On the Correlation Between Span-Wise Inducer Incidence and Impeller Diffusion for Ruled Surface and Barreled Sweep-Bow Impeller Design at IGV-Off-Design

In the present paper, three centrifugal stages of high volume flow coefficient are compared to each-other regarding their aerodynamic performance in design point and off-design point conditions at different speed and IGV-setting angle: two stages with full-blade design (no splitter blades) have been numerically designed with different design geometry methodology. One geometry is based on a classical ruling surface design with a linear leading edge, the second geometry based on a fully-3d surface including a blade bow at the trailing edge and a barreled sweep at the leading edge. According to impeller test rig measurements and CFD-calculation, the classical ruling surface designed impeller outperforms the more sophisticated centrifugal stage with fully-3D-blade at fully axially guided IGV-flow. In the contrary, at closing IGV-off-design setting angles, towards surge operation, the fully-3D-blade-impeller performs with higher efficiency and steeper negative pressure slope. On the search of the geometrical causes for the different aerodynamic performance (especially at IGV-off-design conditions), focus is set on the analysis of IGV-flow-interaction with the inducer flow, and impeller diffusion. The one-dimensional -analysis of the span-wise flow at the impeller leading edge reveals that, compared with the ruling surface impeller, the fully 3D-blade performs with lower flow incidence losses in favor to IGV-off-design operation than at IGV-neutral position. The stream-wise flow analysis confirms the improved flow incidence characteristics of the 3D-blade impeller due to reduction of aerodynamic blockage and entropy production in the vicinity of the impeller leading edge. Based on CFD-calculations, a new correlation of secondary flow and flow incidence is proposed, to be used for one-dimensional modelling.

Modeling Results of Gas-Dynamic Characteristics of Low and Medium Flow Rate Model Stages for an Industrial Centrifugal Compressor

The paper presents the results of CFD calculations of two model stages with 2D impellers. The results were compared with the experimental characteristics obtained at the LPI Problem Laboratory. The centrifugal stage of the 2D impeller 0028-056-0373 was calculated for three different Mach numbers, with and without the gaps in the labyrinth seals. Calculations for the sector with one blade were performed using the NUMECA software, those for the full 360-degree model — in the ANSYS CFX software package. CFD calculations in all the cases gave an unacceptably high overestimation of the loading factor compared to the experimental data. It was established that the calculated characteristics of the stage efficiency leant towards high flow rates compared to the measured values. A stage of the 2D impeller 0048-048-029 was calculated for one Mach number without taking into account the gap in the labyrinth seals and for the full 360-degree model. A study of semi-empirical parameters and coefficients included in the SST turbulence model implemented in the ANSYS CFX software was carried out. The calculations showed that their choice for solving this class of problems had little effect on the calculation results, thus it was not possible to influence the loading factor.

Proteomic method to extract, concentrate, digest and enrich peptides from fossils with coloured (humic) substances for mass spectrometry analyses

Humic substances are breakdown products of decaying organic matter that co-extract with proteins from fossils. These substances are difficult to separate from proteins in solution and interfere with analyses of fossil proteomes. We introduce a method combining multiple recent advances in extraction protocols to both concentrate proteins from fossil specimens with high humic content and remove humics, producing clean samples easily analysed by mass spectrometry (MS). This method includes: (i) a non-demineralizing extraction buffer that eliminates protein loss during the demineralization step in routine methods; (ii) filter-aided sample preparation (FASP) of peptides, which concentrates and digests extracts in one filter, allowing the separation of large humics after digestion; (iii) centrifugal stage tipping, which further clarifies and concentrates samples in a uniform process performed simultaneously on multiple samples. We apply this method to a moa fossil (approx. 800–1000 years) dark with humic content, generating colourless samples and enabling the detection of more proteins with greater sequence coverage than previous MS analyses on this same specimen. This workflow allows analyses of low-abundance proteins in fossils containing humics and thus may widen the range of extinct organisms and regions of their proteomes we can explore with MS.

Assessment of Flow Control Strategies for Improving Centrifugal Compressor Efficiency

This paper describes a preliminary assessment of two flow control strategies for improving the adiabatic efficiency of centrifugal compressors for aero-engine applications. Given that the diffuser loss and pressure recovery play and important role in centrifugal stage efficiency, a centrifugal compressor with “fishtail” pipe diffusers is chosen for the study. This type of diffuser, which is among the most efficient diffusers, turns the flow directly from a high-swirl radial flow toward an axial flow, thus providing a smaller outer compressor diameter. As such, they are ideal for aero-propulsion applications. Past researches indicate that the diffuser performance is very much dependent on the impeller exit flow (diffuser inlet flow) uniformity. Two passive candidate flow control strategies that could improve impeller exit flow uniformity are proposed, namely slots casing treatment near the impeller radial bend and flow recirculation with injection in this area. They are aimed at attenuating the significant low-momentum region near the shroud that grows from the radial bend to the impeller exit. Iterations of the two proposed flow control strategies were evaluated through unsteady RANS CFD simulations on a low-speed centrifugal compressor stage with fishtail pipe diffusers. A comparison in terms of component and stage performance as well as an analysis of the flow field was carried out from the simulation results of the early iterations of the two flow control strategies. They show that both strategies have good potential for improving impeller exit flow uniformity and reducing losses in the fishtail pipe diffusers. However, the casing treatment strategy is more promising for improving stage efficiency due to lower penalty in impeller efficiency.

