On the Interactions of a Rotor Blade Tip Flow With Axial Casing Grooves in an Axial Compressor Near the Best Efficiency Point

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
Joseph Katz
Keyword(s):  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Maximum Efficiency ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Angle ◽  
Tip Leakage ◽  
Blade Tip ◽  
The Impact

Experiments in a refractive index-matched axial turbomachine facility show that semicircular skewed axial casing grooves (ACGs) reduce the stall flowrate by 40% but cause a 2.4% decrease in the maximum efficiency. Aiming to elucidate mechanism that might cause the reduced efficiency, stereo-PIV measurements examine the impact of the ACGs on the flow structure and turbulence in the tip region near the best efficiency point (BEP), and compare them to those occurring without grooves and at low flowrates. Results show that the periodic inflow into the groove peaks when the rotor blade pressure side (PS) overlaps with the downstream end of the groove, but diminishes when this end faces the suction side (SS). Entrainment of the PS boundary layer and its vorticity generates a vortical loop at the entrance to the groove, and a “discontinuity” in the tip leakage vortex (TLV) trajectory. During exposure to the SS, the backward tip leakage flow separates at the entrance to the groove, generating a counter-rotating circumferential “corner vortex,” which the TLV entrains into the passage at high flowrates. Interactions among these structures enlarge the TLV and create a broad area with secondary flows and elevated turbulence near the groove's downstream corner. A growing shear layer with weaker turbulence also originates from the upstream corner. The groove also increases the flow angle upstream of the blade tip and varies it periodically. Accordingly, the circulation shed from the blade tip and strength of leakage flow increase near the blade leading edge (LE).

On the Interactions of a Rotor Blade Tip Flow With Axial Casing Grooves in an Axial Compressor Near the Best Efficiency Point

2018 ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
Joseph Katz
Keyword(s):  
Flow Rate ◽  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Leakage Flow ◽  
Flow Rates ◽  
Tip Leakage ◽  
Flow Features ◽  
Blade Tip ◽  
Corner Vortex

Previous studies have shown that axial casing grooves (ACGs) are effective in delaying the onset of stall, but degrade the performance of axial turbomachines around the best efficiency point (BEP). Our recent experimental study [1] in the JHU refractive index-matched liquid facility have examined the effects of ACGs on delaying stall of a one and half stage compressor. The semicircular ACGs based on Müller et al. [2] reduce the stall flow rate by 40% with a slight decrease in pressure rise at higher flow rates. Stereo-PIV (SPIV) measurements at a flow rate corresponding to the pre-stall condition of the untreated machine have identified three flow features that contribute to the delay in stall. Efficiency measurements conducted as part of the present study show that the ACGs cause a 2.4% peak efficiency loss. They are followed by detailed characterizations of the impact of the ACGs on the flow structure and turbulence in the tip region at high flow rates away from stall. Comparisons with the flow structure without casing grooves and at low flow rate are aimed at exploring relevant flow features that might be associated with the reduced efficiency. The SPIV measurements in several meridional and radial planes show that the periodic inflow into the groove peaks when the rotor blade pressure side (PS) overlaps with the downstream end of the groove, but diminishes when this end faces the blade suction side (SS). The inflow velocity magnitude is substantially lower than that occurring at a flow rate corresponding to the pre-stall conditions of the untreated machine. Yet, entrainment of the PS boundary layer and its vorticity during the inflow phase generates counter-rotating radial vortices at the entrance to the groove, and a “discontinuity” in the appearance of the tip leakage vortex (TLV). While being exposed to the blade SS, the backward tip leakage flow causes flow separation and formation of a counter-rotating vortex at the downstream corner of the groove, which migrates towards the passage with increasing flow rate. Interactions of this corner vortex with the TLV cause fragmentation of the latter, creating a broad area with secondary flows and elevated turbulence level. Consequently, the vorticity shed from the blade tip remains scattered from the groove corner to the blade tip long after the blade clears this groove. The turbulence peaks around the corner vortex, the TLV, and the shear layer connecting it to the SS corner. During periods of inflow, there is a weak outflow from the upstream end of the groove. At other phases, most of the high secondary flows are confined to the downstream corner, leaving only weak internal circulation in the rest of the groove, but with a growing shear layer with elevated (but weak) turbulence originating from the upstream corner. Compared to a smooth endwall, the groove also increases the flow angle near the blade tip leading edge (LE) and varies it periodically. Accordingly, the magnitude of circulation shed from the blade tip and leakage flow increase near the leading edge. The insight from these observations might guide the development of ACGs that take advantage of the effective stall suppression by the ACGs but alleviate the adverse effects at high flowrates.

