scholarly journals Investigation on Unsteady Flow Characteristics of a SCO2 Centrifugal Compressor

2017 ◽  
Vol 7 (4) ◽  
pp. 310 ◽  
Author(s):  
Yuqi Wang ◽  
Dongbo Shi ◽  
Di Zhang ◽  
Yonghui Xie
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Flow Characteristics

Numerical Investigation of the Unsteady Flow Fields in Centrifugal Compressor Diffusers

2010 ◽  
Author(s):  
Ahmed Abdelwahab
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Wake Flow ◽  
Vortical Structures ◽  
Centrifugal Stage ◽  
Unsteady Wake ◽  
Flow Interactions

The performance of radial diffusers in centrifugal compressor stages is influenced by the impeller exit flow characteristics as well as the vaneless and semi-vaneless space flow characteristics. Both steady and unsteady flow interactions are present due to the propagation of pressure fields upstream and downstream between the impeller and diffuser. Furthermore, unsteady flow interactions occur when the impeller moving wakes developed due to secondary and tip clearance flows propagate through the diffuser passages. The present study aims at presenting a model that describes the unsteady wake propagation in the centrifugal compressor diffuser using vorticity principles. 3D unsteady Reynolds-Averaged Navier Stokes simulations are performed for both a vaned and a vaneless diffuser centrifugal stage. The simulations are used to examine the mechanism for the unsteady wake flow interactions in the diffuser. The unsteady streamwise vortical structures present in the impeller wakes and their propagation through the diffuser flow field is presented. The effect of the unsteady flow on loss production in the compressor stage is investigated. The velocity perturbations due to these vortical structures are presented. The present study indicates that the impeller wake propagation in the diffuser can be represented by a series of unsteady streamwise vortices superimposed on a uniform flow field. These vortices result in velocity perturbations that take the form of both positive and negative jets in the diffuser.

Unsteady Flow in a Centrifugal Compressor With Different Types of Vaned Diffusers

1988 ◽  
Vol 110 (3) ◽  
pp. 293-302 ◽  
Author(s):  
U. Haupt ◽  
U. Seidel ◽  
A. N. Abdel-Hamid ◽  
M. Rautenberg
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Nonuniform Flow ◽  
Unsteady Pressure ◽  
Wide Range

Experiments were conducted to investigate the characteristics of self-excited flow oscillations in a high-performance centrifugal compressor system with a straight channel radial vaned diffuser. Fast response dynamic pressure transducers on the shroud wall and blade-mounted strain gages were used to identify the onset of the oscillations and their characteristics in space and time. In addition, flow characteristics near the shroud wall were visualized by an oil injection method, showing the extent of upstream directed reverse flow in the impeller range during significant unsteady flow compressor operation. Rotating nonuniform flow patterns were found in a wide range of operating speeds before the occurrence of surge. The number of lobes in the nonuniform flow patterns was dependent on the operating conditions and varied from two to four. Results of this experimental investigation were compared with those obtained from a previous investigation of the same compressor but with a cambered vane diffuser. Considerable similarity between the two configurations was found in the spatial distribution of the unsteady pressure field and in the frequencies of the fluctuations. The stability margin before the occurrence of surge and the operating regimes in which very intense pressure fluctuations were found were however different. In both cases, flow visualization techniques revealed the occurrence of reversed flow near the shroud wall of the impeller. Reverse flow extent up to the leading edge of the splitter blades systematically correlated with the occurrence of a nonuniform pressure pattern rotating with relatively high speed. Low rotational speed pressure patterns were observed when the extent of the reverse flow was up to the leading edge of the long blade. These different flow characteristics can be related to the occurrence of distinct rotating stall cell numbers. This result could be confirmed by unsteady pressure and blade vibration measurements.

