Our principle goal of this study is to develop a CFD based analysis procedure that could be used to analyze the geometric tradeoffs in scroll geometry when space is limited. In the study, a full centrifugal compressor stage at four different operating points from near surge to near choke is analyzed using Computational Fluid Dynamics (CFD) and laboratory measurement. The study concentrates on scroll performance and its interaction with a vaneless diffuser and impeller. The numerical results show good agreement with test data in scroll circumferential pressure distribution at different ΛAR, total pressure loss coefficient, and pressure distortion at the tongue. The CFD analysis also predicts a reasonable choke point of the stage. The numerical results provide overall flow field in the scroll and diffuser at different operating points. From examining the flow fields, one can have a much better understanding of rather complicated flow behavior such as jet-wake mixing, and choke. One can examine total pressure loss in detail to provide crucial direction for scroll design improvement in areas such as volute tongue, volute cross-section geometry and exit conical diffuser.

The objective of this work was to perform numerical analysis of the flow inside a modified single stage CVHF 1280 Trane centrifugal compressor’s vaneless diffuser and volute. Gambit was utilized to read the casing geometry and generating the vaneless diffuser. An unstructured mesh was generated for the path from vaneless diffuser inlet to conic diffuser outlet. At the same time a meanline analysis was performed corresponding to speeds and mass flow rates of the experimental data in order to obtain the absolute velocity and flow angle leaving the impeller for those operating conditions. These values and experimental data were used as inlet and outlet boundary conditions for the simulations. Simulations were performed in Fluent 5.0 for three speeds of 2000, 3000 and 3497 RPM and mass flow rates of minimum, medium and maximum. Results are in good agreement with the experimental ones and present the flow structures inside the vaneless diffuser and volute.

The objective of this work was to establish an advanced testing facility for studying the flow structure and loss mechanism in a single stage centrifugal compressor. A Trane’s CVHF 1280, two stage centrifugal compressor was modified to a single stage for laboratory environment. This modification included new fluid medium, driving motor, inlet and outlet designs. In this study, experiments were performed in order to evaluate the performance of the vaneless diffuser and volute. However, the modifications enable the flow structure investigation in all components of the compressor as well. In addition the testing facility would accommodate installation of the rest of the unit for investigation of the flow in the vaned diffuser and return channel of the two-stage compressor in the laboratory environment. Experiments were performed in three speeds and eight mass flow rates per speed. Static and total pressures were measured at the inlet and outlet of the stage. Static pressure distributions were mapped on the vaneless diffuser and volute casings. These data evaluates the characteristics of these components after the modifications.

A two-dimensional, two-phase and multi-component flow and transport model has been developed to simulate the flow and transport phenomena in the cathodes of PEM fuel cells. First, the governing equations based on a “two-phase mixture model” are derived by using a unified approach that describes the flow and transport in the gas channel and gas diffuser simultaneously. Then, the detailed boundary conditions are discussed especially at the gas diffuser/catalyst layer interface, which couples the flow, transport, potential and current density in the anode, the catalyst layer and membrane. Next, the model is validated by comparing the modeling results with experimental data. Further, typical distributions of oxygen and water-mass fraction in the “two-phase mixture,” as well as water vapor mass fraction, liquid saturation and liquid velocity vector are presented. Finally, the model is used to study the influences of two of the most critical issues of PEM fuel cell operation: i.e., the water and the thermal management on the two-phase flow. It was found that the two-phase flow characteristics in the cathode depend on some of the following factors: current density, operating temperature, and cathode and anode humidification temperatures. The dependence of the formation and the distribution of the two-phase flow in the gas diffuser and gas channel on these factors is explored. By studying the effects of these parameters on the two-phase flow and the fuel cell performance, the model can be used to study a water and thermal management scheme.

This paper presents the results of a series of numerical simulations exploring the stability of fluid flow in vaneless diffusers of centrifugal compressors. Three-dimensional, time-dependent, Reynolds-averaged Navier-Stokes simulations were performed for a fixed diffuser width ratio. Effective flow angle was varied from simulation to simulation in order to predict the threshold angle at which the instability — rotating stall — is manifested and maintained. The predicted threshold angle or stability limit is in excellent agreement with experimental data. The simulations reveal a two-stall cell configuration at the threshold condition.