scholarly journals Effects of Rotor Tip Blade Loading Variation on Compressor Stage Performance

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Aniwat Tiralap ◽  
Choon S. Tan ◽  
Eric Donahoo ◽  
Matthew Montgomery ◽  
Christian Cornelius
Keyword(s):  
Rotor Blade ◽  
Rotor Blades ◽  
Leakage Flow ◽  
Angle Distribution ◽  
Compressor Stage ◽  
Tip Leakage Flow ◽  
Flow Angle ◽  
Blade Loading ◽  
Tip Leakage ◽  
Blade Tip

Changes in loss generation associated with altering rotor tip blade loading of an embedded rotor–stator compressor stage are assessed with unsteady three-dimensional computations, complemented by control volume analyses. Tip-fore-loaded and tip-aft-loaded rotor blades are designed to provide variation in rotor tip blade loading distributions for determining a compressor design hypothesis that aft-loading a rotor blade tip yields a reduction in loss generation in a stage environment. Aft-loading a rotor blade tip delays the formation of tip leakage flow, resulting in a relatively less mixed-out tip leakage flow at the rotor outlet and a reduction in overall tip leakage mass flow, hence a lower loss generation. However, the attendant changes in tip flow angle distribution are such that there is an overall increase in the flow angle mismatch between tip flow and main flow, leading to higher loss generation. The latter outweighs the former; therefore, rotor passage loss from aft-loading a rotor tip is higher unless a constraint is imposed on tip flow angle distribution so that the associated induced loss is negligible. Tip leakage flow, which is not mixed-out at the rotor outlet, is recovered in the downstream stator. The tip leakage flow recovery process yields a higher benefit for a relatively less mixed-out tip leakage flow in the tip-aft-loaded rotor blades on a time-averaged basis. These characterizing parameters together determine the attendant overall loss associated with rotor tip leakage flow in a compressor stage environment. The revised design hypothesis is thus as follows: A rotor should be tip-aft-loaded and hub-fore-loaded while a stator should be hub-aft-loaded and tip-fore-loaded with tip/hub leakage flow angle distribution such that it results in no additional loss. For the compressor stage being assessed here, an estimated 0.15 points enhancement in stage efficiency is possible from aft-loading rotor tip only.

scholarly journals Effects of Rotor Tip Blade Loading Variation on Compressor Stage Performance

2016 ◽  
Author(s):  
Aniwat Tiralap ◽  
Choon S. Tan ◽  
Eric Donahoo ◽  
Matthew Montgomery ◽  
Christian Cornelius
Keyword(s):  
Rotor Blade ◽  
Recovery Process ◽  
Leakage Flow ◽  
Angle Distribution ◽  
Compressor Stage ◽  
Tip Leakage Flow ◽  
Flow Angle ◽  
Blade Loading ◽  
Tip Leakage ◽  
Blade Tip

