Effects of a slotted diffuser on the aerodynamic performance of a highly loaded centrifugal compressor

2019 ◽  
Vol 233 (19-20) ◽  
pp. 6879-6891
Author(s):  
Yingjie Zhang ◽  
Yanfeng Zhang ◽  
Xingen Lu ◽  
Ge Han ◽  
Ziliang li
Keyword(s):  
Flow Separation ◽  
Aerodynamic Performance ◽  
Low Flow ◽  
Suction Surface ◽  
Flow Rates ◽  
Stall Margin ◽  
Operating Range ◽  
Pressure Surface ◽  
Large Flow ◽  
Highly Loaded

High-pressure ratio centrifugal compressors usually adopt vaned diffusers to reach high efficiency. Nevertheless, the compressor operating range might be narrow on account of the diffuser stall resulting from the large flow separations in diffuser passages at low flow rates. Flow control techniques, aimed at expanding the compressor operating range, are required to suppress these flow separations. In this paper, the flow control strategy, in terms of the slotted diffuser was used to widen the operating range for a highly loaded centrifugal compressor. The main focus of the research is to address the effects of the slotted diffuser vane on the aerodynamic performance, including the underlay flow physics of the compressor. In the case of the baseline compressor, a large flow separation exists near the pressure surface between the hub and approximately 40% of the span inside diffuser passages over the entire flow range. In addition, flow separation appears at the junction of hub and suction surface at low flow rates, which promotes compressor stall. Therefore, a hub-side slotted diffuser is utilized to mitigate the flow separations inside diffuser passages. Through application of the slotted diffuser, the stall margin is improved a lot without performance decline as a result of the improvement of the flow field within diffuser passages. The flow separation on the suction surface is suppressed by a vortex induced by the leakage flow. Additionally, the flow angle at the diffuser inlet becomes more circumferential owing to the leakage flow passing through the slot; thus, the incidence angle is increased, which results in mitigation of the flow separation at the junction of hub and pressure surface. As a result, a 13.5% stall margin increment is gained in the presence of the slotted diffuser vane.

Acoustic Measurements From an Automotive Centrifugal Compressor With a Switchable Dual-Port Casing Treatment for Extended Operating Range

2016 ◽  
Author(s):  
Rick Dehner ◽  
Ahmet Selamet ◽  
Michael Steiger ◽  
Harold Sun ◽  
Dave Hanna ◽  
...  
Keyword(s):  
Flow Rate ◽  
Broadband Noise ◽  
High Flow ◽  
Low Flow ◽  
Acoustic Measurements ◽  
Suction Surface ◽  
Flow Rates ◽  
Casing Treatment ◽  
Operating Range ◽  
Operating Region

An effective measure to improve the surge margin of a centrifugal compressor, without sacrificing efficiency, is to implement a recirculating casing treatment inside the compressor cover. However, introduction of an additional sound propagation path directly over the rotating impeller blades exposes the inherently unsteady internal flow-field as an added potential noise source, which is of concern for automotive applications. The present study conducts performance and acoustic measurements of a new compressor which was designed to achieve high isentropic efficiency over a wide flow range, featuring an impeller with splitter blades and a vaneless diffuser. A dual-port active casing treatment (ACT) was also incorporated into the compressor cover to independently extend both the low and high flow rate operating regions of the compressor. The slot of the first (surge) port is positioned between the main and splitter blades of the impeller, similar to passive casing treatments that are already widely adopted. This port extends the low-flow boundary of the compressor operating range by reducing flow separation on the suction surface of the main blades near the shroud. The slot of the second (choke) port is located just behind the splitter blades, and it is studied in both the open and closed positions. This second port allows for increased air flow near choke, due to the slot position just downstream of the aerodynamic throat of the compressor. The current ACT design leaves the surge port open at all times, while the choke port is only opened when the compressor operates near choke conditions. In addition to comparing experimental results from this new compressor in both configurations (choke port open and closed), measurements from a comparable (baseline) compressor without splitter blades and a single-port shroud are utilized to assess the acoustics of the new design. Acoustic measurements were completed over the low to mid-speed operating range, which is a region heavily weighted in customer drive cycles for light and medium duty vehicles. The conscientious design of the impeller and surge slot of the new compressor to minimize flow separation on the suction surface of the inducer blades is shown to not only improve efficiency and extend the low-flow operating range, but (with the choke port closed) broadband noise is significantly reduced in the mid to high flow rate operating region. At low flow rates, the new compressor (with the choke port closed) is slightly louder than the baseline compressor at the inlet duct measurement location, but essentially equal to the baseline compressor at the external microphone location near the compressor inlet duct opening. When the choke port of the new compressor is open, broadband noise increases slightly relative to the closed configuration. More importantly, the peak sound pressure level at (main) blade-pass frequency is reduced by opening the choke port, and the operating region of elevated tonal noise shifts from mid to high flow rates.

