2 compressor designed and fabricated by DLR (German Aerospace Center). Numerical simulations showed significant increase in the stall margin and operating range by bargaining on pressure ratio and isentropic efficiency. Reynolds Averaged Navier Stokes (RANS) based k-ε model is used to predict turbulence using numerical simulations. The value of Y plus for the structured mesh near the boundaries is kept 35. Blade hub line being the important parameter, has substantial performance improvement of centrifugal compressor. The novel design improved the stall margin by 44 percent while operating range from stall to choke has been upgraded by 7.5 percent.

Theoretical and experimental study on effects of humidity on centrifugal compressor performance

As one of the core components of CAES system, the compressor plays a crucial role in system performance. However, intake humidity can significantly change the performance of the compressor, so it is necessary to accurately evaluate the influence of humidity on the performance. In this paper, the influence of humidity on compressor performance and its mechanism were studied theoretically and experimentally, and an improved humidity correction model based on similarity criterion was proposed. The results showed that the increase of humidity decreases the total pressure ratio and peak isentropic efficiency, and shifts the performance curve towards smaller mass flow. The influence of humidity on compressor performance is essentially the impact of change of gas properties on performance, wherein the gas constant plays a dominant role. Converting the humid air to corresponding dry air by flow similarity, it is founded that the performance variation is mainly attributed to the decrease of rotational speed and increase of mass flow of corresponding dry air. This humidity correction model well agrees with the experimental results and could meet the requirement for assessing the effect of humidity on compressor performance.

Performance analysis of the water-injected centrifugal vapor compressor

In industrial production, mechanical vapor recompression (MVR) technology is becoming more widely used. The performance of MVR will be further enhanced, if it can be combined with the wet compression technology. However, the water-injected vapor compression is different from the wet air compression. In addition, the working environment of the centrifugal compressor is more complicated, which has tremendous potential in the MVR system. In this paper, the performance of the water-injected centrifugal vapor compressor was analyzed by adopting numerical simulation and experimental methods. Since the injected water is atomized before entering the compressor, this study mainly analyses the impact of atomization uniformity on the water-injected compression and proposes a method to improve atomization uniformity only by changing the parameter of the system. The results showed that excessive diameter of droplets after atomization affects the stable operation of the compressor and enhancing the atomization uniformity can greatly reduce the outlet temperature of the compressor. Moreover, increasing the water-injection mass flow rate not only reduce the outlet temperature but also improve atomization uniformity and compression performance, but the excessive water-injection mass flow rate may cause the compressor to surge.

Effect of Vaneless Diffuser Shape on Performance of Centrifugal Compressor

The influence of four different vaneless diffuser shapes on the performance of centrifugal compressors is numerically studied in this paper. One of the studied shapes was a parallel wall diffuser. Two others had the width reduced only from hub and shroud and the rest had the width reduced from hub and shroud divided evenly. Then the numerical simulation was employed and the overall compressor aerodynamic performance was studied. The detailed velocity and pressure distribution and energy loss within the centrifugal compressor with different diffuser geometries and different operating conditions were analyzed. The results revealed that shroud pinch significantly improved the overall compressor aerodynamic performance more than any other pinch types, and the best performance can be achieved by pinched diffusers under the design condition compared with pinched diffusers under the near surge condition or choking condition. The range of energy loss, namely the static entropy area in the compressor, become reduced with the above three pinches diffusers.