Analysis of the Flow Field in a Radial Compressor

A centrifugal compressor is often equipped with a vaneless diffuser because the operation range of a vaneless diffuser is wider than the operation range of vaned diffuser, and the geometry of the vaneless diffuser is simple and inexpensive. The flow field after the centrifugal compressor rotor is highly complicated and the velocity is high. A moderate amount of this velocity should be recovered to the static pressure. It is important to study the flow field in the vaneless diffuser in order to achieve guidelines for design and an optimal performance. In this article, the experimental study of the pinch in the vaneless diffuser is conducted. Five different diffuser heights were used, b/b2 = 1, b/b2 = 0.903, b/b2 = 0.854, b/b2 = 0.806 and b/b2 = 0.903 (shroud). In three of the cases, the pinch was made to both walls of the diffuser, hub and shroud, and in one case, the pinch was made to the shroud wall. The total and the static pressure, the total temperature and the flow angle were measured at the diffuser inlet and outlet by using a cobra-probe, kiel-probes and flush-mounted pressure taps. In addition, the static pressure in the diffuser was measured at three different radius ratios. The overall performance, the mass flow, the pressure ratio and the isentropic efficiency of the compressor stage were also monitored. Detailed flow field measurements were carried out at the design rotational speed and at the three different mass flows (close to the surge, design and close to the choke). The isentropic efficiency and the pressure ratio of the compressor stage was increased with the pinched diffuser. The efficiency of the rotor and the diffuser was increased, whereas the efficiency of the volute/exit cone was decreased. The pinch made to the shroud wall was the most effective. The pinch made the flow angle more radial and increased the velocity at the shroud where the secondary flow (passage wake) from the rotor is present.

Experimental Flow Field Investigation in a Centrifugal Compressor Vaned Diffuser

Volume 1: Turbomachinery ◽

10.1115/95-gt-080 ◽

1995 ◽

Cited By ~ 1

Author(s):

Ali Pinarbasi ◽

Mark W. Johnson

Keyword(s):

Kinetic Energy ◽

Flow Field ◽

Centrifugal Compressor ◽

Field Investigation ◽

Vaneless Diffuser ◽

Mean Velocity ◽

Cross Sectional ◽

Impeller Blade ◽

Vaned Diffuser ◽

Flow Angle

The purpose of this study was to improve the understanding of the flow physics in a centrifugal compressor vaned diffuser. A low speed compressor with a 19 bladed backswept impeller and diffuser with 16 wedge vanes was used. The measurements were made at three inter-vane positions and are presented as mean velocity, turbulent kinetic energy and flow angle distributions on eight diffuser cross sectional planes. The impeller blade wakes mix out rapidly within the vaneless space and more rapidly than in an equivalent vaneless diffuser. Although the flow is highly non uniform in velocity at the impeller exit, there is no evidence in the results of any separation from the diffuser vanes. The results do however suggest that the use of twisted vanes within the diffuser would be beneficial in reducing losses.

Rotating Stall Measurements in the Vaneless Diffuser of a Radial Flow Compressor

Volume 1: Turbomachinery ◽

10.1115/82-gt-257 ◽

1982 ◽

Author(s):

P. M. Ligrani ◽

R. Van Den Braembussche ◽

M. Roustan

Keyword(s):

Flow Behavior ◽

Reynolds Numbers ◽

Rotating Stall ◽

Hot Wire ◽

Vaneless Diffuser ◽

Inlet Flow ◽

Flow Angle ◽

Measurement Results ◽

Flow Compressor ◽

Hot Film

Results from an experimental study of flow behavior at the inlet of a vaneless diffuser of a centrifugal compressor are presented. Hot-film measurements and measurement results from a crossed hot-wire probe are discussed for operating points having inlet flow coefficients ranging from 0.006 to 0.019 at different Reynolds numbers. Instantaneous, time-averaged, and phase-averaged absolute velocity and flow angle at the diffuser inlet are deduced from the hot-wire signals after correction for mean density variations. These results show how flow behavior varies in stable, rotating stall and surge regimes of compressor operation. The critical flow angle at the onset of rotating stall shows agreement with other measurements confirming the importance of diffuser inlet width and diffuser inlet flow angle on the onset of rotating stall in vaneless diffusers.