Parametric study of slotted diffuser effects on a highly loaded centrifugal compressor

2019 ◽  
Vol 233 (6) ◽  
pp. 702-714
Author(s):  
Yingjie Zhang ◽  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Ge Han ◽  
Junqiang Zhu
Keyword(s):  
Centrifugal Compressor ◽  
Flow Separation ◽  
Parametric Study ◽  
Control Technique ◽  
Leakage Flow ◽  
Suction Surface ◽  
Flow Angle ◽  
Stall Margin ◽  
Compressor Performance ◽  
Highly Loaded

Flow separations in the vaned diffuser play a critical role in the stall margin of centrifugal compressors. To extend the stable operating range of a highly loaded centrifugal compressor, a flow control technique of locating a slot near the vaned diffuser's leading edge is proposed. A parametric study of slot geometry variations, in terms of the slotted portion depth and length, is carried out to summarize the trend of compressor performance and to reveal the corresponding flow physics related to the slot geometries. The design methodology is concluded to provide a guideline for stall margin improvement by the slotted diffuser. Application of a well-designed slotted diffuser shows that the flow separations inside the diffuser passages are suppressed at low flow rates, and the stall margin is increased without performance deterioration. The leakage flow passing through the slotted portion intensifies the passage vortex at the hub/suction surface corner, and decreases the flow angle at the diffuser inlet, leading to the suppression of flow separations on both the suction and pressure surfaces of the diffuser, respectively. However, it is found that the compressor performance deteriorates with increasing slotted portion depth and length, even though the stall margin is increased. When the slot depth is increased by up to 12% of the diffuser vane height, the leakage flow is not able to roll-up into a vortex that has the potential to mitigate the flow separation at the hub/suction surface corner. Instead, it enhances the flow separation region near the suction surface due to the negative effect of leakage flow; eventually, the stage performance is deteriorated. In conclusion, the slot depth should not exceed 9% of the diffuser vane height, and the optimum slot length is no greater than 6%–12% of the diffuser chord length, which provides a basic guideline for slotted diffuser design.

scholarly journals Simulation of Flow in Turbopump Vaneless and Vaned Diffusers with Fluid Injection

2000 ◽  
Vol 6 (1) ◽  
pp. 57-65
Author(s):  
Ali Ogut ◽  
Diego Garcia Pastor
Keyword(s):  
Flow Separation ◽  
Flow Region ◽  
Design Flow ◽  
Low Flow ◽  
Fluid Injection ◽  
Bottom Surface ◽  
Suction Surface ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Wide Range

In future space missions by NASA there will be a need for “Space Transfer Vehicles” to perform varying orbital transfers and descents. This requires engines capable of producing different levels of thrust. To accomplish this, the turbopumps employed in these engines should efficiently provide a wide range of flow outputs. However, current fuel and oxidizer turbopumps with vaned diffusers do not perform efficiently at off-design (low) flow rates mainly due to flow separation in the vaned diffuser.This paper evaluates the effectiveness of boundary layer control by fluid injection (blowing) for suppressing or eliminating the flow separation in a vaned diffuser. A 3-D flow model including vaneless and vaned diffusers of a liquid hydrogen (LH2) turbopump is studied using the CFD code FIDAP. The paper presents the results of the model at design and offdesign flow conditions.The model results showed that flow separation occurs at the top or suction surface of the vaneless diffuser and at the bottom or pressure surface of the vaned diffuser at off-design flow rates. When fluid injection was applied through the bottom surface of the vaned diffuser, the separated flow region was reduced almost entirely, resulting in an increase in pressure recovery of up to 21% with varying fluid injection rates. Results also showed that there is an optimum injection rate which is most effective in reducing or eliminating the region of flow separation.

