Статті в журналах: "Vaneless diffusers"

1

Калінкевич, Микола Васильович, та Микола Іванович Радченко. "ЗБІЛЬШЕННЯ ДІАПАЗОНУ СТІЙКОЇ РОБОТИ СТУПЕНЯ ВІДЦЕНТРОВОГО КОМПРЕСОРА З БЕЗЛОПАТКОВИМ ДИФУЗОРОМ". Aerospace technic and technology, № 6 (24 грудня 2019): 4–9. http://dx.doi.org/10.32620/aktt.2019.6.01.

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Centrifugal compressors often operate at different capacities, so it is important to ensure their stable operation over a wide flow range. Stages with vaneless diffusers have several advantages compared to stages with other types of diffusers: they are more technologically advanced to manufacture, and more uniform pressure distribution behind the impeller improves the dynamics of the rotor. At low flows, due to the occurrence of a rotating stall and surge, the efficiency of stages with vaneless diffusers rapidly decreases. The occurrence of unstable operating modes of centrifugal compressor stages at low flow rates is associated with the appearance of developed backflows in the flow part. To expand the range of stable operation of the stages, it is necessary to use methods of flow separation control. Separation of the flow can be controlled either by special profiling the flow part channels or by actively influencing the flow, for example, by injecting gas. To solve this problem, a mathematical model of the gas flow in a vaneless diffuser with gas injection is developed. The characteristics and parameters of the flow in the vaneless diffusers with various meridional profiles with and without injecting gas were calculated. A comparison of the calculated and experimental characteristics of the vaneless diffusers and flow parameters in diffusers with different geometries and with different injection modes confirms the adequacy of the mathematical model. Investigations have confirmed the possibility of improving the characteristics of the stages of centrifugal compressors through the use of vaneless diffusers and diffusers with gas injection. Gas injection diffusers extend the stable operation range of the stages. The use of gas injection in a vaneless diffuser allows reducing the power consumption during antisurge control in comparison with the widespread bypass suction system at the entrance to the impeller

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2

Galerkin, Y. B., A. F. Rekstin, and O. A. Solovyeva. "Selecting the Dimensions of the Vaneless Diffuser of a Centrifugal Compressor Stage at the Primary Design Phase." Proceedings of Higher Educational Institutions. Маchine Building, no. 10 (715) (October 2019): 43–57. http://dx.doi.org/10.18698/0536-1044-2019-10-43-57.

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The advances in the primary design method of centrifugal compressors of the Universal Modeling Method have led to the need to analyze and revise the recommendations for the optimal size and configuration selection of vaneless diffusers of centrifugal compressor stages. The results of CFD calculations of a family of vaneless diffusers with different relative width, radial length, velocity coefficients and flow angles at the inlet are used to develop new recommendations. The choice of the optimal width of the vaneless diffuser is based on ensuring a non-separable flow in it at the boundary of the surge. The optimal value of the relative radial length of the diffuser is in the range of 1.65–2.0. Considering the above, a formula for selecting the vaneless diffuser outer diameter is proposed depending on the design flow rate coefficient. The developed primary design method of vaneless diffusers is included in the software programs of the Universal Modeling Method and is used in design and research practice.

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3

Zhang, Qian, Liang Zhang, Qiuhong Huo, and Lei Zhang. "Study on Two Types of Stall Patterns in a Centrifugal Compressor with a Wide Vaneless Diffuser." Processes 8, no. 10 (October 4, 2020): 1251. http://dx.doi.org/10.3390/pr8101251.

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Two types of stall patterns in the centrifugal compressor with a wide vaneless diffuser were numerically studied in this paper. We carried out kinds of three-dimensional numerical simulations of the instability process in wide vaneless diffusers with different radius ratios. The results show that there are two kinds of stall patterns in wide vaneless diffusers with different radius ratios. For a short diffuser with a radius ratio of 1.5, the speed of the propagation of stalled cells is relatively high, and the propagation speed and frequency of stall cells do not change with the decrease in the flow rate. For a long diffuser with a radius ratio of 1.8, the propagation velocity of stall cells is smaller to the one in the short diffuser, and increases with the decrease in flow rate. For wide vaneless diffusers with different radius ratios, the main factor causing stall is the outlet reflux. Reducing the radius ratio of the wide vaneless diffuser has an important influence on the stability of the centrifugal compressor.

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4

Engeda, A. "The design and performance results of simple flat plate low solidity vaned diffusers." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 215, no. 1 (February 1, 2001): 109–18. http://dx.doi.org/10.1243/0957650011536471.

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Vaned diffusers for centrifugal compressors have decades of development history, but most of it is of a proprietary and empirical nature. Centrifugal compressor designers are continuously searching for a diffuser system that combines the good qualities of vaneless and vaned diffuser systems. Vaneless diffusers are known to possess wide operating range with relatively low efficiency while current conventional vaned diffusers have narrow range and high efficiency. The low solidity vaned diffuser (LSVD) has shown good performance from both range and efficiency standpoints. Its relatively high efficiency and wide flow range potentials are strong current factors, leading the compressor manufacturer to seriously consider it as the best compromise diffuser that has been sought through the years. This paper discusses the design and experimental performance results of eight flat plate LSVDs. These diffusers had a solidity of 0.9, 0.8, 0.7 and 0.6. Eight low solidity vaned diffusers (LSVD1 to LSVD8) and for comparison purposes two vaneless diffusers (VNL1 and VNL2) and a conventional vaned diffuser (CVND) were all tested downstream of the same impeller at three speeds.

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5

Zhu, Xiaocheng, Chenxing Hu, and Zhaohui Du. "Formation and suppression of the instability in radial vaneless diffusers." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 12 (February 10, 2019): 4606–22. http://dx.doi.org/10.1177/0954410019827390.

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The change of width radius ratio may lead to different physical mechanisms for the instabilities in vaneless diffusers. Reynolds-averaged Navier–Stokes numerical simulations were performed and the results were used to present the mean flow. A quasi-laminar mixed approach based was applied on the vaneless diffusers with narrow and moderate width. The frequency of the perturbations in the vaneless diffuser flow with different axial widths was validated against the experimental data. Moreover, in order to reveal the wavemaker region, the structural sensitivity analysis of the vaneless diffuser flow was carried out. The sensitivity of the eigenvalue to the mean flow modifications were used to guide the flow control. The results indicate that the viscosity tends to stabilize the narrow diffusers but destabilize the moderate width diffusers. For narrow diffusers, the wavemaker regions lie at the centerline near the intersection region of boundary layers. However, the wavemaker regions lie beside the centerline for moderate width diffusers. The occurrence of instabilities may be related with the inflection point of the velocity distribution in axial direction. Given the distribution of the sensitivity to mean flow modifications, the flow control effect may be associated with the amplitude of viscosity stress at the local flow field.

