Experimental Study of Centrifugal Impeller Discharge Flow in Vaneless and Vaned Diffusers

1984 ◽  
Vol 106 (2) ◽  
pp. 455-467 ◽  
Author(s):  
M. Inoue ◽  
N. A. Cumpsty
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Centrifugal Impeller ◽  
Data Logging ◽  
Reference Case ◽  
Vaned Diffuser ◽  
Impeller Outlet ◽  
On Line ◽  
Made In

The flow discharged from centrifugal impellers is highly distorted and its behavior in the diffuser could be expected to have a determining effect on the performance of the compressor. The present work sets out to investigate this. The experimental work reported in this paper was designed to investigate the interaction between the vaned diffuser and the impeller. Unsteady measurements of velocity and wall static pressure were made at numerous positions in a vaned diffuser using an on-line data logging system. Experiments were carried out at a range of flow coefficients for three diffusers with 10, 20, and 30 vanes set at each of three different radius ratios, 1.04, 1.1, and 1.2. A limited number of experiments were also carried out with restaggered diffuser vanes and as a reference case extensive measurements were made in a vaneless diffuser build. The impeller, which was designed for a pressure ratio of 4.6, was run at low speed (3000 rpm) after modification to make its overall diffusion equivalent to that at the high speed for which it was designed. The circumferential distortion from the impeller was attenuated very rapidly in the entrance region of the diffuser vanes and suprisingly had only minor effects on the flow inside the vaned diffuser passage. The effect of the diffuser vanes on the flow discharged from the impeller was evident and reversal of flow back into the impeller was detected when the diffuser vanes were close to the impeller and the flow rate was not very high. The time-mean total and static pressure at impeller outlet were found to vary over the pitch of a diffuser vane, and a variation in the strength of the impeller wake was also observed.

An Experimental Investigation of Stator Induced Unsteadiness on Centrifugal Impeller Outflow

1996 ◽  
Vol 118 (1) ◽  
pp. 41-51 ◽  
Author(s):  
M. Ubaldi ◽  
P. Zunino ◽  
G. Barigozzi ◽  
A. Cattanei
Keyword(s):  
Static Pressure ◽  
Fast Response ◽  
Centrifugal Impeller ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Pressure Transducers ◽  
Front End ◽  
Impeller Outlet ◽  
Instantaneous Flow Field ◽  
Response Pressure

Detailed flow measurements were taken in a centrifugal turbomachine model to investigate the aerodynamic influence of the vaned diffuser on the impeller flow. The model consists of an unshrouded centrifugal impeller with backswept blades and a rotatable vaned diffuser, which enables a continuous variation of the vaned diffuser location with respect to the measuring points. Phase-locked ensemble-averaged velocity components have been measured with hot-wire probes at the impeller outlet for 30 different relative positions of the probe with respect to the diffuser vanes. The data also include the distribution of the ensemble-averaged static pressure at the impeller front end, taken by means of miniature fast response pressure transducers flush-mounted at the impeller stationary casing. By circumferentially averaging the results obtained for the different circumferential probe locations, the periodically perturbed impeller flow has been split into a relative steady flow and a stator-generated unsteadiness. The results for the different probe positions have also been correlated in time to obtain instantaneous flow field images in the relative frame, which provide information on the various aspects of the diffuser vane upstream influence on the relative flow leaving the impeller.

An Experimental Investigation of Stator Induced Unsteadiness on Centrifugal Impeller Outflow

1994 ◽  
Author(s):  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Glovanna Barigozzi ◽  
Andrea Cattanel
Keyword(s):  
Static Pressure ◽  
Fast Response ◽  
Centrifugal Impeller ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Pressure Transducers ◽  
Front End ◽  
Impeller Outlet ◽  
Instantaneous Flow Field ◽  
Response Pressure