Optimization of Fuel Two-Stage Screw Centrifugal Pump of Rocket Powerful Turbopump Unit

The article describes a refining method for a fuel pump of rocket powerful turbo-pump unit by the joint usage of mathematical optimization software IOSO, meshing complex NUMECA and CFD complex ANSYS CFX. The optimization software was used for automatic change of the geometry of low-pressure impeller, transition duct and high-pressure impeller to find the optimal design. It was mandatory to keep the original variant of the remaining parts of the pump. For this reason, only geometrical parameters of the blades were varied without changing the contours of the pump meridional flow part. The investigated pump consists of five parts: inlet duct, low-pressure screw centrifugal stage, transition duct, high-pressure screw centrifugal stage and volute outlet duct. The pump main parameters with water as the working fluid (based on experiment data) were the following: high-pressure stage rotor speed was 13300 rpm; low-pressure rotor speed was 3617 rpm by gearbox; inlet total pressure was 0.4 MPa; outlet mass flow was 132.6 kg/s at the nominal mode. Creation of vane unit mesh (rotors and stator transition duct) was performed using NUMECA AutoGrid5. Sector models were used for the calculation simplification. The flow around only one blade or screw was considered. Setting up and solution of the task were carried out in the ANSYS CFX solver. Comparison of calculated characteristics of the basic pump with the experimental data was performed before the optimization. The analysis of characteristics for the obtained optimized pump geometry was carried out. It was found that pump with optimized geometry has greater efficiency in comparison with the original pump variant. The obtained reserve can be used to boost the rocket engine, and/or to reduce the loading of the main turbine, which operates in aggressive oxidizing environment.

Numerical Investigation of the Effect of Diffuser and Volute Design Parameters on the Performance of a Centrifugal Compressor Stage

In this effort, 3D CFD simulations are carried out for real gas flow in a refrigeration centrifugal compressor. Both commercial and the in-house CFD codes are used for steady and unsteady simulations, respectively. The impact on the compressor performance with various volute designs and diffuser modifications are investigated with steady simulations and the analysis is focused on both the diffuser and the volute loss, in addition to the flow distortion at impeller exit. The influence of the tongue, scroll diffusion ratio, diffuser length, and cross sectional area distribution is examined to determine the impact on size and performance. The comparisons of total pressure loss, static pressure recovery, through flow velocity, and the secondary flow patterns for different volute designs show that the performance of the centrifugal compressor depends upon how well the scroll portion of the volute collects the flow from the impeller and achieves the required pressure rise with minimum flow losses in the overall diffusion process. Finally, the best design is selected based on compressor stage pressure rise and peak efficiency improvement. An unsteady simulation of the full wheel compressor stage was carried out to further examine the interaction of impeller, diffuser and the volute. The unsteady flow interactions are shown to have a major impact on the performance of the centrifugal stage.

The Development of a Low Specific Speed Centrifugal Compressor Research Facility

To achieve aggressive specific fuel consumption goals, aircraft engines are tending toward higher overall pressure ratios and higher bypass ratios for turbofans. As sizes decrease to meet these requirements, centrifugal compressors become a viable option as the last stage of the high pressure compressor. The last stages of an axial compressor in a small core engine face reduced efficiency due to the relatively large tip clearances with respect to blade height, and therefore, it may be more appropriate to finish the final compression stage with a low specific speed centrifugal compressor. A new facility, the Centrifugal STage for Aerodynamics Research (CSTAR) Facility, has been developed at Purdue University in cooperation with Rolls-Royce to gain further understanding of the complex aerodynamics found in such centrifugal compressors. The experimental data acquired in this facility will be utilized to develop and validate design tools for centrifugal compressors used in axial-centrifugal high-pressure compressors. The facility models the last (centrifugal) stage of an axial-centrifugal compressor and operates at engine-representative Mach numbers. In this paper, the facility is described in detail, and the baseline steady-state performance of the compressor is presented.

CFD Wind Tunnel Tests of Centrifugal Stage Return Channel Vane Cascades

Stator part of a centrifugal compressor stage is a proper object of study by CFD calculations meaning better understanding of flow behavior, checking of field type design methods and possible improvements. Several stators with vane and vaneless diffusers for stages with different specific speed were designed by standard methodology and numerically analyzed. Results were verified. Calculation in a whole has demonstrated validity of existing recommendation. The specific velocity for stators is introduced which can be applied to match an impeller and a stator. Calculations demonstrated quick efficiency drop for stators with specific speed less than 0,215. Return channel vane cascades were studied in wide range of solidity with constant vane height and with constant radial component of velocity. Empirical formulae with non-dimensional circulation as an argument are proposed for loss coefficient, profile loss coefficient, optimal incidence angle and exit lag angle. Candidates of the low specific speed stator have demonstrated that an arbitrary channels’ wideness to diminish friction losses is not effective. Better flow organization is preferable. Modification of a crossover demonstrated positive results for high and low specific speed stators.