Experimental Study of the Effect of the Tip Clearance to the Diffuser Flow Field and Stage Performance of a Centrifugal Compressor

2012 ◽  
Author(s):  
Ahti Jaatinen ◽  
Teemu Turunen-Saaresti ◽  
Aki Grönman ◽  
Pekka Röyttä ◽  
Jari Backman
Keyword(s):  
Centrifugal Compressor ◽  
Total Pressure ◽  
High Speed ◽  
Flow Region ◽  
Flow Fields ◽  
Tip Clearance ◽  
Flow Angle ◽  
Lower Stage ◽  
Diffuser Flow ◽  
Stage Efficiency

The effect of tip clearance to the centrifugal compressor diffuser flow fields and stage overall performance are studied experimentally. The relative tip clearance (tip clearance divided by the impeller exit blade height) is increased by shimming the shroud side casing of a high-speed variable speed driven industrial centrifugal compressor. Four different relative tip clearances are studied: 0.027, 0.053, 0.082, and 0.106. The stage efficiency and pressure ratios are measured, as well as the diffuser flow fields. The diffuser flow fields are measured both at the diffuser inlet and outlet. The total pressure and flow angle are measured with a cobra probe, and the total pressure and temperature with three Kiel probes. Static pressures are measured adjacent to the probe measurements. As expected, increasing the tip clearance leads to lower stage efficiency and pressure ratios. The decrement in the efficiency due to the increasing of the tip clearance is higher with higher mass flows, and at lower rotational speeds. Increasing tip clearance increases the size of the secondary flow region present at the impeller outlet near the shroud.

scholarly journals Experimental study of centrifugal compressor tip clearance and vaneless diffuser flow fields

2013 ◽  
Vol 227 (8) ◽  
pp. 885-895 ◽  
Author(s):  
Ahti Jaatinen-Värri ◽  
Teemu Turunen-Saaresti ◽  
Pekka Röyttä ◽  
Aki Grönman ◽  
Jari Backman
Keyword(s):  
Experimental Study ◽  
Centrifugal Compressor ◽  
Flow Fields ◽  
Tip Clearance ◽  
Vaneless Diffuser ◽  
Diffuser Flow

scholarly journals Investigation of the Stage Performance and Flow Fields in a Centrifugal Compressor with a Vaneless Diffuser

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Ahti Jaatinen-Värri ◽  
Aki Grönman ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Centrifugal Compressor ◽  
Flow Fields ◽  
Tip Clearance ◽  
Vaneless Diffuser ◽  
Flow Area ◽  
Tip Clearance Flow ◽  
Diffuser Flow ◽  
Clearance Flow ◽  
Stage Performance ◽  
Large Width

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.

Numerical Investigation of Centrifugal Compressor Tip Clearance

2015 ◽  
Author(s):  
Ahti Jaatinen-Värri ◽  
Teemu Turunen-Saaresti ◽  
Aki Grönman ◽  
Jari Backman ◽  
Jonna Tiainen
Keyword(s):  
Centrifugal Compressor ◽  
Tangential Velocity ◽  
Suction Side ◽  
Axial Direction ◽  
Flow Fields ◽  
Velocity Fields ◽  
Tip Clearance ◽  
Pressure Side ◽  
The Difference ◽  
Stage Efficiency

In this paper, the effect of the axial tip clearance on the performance and flow fields of a centrifugal compressor is studied numerically. The compressor is equipped with a pinched vane-less diffuser. Six different axial clearances were modelled and the relative axial tip clearance was varied from 0.027 to 0.154. The tip clearance was changed by transferring the shroud in the axial direction. The modelled results are compared to measured results obtained in previous projects. The results indicate that the effect of tip clearance to the impeller performance is linear, even though the clearance is increased to such amounts which are seldom used in traditional compressors. The clearance has significant effect on the flow fields. Even though the mass flow averaged tangential velocity remained constant with the increasing clearance, the velocity fields show increase in tangential velocity in the passage wake between the suction side of the splitter blade and pressure side of the full blade and decreased in the other blade passage with increasing clearance. Radial velocity contours showed that the backflow region near the shroud increased in size when the clearance is increased. The growth was stronger on the suction side of the splitter blade. Even though there is quite a difference in the stage efficiency between the highest and lowest clearance, the difference in velocity triangles at the impeller exit is small. This should be taken into a consideration when compressors with high relative axial tip clearances are designed.