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6

Seralathan, S., and D. G. Roy Chowdhury. "Numerical Study on the Effect of Free Rotating Vaneless Diffuser of Exit Diameter to Inlet Diameter Ratio 1.3 with Speed Ratio 0.50 on Centrifugal Compressor Performance." Applied Mechanics and Materials 813-814 (November 2015): 1063–69. http://dx.doi.org/10.4028/www.scientific.net/amm.813-814.1063.

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Innovative methods in the design of radial diffuser are necessary for reducing the energy losses associated with diffusion in order to design an efficient centrifugal compressor. Rotating vaneless diffusers is one such concept, in which a particular type, free rotating vaneless diffuser, the diffuser speed becomes a fraction of the rotating impeller speed and rotates independently. In this paper, an impeller with stationary vaneless diffuser alone of diffuser diameter ratio 1.40 and the same impeller with a freely rotating vaneless diffuser of diffuser diameter ratio 1.30 along with stationary vaneless diffuser at downstream for the remaining radius ratio are analyzed for flow diffusion and performance. Higher static pressure rise with reduced stagnation pressure losses and a marginally lesser efficiency by around 3.5% compared to SVD is achieved by the free rotating vaneless diffuser configuration (FRVD30SR0.5).

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7

Solovyeva, О. А., А. А. Drozdov, E. Yu Popova, and K. V. Soldatova. "CFD-model of Vaneless Diffuser of Centrifugal Compressor." Herald of the Bauman Moscow State Technical University. Series Mechanical Engineering, no. 2 (137) (June 2021): 109–30. http://dx.doi.org/10.18698/0236-3941-2021-2-109-130.

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The centrifugal compressor design involves the use of approximate engineering techniques based on mathematical modeling. One of such techniques is the universal modeling method, which proves to be practically applicable. Having generalized a series of CFD calculations, we used a mathematical model in the latest version of the compressor model to calculate flow parameters in vaneless diffusers. The diffuser model was identified based on the results of experimental studies of average-flow model stages carried out at SPbPU. The model is also used to calculate Clark low-flow centrifugal compressor stages with narrow diffusers with a relative width in the range of 0.5--2.0 %. For these stages, the developed mathematical model showed insufficient efficiency, since the dimensions of the diffusers go beyond the limits of its applicability. To solve this problem, we calculated a series of vaneless diffusers with a relative width in the range of 0.6--1.2 % in the ANSYS CFX software package. Relying on the results of CFD calculations, we plotted the gas dynamic characteristics of the loss coefficients and changes in the flow angle depending on the flow angle at the inlet to the vaneless diffuser. To process the calculated data, the method of regression analysis was applied, with the help of which a system of algebraic equations was developed that connects geometric, gas-dynamic parameters and similarity criteria. The obtained equations are included in a new mathematical model of the universal modeling method for calculating the flow parameters of vaneless diffusers. Comparison of the calculated gas-dynamic characteristics according to the new model with experimental data showed the average error of modeling the calculated (maximum) efficiency equal to 1.08 %

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8

Pinarbasi, A., and M. W. Johnson. "Three-Dimensional Flow Measurements in Conical and Straight Wall Centrifugal Compressor Vaneless Diffusers." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 210, no. 1 (January 1996): 51–61. http://dx.doi.org/10.1243/pime_proc_1996_210_169_02.

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In the current work three-dimensional flow measurements in two types of centrifugal compressor vaneless diffuser were obtained using hot wire anemometry. The first diffuser was conical, designed to give a constant flow area, while the second straight wall diffuser had a constant axial width. Measurements of mean velocity, flow angle and velocity fluctuation level were obtained on eight cross-sectional planes in each diffuser. The jet-wake flow pattern and the impeller blade wakes are clearly visible at the inlet of both diffusers. Mixing out of the blade wake proceeds more rapidly in the straight diffuser. The hub boundary layer also develops more rapidly in this diffuser because of the adverse pressure gradient. Velocity fluctuation level measurements highlight the mixing regions within the diffusers. Recommendations are also made for the design of vaned diffusers. A larger vaneless space would be required with a straight wall diffuser and significant twisting of the vane would be required for both diffuser geometries if significant incidence losses are to be avoided.

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9

Dou, H. S., and S. Mizuki. "Analysis of the Flow in Vaneless Diffusers With Large Width-to-Radius Ratios." Journal of Turbomachinery 120, no. 1 (January 1, 1998): 193–201. http://dx.doi.org/10.1115/1.2841381.

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The flow in vaneless diffusers with large width-to-radius ratios is analyzed by using three-dimensional boundary-layer theory. The variations of the wall shear angle in the layer and the separation radius of the turbulent boundary layer versus various parameters are calculated and compared with experimental data. The effect of the separation point on the performance of vaneless diffusers and the mechanism of rotating stall are discussed. It is concluded that when the flow rate becomes very low, the reverse flow zone on the diffuser walls extends toward the entry region of diffusers. When the rotating jet-wake flow with varying total pressure passes through the reverse flow region near the impeller outlet, rotating stall is generated. The influences of the radius ratio on the reverse flow occurrence as well as on the overall performance are also discussed.

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10

Zhang, Qian, Qiuhong Huo, Lei Zhang, Lei Song, and Jianmeng Yang. "Effect of Vaneless Diffuser Shape on Performance of Centrifugal Compressor." Applied Sciences 10, no. 6 (March 12, 2020): 1936. http://dx.doi.org/10.3390/app10061936.

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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.

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11

Gao, Chuang, Chuangang Gu, Tong Wang, and Bo Yang. "Analysis of Geometries' Effects on Rotating Stall in Vaneless Diffuser with Wavelet Neural Networks." International Journal of Rotating Machinery 2007 (2007): 1–10. http://dx.doi.org/10.1155/2007/76476.

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Wavelet neural network (WNN), which combines the capability of neural network in learning from process and that of wavelet decomposition, was used to study geometry factors on rotating stall in vaneless diffusers. A new error function called cross entropy squared (CSE) function was derived and put forward for the purpose of convergence acceleration. WNN was trained and validated with experimental data from literature. Comparison results showed the reliability. With the trained WNN, detailed investigation was carried out mainly to understand the effects of impeller blade number, blade-exit angle, impeller rotating speed, diffuser radius ratio, and width ratio on stall inception and cell speed of vaneless diffuser. Network results clearly show the existence of distinct stall mechanisms for narrow and wide diffusers, which also make different responses to variation of the above- mentioned parameters.

