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.

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 Unsteady Tip Clearance Flow in a Low-Speed One and Half Stage Axial Compressor With LES and PIV

2015 ◽  
Author(s):  
Chunill Hah ◽  
Michael Hathaway ◽  
Joseph Katz ◽  
David Tan
Keyword(s):  
Axial Compressor ◽  
Suction Side ◽  
Flow Fields ◽  
Tip Clearance ◽  
Gap Size ◽  
Tip Clearance Flow ◽  
Gap Flow ◽  
Clearance Flow ◽  
Single Structure ◽  
Tip Clearance Vortex

The primary focus of this paper is to investigate how a rotor’s unsteady tip clearance flow structure changes in a low speed one and half stage axial compressor when the rotor tip gap size is increased from 0.5 mm (0.49% of rotor tip blade chord, 2% of blade span) to 2.4 mm (2.34% chord, 4% span) at the design condition are investigated. The changes in unsteady tip clearance flow with the 0.62 % tip gap as the flow rate is reduced to near stall condition are also investigated. A Large Eddy Simulation (LES) is applied to calculate the unsteady flow field at these three flow conditions. Detailed Stereoscopic PIV (SPIV) measurements of the current flow fields were also performed at the Johns Hopkins University in a refractive index-matched test facility which renders the compressor blades and casing optically transparent. With this setup, the unsteady velocity field in the entire flow domain, including the flow inside the tip gap, can be measured. Unsteady tip clearance flow fields from LES are compared with the PIV measurements and both LES and PIV results are used to study changes in tip clearance flow structures. The current study shows that the tip clearance vortex is not a single structure as traditionally perceived. The tip clearance vortex is formed by multiple interlaced vorticities. Therefore, the tip clearance vortex is inherently unsteady. The multiple interlaced vortices never roll up to form a single structure. When phased-averaged, the tip clearance vortex appears as a single structure. When flow rate is reduced with the same tip gap, the tip clearance vortex rolls further upstream and the tip clearance vortex moves further radially inward and away from the suction side of the blade. When the tip gap size is increased at the design flow condition, the overall tip clearance vortex becomes stronger and it stays closer to the blade suction side and the vortex core extends all the way to the exit of the blade passage. Measured and calculated unsteady flow fields inside the tip gap agree fairly well. Instantaneous velocity vectors inside the tip gap from both the PIV and LES do show flow separation and reattachment at the entrance of tip gap as some earlier studies suggested. This area at the entrance of tip gap flow (the pressure side of the blade) is confined very close to the rotor tip section. With a small tip gap (0.5mm), the gap flow looks like a simple two-dimensional channel flow with larger velocity near the casing for both flow rates. A small area with a sharp velocity gradient is observed just above the rotor tip. This strong shear layer is turned radially inward when it collides with the incoming flow and forms the core structure of the tip clearance vortex. When tip gap size is increased to 2.4 mm at the design operation, the radial profile of the tip gap flow changes drastically. With the large tip gap, the gap flow looks like a two-dimensional channel flow only near the casing. Near the rotor top section, a bigger region with very large shear and reversed flow is observed.

Experimental and Computational Results From the NASA Lewis Low-Speed Centrifugal Impeller at Design and Part-Flow Conditions

1996 ◽  
Vol 118 (1) ◽  
pp. 55-65 ◽  
Author(s):  
R. M. Chriss ◽  
M. D. Hathaway ◽  
J. R. Wood
Keyword(s):  
Boundary Layers ◽  
Centrifugal Compressor ◽  
Flow Condition ◽  
Tip Clearance ◽  
Computational Results ◽  
Flow Conditions ◽  
Lower Mass ◽  
Computational Tools ◽  
Tip Clearance Flow ◽  
Clearance Flow

