Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor: Part 1—Particle Image Velocimetry

Author(s):  
M. Voges ◽  
R. Schnell ◽  
C. Willert ◽  
R. Mo¨nig ◽  
M. W. Mu¨ller ◽  
...  

A single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per rotor pitch in order to investigate the predicted extension of the stall margin characteristics both numerically and experimentally. Contrary to most other studies the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. Part 1 of this two-part contribution describes the experimental investigation of the blade tip interaction with casing treatment using Particle image velocimetry (PIV). The nearly rectangular geometry of the CT cavities allowed a portion of it to be made of quartz glass with curvatures matching the casing. Thus the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the rotor passage (87.5%, 95% and 99%). For the outermost radial position the light sheet probe was placed behind the rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the rotor blades. The chosen type of smoke-based seeding with very small particles (about 0.5 μm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5 × 0.5 mm. The PIV data base established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying CFD calculations using the TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry a better understanding of the complex flow characteristics can be achieved, as detailed in Part 2 of this paper.

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
M. Voges ◽  
R. Schnell ◽  
C. Willert ◽  
R. Mönig ◽  
M. W. Müller ◽  
...  

A single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per rotor pitch in order to investigate the predicted extension of the stall margin characteristics both numerically and experimentally. Contrary to most other studies, the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. Part I of this two-part contribution describes the experimental investigation of the blade tip interaction with casing treatment using particle image velocimetry (PIV). The nearly rectangular geometry of the CT cavities allowed a portion of it to be made of quartz glass with curvatures matching the casing. Thus, the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the rotor passage (87.5%, 95%, and 99%). For the outermost radial position, the light sheet probe was placed behind the rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the rotor blades. The chosen type of smoke-based seeding with very small particles (about 0.5 μm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5×0.5 mm2. The PIV database established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying computational fluid dynamics (CFD) calculations using the TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry, a better understanding of the complex flow characteristics can be achieved, as detailed in Part II of this paper.


Author(s):  
Christian T. Pixberg ◽  
Heinz-Peter Schiffer ◽  
M. H. Ross ◽  
J. D. Cameron ◽  
S. C. Morris

The beneficial impact of casing treatments on the stall margin of tip-critical compressors has been proven many times. However, there is still no simple and general method to predict their actual effectiveness. The present work considers the axial velocity deficit that is generally observed at the blade tip. This so called tip-blockage is caused by the tip clearance flow. That is investigated for different configurations of the transonic compressor test facilities in Darmstadt and Notre Dame and the results are presented in this paper. Similar circumferential groove casing treatments were applied to different single-stage and 1.5-stage compressors. They all had a tip critical behavior in common, but exhibited different design philosophies. The effectiveness of similar casing treatments on different stages was observed. A new method for calculating tip-blockage is introduced based on compressor performance and the results of a through-flow tool. A direct link between blockage growth and stall margin improvement was found for circumferential grooves casing treatments. Additionally, the results of an axial slot casing treatment are taken into account.


Author(s):  
J. Anton Streit ◽  
Frank Heinichen ◽  
Hans-Peter Kau

A state-of-the-art transonic compressor rotor has a distinct potential for increased efficiency if modified for improved interaction with an axial-slot type casing treatment. Reducing the number of blades and thus the surface lowers friction losses but increases tip clearance effects and deteriorates the stall margin due to the higher aerodynamic blade loading. The latter two negative effects can be compensated for by the casing treatment, thus restoring the required stall margin and gaining an overall reduction of losses. For the specific compressor rotor under investigation, the potential in polytropic efficiency is as high as 0.7%. The present study was performed using time-accurate CFD (URANS) simulations. Both the reference rotor as well as the modified design are analyzed regarding their interaction with the casing treatment. The traceability of the conclusions is assured by interpreting the detailed flow phenomena. The newly designed rotor is found to be favorably influenced by the casing treatment at design operating conditions whilst the reference only benefits at throttled operating points. Casing treatments are commonly used to broaden the operating range of existing compressors without changing the design of the compressor rotor itself. This study aims to show the possible transformation of this potential in the stall margin into efficiency at design operating conditions by implementing an appropriate rotor design.


Author(s):  
Warjito ◽  
Elang Pramudya Wijaya ◽  
Budiarso ◽  
Sanjaya Baroar Sakti Nasution ◽  
Agil Fadhel Kurnianto

One of the solutions to overcome the lack of electricity problem in rural area is Crossflow pico-scale hydropower. In improving cross-flow turbine performance, understanding fluid phenomena is needed. Particle image velocimetry (PIV) measurement is one of the methods used to visualize the fluid flow phenomena inside the turbine. Expensive price of seeding particle leads to find the solution for this PIV method. The objective of this study is to use a cheap seeding particle from cheaper materials, mainly resin and rhodamine B. Besides that, in this study, PIV measurement is compared to 2D computational fluid dynamics (CFD) with multiphase volume of fluid model. From the results, several phenomenon can be observed at both of the methods (PIV and CFD) such as separation in the blade tip. Therefore, this study showed that an inexpensive material resin and rhodamine B as a seeding particle has a potential and ability to represent flow inside pico-hydro cross-flow turbine.


