Clearance Effects on the Onset of Instability in a Centrifugal Compressor

2006 ◽  
Author(s):  
Matthias Schleer ◽  
Seung Jin Song ◽  
Reza S. Abhari
Keyword(s):  
Pressure Distribution ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Operating Conditions ◽  
High Mass ◽  
Time Resolved ◽  
Flow Rates ◽  
Blade Loading

This report intends to shed an insight into the effect of large relative tip clearances on the onset of instability in a highly loaded centrifugal compressor. Time-resolved pressure measurements have been performed along the casing of a scaled-up model of a small compressor for two clearances at a wide range of operating conditions. Based on these time-resolved measurements the pressure distribution along the meridional length and the blade loading distribution are calculated for each operating condition. In addition, the phase locked pressure fluctuation and its deviation are computed. The results show the behavior of each sub-component of the compressor at different flow conditions and explain the role of the relative tip clearance on the onset of instability. For high mass flow rates the steady pressure distribution along the casing reveals that the inducer acts as an accelerating nozzle. Pressure is only built up in the radial part due to the centrifugal forces and in the subsequent diffuser due to area change. For off-design conditions incidence effects are seen in the blade loading distribution at the leading edge while the inducer is unloaded. A region of high pressure deviation originates at the leading edge of the main blade and convects downstream. This feature is interpreted as the trajectory of the leakage vortex. The trajectory of these vortices is strongly affected by the mass flow coefficient. If the mass flow rate is sufficiently small the trajectory of the leakage vortex becomes perpendicular to the axis of rotation, the leakage vortex interacts with the adjacent blade, and inlet tip recirculation is triggered. If the flow rate is further reduced, the leakage vortex vanishes and rotating stall is initiated in the diffuser. For larger clearances, stronger vortices are formed, stall is triggered at higher flow rates and the overall compressor performance deteriorates.

Clearance Effects on the Onset of Instability in a Centrifugal Compressor

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Matthias Schleer ◽  
Seung Jin Song ◽  
Reza S. Abhari
Keyword(s):  
Pressure Distribution ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Leading Edge ◽  
Operating Conditions ◽  
High Mass ◽  
Time Resolved ◽  
Flow Rates ◽  
Blade Loading

This report intends to shed an insight into the effect of large relative tip clearances on the onset of instability in a highly loaded centrifugal compressor. Time-resolved pressure measurements have been performed along the casing of a scaled-up model of a small compressor for two clearances at a wide range of operating conditions. Based on these time-resolved measurements, the pressure distribution along the meridional length and the blade loading distribution are calculated for each operating condition. In addition, the phase locked pressure fluctuation and its deviation are computed. The results show the behavior of each subcomponent of the compressor at different flow conditions and explain the role of the relative tip clearance on the onset of instability. For high mass-flow rates, the steady pressure distribution along the casing reveals that the inducer acts as an accelerating nozzle. Pressure is only built up in the radial part due to the centrifugal forces and in the subsequent diffuser due to area change. For off-design conditions, incidence effects are seen in the blade loading distribution at the leading edge while the inducer is unloaded. A region of high pressure deviation originates at the leading edge of the main blade and convects downstream. This feature is interpreted as the trajectory of the leakage vortex. The trajectory of these vortices is strongly affected by the mass-flow coefficient. If the mass-flow rate is sufficiently small, the trajectory of the leakage vortex becomes perpendicular to the axis of rotation, the leakage vortex interacts with the adjacent blade, and inlet tip recirculation is triggered. If the flow rate is further reduced, the leakage vortex vanishes and rotating stall is initiated in the diffuser. For larger clearances, stronger vortices are formed, stall is triggered at higher flow rates, and the overall compressor performance deteriorates.

Flashing Flow Mechanisms of HFC-134a and HFC-410a Through Short-Tube Orifices

2011 ◽  
Author(s):  
Kitti Nilpueng ◽  
Somchai Wongwises
Keyword(s):  
Temperature Distribution ◽  
Pressure Distribution ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Operating Conditions ◽  
Evaporator Temperature ◽  
Hfc 134A ◽  
Flow Mechanisms ◽  
Short Tube

In this study, the flow mechanisms of HFC-134a and HFC-410A, including flow pattern, pressure distribution, temperature distribution, and mass flow rate inside short-tube orifice are presented and compared under the same working temperature. The test runs are performed at condenser temperature ranging between 35 and 45°C, evaporator temperature ranging between 2 and 12°C, and degree of subcooling ranging between 1 and 12 °C. The results show that the temperature distribution along the short-tube orifice obtained from HFC-410A is slightly higher than that obtained from HFC-134a. On the other hand, the pressure distribution between both refrigerants shows the large difference. It is also found that the tendency of mass flow rate obtained from HFC-134a almost coincides with those obtained HFC-410A as the operating conditions and short-tube orifice size are varied. However, the average mass flow rate of HFC-134a is slightly lower than that of HFC-410A.