EFFECTS OF BOUNDARY-LAYER THICKNESS ON UNSTEADY FLOW CHARACTERISTICS INSIDE OPEN CAVITIES AT SUBSONIC AND TRANSONIC SPEEDS

2012 ◽  
Vol 19 ◽  
pp. 206-213
Author(s):  
DANG-GUO YANG ◽  
JIAN-QIANG LI ◽  
ZHAO-LIN FAN ◽  
XIN-FU LUO
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Sound Pressure ◽  
Flow Characteristics ◽  
Open Cavity ◽  
Aerodynamic Noise ◽  
Sustained Oscillation ◽  
Cavity Depth

An experimental study was conducted in a 0.6m by 0.6m wind-tunnel to analyze effects of boundary-layer thickness on unsteady flow characteristics inside a rectangular open cavity at subsonic and transonic speeds. The sound pressure level (SPL) distributions at the centerline of the cavity floor and Sound pressure frequency spectrum (SPFS) characteristics on some measurement positions presented herein was obtained with cavity length-to-depth ratio (L/D) of 8 over Mach numbers (Ma) of 0.6 and 1.2 at a Reynolds numbers (Re) of 1.23 × 107 and 2.02 × 107 per meter under different boundary-layer thickness to cavity-depth ratios (δ/D). The experimental angle of attack, yawing and rolling angles were 0°. The results indicate that decrease in δ/D leads to severe flow separation and unsteady pressure fluctuation, which induces increase in SPL at same measurement points inside the cavity at Ma of 0.6. At Ma of 1.2, decrease in δ/D results in enhancing compressible waves. Generally, decrease in δ/D induces more flow self-sustained oscillation frequencies. It also makes severer aerodynamic noise inside the open cavity.

scholarly journals Numerical study of unsteady flow and exciting force for swept turbomachinery blades

2016 ◽  
Vol 20 (suppl. 3) ◽  
pp. 669-676
Author(s):  
Di Zhang ◽  
Ma Jiao-Bin ◽  
Qi Jing
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Pressure Fluctuation ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Aerodynamic Performance ◽  
Rotor Blades ◽  
Stable Operation ◽  
Straight Blade ◽  
Excitation Force

The aerodynamic performance of blade affects the vibration characteristics and stable operation of turbomachinery closely. The aerodynamic performance of turbine stage can be improved by using swept blade. In this paper, the RANS method and the RNG k-? turbulence mode were adopted to investigate the unsteady flow characteristics and excitation force of swept blade stage. According to the results, for the swept blade, the fluid of boundary layer shifts in radial direction due to the influence of geometric construction. It is observed that there is similar wake development for several kinds of stators, and the wake has a notable effect on the boundary layer of the rotor blades. When compared with straight blade, pressure fluctuation of forward-swept blade is decreased while the pressure fluctuation of backward-swept blade is increased. The axial and tangential fundamental frequency excitation force factors of 15?forward-swept blade are 0.139 and 0.052 respectively, which are the least, and all excitation force factors are in the normal range. The excitation factor of the forward-swept blade is decreased compared with straight blade, and the decreasing percentage is closely related to the swept angle. As for backward-swept blades, the situation is the other way around. Additionally, the change of axial excitation factor is more obvious. So the vibration reduction performance of forward-swept blade is better.

Unsteady flow characteristics regarding hump instability in the first stage of a multistage pump-turbine in pump mode

2018 ◽  
Vol 127 ◽  
pp. 377-385 ◽  
Author(s):  
Jun Yang ◽  
Giorgio Pavesi ◽  
Xiaohua Liu ◽  
Tian Xie ◽  
Jun Liu
Keyword(s):  
Unsteady Flow ◽  
Flow Characteristics ◽  
Pump Mode ◽  
Pump Turbine ◽  
Multistage Pump

Studies on Characteristic Frequency and Length Scale of Shock Induced Motion in Transonic Diffuser Using a High Order LES Approach

2015 ◽  
Author(s):  
Debasish Biswas ◽  
Tomohiko Jimbo
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Unsteady Flow ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Propulsion Systems ◽  
Shock Oscillation ◽  
Shock Location ◽  
Suction Slot