Influence of Unsteady Wakes on the Secondary Flows in the Linear T106 Turbine Cascade

Volume 2D: Turbomachinery ◽

10.1115/gt2016-56350 ◽

2016 ◽

Author(s):

Ilker Kirik ◽

Reinhard Niehuis

Keyword(s):

Boundary Layer ◽

Flow Field ◽

Secondary Flow ◽

High Speed ◽

Base Flow ◽

Secondary Flows ◽

Pressure Probe ◽

Hot Wire ◽

Flow Angle ◽

Secondary Flow Field

The present work extends previous investigations on the secondary flows around a steady and unsteady base flow to detailed time-averaged and time-resolved flow field measurements up- and downstream of the cascade. As a representative of modern low pressure turbine rotors of moderate aerodynamic loading, the LPT cascade T106 with parallel sidewalls was chosen for these investigations. Previous investigations have shown that the intensity of secondary flows in the endwall region within a first test set-up was fairly low due to the thin endwall boundary layer at the inlet of the cascade which impeded to study the influence of periodically incoming wakes on the temporal development of the secondary flow field. For that reason a new test-up was built providing a thicker inlet boundary. Measurements have been performed in the High-Speed Cascade Wind Tunnel of the University of the Federal Armed Forces Munich under realistic Mach and Reynolds numbers. In order to simulate real turbomachinery situtations, a wake generator is installed generating temporally representative wakes in the inlet plane of the cascade by a moving bar system. The inlet conditions were determined using a hot wire and a Pitot probe. Detailed measurements of the three-dimensional flow field were carried out downstream of the cascade with a triple hot wire probe, a conventional five hole pressure probe, and a dynamic pressure probe equipped with a single Kulite sensor. All measurements were performed with and without moving bars. Based on previous investigations, a pitch of the moving bars of 40 mm and a circumferential speed of 20 m/s was chosen as the configuration with the highest influence on the secondary flow field. It is shown that the intended increase of the inlet boundary layer was achieved by putting plates on top of each other in the inlet plane endwalls. This leads to more pronounced secondary flow parameters in the spanwise distribution of the pitchwise averaged secondary flow angle (Δβ2,sec) and the secondary losses (ζ2,sec).

Stability of Conical and Curved Annular Diffusers for Mixed-Flow Compressors

Volume 1: Turbomachinery ◽

10.1115/87-gt-191 ◽

1987 ◽

Author(s):

A. Abir ◽

A. Whitfield

Keyword(s):

Internal Flow ◽

Wall Pressure ◽

Hot Wire ◽

Vaneless Diffuser ◽

Mixed Flow ◽

Flow Measurements ◽

Pressure Transducers ◽

Flow Profiles ◽

Annular Diffuser ◽

Unsteady Conditions

For mixed-flow compressors the downstream vaneless diffuser can be either a straight or curved annular passage. Investigations have been carried out on model diffusers six times larger than those employed in a turbocharger study, Whitfield et al (1978). This made it possible to carry out detailed internal flow measurements using a five hole yaw probe and a hot wire anemometer. The development of the flow profiles throughout the diffuser were studied with particular reference to the onset of unstable conditions. Flush mounted wall pressure transducers were also used to detect the onset of unstable flows and to measure the extent and development of the unsteady conditions. Two curved and one straight annular diffusers have been tested in order to study their relative merits. In addition, the results obtained with a straight radial diffuser are included for comparison. It has generally been observed that the straight annular diffuser was the least stable, with the radial diffuser exhibiting the best stability characteristics. Of the two curved annular diffusers tested flow stability was improved by reducing the passage width. In both cases, however, the curved diffuser proved to be clearly superior to the simpler straight design.

Experimental and Numerical Investigation of the Flow Field in the Radial Inlet of a Centrifugal Compressor

Volume 8: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2012-69353 ◽

2012 ◽

Cited By ~ 1

Author(s):

Fenghui Han ◽

Datong Qi ◽

Jiajian Tan ◽

Li Wang ◽

Yijun Mao

Keyword(s):

Flow Field ◽

Centrifugal Compressor ◽

Numerical Study ◽

Internal Flow ◽

Structure Design ◽

Outlet Section ◽

Complex Flow ◽

Flow Angle ◽

Flow Phenomena ◽

Probe Calibration

This paper presents an experimental and numerical study of the flow field in a typical geometry of a centrifugal compressor radial inlet. A five-hole probe system, which makes the probe calibration and the data acquisition automatically controlled by computer, was developed and used to measure the pressure, velocity and flow angle distributions inside the radial inlet. The testing portion consists of the entrance and exit of the radial inlet, the outlet section of the suction nozzle and the exit of the plenum, including 46 sampling holes and 923 measuring points. In parallel with the experiment, a computational analysis was also carried out to simulate the internal flow of the radial inlet with a commercial CFD Code. The numerical results are compared with the experimental data. It shows a good agreement between CFD and the measurement on most sections. Based on the experiment and simulation, this study reveals the detailed flow conditions in a radial inlet, which helps to figure out how the complex flow pattern in a radial inlet forms and develops as well as the influences on the downstream components. It yields an improved understanding of the principle of flow phenomena in radial inlets, and gives recommendations for optimizing the structure design of the radial inlet of centrifugal compressors.