The NASA Lewis Low-Speed Centrifugal Compressor (LSCC) has been investigated with laser anemometry and computational analysis at two flow conditions: the design condition as well as a lower mass flow condition. Previously reported experimental and computational results at the design condition are in the literature (Hathaway et al., 1993). In that paper extensive analysis showed that inducer blade boundary layers are centrifuged outward and entrained into the tip clearance flow and hence contribute significantly to the throughflow wake. In this report results are presented for a lower mass flow condition along with further results from the design case. The data set contained herein consists of three-dimensional laser velocimeter results upstream, inside, and downstream of the impeller. In many locations data have been obtained in the blade and endwall boundary layers. The data are presented in the form of throughflow velocity contours as well as secondary flow vectors. The results reported herein illustrate the effects of flow rate on the development of the through flow momentum wake as well as on the secondary flow. The computational results presented confirm the ability of modern computational tools to model the complex flow in a subsonic centrifugal compressor accurately. However, the blade tip shape and tip clearance must be known in order to properly simulate the flow physics. In addition, the ability to predict changes in the throughflow wake, which is largely fed by the tip clearance flow, as the impeller is throttled should give designers much better confidence in using computational tools to improve impeller performance.

scholarly journals Laser Anemometer Measurements of the Flow Field in a 4:1 Pressure Ratio Centrifugal Impeller

1997 ◽  
Author(s):  
G. J. Skoch ◽  
P. S. Prahst ◽  
M. P. Wernet ◽  
J. R. Wood ◽  
A. J. Strazisar
Keyword(s):  
Flow Field ◽  
Pressure Ratio ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Vaneless Diffuser ◽  
Suction Surface ◽  
Tip Clearance Flow ◽  
Through Flow ◽  
Clearance Flow ◽  
Flow Velocities

A laser-doppler anemometer was used to obtain flow-field velocity measurements in a 4:1 pressure ratio, 4.54 kg/s (10 lbm/s), centrifugal impeller, with splitter blades and backsweep, which was configured with a vaneless diffuser. Measured through-flow velocities are reported for ten quasi-orthogonal survey planes at locations ranging from 1% to 99% of main blade chord. Measured through-flow velocities are compared to those predicted by a 3-D viscous steady flow analysis (Dawes) code. The measurements show the development and progression through the impeller and vaneless diffuser of a through-flow velocity deficit which results from the tip clearance flow and accumulation of low momentum fluid centrifuged from the blade and hub surfaces. Flow traces from the CFD analysis show the origin of this deficit which begins to grow in the inlet region of the impeller where it is first detected near the suction surface side of the passage. It then moves toward the pressure side of the channel, due to the movement of tip clearance flow across the impeller passage, where it is cut by the splitter blade leading edge. As blade loading increases toward the rear of the channel the deficit region is driven back toward the suction surface by the cross-passage pressure gradient. There is no evidence of a large wake region that might result from flow separation and the impeller efficiency is relatively high. The flow field in this impeller is quite similar to that documented previously by NASA Lewis in a large low-speed backswept impeller.

Assessment of Turbulence Model Predictions for an Aero-Engine Centrifugal Compressor

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Jason A. Bourgeois ◽  
Robert J. Martinuzzi ◽  
Eric Savory ◽  
Chao Zhang ◽  
Douglas A. Roberts
Keyword(s):  
Centrifugal Compressor ◽  
Turbulence Modeling ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Flow Fields ◽  
Reynolds Stress Model ◽  
Tip Clearance ◽  
Mean Flow ◽  
Tip Clearance Flow ◽  
Sst Model

The accurate prediction of mean flow fields with high degrees of curvature, adverse pressure gradients, and three-dimensional turbulent boundary layers typically present in centrifugal compressor stages is a significant challenge when applying Reynolds averaged Navier–Stokes turbulence modeling techniques. The current study compares the steady-state mixing plane predictions using four turbulence models for a centrifugal compressor stage with a tandem impeller and a “fish-tail” style discrete passage diffuser. The models analyzed are the k-ε model (an industry standard for many years), the shear stress transport (SST) model, a proposed modification to the SST model denoted as the SST-reattachment modification (RM), and the Speziale, Sarkar, and Gatski Reynolds stress model (RSM-SSG). Comparisons with measured performance parameters—the stage total-to-static pressure and total-to-total temperature ratios—indicate more accurate performance predictions from the RSM-SSG and SST models as compared to the k-ε and SST-RM models. Details of the different predicted flow fields are presented. Estimates of blockage, aerodynamic slip factor, and impeller exit velocity profiles indicate significant physical differences in the predictions at the impeller-diffuser interface. Topological flow field differences are observed: the separated tip clearance flow is found to reattach with the SST, SST-RM, and RSM-SSG models, while it does not with the k-ε model, a larger shroud separation at the impeller exit seen with the SST and SST-RM models, and core flow differences are in the complex curved diffuser geometry. The results are discussed in terms of the production and dissipation of k predicted by the various models due to their intrinsic modeling assumptions. These comparisons will assist aerodynamic designers in choosing appropriate turbulence models, and may benefit future modeling research.