Effect of Tip Clearance in a Low Speed Centrifugal Compressor

2005 ◽  
Author(s):  
P. Usha ◽  
N. Sitaram
Keyword(s):  
Centrifugal Compressor ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Coefficient ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Velocity Variation ◽  
Fine Grid ◽  
Flow Angle ◽  
Low Speed

Effect of tip clearance on flow field of a low speed centrifugal compressor is presented. Computational study of centrifugal compressor is carried out using structured multi block grid with fine grid in the tip clearance region. Results are obtained with finite volume method upwind scheme using TASCflow software. Centrifugal compressor impeller with four values of clearances i.e., τ = 0%, 1%, 2% and 5% of blade height at trailing edge are examined at five flow coefficients 0.28, 0.34, 0.42 (design value), 0.48 and 0.52. The effect of tip clearance on total pressure coefficient and static pressure coefficient from inlet to outlet of the compressor is analysed at flow coefficient of 0.52. The drop in static pressure coefficient and total pressure coefficient with increase in tip clearance is found to be high at the tip of the blade due to high pressure fluid leakage at the tip of the blade. The static pressure coefficient, total pressure coefficient and tangential velocity variation at outlet are presented at flow coefficient of 0.52. Mass averaged performance graph show the reduction of performance with tip clearance. Total pressure coefficient contours are analysed in five meridional locations at φ = 0.42. Relative velocity vectors are plotted at five meridional locations for τ = 5% at φ = 0.48. Relative flow angle contours are presented at five meridional locations for all clearances at φ = 0.28.

scholarly journals Characterization of Periodic Incoming Wakes in a Low-Pressure Turbine Cascade Test Section by Means of a Fast-Response Single Sensor Virtual Three-Hole Probe

2019 ◽  
Vol 4 (3) ◽  
pp. 26
Author(s):  
Julien Clinckemaillie ◽  
Tony Arts
Keyword(s):  
Total Pressure ◽  
High Speed ◽  
Control Volume ◽  
Low Pressure ◽  
Fast Response ◽  
Pressure Probe ◽  
Flow Angle ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Good Agreement

This paper aims at evaluating the characteristics of the wakes periodically shed by the rotating bars of a spoked-wheel type wake generator installed upstream of a high-speed low Reynolds linear low-pressure turbine blade cascade. Due to the very high bar passing frequency obtained with the rotating wake generator (fbar = 2.4−5.6 kHz), a fast-response pressure probe equipped with a single 350 mbar absolute Kulite sensor has been used. In order to measure the inlet flow angle fluctuations, an angular aerodynamic calibration of the probe allowed the use of the virtual three-hole mode; additionally, yielding yaw corrected periodic total pressure, static pressure and Mach number fluctuations. The results are presented for four bar passing frequencies (fbar = 2.4/3.2/4.6/5.6 kHz), each tested at three isentropic inlet Mach numbers M1,is = 0.26/0.34/0.41 and for Reynolds numbers varying between Re1,is = 40,000 and 58,000, thus covering a wide range of engine representative flow coefficients (ϕ = 0.44−1.60). The measured wake characteristics show fairly good agreement with the theory of fixed cylinders in a cross-flow and the evaluated total pressure losses and flow angle variations generated by the rotating bars show fairly good agreement with theoretical results obtained from a control volume analysis.

scholarly journals Flow Measurements Behind the Inlet Guide Vane of a Centrifugal Compressor

1998 ◽  
Author(s):  
I. Kassens ◽  
M. Rautenberg
Keyword(s):  
Centrifugal Compressor ◽  
Total Pressure ◽  
Guide Vane ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Inlet Guide Vane ◽  
Flow Measurements ◽  
Flow Angle ◽  
Partial Load ◽  
Measurement Location