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12

Solovyeva, Olga, and Aleksandr Drozdov. "Mathematical model of centrifugal compressor vaneless diffuser based on CFD calculations." E3S Web of Conferences 178 (2020): 01014. http://dx.doi.org/10.1051/e3sconf/202017801014.

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The approximate engineering techniques based on mathematical modelling are used in centrifugal compressor design. One of such methods is the well-proven Universal Modelling Method, developed in the scientific and research laboratory “Gas dynamics of turbo machines”, SPbPU. In the modern version of the compressor model, vaneless diffusers mathematical model was applied based on a generalization of the CFD calculations. The mathematical model can be used for vaneless diffusers with a relative width in the range of 1.4 – 10.0%, with a radial length up to 2.0, in the range of inlet flow angles 10 to 90 degrees, the inlet velocity coefficient in the range of 0.39 – 0.82, Reynolds number varying from 87 500 to 1 030 000. The model was also used for calculating low-flow-rate model stages with narrow diffusers with diffusers’ relative width in the range of 0.5 – 2.0%. The mathematical model showed lesser accuracy. To widen the model applicability, new series of CFD-calculations were executed. A series of vaneless diffusers was designed with relative width in the range of 0.6 – 1.2%, The gas-dynamic characteristics of loss coefficients and outlet flow angle versus inlet flow angle of diffuser were calculated. Regression analysis was used to process the calculated data. System of algebraic equations linking geometric, gas-dynamic parameters and similarity criteria was developed. The obtained equations are included in a new mathematical model of the Universal Modelling Method.

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13

Ljevar, S., H. C. de Lange, and A. A. van Steenhoven. "Two-Dimensional Rotating Stall Analysis in a Wide Vaneless Diffuser." International Journal of Rotating Machinery 2006 (2006): 1–11. http://dx.doi.org/10.1155/ijrm/2006/56420.

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We report a numerical study on the vaneless diffuser core flow instability in centrifugal compressors. The analysis is performed for the purpose of better understanding of the rotating stall flow mechanism in radial vaneless diffusers. Since the analysis is restricted to the two-dimensional core flow, the effect of the wall boundary layers is neglected. A commercial code with the standard incompressible viscous flow solver is applied to model the vaneless diffuser core flow in the plane parallel to the diffuser walls. At the diffuser inlet, rotating jet-wake velocity pattern is prescribed and at the diffuser outlet constant static pressure is assumed. Under these circumstances, two-dimensional rotating flow instability similar to rotating stall is found to exist. Performed parameter analysis reveals that this instability is strongly influenced by the diffuser geometry and the inlet and outlet flow conditions.

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14

Abdel-Hamid, A. N. "A New Technique for Stabilizing the Flow and Improving the Performance of Vaneless Radial Diffusers." Journal of Turbomachinery 109, no. 1 (January 1, 1987): 36–40. http://dx.doi.org/10.1115/1.3262067.

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Experiments were conducted to investigate the effects of using small exit vanes on the characteristics of an otherwise vaneless radial diffuser of outer radius and width-to-inlet radius ratios of 1.75 and 0.116, respectively. The steady and unsteady characteristics of the diffuser were evaluated as the angle of the vanes was varied continuously at several diffuser inlet conditions. The measurements showed that the influence of the adjustable exit vanes on the diffuser flow field increased as the diffuser inlet flow angle was decreased. Elimination of the self-excited flow oscillations in the diffuser was possible for all operating conditions by appropriate setting of the exit vane angle. Moreover for the diffuser investigated here and with optimum setting of the exit vanes angle the static pressure rise coefficient was significantly improved compared to the case of a pure vaneless diffuser and was found to remain almost constant at low values of diffuser inlet angles. Relative to other techniques for controlling flow instability in vaneless diffusers the proposed method offers mechanical simplicity and improved overall performance.

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15

Galerkin, Y. B., A. G. Nikiforov, O. A. Solovyeva, and E. Y. Popova. "Simulating Characteristics of Vaneless Diffusers Using Neural Networks." Proceedings of Higher Educational Institutions. Маchine Building, no. 07 (724) (July 2020): 29–42. http://dx.doi.org/10.18698/0536-1044-2020-7-29-42.

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To calculate flow parameters of a vaneless diffuser of the centrifugal compressor stage, it is sufficient to determine the loss coefficient and the flow direction at the outlet. The paper presents the results of modeling the characteristics of these two parameters using neural networks and CFD methods. To obtain mathematical models, ANSYS calculation data was used for vaneless diffusers with a relative width of 0.014–0.1, relative outlet diameter of 1.4–2.0, inlet flow angle of 10–90° and velocity coefficient of 0.39–0.82, with the Reynolds number being in the range of 87 500–1 030 000. A comparison with the theory showed the regularity of gas-dynamic characteristics, and comparison with well-known experiments showed the correspondence of the flow structure. In order to improve the accuracy of simulation using neural networks, various recommendations on the preparation and processing of the initial data were collected and tested: identification of conflict examples and outliers, data normalization, improving the quality of the neural network training under the insufficient amount of sampling, etc. The application of the aforementioned recommendations significantly improved the accuracy of simulation. A simulation experiment based on neural models for studying the influence of dimensions, diffuser shape and similarity criteria on the diffuser gas dynamic characteristics made it possible to verify physical adequacy of the mathematical models, obtain new data on energy conversion processes and produce a set of recommendations on the optimal design of vaneless diffusers.

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16

Shen, F., H. Chen, and X.-C. Zhu. "A three-dimensional vaneless diffuser stall model." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, no. 9 (September 1, 2010): 1933–45. http://dx.doi.org/10.1243/09544062jmes1985.

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A three-dimensional (3D) model is presented to study the occurrence of weak rotating waves in vaneless diffusers of centrifugal compressors. The model is an extension of the 2D one developed by Moore. 3D incompressible linearized Euler equations are cast on a rotating frame of reference travelling at the same circumferential speeds as the waves and the viscous effects are ignored. The diffuser is assumed to have two parallel walls and discharge into a large plenum. Solutions to the equations are obtained by a finite difference method and the singular value decomposition technique. Disturbances along the axial direction are found under zero undisturbed axial velocity. Resonant disturbances in the diffuser flow regardless of the compressor characteristics are also found as in the 2D cases found by Moore. Computational results show that both the critical flow angle and the propagation velocity of the wave are affected by the departure from the axial uniform distribution of the undisturbed radial velocity at the diffuser inlet, but the angle is less affected than the wave speed. The velocity distribution that satisfies Fj0rtoft's necessary conditions for flow instability is found slightly less stable and is more affected by the departure than those that do not. Shorter diffusers are affected more by the departure than the longer ones. The critical angle is shown to be increased non-linearly with the wave number and this helps to explain why wave numbers 2 to 4 are commonly observed in experiments. Finally, comparison with the experimental results in the open literature is made and a good agreement is shown.