The PIV (Particle Image Velocimetry) technology is a brand-new technique of measuring velocity. It started in the 1980’s with the development of high-speed photography and the image processing technique of computers. This article deals with PIV applied to the study of unsteady impeller-vaneless diffuser interaction in centrifugal fen. Experiments were carried out at The Turbomachinery Laboratory of Shanghai Jiaotong University. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A series of performance measurements were carried out at different speeds and different vaneless diffuser widths. PIV measurements were applied to measure the unsteady flow at the exit part of the impeller and the inlet part of the diffuser for the case of the same width vaneless diffuser. The absolute flow field is measured at medium flow rate and at maximum flow rate. It is informative to capture the whole flow field at the same instant of time, and it might be more revealing to observe the unstable flow in real time.

The real flow inside a turbomachinery passage is unsteady and strongly affected by wakes between stator and rotor. The aim of this study was to help our understanding of the complex unsteady flow associated with the interaction between the impeller and its vaned diffuser of a centrifugal plexiglass fan where the number of impeller and diffuser blades are 13 for each. The purpose of this paper is to present the first trial of measuring the instantaneous whole field in a part of the impeller and diffuser together at different relative locations between them. The velocity measurements utilizing a PIV system from Dantec Measurement Technology were performed. The measurements were performed at medium, maximum and minimum flow rate, near the hub, the middle and near the shroud. The Laser sheet is adjusted to go through the outer casing, the diffuser and to reach the impeller blades. The instantaneous whole field velocity measurements were taken at the exit half of the impeller and the inlet half of the diffuser including the vaneless space before the diffuser blades. The absolute radial and circumferential velocities are measured. The unsteady interaction between the impeller and vaned diffuser was measured at different relative positions between the impeller and diffuser. Further analyses concerning the relative velocity, streamlines and vorticity are also presented.

The performance of a centrifugal compressor can be seriously affected by inlet flow distortions due to the unsatisfactory nature of the inlet configuration and the resulting inlet flow structure. In the previous work, experimental tests were carried out for the comparison of a centrifugal compressor stage performance with two different inlet configurations: one of which was a straight pipe with constant cross-sectional area as an ideal model and the other is a 90-degree curved pipe with nozzle shape as an actual model. The comparative test results indicated significant compressor stage performance difference between the two different inlet configurations. In addition, the numerical simulation part of the previous work clearly showed that the inlet flow distortion is caused by the pressure driven secondary flow developed in the curved section in the case of the bend inlet, resulting in locally concentrated incidence at the impeller inlet and thus the compressor stage performance degradation. An improved inlet model with the design method has been proposed based on the comparisons of the designated flow properties. In the present work, further numerical simulations on the compressor stage including the impeller and the diffuser with three different inlets are carried out to investigate the performance behavior of the compressor exposed to different inlet configurations. The three different inlet systems include the original bend inlet as well as the proposed inlet model based on the developed design method. Since the flow from the bend inlet is not axisymmetric due to the circumferential and radial distortion on the cross-section, the impeller and the diffuser are modeled with fully 360-degree passages, which accommodates the inlet flow distortion and the impeller-diffuser interaction influence on the entire flow passage of the compressor. The stage performance with the different inlet systems are evaluated and compared with the previous experimental result. The diffuser performance and the flow properties in the vaneless region are compared among those inlet models. The proposed inlet system indicated the benefit of performance improvement over the original inlet system.

The use of fully unsteady CFD computations for centrifugal turbomachinery during preliminary design calculations is still infeasible due to the extensive computational efforts required. Most design-based CFD analyses for centrifugal machines are conducted on individual components using steady-state calculations. These steady calculations do not represent the interactions of the components with their neighboring blade rows, including the upstream rotating component. In this paper, commonly accepted CFD procedures for steady-state calculations are applied to the components of a centrifugal pump with a shrouded impeller and a vaned diffuser/volute. Evaluation of the validity of these calculations is conducted by comparing the predicted flow field with detailed measurements at the interface between the rotating impeller and the stationary diffuser and volute.