In a centrifugal compressor adjustable inlet guide vanes (IGV) in front of the impeller are used to regulate the pressure ratio and the mass flow. The stationary measurement of the velocity profile in front of the impeller with different angles of the IGV displays shock losses at the inlet edge of blade of the impeller. In the partial-load region (e.g. partial-load efficiency) the radial distribution of the flow influences considerably the performance of the impeller. The tested compressor consists of an adjustable IGV with straight vanes, a shrouded impeller and a vaneless, parallel diffuser. In the first measurement location, behind the IGV, total pressure, static pressure and flow angle were measured with a 5-hole cylinder probe. In the second measurement location, in front of the impeller, the measurement of the total pressure was carried out with a Kiel probe and the flow angle with a Cobra probe accordingly the static wall pressure was measured. Taking into consideration the fundamental thermodynamical equations it was possible to determine the velocity profiles because of the measured distributions of the flow angle in these two measurement locations. For different angles of the IGV and with various mass flows the distributions of the deflection defect behind the IGV are described. Starting with the measured distributions of the flow in front of the impeller the flow angles at the impeller inlet are calculated and the distributions of the incidence angle at the impeller inlet are figured out.

The Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser

2020 ◽  
Author(s):  
Hiroshi Miida ◽  
Kenta Tajima ◽  
Nobumichi Fujisawa ◽  
Yutaka Ohta
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
Rotational Speed ◽  
Flow Region ◽  
Cfd Analysis ◽  
Vaneless Diffuser ◽  
Low Velocity ◽  
Flow Angle ◽  
Boundary Separation ◽  
Low Mass

Abstract The unsteady diffuser stall behavior in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. The diffuser stall generated as the mass flow rate decreased. The diffuser stall cell rotated at 25–30% of the impeller rotational speed, with diffuser stall fluctuations observed at 180° from the cutoff. The diffuser stall fluctuation magnitude gradually increased near the cutoff. Based on diffuser inlet velocity measurements, the diffuser stall fluctuations generated near both the shroud and hub sides, and the diffuser stall appeared at 180° and 240° from the cutoff. According to the CFD analysis, the mass flow fluctuations at the diffuser exit showed a low mass flow region, rotating at approximately 25% of the impeller rotational speed. They began at 180° from the cutoff and developed as this region approached the cutoff. Therefore, the diffuser stall could be simulated by CFD analysis. First, the diffuser stall cell originated at 180° from the cutoff by interaction with boundary separation and impeller discharge vortex. Then, the diffuser stall cell further developed by boundary separation accumulation and the induced low velocity area, located at the stall cell center. The low velocity region formed a blockage across the diffuser passage span. The diffuser stall cell expanded in the impeller rotational direction due to boundary separation caused by a positive flow angle. Finally, the diffuser stall cell vanished when it passed the cutoff, because mass flow recovery occurred.

Experimental Investigation of the Flow in the Pipe Diffuser of a Centrifugal Compressor Stage Under Selected Parameter Variations

2009 ◽  
Author(s):  
Uwe Zachau ◽  
Reinhard Niehuis ◽  
Herwart Hoenen ◽  
David C. Wisler
Keyword(s):  
Centrifugal Compressor ◽  
Measurement Techniques ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Test Facility ◽  
Experimental Investigations ◽  
Pressure Side ◽  
Compressor Stage ◽  
Diffuser Flow ◽  
Parameter Variations

On a centrifugal compressor test facility various experimental investigations have been carried out contributing a valuable gain in knowledge on the fundamental flow physics within passage type diffusers. An extensive measurement series using various steady, unsteady and laser optical measurement techniques has been performed to detect the unsteady, highly three dimensional diffuser flow under various realistic operating conditions. Zachau et al. [1] presented the test facility and the results gathered under nominal conditions. As a follow-up the results of investigated parameter variations are now presented, covering bleed variations, impeller tip clearance and impeller-diffuser misalignment studies. The data is compared to the benchmark created from the nominal baseline data sets and evaluated with respect to the compressor stage performance. Zachau et al. [1] found that under nominal conditions the flow in the pipe diffuser separates on the pressure side in the first half of the pipe. In the last 30% of the pipe hardly any deceleration of the flow takes place. From this, special attention is given to the investigated parameter variations regarding a first proposal for a diffuser design change, which consists in shortening the diffuser. The results for each parameter variation are evaluated in detail in direct comparison to the nominal baseline configuration underlining the conclusion made earlier that the diffuser flow always separates on the pressure side with negligible deceleration in the last third of the diffusing pipe.