Pulsed suction control in a highly-loaded compressor cascade with low suction flow rates

2021 ◽  
pp. 1-39
Author(s):  
Hongxin Zhang ◽  
Shaowen Chen
Keyword(s):  
Flow Rate ◽  
Flow Separation ◽  
Aerodynamic Performance ◽  
Compressor Cascade ◽  
Control Effect ◽  
Suction Force ◽  
Flow Rates ◽  
Suction Control ◽  
Suction Flow ◽  
Highly Loaded

Abstract The influence of pulsed suction (PS) on flow separation and aerodynamic performance in a highly loaded compressor cascade is experimentally studied herein. The excitation frequency is investigated as it determines the effectiveness of PS in flow control. Low suction flow rates are examined to analyze the potential of PS in providing a satisfactory cascade performance. For comparison, the corresponding parameters of steady continuous suction (SCS) are studied as well. Oil flow visualizations and steady and unsteady pressure data are used to characterize the control effects of SCS and PS. The experimental results validate the efficacy of PS in controlling flow separation, even at a reduced suction flow rate of 0.1%. It suppresses passage vortex is suppressed, improving aerodynamic performance. PS provides a better control effect than SCS at different excitation parameters, which can be attributed to twofold main reasons: first, at the same suction flow rate, PS has a larger suction momentum than SCS during the suction phase, resulting in a stronger suction force and having a more profound effect on the flow characteristics; and second, owing to the introduction of pulsed excitation to the suction, PS creates additional vortex structures that energize the boundary layer by transporting high momentum free-stream fluid near the wall. PS is also effective at a higher incidence angle, but its control effect is reduced.

Numerical Investigation of a Cantilevered Compressor Stator at Varying Clearance Sizes

2015 ◽  
Author(s):  
Chengwu Yang ◽  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Shengfeng Zhao ◽  
Junqiang Zhu
Keyword(s):  
Flow Field ◽  
Axial Compressor ◽  
High Flow ◽  
Leakage Flow ◽  
Streamwise Direction ◽  
Stall Margin ◽  
Axial Compressors ◽  
Pressure Surface ◽  
The Impact ◽  
Highly Loaded

The clearance size of cantilevered stators affects the performance and stability of axial compressors significantly. Numerical calculations were carried out using the commercial software FINE/Turbo for a 2.5-stage highly loaded transonic axial compressor, which is of cantilevered stator for the first stage, at varying hub clearance sizes. The aim of this work is to improve understanding of the impact mechanism of hub clearance on the performance and the flow field in high flow turning conditions. The performance of the front stage and the compressor with different hub clearance sizes of the first stator has been analyzed firstly. Results show that the efficiency decreases as clearance size varies from 0 to 3% of hub chordlength, but the operating range has been extended. For the first stage, the efficiency decreases about 0.5% and the stall margin is extended. The following analysis of detailed flow field in the first stator shows that the clearance leakage flow and elimination of hub corner separation is responsible for the increasing loss and stall margin extending respectively. The effects of hub clearance on the downstream rotor have been discussed lastly. It indicates that the loss of the rotor increases and the flow deteriorates due to increasing of clearance size and hence the leakage mass flow rate, which mainly results from the interaction of upstream leakage flow with the passage flow near pressure surface. The affected region of rotor passage flow field expands in spanwise and streamwise direction as clearance size grows. The hub clearance leakage flow moves upward in span as it flows toward downstream.

scholarly journals Laser Velocimeter Measurements in the Stator of an Automotive Torque Converter

2000 ◽  
Vol 6 (6) ◽  
pp. 417-431 ◽  
Author(s):  
Steven B. Ainley ◽  
Ronald D. Flack
Keyword(s):  
Secondary Flow ◽  
Mass Flow ◽  
Torque Converter ◽  
Speed Ratio ◽  
Pressure Side ◽  
Suction Surface ◽  
General Direction ◽  
Flow Rates ◽  
Pressure Surface ◽  
Mass Flow Rates