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17

Hayami, H., Y. Senoo, and K. Utsunomiya. "Application of a Low-Solidity Cascade Diffuser to Transonic Centrifugal Compressor." Journal of Turbomachinery 112, no. 1 (January 1, 1990): 25–29. http://dx.doi.org/10.1115/1.2927416.

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Low-solidity circular cascades, conformally transformed from high-stagger linear cascades of double-circular-arc vanes with solidity 0.69, were used as a part of the diffuser system of a transonic centrifugal compressor. Performance test results were compared with data of the same compressor with a vaneless diffuser. Good compressor performance and a wider flow range as well as a higher pressure ratio and a higher efficiency, superior to those with a vaneless diffuser, where the flow range was limited by choke of the impeller, were demonstrated. The test circular cascade diffusers demonstrated a good pressure recovery over a wide range of flow angles, even when the inflow Mach number to the cascade was over unity.

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18

Tsurusaki, Hiromu. "Effects of Diffuser Geometry on Rotating Stall in Vaneless Diffusers." Transactions of the Japan Society of Mechanical Engineers Series B 59, no. 566 (1993): 3133–39. http://dx.doi.org/10.1299/kikaib.59.3133.

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19

Sitaram, N., and J. M. Issac. "An experimental investigation of a centrifugal compressor with hub vane diffusers." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 211, no. 5 (August 1, 1997): 411–27. http://dx.doi.org/10.1243/0957650971537312.

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Анотація:

The present investigation reports results of experimental studies on a centrifugal compressor equipped with hub vane diffusers. The diffuser vane height ( h/b) is varied as follows: 0 (vaneless), 0.2, 0.3, 0.4 and 1 (vane). The experiments were carried out on a low specific speed centrifugal compressor with a radial tipped impeller with an inducer at the inlet. The measurements consist of determining performance characteristics, measuring static pressures on the hub and shroud and flow traverses with a precalibrated cobra probe at the diffuser exit over one passage at five flow coefficients, viz. φ = 0.23 (near surge), 0.34 (near peak pressure rise), 0.45, 0.60 and 0.75 (near maximum flow). The peak energy coefficient is maximum for the hub vane diffuser with an h/b ratio of 0.2. The hub vane diffusers have a wider operating range than the vane diffuser. At high flow coefficients, the static pressure rise is substantially low at the throat region of the vane diffuser as the incidence on to the vane leading edge is very high. The mass averaged static pressure coefficient is high in the low-volume range for the hub vane diffuser of h/b = 0.3, but in the high-volume range it is high for the vaneless diffuser.

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20

Kinoshita, Y., and Y. Senoo. "Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers." Journal of Engineering for Gas Turbines and Power 107, no. 2 (April 1, 1985): 514–19. http://dx.doi.org/10.1115/1.3239761.

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The limit of rotating stall was experimentally determined for three very small specific speed centrifugal blowers. The impellers were specially designed for stall-free at very small flow rates, so that the cause of rotating stall could be attributed to the vaneless diffusers. Experimental results demonstrated that the blowers did not stall until the flow coefficient was reduced to very small values, which had never been reported in the literature. The critical flow coefficient for rotating stall agreed very well with the prediction based on a flow analysis and a criterion for rotating stall in vaneless diffusers developed by the authors.

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21

Zhu, Yingkang, and S. A. Sjolander. "Effect of Geometry on the Performance of Radial Vaneless Diffusers." Journal of Turbomachinery 109, no. 4 (October 1, 1987): 550–56. http://dx.doi.org/10.1115/1.3262147.

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The paper presents measurements of the steady aerodynamic characteristics of a series of five radial vaneless diffusers with walls varying from mildly divergent to strongly convergent. The static pressure recovery was determined and the flow was traversed at the inlet and the outlet of the diffuser for a broad range of flow rates in each case. It was found that wall convergence results in a negative (stabilizing) slope in the pressure rise curve for the diffuser. Furthermore, at high flow rates convergence was found to reduce the pressure recovery far less than one would expect and at intermediate flow rates convergence actually improved the pressure recovery. The better-than-expected performance is thought to be closely related to the observed improvement in the flow uniformity at the diffuser outlet when convergent walls are used.

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22

Sheng, Feng, Hua Chen, Xiao-cheng Zhu, and Zhao-hui Du. "A three-dimensional compressible flow model for rotating waves in vaneless diffusers with unparallel walls." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, no. 9 (February 7, 2012): 2230–49. http://dx.doi.org/10.1177/0954406211435035.

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A three-dimensional compressible flow model is presented to study the occurrence of weak rotating waves in unparallel wall vaneless diffusers in centrifugal compressors. The model extends the three-dimensional compressible flow model for parallel wall diffusers recently developed by present authors. Linearised three-dimensional compressible Euler equations casted on a rotating frame of reference travelling at the same speeds as the waves are employed and the viscous effects are ignored. Complex functions of the solutions to the linearised Euler equations are then obtained by a second-order finite difference method and the singular value decomposition technique. Undisturbed flow is assumed potential and first solved by numerical method of strongly implicit procedure. Critical inlet flow rate and rotating wave speed of diffusers of three different shroud wall shapes, namely, convergent, convergent then divergent and constant area tapered, are studied for three different diffuser outlet-to-inlet radius ratios and for different inlet Mach numbers, and results compared with those from diffusers with parallel walls. The results show suppression effects on rotating stall by the contracting walls and the suppression effects vary with wall contraction rate, wall shape, inlet Mach number and the diffuser radius ratio. Further, the effects of diffuser inlet contraction are studied and prediction of the model is compared with experimental result.

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23

Tsujimoto, Yoshinobu, Yoshiki Yoshida, and Yasumasa Mori. "Study of Vaneless Diffuser Rotating Stall Based on Two-Dimensional Inviscid Flow Analysis." Journal of Fluids Engineering 118, no. 1 (March 1, 1996): 123–27. http://dx.doi.org/10.1115/1.2817489.

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Анотація:

Rotating stalls in vaneless diffusers are studied from the viewpoint that they are basically two-dimensional inviscid flow instability under the boundary conditions of vanishing velocity disturbance at the diffuser inlet and of vanishing pressure disturbance at the diffuser outlet. The linear analysis in the present report shows that the critical flow angle and the propagation velocity are functions of only the diffuser radius ratio. It is shown that the present analysis can reproduce most of the general characteristics observed in experiments: critical flow angle, propagation velocity, velocity, and pressure disturbance fields. It is shown that the vanishing velocity disturbance at the diffuser inlet is caused by the nature of impellers as a “resistance” and an “inertial resistance,” which is generally strong enough to suppress the velocity disturbance at the diffuser inlet. This explains the general experimental observations that vaneless diffuser rotating stalls are not largely affected by the impeller.