Changes in loss generation associated with altering the rotor tip blade loading of an embedded rotor-stator compressor stage are assessed with unsteady three-dimensional computations, complemented by control volume analyses. Tip-fore-loaded and tip-aft-loaded rotor blades are designed and assessed to provide variation in rotor tip blade loading distributions for determining if aft-loading rotor tip would yield a stage performance benefit in terms of a reduction in loss generation. Aft-loading rotor blade tip delays the formation of tip leakage flow resulting in a relatively less mixed-out tip leakage flow at the rotor outlet and a reduction in overall tip leakage mass flow, hence a lower loss generation; however, the attendant changes in tip flow angle distribution are such that there is an overall increase in the flow angle mismatch between tip flow and main flow leading to higher loss generation. The latter outweighs the former so that rotor passage loss from aft-loading rotor tip is marginally higher unless a constraint is imposed on tip flow angle distribution so that associated induced loss is negligible; a potential strategy for achieving this is proposed. Tip leakage flow, which is not mixed-out at the rotor outlet, enters the downstream stator, where it can be recovered. The tip leakage flow recovery process yields a higher benefit for a relatively less mixed-out tip leakage flow from aft-loading a rotor blade tip. These characterizing parameters together determine the attendant loss associated with rotor tip leakage flow in a compressor stage environment. A revised design hypothesis is thus as follows: rotor should be tip-aft-loaded and hub-fore-loaded while stator should be hub-aft-loaded and tip-fore-loaded with tip/hub leakage flow angle distribution such that it results in no additional loss. For the compressor stage being assessed here, an estimated 0.15 points enhancement in stage efficiency is possible from aft-loading rotor tip only. In the course of assessing the benefit from unsteady tip leakage flow recovery in the downstream stator, it was determined that tip clearance flow is inherently unsteady with a time-scale distinctly different from the blade passing time. The disparity between the two timescales: (i) defines the periodicity of the unsteady rotor-stator flow, which is an integral multiple of blade passing time; and (ii) causes tip leakage vortex to enter the downstream stator at specific pitchwise locations for different blade passing cycles, a tip leakage flow phasing effect. Despite the inherent unsteadiness from tip leakage flow, the recovery process is demonstrated to be beneficial on a time-averaged basis.

EFFECT OF AXIAL CASING GROOVE GEOMETRY ON ROTOR-GROOVE INTERACTIONS IN THE TIP REGION OF A COMPRESSOR

2021 ◽  
pp. 1-54
Author(s):  
Subhra Shankha Koley ◽  
Huang Chen ◽  
Ayush Saraswat ◽  
Joseph Katz
Keyword(s):  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Low Flow ◽  
Flow Angle ◽  
Flow Rates ◽  
Piv Measurements ◽  
Tip Leakage ◽  
Large Vortex ◽  
Blade Leading Edge

Abstract This experimental study characterizes the interactions of axial casing grooves with the flow in the tip region of an axial turbomachine. The tests involve grooves with the same inlet overlapping with the rotor blade leading edge, but with different exit directions located upstream. Among them, U grooves, whose circumferential outflow opposes the blade motion, achieve a 60% reduction in stall flowrate, but degrade the efficiency around the best efficiency point (BEP) by 2%. The S grooves, whose outlets are parallel to the blade rotation, improve the stall flowrate by only 36%, but do not degrade the BEP performance. To elucidate the mechanisms involved, stereo-PIV measurements covering the tip region and interior of grooves are performed in a refractive index matched facility. At low flow rates, the inflow into both grooves, which peaks when they are aligned with the blade pressure side, rolls up into a large vortex that lingers within the groove. By design, the outflow from S grooves is circumferentially positive. For the U grooves, fast circumferentially negative outflow peaks at the base of each groove, causing substantial periodic variations in the flow angle near the blade leading edge. At BEP, interactions with both grooves become milder, and most of the tip leakage vortex remains in the passage. Interactions with the S grooves are limited hence they do not degrade the efficiency. In contrast, the inflow into and outflow from the U grooves reverses direction, causing entrainment of secondary flows, which likely contribute to the reduced BEP efficiency.