Detailed flow measurements were taken in a centrifugal turbomachine model to investigate the aerodynamic influence of the vaned diffuser on the impeller flow. The model consists of an unshrouded centrifugal impeller with backswept blades and a rotatable vaned diffuser which enables a continuous variation of the vaned diffuser location with respect to the measuring points. Phase locked ensemble averaged velocity components have been measured with hot wire probes at the impeller outlet for 30 different relative positions of the probe with respect to the diffuser vanes. The data also include the distribution of the ensemble averaged static pressure at the impeller front end, taken by means of miniature fast response pressure transducers flush mounted at the impeller stationary casing. By circumferentially averaging the results obtained for the different circumferential probe locations, the periodically perturbed impeller flow has been split into a relative steady flow and a stator generated unsteadiness. The results for the different probe positions have also been correlated in time to obtain instantaneous flow field images in the relative frame, which provide information on the various aspects of the diffuser vane upstream influence on the relative flow leaving the impeller.

Performance of Strongly Bowed Stators in a Four-Stage High-Speed Compressor

2004 ◽  
Vol 126 (3) ◽  
pp. 333-338 ◽  
Author(s):  
Axel Fischer ◽  
Walter Riess ◽  
Joerg R. Seume
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Maximum Pressure ◽  
Controlled Diffusion ◽  
Stage 4 ◽  
The University

The FVV sponsored project “Bow Blading” (cf. acknowledgments) at the Turbomachinery Laboratory of the University of Hannover addresses the effect of strongly bowed stator vanes on the flow field in a four-stage high-speed axial compressor with controlled diffusion airfoil (CDA) blading. The compressor is equipped with more strongly bowed vanes than have previously been reported in the literature. The performance map of the present compressor is being investigated experimentally and numerically. The results show that the pressure ratio and the efficiency at the design point and at the choke limit are reduced by the increase in friction losses on the surface of the bowed vanes, whose surface area is greater than that of the reference (CDA) vanes. The mass flow at the choke limit decreases for the same reason. Because of the change in the radial distribution of axial velocity, pressure rise shifts from stage 3 to stage 4 between the choke limit and maximum pressure ratio. Beyond the point of maximum pressure ratio, this effect is not distinguishable from the reduction of separation by the bow of the vanes. Experimental results show that in cases of high aerodynamic loading, i.e., between maximum pressure ratio and the stall limit, separation is reduced in the bowed stator vanes so that the stagnation pressure ratio and efficiency are increased by the change to bowed stators. It is shown that the reduction of separation with bowed vanes leads to a increase of static pressure rise towards lower mass flow so that the present bow bladed compressor achieves higher static pressure ratios at the stall limit.

Some Studies on Low Solidity Vaned Diffusers of a Centrifugal Compressor Stage

2005 ◽  
Author(s):  
T. Ch. Siva Reddy ◽  
G. V. Ramana Murty ◽  
Prasad Mukkavilli ◽  
D. N. Reddy
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Pressure Recovery ◽  
Compressor Stage ◽  
Recovery Coefficient ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage ◽  
Pressure Recovery Coefficient

Numerical simulation of impeller and low solidity vaned diffuser (LSD) of a centrifugal compressor stage is performed individually using CFX- BladeGen and BladeGenPlus codes. The tip mach number for the chosen study was 0.35. The same configuration was used for experimental investigation for a comparative study. The LSD vane is formed using standard NACA profile with marginal modification at trailing edge. The performance parameters obtained form numerical studies at the exit of impeller and the diffuser have been compared with the corresponding experimental data. These parameters are pressure ratio, polytropic efficiency and flow angle at the impeller exit where as the parameters those have been compared at the exit of diffuser are the static pressure recovery coefficient and the exit flow angle. In addition, the numerical prediction of the blade loading in terms of blade surface pressure distribution on LSD vane has been compared with the corresponding experimental results. Static pressure recovery coefficient and flow angle at diffuser exit is seen to match closely at higher flows. The difference at lower flows could be due to the effect of interaction between impeller and diffuser combinations, as the numerical analysis was done separately for impeller and diffuser and the effect of impeller diffuser interaction was not considered.

scholarly journals Interpreting Aerodynamics of a Transonic Impeller from Static Pressure Measurements

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Fangyuan Lou ◽  
John Charles Fabian ◽  
Nicole Leanne Key
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Pressure Measurements ◽  
High Loss ◽  
Supersonic Inlet ◽  
Mach Numbers ◽  
Inlet Conditions