The flow field in the stator of a clear torque converter was studied using laser velocimetry. Five planes in the stator were studied at a speed ratio of 0.800 and three planes were studied at a speed ratio of 0.065. Data complements previously available pump and turbine data. Flow in the stator inlet plane is highly non-uniform due to the complicated flow exiting the turbine. At the 0.800 speed ratio, separation regions are located in the 1/4 and mid-planes in the corepressure corner region. In the 3/4 and exit planes, separation regions are located in the shellsuction corner. In the inlet plane a region of high velocities is located along the shell near the pressure side for a speed ratio of 0.800. The high velocity region migrated to the shell-suction corner and suction side in the 1/4 and mid-planes. The overall velocity field for the speed ratio of 0.065 changes significantly from the inlet plane to the mid-plane. The velocity magnitude generally decreases from the suction to the pressure side of the inlet plane and the general direction of the tangential velocity is from pressure-to-suction surface. At the speed ratio of 0.065 a strong secondary flow in the inlet from suction surface to pressure surface was seen. However, at the high speed ratio a moderate secondary flow in the inlet from pressure surface to suction surface was observed. Mass flow rates at the different planes are within the experimental uncertainty and also within the uncertainty of pump and turbine mass flow rates. The flow in the stator inlet plane are significantly influenced by the turbine relative blade position. The turbine influence on the mid-plane data is significantly less than on the inlet plane data. The influence of the pump blade position on the stator exit plane is small.

Behavior of Secondary Flow in a Low Solidity Tandem Cascade Diffuser

2012 ◽  
Author(s):  
Daisaku Sakaguchi ◽  
Hironobu Ueki ◽  
Masahiro Ishida ◽  
Hiroshi Hayami
Keyword(s):  
Secondary Flow ◽  
Flow Rate ◽  
Flow Separation ◽  
Lift Coefficient ◽  
Pressure Recovery ◽  
Suction Surface ◽  
Flow Rates ◽  
Blade Loading ◽  
Small Flow Rate ◽  
Small Flow

Low solidity circular cascade diffuser abbreviated by LSD was proposed by Senoo et al. showing a high blade loading or a high lift coefficient without stall even under small flow rate conditions. These high performances were achieved by that the flow separation on the suction surface of the LSD blade was successfully suppressed by the secondary flow formed along the side walls. The higher performance of the LSD was achieved in both pressure recovery and operating range by adopting the tandem cascade because the front blade of the tandem cascade was designed suitably for small flow rates while the rear blade of the tandem cascade was designed suitably for large flow rates. In order to clarify the reason why the tandem cascade could achieve a high pressure recovery in a wide range of flow rate, the flow in the LSD with the tandem cascade is analyzed numerically in the present study by using the commercial CFD code of ANSYS-CFX 13.0. The behavior of the secondary flow is compared between the cases with the single cascade and the tandem one. It is found that the high blade loading of the front blade is achieved at the small flow rate by formation of the favorable secondary flow which suppresses the flow separation on suction surface of the front blade, and the flow separation on pressure surface of the front blade appeared at the design flow rate can be suppressed by the accelerated flow in the gap between the trailing edge of the front blade and the leading edge of the rear blade, resulting in the positive lift coefficient in spite of a large negative angle of attack.

Effect of Axial Sweep and Tip Extension on Performance of an Axial Fan

2016 ◽  
Author(s):  
Ankit Bhai Patel ◽  
K. Viswanath ◽  
Dhyanjyoti Deb Nath
Keyword(s):  
Performance Improvement ◽  
Flow Direction ◽  
Pressure Rise ◽  
Aerodynamic Performance ◽  
Secondary Flows ◽  
Tip Vortex ◽  
Low Flow ◽  
Pressure Probe ◽  
Axial Fan ◽  
Stall Margin

Performance enhancement in terms of stall margin increment, increased pressure rise coefficient and increased efficiency is of great need for low speed axial fans. Stacking line modifications in terms of sweep, skew, dihedral or combination of these, as well as blade tip geometry modifications are assumed to be one of the ways to achieve finite performance improvement. Non radial stacking of blade profiles modifies secondary flows, tip vortex effects, hub passage vortex and thus affects aerodynamic performance parameters such as stall margin, efficiency, pressure rise, blade loading. In literature many studies have confined to comparison of few cases which led to conflicting results as modification of stacking line may have different effects in different cases. In the present work, comparison of performance of axial fan rotor with three different blade configurations BSL (baseline), SWP (swept blade) and EXTN (swept blade with extended tip) are considered. The BSL configuration is designed on basis of non-free vortex design. The SWP configuration is obtained by shifting radial stacking line of the BSL in axial flow direction by 10° (Forward sweep). The EXTN configuration is obtained by extending tip profile on pressure surface as well as suction surface by 3% locally. Experiments have been conducted on these three configurations to study effects of these modifications on aerodynamic performance. The flow field has been surveyed using Kiel probe, Three hole pressure probe at many flow rates starting from fully open to fully closed. Unsteady flow analysis at exit of rotors of all configurations is carried out using fast response pressure probe. Experimental results show slight performance improvement in terms of increased stall margin, efficiency, as well as total pressure rise for SWP rotor as well as EXTN rotor compared to BSL rotor at low flow coefficients.