Influence of different blade numbers on the performance of “saddle zone” in a mixed flow pump

2021 ◽  
pp. 095765092110460
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi ◽  
Fei Tian ◽  
Shuo Li ◽  
...  
Keyword(s):  
Flow Field ◽  
Leading Edge ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Mixed Flow ◽  
Impeller Blade ◽  
Flow Angle ◽  
Tip Leakage ◽  
Vorticity Transport ◽  
Flow Pump

In order to study the effect of different numbers of impeller blades on the performance of mixed-flow pump “saddle zone”, the external characteristic test and numerical simulation of mixed-flow pumps with three different impeller blade numbers were carried out. Based on high-precision numerical prediction, the internal flow field and tip leakage flow field of mixed flow pump under design conditions and stall conditions are investigated. By studying the vorticity transport in the stall flow field, the specific location of the high loss area inside the mixed flow pump impeller with different numbers of blades is located. The research results show that the increase in the number of impeller blades improve the pump head and efficiency under design conditions. Compared to the 4-blade impeller, the head and efficiency of the 5-blade impeller are increased by 5.4% and 21.9% respectively. However, the increase in the number of blades also leads to the widening of the “saddle area” of the mixed-flow pump, which leads to the early occurrence of stall and increases the instability of the mixed-flow pump. As the mixed-flow pump enters the stall condition, the inlet of the mixed-flow pump has a spiral swirl structure near the end wall for different blade numbers, but the depth and range of the swirling flow are different due to the change in the number of blades. At the same time, the change in the number of blades also makes the flow angle at 75% span change significantly, but the flow angle at 95% span is not much different because the tip leakage flow recirculates at the leading edge. Through the analysis of the vorticity transport results in the impeller with different numbers of blades, it is found that the reasons for the increase in the values of the vorticity transport in the stall condition are mainly impacted by the swirl flow at the impeller inlet, the tip leakage flow at the leading edge and the increased unsteady flow structures.

Three-Dimensional Navier-Stokes Analysis of Turbine Rotor and Tip-Leakage Flowfield

1997 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The 3-D viscous flowfield in the rotor passage of a single-stage turbine, including the tip-leakage flow, is computed using a Navier-Stokes procedure. A grid-generation code has been developed to obtain embedded H grids inside the rotor tip gap. The blade tip geometry is accurately modeled without any “pinching”. Chien’s low-Reynolds-number k-ε model is employed for turbulence closure. Both the mean-flow and turbulence transport equations are integrated in time using a four-stage Runge-Kutta scheme. The computational results for the entire turbine rotor flow, particularly the tip-leakage flow and the secondary flows, are interpreted and compared with available data. The predictions for major features of the flowfield are found to be in good agreement with the data. Complicated interactions between the tip-clearance flows and the secondary flows are examined in detail. The effects of endwall rotation on the development and interaction of secondary and tip-leakage vortices are also analyzed.

Tip Leakage Flow and Heat Transfer Characteristics on Rotor Casing and Blade Tip in an Axial Gas Turbine Engine: Steady Analysis

2008 ◽  
Author(s):  
Md Hamidur Rahman ◽  
Sung In Kim ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Rotor Blade ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Heat Transfer Characteristics ◽  
Turbine Engine ◽  
Tip Leakage ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Blade Tip

Steady simulations have been performed to investigate tip leakage flow and heat transfer characteristics on the casing and rotor blade tip in a single stage turbine engine. A turbine stage of stator and rotor was modeled with a pressure ratio of 3.2. The predicted isentropic Mach number and adiabatic wall temperature on the casing showed good agreement with available experimental data. The effects of tip clearance height and rotor rotational speed on the blade tip and casing heat transfer characteristics are mainly considered. It is observed that the tip leakage flow structure is highly dependent on the height of the tip gap as well as speeds of the rotor blade. In all cases, flow separates just around the corner of the pressure side of the blade tip. The region of recirculating flow increases with the increase of the clearance height. Then the flow reattaches on the tip surface near the suction side beyond the flow separation. This flow reattachment enhances surface heat transfer. The leakage flow interaction with the reverse cross flow, induced by relative casing motion, is found to have significant effect on the blade tip and casing heat transfer distribution. Critical region of high heat transfer on the casing exists near the blade tip leading edge and along the pressure side edge at all clearance height. Whereas, at high speed rotation, it tends to move towards the trailing edge due to the change of inflow angle.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