Unsteady transonic flows in diffuser have become increasingly important, because of its application in new propulsion systems. In the development of supersonic inlet, air breathing propulsion systems of aircraft and missiles, detail investigations of these types of flow behavior are very much essential. In these propulsion systems, naturally present self-sustaining oscillations, believed to be equivalent to dynamically distorted flow fields in operational inlets, were found under all operating conditions. The investigations are also relevant to pressure oscillations known to occur in ramjet inlets in response to combustor instabilities. The unsteady aspects of these flows are important because the appearance of undesirable fluctuations generally impose limitation on the inlet performance. Test results of ramjet propulsion systems have shown undesirable high amplitude pressure fluctuations caused by the combustion instability. The pressure fluctuations originated from the combustor extend forward into the inlet and interact with the diffuser flow-field. Depending on different parameters such as the diffuser geometry, the inlet/exit pressure ratio, the flow Mach number, different complicated phenomena may occur. The most important characteristics are the occurrence of shock induced separation, the length of separation region downstream of the shock location, and the oscillation of shock location as well as the oscillation of the whole downstream flow. Sajben experimentally investigated in detail the time mean and unsteady flow characteristics of supercritical transonic diffuser as a function of flow Mach number upstream the shock location and diffuser length. The flows exhibited features similar to those in supersonic inlets of air-breathing propulsion systems of aircraft. A High-order LES turbulence model developed by the author is assessed with experimental data of Sajben on the self-excited shock oscillation phenomena. The whole diffuser model configuration including the suction slot located at certain axial location around the bottom and side walls to remove boundary layer, are included in the present computation model. The time-mean and unsteady flow characteristics in this transonic diffuser as a function of flow Mach number and diffuser length are investigated in detail. The results of study showed that in the case of shock-induced separation flow, the length and thickness of the reverse flow region of the separation-bubble change, as the shock passed through its cycle. The instabilities in the separated layer, the shock /boundary layer interaction, the dynamics of entrainment in the separation bubble, and the interaction of the travelling pressure wave with the pressure fluctuation region caused by the step-like structure of the suction slot play very important role in the shock-oscillation frequency.

Flow Characteristics of a Novel Centrifugal Compressor Design

2016 ◽  
Author(s):  
Shashank Mishra ◽  
Shaaban Abdallah ◽  
Mark Turner
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Axial Compressor ◽  
Low Pressure ◽  
Flow Path ◽  
Optimization Techniques ◽  
Single Stage ◽  
Multi Stage ◽  
Compressor Design

Multistage axial compressor has an advantage of lower stage loading as compared to a single stage. Several stages with low pressure ratio are linked together which allows for multiplication of pressure to generate high pressure ratio in an axial compressor. Since each stage has low pressure ratio they operate at a higher efficiency and the efficiency of multi-stage axial compressor as a whole is very high. Although, single stage centrifugal compressor has higher pressure ratio compared with an axial compressor but multistage centrifugal compressors are not as efficient because the flow has to be turned from radial at outlet to axial at inlet for each stage. The present study explores the advantages of extending the axial compressor efficient flow path that consist of rotor stator stages to the centrifugal compressor stage. In this invention, two rotating rows of blades are mounted on the same impeller disk, separated by a stator blade row attached to the casing. A certain amount of turning can be achieved through a single stage centrifugal compressor before flow starts separating, thus dividing it into multiple stages would be advantageous as it would allow for more flow turning. Also the individual stage now operate with low pressure ratio and high efficiency resulting into an overall increase in pressure ratio and efficiency. The baseline is derived from the NASA low speed centrifugal compressor design which is a 55 degree backward swept impeller. Flow characteristics of the novel multistage design are compared with a single stage centrifugal compressor. The flow path of the baseline and multi-stage compressor are created using 3DBGB tool and DAKOTA is used to optimize the performance of baseline as well novel design. The optimization techniques used are Genetic algorithm followed by Numerical Gradient method. The optimization resulted into improvements in incidence and geometry which significantly improved the performance over baseline compressor design. The multistage compressor is more efficient with a higher pressure ratio compared with the base line design for the same work input and initial conditions.

Numerical Investigation of the Unsteady Flow Inside a Centrifugal Compressor Stage With Pipe Diffuser

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Daniel R. Grates ◽  
Peter Jeschke ◽  
Reinhard Niehuis
Keyword(s):  
Experimental Data ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Measurement Techniques ◽  
Navier Stokes ◽  
Compressor Stage ◽  
Centrifugal Compressor Stage ◽  
Transonic Centrifugal Compressor ◽  
Computational Fluid Dynamics Cfd ◽  
The Subject

The subject of this paper is the investigation of unsteady flow inside a transonic centrifugal compressor stage with a pipe-diffuser by utilizing unsteady 3D Reynolds-averaged Navier–Stokes simulations (unsteady 3D URANS). The computational fluid dynamics (CFD) results obtained are compared with detailed experimental data gathered using various steady and unsteady measurement techniques. The basic phenomena and mechanisms of the complex and highly unsteady flow inside the compressor with a pipe-diffuser are presented and analyzed in detail.

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