Simulations for turbomachinery applications in various flow regimes are presented using a multi-element unstructured CFD code CRUNCH. The unstructured framework permits the generation of a contiguous grid without internal boundaries between different components of a turbomachinery system, and provides good local resolution in regions where the flow physics becomes important. The increased numerical stability resulting from these factors coupled with the parallel solution framework yields an efficient solution procedure for complex turbomachinery flows. Numerical results are presented for a transonic diffuser-volute configuration and rotor stator interaction.

This paper presents the design and fabrication of a micropump for cerebrospinal fluid shunt. The micropump is to be implanted in hydrocephalus patients, The micropump consist of a corrugated parylene diaphragm and a set of nozzle and diffuser. The electromagnetic force drives the diaphragm. The static or dynamic characteristics of the fabricated devices have been obtained experimentally. The size of the micropump is 14 × 12 × 8mm 3 . The increased flow rate of the micropump is about 50 μl/min at operational range.

A gas or vapor compressor is one of the key components of many engineering systems, such as certain designs of vapor compression refrigeration systems, cryo-coolers, air handlers. For meso-scale systems with linear dimensions of a few centimeters, conventional designs do not work efficiently because of rather large relative tolerances, and hence these meso-scale systems require micro-fabricated components for efficient operation. This paper presents a meso-scale centrifugal compressor fabricated by photo-lithographic techniques. A preliminary design based on 1-D flow analysis using air as the working fluid shows that a 50 mm diameter centrifugal compressor with a blade height of 200 μm gives a static pressure ratio of 1.12. In this design, the impeller has 10 full blades and 10 splitter blades. Each blade has the NACA profile 9510 with the maximum camber at 50% of the chord. These impeller blades have exit angles 35° with exit flow angles of 60°. A vaned diffuser having 20 equally spaced vanes with the same NACA profile is used to improve compressor efficiency. A 3-D compressible, viscous flow analysis has been done using a commercial finite volume software. The results of this analysis allowed the verification of the flow characteristics inside the meso-scale centrifugal compressor. The compressor has been fabricated using micro-fabrication techniques. The rotor and the stator are made by etching a silicon wafer by using DRIE (Deep Reactive Ion Etching) technique. A Pyrex wafer is then bonded to the stator for visual access inside the compressor.

The high-energy boiler feedwater pump is the heart of the steam-generation cycle in modern high-pressure boiler systems. These multi-stage centrifugal pumps are engineered to produce system pressures from 12 MPa (1800 lb/in 2 ) to 45 MPa (6500 lb/in 2 ) at temperatures ranging from 150°C (300°F) to 312°C (600°F). To optimize pump hydraulic performance, pump designers have focused on impeller and diffuser vane angles, hydraulic passageway shapes and minimized impeller-to-diffuser vane clearances to maximize performance within a narrow range of operation. This was the approach that had been applied successfully on lower energy pump design of an earlier era. However, in the mid-1980s, in response to market forces, operators began to cycle and operate plants over a wide range of loads, which was contrary to the original plant designs. This new operating paradigm has resulted in unacceptable vibration and acoustic emissions that are often attributable to impeller-to-diffuser vane interaction (a result of the minimized clearances referenced previously). Efforts to reduce these emissions by changing the design must always be balanced with the potential impact on hydraulic performance. This paper uses operating field data taken from boiler feedwater pumps to prove that by: • optimizing hydraulic passageways and • changing the internal geometry, specifically, impeller-to-diffuser vane combinations, vibration and acoustic emissions are reduced without compromising hydraulic performance.

An extensive investigation surrounding a performance shortfall of a pipeline compressor is presented. Regions of high aerodynamic loss are identified from an extensive flange-to-flange numerical investigation. Special attention is placed on understanding the impact of the interface model between the rotating and stationary components on the performance of each individual component and the whole machine. This process lead to the redesign of the radial inlet, the diffuser region, and the volute. Upon numerical validation of the proposed design changes, the components were manufactured and installed into the compressor that was already operating in the field. “Field” testing showed the new design to have a peak efficiency improvement of 4 points surpassing the contract guarantee.