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24

Petukhov, E. P., Y. B. Galerkin, and A. F. Rekstin. "A Study of Testing Procedures of Vaned Diffusers of a Centrifugal Compressor Stage in a Virtual Wind Tunnel." Proceedings of Higher Educational Institutions. Маchine Building, no. 8 (713) (August 2019): 51–64. http://dx.doi.org/10.18698/0536-1044-2019-8-51-64.

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A mathematical model of a vaned diffuser of a centrifugal compressor stage can be constructed based on the results of mass CFD-calculations, similar to that of vaneless diffusors. The methods for calculating the annular cascade and the straight cascade differ due to the existence of vaneless diffusor sections in front of the cascade and behind it. The rational dimensions of these sections are determined. The calculations of two-dimensional cascades without restricting walls appear to be irrational. The calculation is effective for a sector with one vane channel, a moderate number of cells, and the turbulence model k–ε. Averaging the flow parameters at the blade cascade exit leads to ambiguous results. To calculate the characteristics of the blade cascade, the parameters in a section with a diameter equal to 1.85 of the diameter of the blade cascade exit should be used. In domestic and foreign literature, it is customary to emphasize the effectiveness of the CFD methods that replace physical experiments. Calculations of the compressor stages are called virtual rig testing, while those of the blade cascade are known as virtual wind tunnel testing. To study stationary flow, as a virtual wind tunnel, it suffices to consider the blade cascade itself, the preceding and the subsequent vaneless spaces.

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25

Ogut, Ali, and Diego Garcia Pastor. "Simulation of Flow in Turbopump Vaneless and Vaned Diffusers with Fluid Injection." International Journal of Rotating Machinery 6, no. 1 (2000): 57–65. http://dx.doi.org/10.1155/s1023621x00000063.

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In future space missions by NASA there will be a need for “Space Transfer Vehicles” to perform varying orbital transfers and descents. This requires engines capable of producing different levels of thrust. To accomplish this, the turbopumps employed in these engines should efficiently provide a wide range of flow outputs. However, current fuel and oxidizer turbopumps with vaned diffusers do not perform efficiently at off-design (low) flow rates mainly due to flow separation in the vaned diffuser.This paper evaluates the effectiveness of boundary layer control by fluid injection (blowing) for suppressing or eliminating the flow separation in a vaned diffuser. A 3-D flow model including vaneless and vaned diffusers of a liquid hydrogen (LH2) turbopump is studied using the CFD code FIDAP. The paper presents the results of the model at design and offdesign flow conditions.The model results showed that flow separation occurs at the top or suction surface of the vaneless diffuser and at the bottom or pressure surface of the vaned diffuser at off-design flow rates. When fluid injection was applied through the bottom surface of the vaned diffuser, the separated flow region was reduced almost entirely, resulting in an increase in pressure recovery of up to 21% with varying fluid injection rates. Results also showed that there is an optimum injection rate which is most effective in reducing or eliminating the region of flow separation.

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26

Yoshinaga, Y., T. Kaneki, H. Kobayashi, and M. Hoshino. "A Study of Performance Improvement for High Specific Speed Centrifugal Compressors by Using Diffusers With Half Guide Vanes." Journal of Fluids Engineering 109, no. 4 (December 1, 1987): 359–66. http://dx.doi.org/10.1115/1.3242672.

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Анотація:

The experimental results from eighteen different centrifugal compressor stages showed that the pressure recovery of vaneless diffusers for high specific speed compressors was extremely low compared with the value expected by an ideal two-dimensional analysis. Consequently a new type of diffuser with half guide vanes on the shroud side wall was proposed. The pressure recovery of this diffuser at distorted inlet flow was considerably improved by the half guide vanes. The optimum height of the vanes was a little less than one half of the diffuser width. Measurements of the velocity distribution in the diffusers using Pitot tubes and a laser-two-focus velocimeter, clearly showed that the small height guide vanes gave a uniform flow in the axial direction and improved the pressure recovery of the diffuser.

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27

KINOSHITA, Yoshifumi, Akihiro HAYASHI, and Syouzo TSUZUKI. "Mechanism of Stall Induced in Centrifugal Vaneless Diffusers." Proceedings of Conference of Kyushu Branch 2003 (2003): 231–32. http://dx.doi.org/10.1299/jsmekyushu.2003.231.

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28

Galerkin, Y., K. Soldatova, and O. Solovieva. "Numerical study of centrifugal compressor stage vaneless diffusers." IOP Conference Series: Materials Science and Engineering 90 (August 10, 2015): 012048. http://dx.doi.org/10.1088/1757-899x/90/1/012048.

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29

SAKAI, Toshimichi. "Vaneless Diffusers for Mixed-Flow Blower and Compressor." Journal of the Society of Mechanical Engineers 90, no. 820 (1987): 266–71. http://dx.doi.org/10.1299/jsmemag.90.820_266.

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30

Arnulfi, G. L., D. Micheli, and P. Pinamonti. "Velocity Measurements Downstream of the Impellers in a Multistage Centrifugal Blower." Journal of Turbomachinery 117, no. 4 (October 1, 1995): 593–601. http://dx.doi.org/10.1115/1.2836573.

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The paper presents the results of an experimental investigation on a four-stage centrifugal blower, having the aim of obtaining an accurate description of the flow field behind the impellers in several operative conditions and for different geometric configurations. Actually, the test plant allows one to change the turbomachinery characteristics assembling one, two, three, or four stages and three different types of diffuser. In this first research step, the blower has been tested in the four-stage vaneless diffuser configuration. The unsteady flow field behind the impellers and in the diffusers has been measured by means of a hot-wire anemometer. A phase-locked ensemble-averaging technique has been utilized to obtain the relative flow field from the instantaneous signals of the stationary hot-wire probes. Several detailed measurement sets have been performed using both single and crossed hot-wire probes, to obtain the velocity vectors and turbulence trends, just behind the blower impellers and in several radial positions of the vaneless diffusers. These measurements have been done at different flow rate conditions, covering unsteady flow rate phenomena (rotating stall) also. The results obtained allowed us to get a detailed flow field analysis in the multistage centrifugal blower, in relation to the geometric configuration and to the differing operating conditions.

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31

Galerkin, Yuri, Aleksey Rekstin, Aleksandr Drozdov, Kristina Soldatova, Olga Solovyeva, and Elena Popova. "The optimal gas dynamic design system of industrial centrifugal compressors based on Universal modeling method." E3S Web of Conferences 178 (2020): 01028. http://dx.doi.org/10.1051/e3sconf/202017801028.