Author(s):  
Heiko van der Linden ◽  
Ralph Lindken ◽  
Jerry Westerweel

This paper describes our recently started research into the flow phenomena that occur in microchannels and microcavities during ultrasonic agitation. With micro-particle image velocimetry we have seen rapidly changing flows together with the occurrence of cavitation events. Both these processes suggest that very high shear forces are present in the solution in combination with rapidly changing pressure fluctuations. The research presented here is of importance for the design of ultrasonic mixers and ultrasonic cell lysis devices.


Author(s):  
Hao G Zhang ◽  
Fei Y Dong ◽  
Wei Wang ◽  
Wu L Chu ◽  
Song Yan

This investigation aims to understand the mechanisms of affecting the axial flow compressor performance and internal flow field with the application of self-recirculation casing treatment. Besides, the potentiality of further enhancing the compressor performance and stability by optimizing the geometric structure of self-recirculation casing treatment is discussed in detail. The results show that self-recirculation casing treatment generates about 7.06, 7.89% stall margin improvements in the experiment and full-annulus unsteady calculation, respectively. Moreover, the compressor total pressure and isentropic efficiency are improved among most of operating points, and the experimental and calculated compressor peak efficiencies are increased by 0.7% and 0.6%, respectively. The comparisons between baseline shroud and self-recirculation casing treatment show that the flow conditions of the compressor rotor inlet upstream are improved well with self-recirculation casing treatment, and the degree of the pressure enhancement in the blade top passage for self-recirculation casing treatment is higher than that for baseline. Further, self-recirculation casing treatment can restrain the leading edge-spilled flows made by the blade tip clearance leakage flows and weaken the blade tip passage blockage. Hence, the flow loss near the rotor top passage is reduced after the application of self-recirculation casing treatment. The rotor performance and stability for self-recirculation casing treatment are greater than those for baseline. The flow-field analyses also indicate that the adverse effects caused by the clearance leakage flows of the blades tip rear are greater than those made by the clearance leakage flows of the blades leading edge. When one injecting part of self-recirculation casing treatment is aligned with the inlet of one blade tip passage, the flow-field quality in the passage is not the best among all the passages between two adjacent injecting parts of self-recirculation casing treatment. Further, the flow-field analyses also indicate that the effect of the relative position between the blade and self-recirculation casing treatment on the flows in the self-recirculation casing treatment may be ignored during the optimization of the recirculating loop configuration.


Author(s):  
Yasunori Sakuma ◽  
Toshinori Watanabe ◽  
Takehiro Himeno

Computational analysis has been conducted on the NASA Rotor 37 transonic compressor with various tip clearance gap heights. Using steady rotor-only analysis, the change in overall performance, basic flow characteristics, and near-casing phenomena have been carefully observed. The results have clarified that the peak efficiency of the compressor decreases almost linearly with the increase in gap height. Meanwhile, the stall margin was prone to deterioration in cases of significantly small or significantly large clearance gaps. The peak stall margin was attained when the gap was set to 75% of the original height. Focusing on the flow structures, the tip leakage flow and tip leakage vortex seemed to be dominant loss sources in the case of a large tip clearance gap. On the other hand, trailing edge separation at the blade tip was the major loss source in case of a small tip clearance gap. The difference in the near-casing flow structure also determined the onset process of numerical instability. In case of a large tip clearance gap, the advance of the interface between the main flow and tip leakage flow seemed to cause an accumulation of blockage in the region near the casing, possibly triggering the tip-initiated stall. In the case of a small tip clearance gap, interaction among the wall separation, blade tip trailing edge separation, and shockwave /boundary layer interaction was significant. These phenomena appeared to play a major role in the onset of numerical instability in the blade tip region.


Author(s):  
HaoGuang Zhang ◽  
Feng Tan ◽  
YanHui Wu ◽  
WuLi Chu ◽  
Wei Wang ◽  
...  

For compressor blade tip stall, one effective way of extending stable operating range is with the application of circumferential grooved casing treatment and its validity was proved by a lot of experimental and numerical investigations. The emphases of most circumferential grooved investigations are focused on the influence of groove depth and groove number on compressor stability, and there is few investigations dealt with the center offset degree of circumferential grooves casing treatment. Hence, an axial compressor rotor with casing treatment (CT) was investigated with experimental and numerical methods to explore the effect of center offset degree on compressor stability and performance. In the work reported here, The center offset degree is defined as the ratio of the central difference between rotor tip axial chord and CT to the axial chord length of rotor tip. When the center of CT is located within the upstream direction of the center of rotor tip axial chord, the value of center offset degree is positive. The experimental and numerical results show that stall margin improvement gained with CT is reduced as the value of center offset degree varies from 0 to 0.33 or −0.33, and the CT with −0.33 center offset degree achieves the lowest value of stall margin improvement at 53% and 73% design rotational speed. The detailed analysis of the flow-field in compressor tip indicates that there is not positive effect made by grooves on leading edge of rotor blade tip when the value of center offset degree is −0.33. As the mass flow of compressor reduces further, tip clearance leakage flow results in the outlet blockage due to the absence of the positive action of grooves near blade tip tail when the value of center offset degree is 0.33. Blockage does not appear in rotor tip passage owing to utilizing the function of all grooves with CT of 0 center offset degree.


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