Numerical investigations on tip leakage flow characteristics and vortex trajectory prediction model in centrifugal compressor

2016 ◽  
Vol 230 (8) ◽  
pp. 757-772 ◽  
Author(s):  
Huijing Zhao ◽  
Zhiheng Wang ◽  
Shubo Ye ◽  
Guang Xi
Keyword(s):  
Prediction Model ◽  
Flow Instability ◽  
Leading Edge ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip

To better understand the characteristics of tip leakage flow and interpret the correlation between flow instability and tip leakage flow, the flow in the tip region of a centrifugal impeller is investigated by using the Reynolds averaged Navier–Stokes solver technique. With the decrease of mass flow rate, both the tip leakage vortex trajectory and the mainflow/tip leakage flow interface are shifted towards upstream. The mainflow/tip leakage flow interface finally reaches the leading edge of main blade at the near-stall condition. A prediction model is proposed to track the tip leakage vortex trajectory. The blade loading at blade tip and the averaged streamwise velocity of main flow within tip clearance height are adopted to determine the tip leakage vortex trajectory in the proposed model. The coefficient k in Chen’s model is found to be not a constant. Actually, it is correlated with h/b (the ratio of blade tip clearance height to blade tip thickness), because h/b will significantly influence the flow structure across the tip clearance. The effectiveness of the proposed prediction model is further demonstrated by tracking the tip leakage vortex trajectories in another three centrifugal impellers characterized with different h/b (s).

Prediction of Unsteady Tip Leakage Flow of a Transonic Compressor Rotor by Reynolds-Stress-Constrained Large Eddy Simulation

2018 ◽  
Author(s):  
Yueqing Zhuang ◽  
Hui Liu
Keyword(s):  
Large Eddy Simulation ◽  
Reynolds Stress ◽  
Rotor Blade ◽  
Leading Edge ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Eddy Simulation ◽  
Large Eddy

Since the unsteadiness of tip leakage flow has profound effects on both aerodynamic performance and stall margin of axial compressors, it is important to accurately predict the transient tip flow at affordable computational cost. Limited by the high requirement of grid resolution of wall turbulence flow, large eddy simulation (LES) method is greatly restricted in engineering application. In the present work, a Reynolds-stress-constrained large eddy simulation (CLES) method has been introduced, in which the whole domain is simulated using LES while Reynolds stress constraint is enforced on the subgrid-scale (SGS) stress model for near-wall regions aiming at reducing the near-wall grid resolution. The CLES simulations have been performed to investigate the flow behaviors of the unsteady tip leakage flow in a transonic compressor NASA Rotor 67 at near-stall conditions. Reliability assessments have been conducted through comparisons of experimental measurements and numerical results obtained by RANS, DES, CLES as well as LES, respectively. Both the total pressure ratio and isentropic efficiency calculated by CLES agree well with experiment. The turbulence statistical results show three distinct high flow fluctuation regions near the blade tip. The first one is a long and narrow strip ahead of the leading edge of the rotor caused by the movement of the passage shock wave. The second one is formed on the suction side from the leading-edge of the rotor blade due to the oscillation of the tip leakage vortex. And the third one, which occupies most of the blade passage from the middle part of the rotor blade, is generated under multiple factors. The frequency characteristic of the unsteady tip leakage flow has been analyzed. The energy spectrums of the local transient pressure signals are highly related with the local unsteady flow features. The originating mechanisms of the flow unsteadiness in the rotor tip leakage flow have also been discussed, and the results show that the flow unsteadiness is mainly caused by a combined interaction effect of the double leakage flow, the tip leakage vortex flow spilled from the adjacent blade passage, as well as the involved main flow.

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