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We present the modern stage of development of Universal Modeling Method, a complex of mathematical models and software for optimal design of centrifugal compressors - a new version of simplified mathematical model of efficiency and new software for variation calculations of multistage compressors. Based on this numerical calculation complex we have created a method for preliminary design of flow paths of stages - 2D and 3D impellers, vane and vaneless diffusers and return channels. The new, 9th version of its mathematical model features a quasi-3D calculation method of 2D and 3D impellers design, a new principle of pressure characteristic calculation, a new model of vaneless diffusers and much more. “Digital twin of a centrifugal compressor stage” and “3D compressor” software create digital descriptions of the flow part and its solid model (“digital twin”).

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32

Justen, F., K. U. Ziegler, and H. E. Gallus. "Experimental Investigation of Unsteady Flow Phenomena in a Centrifugal Compressor Vaned Diffuser of Variable Geometry." Journal of Turbomachinery 121, no. 4 (October 1, 1999): 763–71. http://dx.doi.org/10.1115/1.2836730.

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The behavior of vaned radial diffusers is generally considered to be due to the flow phenomena in the vaneless and the semi-vaned space in the diffuser inlet region. Even considering unsteady aspects, the adjacent diffuser channel is regarded as less important. The flat wedge vaned diffuser of the centrifugal compressor stage investigated allows an independent continuous adjustment of the diffuser vane angle and the radial gap between impeller outlet and diffuser vane inlet, so that information about the importance of these geometric parameters can be obtained. The time-dependent pressure distribution on the diffuser front wall and on the suction and pressure surfaces of the diffuser vanes reveal that in the semi-vaned space mainly the region near the vane suction side is influenced by the unsteady impeller-diffuser interaction. Downstream in the diffuser channel the unsteadiness does not decay. Here, pressure fluctuations are appearing that are distinctly higher than the pressure fluctuations in the vaneless space. An estimation of the influence of the unsteadiness on the operating performance of the centrifugal compressor stage is made by measurements at choke and surge limit for different diffuser geometries.

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33

AWAI, Takashi, Tomohiro NAKAGAWA, and Toshimichi SAKAI. "A study of axially curved mixed-flow vaneless diffusers." Transactions of the Japan Society of Mechanical Engineers Series B 51, no. 470 (1985): 3370–75. http://dx.doi.org/10.1299/kikaib.51.3370.

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34

Nikiforov, A., D. Avramenko, A. Kuchumov, S. Terentev, Yu Galerkin, and O. Solovyeva. "Vaneless diffusers characteristics simulating by means of neural networks." IOP Conference Series: Materials Science and Engineering 604 (September 3, 2019): 012046. http://dx.doi.org/10.1088/1757-899x/604/1/012046.

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35

Jiang, P. M., and A. Whitfield. "Investigation of Vaned Diffusers as a Variable Geometry Device for Application to Turbocharger Compressors." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 206, no. 3 (July 1992): 209–20. http://dx.doi.org/10.1243/pime_proc_1992_206_179_02.

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The potential of guide vanes as a variable geometry device, placed in the conventional vaneless diffuser, to extend the operating range of a turbocharger compressor is investigated. Vaned diffusers are not normally employed in turbocharger applications as the consequent reduction in operating range is more damaging than the beneficial improvement in peak efficiency and pressure ratio. The variable geometry concept considered here is primarily one in which the guide vanes are introduced at the near surge flow conditions. The leading edge vane angle is set to accept the highly tangential flow at the near surge conditions, and the vane is then used to guide the fluid towards the radial direction in order to reduce the long flow path through the diffuser. Four types of vane arrangements are considered: (a) 12 and 6 full length vanes, with inlet vane angles of 75° and 80°; (b) 6 short inlet vanes to give a high aspect ratio; (c) 12 and 6 short vanes located in the outer half of the vaneless diffuser passage; and (d) double-row vane rings. It is shown that short vanes deployed at the diffuser outlet not only improve the efficiency and pressure ratio but also extend the high flow operating range. Further, the introduction of short inlet vanes with an inlet angle of 80° improves the peak pressure ratio and efficiency, and extends the near surge operating range.

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36

Kim, Y., A. Engeda, R. Aungier, and N. Amineni. "A centrifugal compressor stage with wide flow range vaned diffusers and different inlet configurations." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 216, no. 4 (June 1, 2002): 307–20. http://dx.doi.org/10.1243/09576500260251156.

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In most cases, the diffuser system of a centrifugal compressor comes in the two general categories of a vaneless or a vaned diffuser. The vaned diffuser can generally be subdivided into two types depending on channel geometry (straight or curved channel) or depending on solidity. For the three different vaned diffusers of a centrifugal compressor stage, the design procedure is presented and experimental data are compared. The primary objective of the diffuser design was to achieve substantial improvement, compared with the stage currently used for the intended application, for the stable operating flow range as well as for the head rise from design to surge flow. The design goals also included achieving competitive efficiency levels, which required a significant efficiency improvement. Test results showed a much wider stable operating range than had been expected. This stage operated well beyond the expected vaned diffuser stall limit. The inlet configuration and inlet flow structure are known significantly to affect the compressor performance. Each of the three diffusers is tested for two different types of inlet configuration, and the relative performances are assessed.

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37

AWAI, Takashi, Tomohiro NAKAGAWA, and Toshimichi SAKAI. "A Study on the Axially Curved Mixed-flow Vaneless Diffusers." Bulletin of JSME 29, no. 252 (1986): 1759–64. http://dx.doi.org/10.1299/jsme1958.29.1759.

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38

Solovyeva, O. A., K. V. Soldatova, Y. B. Galerkin, and A. F. Rekstin. "Primary Design of Vaneless Diffusers of Centrifugal Compressor Stages by the Universal Modeling Method." Proceedings of Higher Educational Institutions. Маchine Building, no. 3 (732) (March 2021): 39–52. http://dx.doi.org/10.18698/0536-1044-2021-3-39-52.

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Vaneless diffusers of industrial centrifugal compressors most often consist of a tapered inlet section and a parallel-walled main section. The study proposes to choose such a width of the main section, at which the flow in the diffuser remains unseparated at the surge limit. To implement the primary design method, an empirical formula was obtained to determine the minimum continuous flow angle depending on the relative width of the diffuser. The primary design of eighteen stages was completed, covering a practically important range of parameters. The corresponding gas-dynamic characteristics were calculated by the universal modeling method, the dimensions and angles of the flow were analyzed. The proposed primary design method is integrated into the universal modeling method and is used in design practice.

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39

Shoji, H., and H. Ohashi. "Lateral Fluid Forces on Whirling Centrifugal Impeller (1st Report: Theory)." Journal of Fluids Engineering 109, no. 2 (June 1, 1987): 94–99. http://dx.doi.org/10.1115/1.3242647.