Experimental Study of an Axial Compressor Rotor Transfer Function With Non-Uniform Inlet Flow

Volume 1A: General ◽

10.1115/78-gt-69 ◽

1978 ◽

Cited By ~ 1

Author(s):

J. Colpin ◽

P. Kool

Keyword(s):

Flow Field ◽

Three Dimensional ◽

Axial Compressor ◽

Hot Wire ◽

Flow Angle ◽

Compressor Rotor ◽

Rotating Blade ◽

Absolute Flow ◽

Blade Row ◽

Upstream Flow

The aim of the investigation is to study the propagation of a non-uniform upstream flow field through a rotating blade row. The flow is investigated using classical pneumatic instrumentation and hot wire anemometry. The latter allows one to determine the average flow values as well as the instantaneous blade-to-blade flow field. These measurements were performed upstream and downstream of a low-speed axial compressor stage rotor. A triangular inlet total pressure distortion was generated with a grid system, movable in the circumferential direction. The hot-wire data were processed with a periodic sampling and averaging technique to obtain the three-dimensional blade-to-blade flow downstream of the rotor at mid-span. The modification of the blade wakes and the existence of large absolute flow angle fluctuations are evidenced for different relative positions of the distortion and stationary hot wire.

Effect of Flow Rate on Turbulence Dissipation Rate Distribution in a Multiphase Pump

Processes ◽

10.3390/pr9050886 ◽

2021 ◽

Vol 9 (5) ◽

pp. 886

Author(s):

Zongliu Huang ◽

Guangtai Shi ◽

Xiaobing Liu ◽

Haigang Wen

Keyword(s):

Flow Rate ◽

Dissipation Rate ◽

Circumferential Direction ◽

Outlet Section ◽

Inlet Section ◽

Distribution Characteristics ◽

Rate Condition ◽

Rate Distribution ◽

Multiphase Pump ◽

Rotating Impeller

The turbulence dissipation will cause the increment of energy loss in the multiphase pump and deteriorate the pump performance. In order to research the turbulence dissipation rate distribution characteristics in the pressurized unit of the multiphase pump, the spiral axial flow type multiphase pump is researched numerically in the present study. This research is focused on the turbulence dissipation rate distribution characteristics in the directions of inlet to outlet, hub to rim, and in the circumferential direction of the rotating impeller blades. Numerical simulation based on the RANS (Reynolds averaged Navier–Stokes equations) and the k-ω SST (Shear Stress Transport) turbulence model has been carried out. The numerical method is verified by comparing the numerical results with the experimental data. Results show that the regions of the large turbulence dissipation rate are mainly at the inlet and outlet of the rotating impeller and static impeller, while it is almost zero from the inlet to the middle of outlet in the suction surface and pressure surface of the first-stage rotating impeller blades. The turbulence dissipation rate is increased gradually from the hub to the rim of the inlet section of the first-stage rotating impeller, while it is decreased firstly and then increased on the middle and outlet sections. The turbulence dissipation rate distributes unevenly in the circumferential direction on the outlet section. The maximum value of the turbulence dissipation rate occurs at 0.9 times of the rated flow rate, while the minimum value at 1.5 times of the rated flow rate. Four turning points in the turbulence dissipation rate distribution that are the same as the number of impeller blades occur at 0.5 times the blade height at 0.9 times the rated flow rate condition. The turbulence dissipation rate distribution characteristics in the pressurized unit of the multiphase pump have been studied carefully in this paper, and the research results have an important significance for improving the performance of the multiphase pump theoretically.

Surge in a Low-Speed Radial Compressor

Volume 1: Turbomachinery ◽

10.1115/98-gt-426 ◽

1998 ◽

Cited By ~ 3

Author(s):

Corine Meuleman ◽

Frank Willems ◽

Rick de Lange ◽

Bram de Jager

Keyword(s):

Flow Rate ◽

Pressure Rise ◽

Flow Coefficient ◽

Lumped Parameter Model ◽

Pressure Oscillations ◽

Vaned Diffuser ◽

Flow Angle ◽

Radial Compressor ◽

Low Speed ◽

Lumped Parameter

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.