Test versus CFD predictions are presented for a medium flow coefficient, centrifugal compressor stage with 10% shorter axial stage space. Short axial length is achieved by reducing the shroud radius of curvature of the upstream return channel inlet. Situations often occur in multistage compressor applications where either rotor dynamics on new equipment or existing casing length on revamped units necessitate shorter stage space. The effect of the reduced space on various stage performance parameters is discussed referenced to the original, full length, stage design. CFD analysis for both configurations is also presented to compare with the test results and help explain the aerodynamic source of the increased losses. The complete stage is modeled on the program CFX-TASCflow beginning with a radial inlet and continuing through the impeller, diffuser and return channel.

Interaction of rotating blades with stationary vanes is a prime consideration for disk design and vibration failure investigations. For a well-designed radial-flow impeller with a cover, the structure is inherently resistant to alternating forces at normal flow conditions. Critical parameters are reviewed with respect to excitation and response. A fundamental parametric equation originally published in 1979 is further explained and verified. Comparisons to open impellers and axial compressor blades that have additional critical design considerations are also presented. Data from strain gages on an impeller gave proof that liquid ingestion was the cause of high excitation, and validated the parametric equation for blade/vane interaction. Particular emphasis is given to avoiding high cycle fatigue failures with stages employing vaned diffusers, which are now much more prevalent. Modal analyses, as well as information from other references that confirms theories are included.

Impeller scallops are intentional cuts in the hub and shroud surfaces at the exit of centrifugal impellers that are intended to prevent high cycle fatigue in these areas. The goal of this analysis is to determine what effect the scallops have on aerodynamic performance, rotordynamic stability, rotating stall criteria, axial thrust, and mechanical shaft power. Furthermore, this study improves the understanding of the interaction with the secondary passage and determines the effect on the flow field entering the diffuser. A 3D viscous CFD model is generated of a single blade passage that couples the primary flow passage with the secondary shroud passage. This approach captures the complex interaction that occurs at the impeller exit due to the presence of the scallops. The predictions show a small penalty in thermodynamic efficiency with the presence of the scallops compared to a baseline case. The results also show a moderate increase in shaft horsepower calculated by integrating static pressure and shear stress acting on the impeller and shroud surfaces. Circumferential swirl in the shroud passage shows only modest increases with the addition of the scallops. Therefore, rotordynamic performance is not significantly affected nor is axial thrust acting on the impeller. The predictions demonstrate the effect the scallops have on the flow field entering the diffuser including variations in flow angle at the impeller exit.

A numerical simulation is performed on a single stage centrifugal compressor using the commercially available CFD software, CFX-TASCflow. The steady flow is obtained by circumferentially averaging the exit fluxes of the impeller. Three runs are made at design condition and off-design conditions. The predicted performance is in agreement with experimental data. The flow details inside the stationary components are investigated, resulting in a flow model describing the volute/diffuser interaction at design and off-design conditions. The recirculation and twin vortex structure are found to explain the volute loss increase at lower and higher mass flows, respectively.

This paper reports on the design procedure to produce radial compressors for high speed applications. These compressors are directly connected to a high speed electric motor. Speed control is used instead of IGV and diffuser vane control, and this sets some additional requirements e.g. for the shape of the compressor performance map. It is required that at the design pressure ratio the compressor has a wide operating range in mass flow, when optimal speed control is used. It is also required that the high efficiency range of the compressor is as wide as possible. One-dimensional computation giving the basic geometry and performance map of the compressor is done with a non-commercial program. Then a geometry generation 3D program is used to define the whole compressor wheel geometry. The wheel geometry data is used in the flow and structure analyses. The compressor flow is calculated with a three-dimensional CFD-program, which has specially been modified for centrifugal compressor flow. Particularly in the optimization process of the volute, also time-dependent computation of the complete compressor using the sliding mesh technique is used. The performance of the final compressor geometry is measured in the University test facility and the test results are used to develop the design process. Up to this date, 15 different high speed compressors have been aerodynamically designed and tested in this design loop. The typical pressure ratio of the compressors ranges from 1.6 to 2.5.

Simulations for a vaneless diffuser-volute configuration at transonic flow conditions are presented using a multi-element unstructured CFD code CRUNCH. The unstructured framework permits the generation of a contiguous grid without internal boundaries between the diffuser-volute interface, and also provides good local resolution around the cut-water region. The increased numerical stability resulting from these factors coupled with the parallel solution framework yields an efficient solution procedure. Numerical results indicate good comparison with experimental data for the baseline geometry where the measured performance was below the design prediction.