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Lateral fluid forces acting on a rotating centrifugal impeller in whirling motion are analyzed using unsteady potential flow theory. Impellers operating in diffusers with and without vanes are modeled and the fluid forces calculated for different whirl speeds and flow rates. The influences of these parameters are clarified by parametric calculations. The results for whirling impellers operating in vaneless diffusers show that the fluid forces exert a damping effect on the rotor whirling motion at all operating conditions. The results for impellers operating in vaned diffusers or guide vanes show that the time averaged values of fluid forces remain almost unchanged, while there are significant instantaneous fluctuations due to the impeller/guide vane interactions.

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40

Pinarbasi, A., K. M. Guleren, and A. Ozturk. "Measurements of Reynolds stresses in centrifugal compressor vaned diffusers." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 222, no. 8 (August 1, 2008): 1487–503. http://dx.doi.org/10.1243/09544062jmes877.

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A phase lock loop sampling technique has been developed in order to perform detailed measurements for the flow field downstream of a turbomachinery rotor. Measurements have been carried out in the vaned diffuser of a low-speed centrifugal compressor using a triple hot wire anemometer. The phase lock loop technique employed in this work has provided a comprehensive representation of the complex three-dimensional unsteady flow in these diffusers. The diffuser vanes were found to have a significant influence on the flow in the vaneless space. The mixing out of the blade wakes is enhanced and accordingly the Reynolds stress levels drop rapidly between the impeller exit and the vane leading edge. The results provide an insight into the flow mechanisms responsible for the losses and hence can be used to develop better design strategies in the future. The flow also exhibits high levels of anisotropy, especially at the mid-vane positions. This suggests that basic Reynolds-averaged Navier—Stokes (RANS) models, including standard one- or two-equation models, might not be sufficient to accurately model the flow in centrifugal compressor diffusers.

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41

Issac, J. M., N. Sitaram, and M. Govardhan. "Performance and wall static pressure measurements on centrifugal compressor diffusers." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 217, no. 5 (January 1, 2003): 547–58. http://dx.doi.org/10.1243/095765003322407593.

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The results of experimental studies on performance and wall static pressure distribution in the diffuser passage of a low specific speed centrifugal compressor are given. The performance tests were carried out with vaneless, vane and low-solidity vane diffusers at speeds of 2500, 3000 and 3500r/min. Diffuser wall static pressures measured at 3000r/min for four flow coefficients on the shroud and hub walls are reported. The peak energy coefficient is maximum for the vane diffuser. The operating range of the low-solidity vane diffuser is wider than that of the vane diffuser. At high flow coefficients, the static pressure rise is substantially lower for the vane diffuser, as the incidence on the vane leading edge is very high. The low-solidity vane diffuser did not suffer a large drop in static pressure near the leading edge. The most probable reason may be the large area available in the low-solidity vane diffuser for flow adjustment and weaker flow separation zones on account of the lower number of vanes.

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42

Lu, Zhaoheng, Ran Tao, Faye Jin, Puxi Li, Ruofu Xiao, and Weichao Liu. "The Temporal-Spatial Features of Pressure Pulsation in the Diffusers of a Large-Scale Vaned-Voluted Centrifugal Pump." Machines 9, no. 11 (November 2, 2021): 266. http://dx.doi.org/10.3390/machines9110266.

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A large-scale, vaned-voluted centrifugal pump can be applied as the key component in water-transfer projects. Pressure pulsation will be an important factor in affecting the operation stability. This paper researches the propagation and spatial distribution law of blade passing frequency (BPF) and its harmonics on the design condition by numerical simulation. Experimental and numerical monitoring is conducted for pressure pulsation on four discrete points in the vaneless region, which shows that the BPF is dominant. The pulsation tracking network (PTN) is applied to research propagation law and spatial distribution law. It provides a reference for frequency domain information and visualization vaned diffuser. The amplitude of BPF and its harmonics decays rapidly in the vaneless region. BPF and BPF’s harmonics influence each other. BPF has local enhancement in the vaneless region when its harmonics attenuate. In the vaned diffuser, the pulsation amplitude of BPF attenuates rapidly, but the local high-pressure pulsation amplitude can be found on the vane blade concave side because of obstruction and accumulation of the vaned diffuser. In the volute, the pulsation amplitude of BPF is low with the decelerating attenuation. This study provides an effective method for understanding the pressure pulsation law in turbomachinery and other engineering flow cases.

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43

Jaatinen-Värri, Ahti, Aki Grönman, Teemu Turunen-Saaresti, and Jari Backman. "Investigation of the Stage Performance and Flow Fields in a Centrifugal Compressor with a Vaneless Diffuser." International Journal of Rotating Machinery 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/139153.

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The effect of the width of the vaneless diffuser on the stage performance and flow fields of a centrifugal compressor is studied numerically and experimentally. The diffuser width is varied by reducing the diffuser flow area from the shroud side (i.e., pinching the diffuser). Seven different diffuser widths are studied with numerical simulation. In the modeling, the diffuser widthb/b2is varied within the range 1.00 to 0.50. The numerical results are compared with results obtained in previous studies. In addition, two of the diffusers are further investigated with experimental measurement. The main finding of the work is that the pinch reduces losses in the impeller associated with the tip-clearance flow. Furthermore, it is shown that a too large width reduction causes the flow to accelerate excessively, resulting in a highly nonuniform flow field and flow separation near the shroud.

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44

Hu, Chenxing, Ce Yang, Xin Shi, Runnan Zou, Lin Liu, and Hua Chen. "Investigation of rotating stall in radial vaneless diffusers with asymmetric inflow." Aerospace Science and Technology 96 (January 2020): 105546. http://dx.doi.org/10.1016/j.ast.2019.105546.

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45

Furukawa, Akinori, Hisasada Takahara, Takahiro Nakagawa, and Yusuke Ono. "Pressure Fluctuation in a Vaned Diffuser Downstream from a Centrifugal Pump Impeller." International Journal of Rotating Machinery 9, no. 4 (2003): 285–92. http://dx.doi.org/10.1155/s1023621x03000265.

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Periodic flows downstream from a centrifugal pump impeller in vaneless and vaned diffusers were measured by using a single hole yawmeter and a phase-locked sampling method. The flows were also calculated by an inviscid flow analysis using the blade-surface singularity method. The periodic variations in calculated static pressure with the impeller rotating quantitatively agree well with the measured ones. The flow behaviors in the vaned diffuser are discussed, citing measured and calculated results. The potential interaction between the impeller and the diffuser blades appears more strongly than the impeller-wake interaction. The appearance of static pressure fluctuations due to the impeller's rotating in the fully vaned zone is different from that in the semivaned zone of the diffuser. The existence of the peripheral blade surface of the impeller outlet with an outlet edge of the pressure surface causes violent pressure fluctuations in the vaned diffuser.