scholarly journals Performance Improvement of Return Channel in Multistage Centrifugal Compressor Using Multi-Objective Optimization

2012 ◽  
Author(s):  
Y. Nishida ◽  
H. Kobayashi ◽  
H. Nishida ◽  
K. Sugimura
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Coefficient ◽  
Swirl Flow ◽  
Optimized Design ◽  
Original Design ◽  
Flow Angle ◽  
Second Stage ◽  
Return Channel ◽  
Multistage Centrifugal Compressor ◽  
Stage Efficiency

The effect of the design parameters of a return channel on the performance of a multistage centrifugal compressor was numerically investigated, and the shape of the return channel was optimized using a multi-objective optimization method based on a genetic algorithm to improve the performance of the centrifugal compressor. The results of sensitivity analysis using Latin hypercube sampling suggested that the inlet-to-outlet area ratio of the return vane affected the pressure loss in the return channel, and that the inlet-to-outlet radius ratio of the return vane affected the outlet flow angle from the return vane. Moreover, this analysis suggested that the number of return vanes affected both the loss and the flow angle at the outlet. As a result of optimization, the number of return vanes was increased from 14 to 22 and the area ratio was decreased from 0.71 to 0.66. The radius ratio was also decreased from 2.1 to 2.0. Performance tests on a centrifugal compressor with two return channels (the original design and optimized design) were carried out using two-stage test apparatus. The measured flow distribution exhibited a swirl flow in the center region and a reversed swirl flow near the hub and shroud sides. The exit flow of the optimized design was more uniform than that of the original design. For the optimized design, the overall two-stage efficiency and pressure coefficient were increased by 0.7% and 1.5%, respectively. Moreover, the second-stage efficiency and pressure coefficient were respectively increased by 1.0% and 3.2%, It is considered that the increase in the second-stage efficiency was caused by the increased uniformity of the flow, and the rise in the pressure coefficient was caused by a decrease in the residual swirl flow. It was thus concluded from the numerical and experimental results that the optimized return channel improved the performance of the multistage centrifugal compressor.

scholarly journals Experimental Investigation of Centrifugal Compressor Stabilization Techniques

2003 ◽  
Author(s):  
Gary J. Skoch
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
External Source ◽  
Tip Clearance ◽  
Stable Operation ◽  
Injection Angle ◽  
Surge Margin ◽  
Air Supply ◽  
Stabilizing Effect ◽  
Design Speed

Results from a series of experiments to investigate techniques for extending the stable flow range of a centrifugal compressor are reported. The research was conducted in a high-speed centrifugal compressor at the NASA Glenn Research Center. The stabilizing effect of steadily flowing air-streams injected into the vaneless region of a vane-island diffuser through the shroud surface is described. Parametric variations of injection angle, injection flow rate, number of injectors, injector spacing, and injection vs. bleed were investigated for a range of impeller speeds and tip clearances. Both the compressor discharge and an external source were used for the injection air supply. The stabilizing effect of flow obstructions created by tubes that were inserted into the diffuser vaneless space through the shroud was also investigated. Tube immersion into the vaneless space was varied in the flow obstruction experiments. Results from testing done at impeller design speed and tip clearance are presented. Surge margin improved by 1.7 points using injection air that was supplied from within the compressor. Externally supplied injection air was used to return the compressor to stable operation after being throttled into surge. The tubes, which were capped to prevent mass flux, provided 9.3 points of additional surge margin over the baseline surge margin of 11.7 points.

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