scholarly journals РЕЗУЛЬТАТЫ УСОВЕРШЕНСТВОВАНИЯ СТУПЕНИ ВЫСОКОНАГРУЖЕННОЙ ТУРБИНЫ НИЗКОГО ДАВЛЕНИЯ

2019 ◽  
pp. 30-37
Author(s):  
Игорь Федорович Кравченко ◽  
Сергей Александрович Хомылев
Keyword(s):  
Flow Separation ◽  
Wedge Angle ◽  
Operating Conditions ◽  
Design Flow ◽  
Flow Coefficient ◽  
Low Flow ◽  
Energy Losses ◽  
Suction Surface ◽  
Experimental Development ◽  
Leading Edges

One of the characteristic features of high loaded low-pressure turbine (LPT) with a low flow coefficient is the high-level flow deflection in the blade rows, which have sufficiently thin and strongly curved cross-section profiles. Such profiles are very sensitive to off-design flow angles, especially to positive incidence. Therefore, the effectiveness of a high loaded LPT strongly depends on the working conditions. At the same time, for various reasons, in the process of research tests or operating the engine, the operating conditions may differ greatly from the design ones. Therefore, the creation of a robust LPT design is an actual task. The article considers the computational approbation of the method of increasing the resistance to large off-design angles of attack of vane and blade rows of the intermediate stage of a high loaded LPT of an experimental engine by changing the shape of the leading edges. The turbine was previously tested as part of a full-scale engine, where it was determined that the operating conditions of the LPT and its efficiency are significantly different from the calculated ones. Numerical (CFD) analysis of the flow showed that one of the reasons for the low efficiency is the large angles of attack on the vane and blade rows of the second stage, which lead to the flow separation and an increase of the energy losses coefficients at final. The modernization of the profiles was carried out by reducing the radius and a local increase of the leading edges wedge angle without changing the basic profiles. According to the calculation results, it was allowed to significantly improve the stream. The intensity of the flow deceleration behind the shock wave at the point of transition from the circumference of the edge to the suction surface was reduced, this made it possible to eliminate or reduce the intensity of the flow separation in the vane row and significantly reduce the energy losses coefficient. A more favorable flow was also achieved in the blade row, where a slight decrease in the losses coefficient was also obtained. As a result, the efficiency of the stage and the whole LPT was increased at the off-design operating conditions. This approach can be recommended both to increase the efficiency of the turbine at the experimental development, and when designing new turbines to increase their robustness.

Compressible Simulation of Flow and Sound Around a Small Axial-Flow Fan With Flow Through Casing Slits

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Hiroshi Yokoyama ◽  
Katsutake Minowa ◽  
Kohei Orito ◽  
Masahito Nishikawara ◽  
Hideki Yanada
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Aerodynamic Performance ◽  
Design Flow ◽  
Low Flow ◽  
Axial Fan ◽  
Flow Rates ◽  
Blade Tip ◽  
Flow Through ◽  
Design Flow Rate

Abstract Small axial fans are used for cooling electronic equipment and are often installed in a casing with various slits. Direct aeroacoustic simulations and experiments were performed with different casing opening ratios to clarify the effects of the flow through the casing slits on the flow field and acoustic radiation around a small axial fan. Both the predicted and measured results show that aerodynamic performance deteriorates at and near the design flow rate and is higher at low flow rates by completely closing the casing slits compared with the fan in the casing with slits. The predicted flow field shows that the vortical structures in the tip vortices are spread by the suppression of flow through the slits at the design flow rate, leading to the intensification of turbulence in the blade wake. Moreover, the pressure fluctuations on the blade surface are intensified, which increases the aerodynamic sound pressure level. The suppression of the outflow of pressurized air through the downstream part of the slits enhances the aerodynamic performance at low flow rates. Also, the predicted surface streamline at the design flow rate shows that air flows along the blade tip for the fan with slits, whereas the flow toward the blade tip appears for the fan without slits. As a result, the pressure distributions on the blade and the torque exerted on the fan blade are affected by the opening ratio of slits.

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