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46

Amirante, R., F. De Bellis, E. Distaso, and P. Tamburrano. "An Explicit, Non-Iterative, Single Equation Formulation for an Accurate One Dimensional Estimation of Vaneless Radial Diffusers in Turbomachines." Journal of Mechanics 31, no. 2 (October 21, 2014): 113–22. http://dx.doi.org/10.1017/jmech.2014.72.

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AbstractThe present paper proposes a very simple one dimensional (1-D) model that accounts for the energy loss caused by the fluid dynamic losses occurring in the vaneless diffusers of centrifugal compressors and pumps. Usually, the present techniques to design turbomachines (pumps, compressors and turbines) emphasize numerical methods and their use is relatively complex because several parameters need to be chosen and a lot of time is required to perform the calculation. For this reason, it is relevant to perform an accurate preliminary design to simplify the numerical computation phase and to choose a very good initial geometry to be used for accelerating and improving the search for the definitive geometry. However, today 1-D modeling is based on the classical theory that assumes that the angular momentum is conserved inside a vaneless diffuser, although the flow evolution is considered as non-isentropic. This means that fluid-dynamic losses are taken into account only for what concerns pressure recovery, whereas the evaluation of the outlet tangential velocity incoherently follows an ideal behavior. Starting from such considerations, a new conservation law for the angular momentum is analytically derived, which incorporates the same fluid-dynamic losses modeled by the thermodynamic transformation law that is employed for correlating pressure recovery with enthalpy increase. Similar arguments hold for incompressible flows. Detailed and very accurate three-dimensional flow simulations are employed to analyze if the new model is capable of predicting the outlet tangential velocity more accurately than the classical theory. Results provided for both compressible (centrifugal compressors) and incompressible (centrifugal pumps) flows and for different inlet velocity profiles show a significant accuracy improvement of the new conservation law in the prediction of the outlet flow conditions when compared with the classical theory, thus demonstrating that the proposed model can be employed in the preliminary design of vaneless diffusers (i.e., in the estimation of the outlet diameter) more effectively than the classical ideal theory. Furthermore, the model is validated against industrial experimental campaigns. Even further experimental data, reported in a previous paper by the same authors, confirm the reliability of the employed approach.

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47

Eynon, P. A., and A. Whitfield. "The effect of low-solidity vaned diffusers on the performance of a turbocharger compressor." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 211, no. 5 (May 1, 1997): 325–39. http://dx.doi.org/10.1243/0954406971522088.

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The design of low-solidity diffuser vanes and the effect on the performance of a turbo-charger compressor is discussed. The effect of vane number and turning angle was investigated while maintaining a basic design with a solidity of 0.69 and a leading edge angle of 75°. This large leading edge angle was specifically chosen so that the vane would be aligned with the low flowrates close to surge. Tests were initially conducted with six, eight and ten vanes and a turning angle of 10°. Based on these results the ten-vane design was selected for further investigation with 15 and 20° of vane turning; this led to vane exit angles of 60 and 55° respectively. All results are compared with those obtained with the standard vaneless diffuser configuration and it was shown that all designs increased and shifted the peak pressure ratio to reduced flowrates. The peak efficiency was reduced relative to that obtained with the vaneless diffuser. Despite the low-solidity configuration none of the vane designs provided a broad operating range without the use of a variable geometry configuration. This was attributed to the selection of a large leading edge vane angle.

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48

Hong, S. S., and S. H. Kang. "Effect of circumferential outlet distortion on the flow characteristics at the impeller exit of a centrifugal pump." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 215, no. 9 (September 1, 2001): 1083–93. http://dx.doi.org/10.1177/095440620121500909.

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Centrifugal impellers are exposed to downstream circumferential outlet distortions due to non-axisymmetric volutes or diffusers. This paper explores the effect of circumferential outlet distortion on the flow characteristics at the impeller exit of a centrifugal pump. A fence with non-uniform height was installed at the vaneless diffuser exit to create the outlet distortion, and then unsteady velocity and static pressure were measured at the impeller exit. The instantaneous and mean flow fields at the impeller exit varied with the circumferential position. Plots of the flows against the local flowrate showed hysteretic loops that deviated from the quasi-steady curves obtained from the flows without the fence. When the assumption of quasi-steady variation was applied to the present impeller-diffuser interaction, the prediction for the total and static pressure was reasonable but showed a phase difference for the absolute velocity.

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49

Tamaki, H., H. Nakao, and M. Saito. "The Experimental Study of Matching Between Centrifugal Compressor Impeller and Diffuser." Journal of Turbomachinery 121, no. 1 (January 1, 1999): 113–18. http://dx.doi.org/10.1115/1.2841218.

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The centrifugal compressor for a marine use turbocharger with its design pressure ratio of 3.2 was tested with a vaneless diffuser and various vaned diffusers. Vaned diffusers were chosen to cover impeller operating range as broad as possible. The analysis of the static pressure ratio in the impeller and the diffusing system, consisting of the diffuser and scroll, showed that there were four possible combinations of characteristics of impeller pressure ratio and diffusing system pressure ratio, The flow rate, QP, where the impeller achieved maximum static pressure ratio, was surge flow rate of the centrifugal compressor determined by the critical flow rate. In order to operate the compressor at a rate lower than QP, the diffusing system, whose pressure recovery factor was steep negative slope near QP, was needed. When the diffuser throat area was less than a certain value, the compressor efficiency deteriorated; however, the compressor stage pressure ratio was almost constant. In this study, by reducing the diffuser throat area, the compressor could be operated at a flow rate less than 40 percent of its design flow rate. Analysis of the pressure ratio in the impeller and diffusing systems at design and off-design speeds showed that the irregularities in surge line occurred when the component that controlled the negative slope on the compressor stage pressure ratio changed.

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50

Cui, Michael M. "Comparative Study of Unsteady Flows in a Transonic Centrifugal Compressor with Vaneless and Vaned Diffusers." International Journal of Rotating Machinery 2005, no. 1 (2005): 90–103. http://dx.doi.org/10.1155/ijrm.2005.90.

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To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In the current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was simulated with a Navier-Stokes solver using thek−εturbulent model. The overall performance parameters are obtained by integrating the field quantities. Both the unsteady flow field and the overall performance are analyzed comparatively for each component. The compressor was tested in a water chiller system instrumented to obtain both the overall performance data and local flow-field quantities. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow-field quantities is defined. The methodology developed and data obtained in these studies can be applied to the centrifugal compressor design and optimization.

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