Investigation of Pre-Stall Behavior in an Axial Compressor Rotor—Part I: Unsteadiness of Tip Clearance Flow

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Yanhui Wu ◽  
Qingpeng Li ◽  
Jiangtao Tian ◽  
Wuli Chu
Keyword(s):  
Unsteady Flow ◽  
Periodic Variation ◽  
Flow Fields ◽  
Low Energy ◽  
Tip Clearance ◽  
Flow Mechanism ◽  
Equilibrium Solutions ◽  
Tip Clearance Flow ◽  
Compressor Rotor ◽  
Clearance Flow

To investigate the pre-stall behavior of an axial flow compressor rotor, which was experimentally observed with spike-type stall inception, systematic experimental and whole-passage simulations were laid out to analyze the internal flow fields in the test rotor. In this part, emphases were put on the analyses of experimental results and the predicted results from steady simulations and unsteady simulations, which converged to equilibrium solutions with nearly periodic fluctuations of efficiency. The objective was to uncover the unsteady behavior of tip clearance flow and its associated flow mechanism at near-stall conditions. To validate the steady simulation results, the predicted total characteristics and spanwise distributions of aerodynamic parameters were first compared with the measured steady data, and a good agreement was achieved. Then, the numerically obtained unsteady flow fields during one period of efficiency fluctuations were analyzed in detail. The instantaneous flow structure near casing showed that tip secondary vortex (TSV), which appeared in the previous unsteady single-passage simulations, did exist in tip flow fields of whole-passage simulations. The cyclical motion of this vortex was the main source of the nearly periodic variation of efficiency. The simulated active period of TSV increased when the mass flow rate decreased. The simulated frequency of TSV at flow condition very close to the measured stall point equaled the frequency of the characteristic hump identified from the instantaneous casing pressure measurements. This coincidence implied that the occurrence of this hump was most probably a result of the movement of TSV. Further flow field analyses indicated that the interaction of the low-energy leakage fluid from adjacent passages with the broken-down tip leakage vortex (TLV) was the flow mechanism for the formation of TSV. Once TSV appeared in tip flow fields, its rearward movement would lead to a periodic variation in near-tip blade loading, which in turn altered the strength of TLV and TSV, accordingly, the low-energy regions associated with the breakdown of TLV and the motion of TSV, thus establishing a self-sustained unsteady flow oscillation in tip flow fields.

scholarly journals Experimental and Computational Results From the Nasa Lewis Low-Speed Centrifugal Impeller at Design and Part Flow Conditions

1994 ◽  
Author(s):  
Randall M. Chriss ◽  
Michael D. Hathaway ◽  
Jerry R. Wood
Keyword(s):  
Boundary Layers ◽  
Centrifugal Compressor ◽  
Flow Condition ◽  
Tip Clearance ◽  
Computational Results ◽  
Flow Conditions ◽  
Lower Mass ◽  
Computational Tools ◽  
Tip Clearance Flow ◽  
Clearance Flow