This paper investigates the aerodynamics of a transonic impeller using static pressure measurements. The impeller is a high-speed, high-pressure-ratio wheel used in small gas turbine engines. The experiment was conducted on the single stage centrifugal compressor facility in the compressor research laboratory at Purdue University. Data were acquired from choke to near-surge at four different corrected speeds (Nc) from 80% to 100% design speed, which covers both subsonic and supersonic inlet conditions. Details of the impeller flow field are discussed using data acquired from both steady and time-resolved static pressure measurements along the impeller shroud. The flow field is compared at different loading conditions, from subsonic to supersonic inlet conditions. The impeller performance was strongly dependent on the inducer, where the majority of relative diffusion occurs. The inducer diffuses flow more efficiently for inlet tip relative Mach numbers close to unity, and the performance diminishes at other Mach numbers. Shock waves emerging upstream of the impeller leading edge were observed from 90% to 100% corrected speed, and they move towards the impeller trailing edge as the inlet tip relative Mach number increases. There is no shock wave present in the inducer at 80% corrected speed. However, a high-loss region near the inducer throat was observed at 80% corrected speed resulting in a lower impeller efficiency at subsonic inlet conditions.

Investigation of the Wake Effect From the Centrifugal Splitter Impeller Blade to the Vaned Diffuser

2012 ◽  
Author(s):  
Xuechen Li ◽  
Guang Xi ◽  
Jiang Hua ◽  
Wuqi Gong
Keyword(s):  
Flow Characteristics ◽  
Suction Side ◽  
Wake Flow ◽  
Centrifugal Impeller ◽  
Wake Effect ◽  
Impeller Blade ◽  
Vaned Diffuser ◽  
Side Pressure ◽  
Unsteady Wake ◽  
Impeller Outlet

In this paper, the unsteady wake effect from an unshrouded centrifugal impeller with splitter blades was numerically and experimentally investigated. The numerical simulated detail flow characteristics of two stations, respectively placed at the impeller outlet and the diffuser inlet, were compared with the measured data. The “jet-wake” flow pattern was observed at the exit of the impeller. And the investigation showed that the wake effect of the splitter was weaker that of the main blade. But both the main blade and the splitter blade wake could affect the diffuser performance at a range of whole-chord length and they provoked the pressure side profile pressure fluctuating intensely from 10% chord to 50% chord, while the suction side pressure varying rapidly at the range from 60% chord to 80% chord.

Experiments With a Model Free Rotating Vaneless Diffuser

1975 ◽  
Vol 97 (2) ◽  
pp. 231-242 ◽  
Author(s):  
C. Rodgers ◽  
H. Mnew
Keyword(s):  
Static Pressure ◽  
Experimental Testing ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Tangential Velocity ◽  
Vaneless Diffuser ◽  
Vaned Diffuser ◽  
High Pressure Ratio ◽  
Model Free ◽  
Inner Diameter

Experimental testing of a model free-rotating vaneless diffuser, for application to high pressure ratio single-stage centrifugal compressors, was conducted to determine diffuser performance under braked and free rotating conditions at entry Mach numbers up to unity. The experimental test rig comprised a swirl generating nozzle upstream of the model vaneless diffuser rotor with an outer-to-inner diameter ratio of 1.3. Additional downstream diffusion was completed with stationary vaneless and vaned diffuser inserts. A significant improvement in diffuser performance was achieved under free-rotating conditions even though large wakes generated by upstream stationary swirl nozzles were present. Overall static pressure recovery for the complete diffusion system increased approximately 20 percent at free-rotating conditions corresponding to a tangential velocity ratio (diffuser rotor/incident stream) of 0.43.

scholarly journals Stall Inception in a High-Speed Low Aspect Ratio Fan Including the Effects of Casing Treatments

1994 ◽  
Author(s):  
S. E. Gorrell ◽  
P. M. Russler
Keyword(s):  
Aspect Ratio ◽  
High Speed ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Stall Inception ◽  
Casing Treatment ◽  
Low Aspect Ratio ◽  
Casing Treatments

The stall inception process in high-speed compressor components is important to understand in order to increase stage loading while maintaining stall margin. This paper presents the results of an in depth experimental investigation on the stall inception of a two stage, high-speed, low aspect ratio fan that is representative of current operational commercial and military fan technology. High-response static pressure measurements are presented which detail the stall inception process of the fan under various operating conditions. These conditions include: varied corrected speeds, a smooth case, a circumferential groove casing treatment, and a recirculating cavity casing treatment. Stage pressure characteristics and radial pressure ratio profiles are presented for the different operating conditions. The stage performance data, together with the static pressure data, are analyzed to provide a clear and thorough understanding of the stall inception process and how the process may vary under different conditions. Experimental results show that a stage may stall on the positive, neutral, or negative sloped part of the pressure characteristic. The three casing treatments had a significant effect on the rotor tip flow and these variations changed the stall inception path of the fan. Stall inception was characterized by the formation of a stall inception cell which grew to fully developed rotating stall. Properties affected by the changing tip flow include the stall inception duration, stall inception cell frequency, existence of modal waves, duration of modal waves, and modal wave frequency. In some instances modal waves appear to play a role in stall inception, in others they do not.

Performance of Strongly Bowed Stators in a 4-Stage High Speed Compressor

2003 ◽  
Author(s):  
Axel Fischer ◽  
Walter Riess ◽  
Joerg R. Seume
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Maximum Pressure ◽  
Controlled Diffusion ◽  
Stage 4 ◽  
The University

The FVV-sponsored-Project “Bow Blading” (c.f. acknowledgments) at the Turbomachinery Laboratory of the University of Hannover addresses the effect of strongly bowed stator vanes on the flow field in an 4-stage high speed axial compressor with controlled diffusion airfoil (CDA) blading. The compressor is equipped with more strongly bowed vanes than have previously been reported in the literature. The performance map of the present compressor is being investigated experimentally and numerically. The results show that the pressure ratio and the efficiency at the design point and at the choke limit are reduced by the increase in friction losses on the surface of the bowed vanes, whose surface area is greater than that of the reference (CDA) vanes. The mass flow at the choke limit decreases for the same reason. Because of the change in the radial distribution of axial velocity, pressure rise shifts from stage 3 to stage 4 between the choke limit and maximum pressure ratio. Beyond the point of maximum pressure ratio, this effect is not distinguishable from the reduction of separation by the bow of the vanes. Experimental results show that in cases of high aerodynamic loading, i.e. between maximum pressure ratio and the stall limit, separation is reduced in the bowed stator vanes so that the stagnation pressure ratio and efficiency are increased by the change to bowed stators. It is shown that the reduction of separation with bowed vanes leads to a increase of static pressure rise towards lower mass flow so that the present bow bladed compressor achieves higher static pressure ratios at the stall limit.

Aerodynamic Optimization Design of Vaned Diffusers for the 100 kW Micro Gas Turbine’s Centrifugal Compressor

2008 ◽  
Author(s):  
Guang Xi ◽  
Zhiheng Wang ◽  
Chunmei Zhang ◽  
Minjian Yuan
Keyword(s):  
Centrifugal Compressor ◽  
Surrogate Model ◽  
High Speed ◽  
Optimization Design ◽  
Performance Test ◽  
Three Dimensional ◽  
Centrifugal Impeller ◽  
Aerodynamic Optimization ◽  
Vaned Diffuser ◽  
Practical Engineering

In this paper the design optimization of vaned diffuser for the 100kW microturbine’s centrifugal compressor is carried out. The forward-loaded and the conventional airfoil diffusers are respectively redesigned based on the surrogate model and the three dimensional viscous flow analyses. The objective of the optimization is to redesign the diffuser that assures, for a given operating condition of the centrifugal impeller, the stage isentropic efficiency to be highest. Using the surrogate model the optimization process is accelerated and the 3D flow analysis’s application to the practical engineering design is efficiently realized. To validate the optimization result, the compressor stage performance test is performed on a high speed centrifugal compressor test rig with one original diffuser and its redesigned, respectively.

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