The NASA Lewis Low-Speed Centrifugal Compressor (LSCC) has been investigated with laser anemometry and computational analysis at two flow conditions: the design condition as well as a lower mass flow condition. Previously reported experimental and computational results at the design condition are in the literature (Hathaway et al. 1993). In that paper extensive analysis showed that inducer blade boundary layers are centrifuged outward and entrained into the tip clearance flow and hence contribute significantly to the throughflow wake. In this report results are presented for a lower mass flow condition along with further results from the design case. The data set contained herein consists of three-dimensional laser velocimeter results upstream, inside and downstream of the impeller. In many locations data have been obtained in the blade and endwall boundary layers. The data are presented in the form of throughflow velocity contours as well as secondary flow vectors. The results reported herein illustrate the effects of flow rate on the development of the throughflow momentum wake as well as on the secondary flow. The computational results presented confirm the ability of modern computational tools to accurately model the complex flow in a subsonic centrifugal compressor. However, the blade tip shape and tip clearance must be known in order to properly simulate the flow physics. In addition, the ability to predict changes in the throughflow wake, which is largely fed by the tip clearance flow, as the impeller is throttled should give designers much better confidence in using computational tools to improve impeller performance.

Role of Tip-Leakage Vortices and Passage Shock in Stall Inception in a Swept Transonic Compressor Rotor

2004 ◽  
Author(s):  
Chunill Hah ◽  
Douglas C. Rabe ◽  
Aspi R. Wadia
Keyword(s):  
Boundary Layer ◽  
Flow Fields ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Stall Inception ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Tip Clearance Vortex

The current paper reports on investigations aimed at advancing the understanding of the flow field near the casing of a forward-swept transonic compressor rotor. The role of tip clearance flow and its interaction with the passage shock on stall inception are analyzed in detail. Steady and unsteady three-dimensional viscous flow calculations are applied to obtain flow fields at various operating conditions. The numerical results are first compared with available measured data. Then, the numerically obtained flow fields are interrogated to identify the roles of flow interactions between the tip clearance flow, the passage shock, and the blade/endwall boundary layers. In addition to the flow field with nominal tip clearance, two more flow fields are analyzed in order to identify the mechanisms of blockage generation: one with zero tip clearance, and one with nominal tip clearance on the forward portion of the blade and zero clearance on the aft portion. The current study shows that the tip clearance vortex does not break down, even when the rotor operates in a stalled condition. Interaction between the shock and the suction surface boundary layer causes the shock, and therefore the tip clearance vortex, to oscillate. However, for the currently investigated transonic compressor rotor, so-called breakdown of the tip clearance vortex does not occur during stall inception. The tip clearance vortex originates near the leading edge tip, but moves downward in the spanwise direction inside the blade passage. A low momentum region develops above the tip clearance vortex from flow originating from the casing boundary layer. The low momentum area builds up immediately downstream of the passage shock and above the core vortex. This area migrates toward the pressure side of the blade passage as the flow rate is decreased. The low momentum area prevents incoming flow from passing through the pressure side of the passage and initiates stall inception. It is well known that inviscid effects dominate tip clearance flow. However, complex viscous flow structures develop inside the casing boundary layer at operating conditions near stall.

Numerical Simulation of a Transonic Centrifugal Compressor Blades Tip Clearance Flow of Vehicle Turbocharger

2008 ◽  
Author(s):  
Gongda Guo ◽  
Yangjun Zhang ◽  
Jianzhong Xu ◽  
Xinqian Zheng ◽  
Weilin Zhuge
Keyword(s):  
Shock Waves ◽  
Centrifugal Compressor ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Transonic Centrifugal Compressor ◽  
Clearance Flow ◽  
Blade Tip ◽  
Blade Tip Clearance

Flow induced by blade tip clearance is important for centrifugal compressor, especially for the high charging ratio transonic centrifugal compressor of the vehicle. Based on three-dimensional CFD method, the evolution and mechanism of tip clearance flow for the high charging ratio transonic centrifugal compressor are investigated. It is verified that shock waves have important effect on blade tip clearance flow. The original position and strength of leakage vortices depend on the position and intensity of shock waves. The tip leakage vortex (TLV) evolution is influenced by the evolution of passage vortex (PV), corner vortex (CV) and separated vortex (SV). Shock wave, adverse pressure gradient and casing boundary layer accelerate the leakage vortices breakdown. Leakage vortex loss is the most important factor of impeller loss. The research on the blades tip leakage flow of transonic centrifugal compressor for vehicle lays a foundation for transonic centrifugal compressor flow control.

Sign in / Sign up

Export Citation Format

Share Document