Delay of Unsteady Flow in a Radial Diffuser

2008 ◽  
Author(s):  
Saad A. Ahmed
Keyword(s):  
Mass Flow ◽  
Flow Rate ◽  
Flow Instability ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Width Ratio ◽  
Flow Rates ◽  
Lower Flow ◽  
Low Mass

The operation of centrifugal compressor systems is limited at low-mass flow rates by fluid flow instabilities leading to rotating stall or surge. These instabilities limit the flow range in which the compressor can operate. They also lower the performance and efficiency of the compressor. Experiments were conducted to investigate a model of radial vaneless diffuser at stall as well as stall-free operating conditions. The speed of the impeller was kept constant at 2000 RPM, while the mass flow rate was reduced gradually to scan the steady and unsteady operating conditions of the compressor. The flow rate through the compressor was gradually decreased until flow instability is initiated at the diffuser. The flow rate was further reduced to study the characteristics of rotating stall. These measurements were reported for diffuser diameter ratios, Do/Di, of 2.0 with diffuser width ratio, b/Di, of 0.055. At lower flow rates than the critical, the rotating stall pattern with one stall cell was dominant over the pattern with two cells. In addition, the instability in the diffuser was successfully delayed to a lower flow coefficient when rough surfaces were attached to one or both sides of the diffuser with the lowest values achieved by attaching the rough surface to the shroud. Results show that the roughness has no significant effect on stall cell characteristics.

Optimization of an Intermittent Slug Injection System for Sawdust Biomass Pyrolysis

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Federico M Berruti ◽  
Lorenzo Ferrante ◽  
Franco Berruti ◽  
Cedric Briens
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Feeding Tube ◽  
Operating Conditions ◽  
Injection System ◽  
Flow Rates ◽  
Pinch Valve ◽  
Mass Flow Rates ◽  
Biomass Materials

Among many other potential applications, intermittent solid slug feeders can be used to effectively inject biomass materials into fluidized bed reactors for pyrolysis. In particular, these feeders can be used to convey biomass materials that are highly cohesive to prevent plugging or undesirable reaction in the feeding tube. Although feeders of this design have been shown to work very effectively, they have not been studied in detail or optimized for the pyrolysis process. In addition, the operating conditions required to obtain predictable and consistent mass flow rates and slugs of desirable characteristics need to be established.The purpose of this work was to design, build and demonstrate the operation of a horizontal intermittent solid slug feeder and to test it with sawdust as the feed material. Sawdust is an extremely cohesive and difficult biomass to inject, but one that holds great potential as an important renewable feedstock for pyrolysis.The intermittent feeder designed for this work consisted of a pressurized vertical solids storage silo leading to a pneumatic pinch valve. The pinch valve, controlled by solenoid valves connected to a relay timer, released the feed into a horizontal feeding tube at a ninety degree angle. Within the silo, a rotating mixer prevented the bridging of solids. Intermittent pulses of gas from a control volume were fed into the horizontal feeding tube, as well as, in some cases, a continuous gas flow. The timing of the pulses was controlled by solenoid valves with a relay timer. While the pinch valve is opened, solids fall into the horizontal feeding tube forming a plug, which is then propelled by the pulsating gas into the reactor. The solid mass flow rate was experimentally measured by collecting the solids and continuously measuring the mass using a digital balance.Several variables were tested in order to optimize the performance of the feeder and the consistency of the feeding rate. They included the silo pressure, mixing rate, gas pulse pressure and volume, continuous gas mass flow rate, and the open pinch-valve time interval. The goals of this optimization were (a) to maximize the solid-to-gas ratio of mass flow rates, since the gas mass flux must be minimized to avoid wasting energy, and (b) to define operating conditions required to inject consistent biomass mass flow rates suitable for a laboratory scale pyrolysis reactor, and (c) to propose initial design criteria and a calibration procedure for intermittent solid slug feeders.The results demonstrated that the intermittent solid slug feeder system successfully achieved the desired objectives and showed how to efficiently select its optimum operating conditions.

scholarly journals Effects of Louvered Parameters on Exergetic Performance of Louvered Finned Solar Air Heater

2021 ◽  
Vol 39 (5) ◽  
pp. 1649-1658
Author(s):  
Subhash Chand ◽  
Prabha Chand
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Operating Conditions ◽  
High Mass ◽  
Solar Air Heater ◽  
Air Heater ◽  
Pitch Ratio ◽  
Exergy Performance

The aim of the present study to improve the performance of solar air heater because of low thermo-physical properties of air. In the current work, an attempt has been made to improve the performance of the heater by employing louvered fins to the absorber plate, as it not only enhances heat transfer coefficient but also improve heat transfer area. The effect of exergy performance on the geometrical parameters of louvered fin i.e., louvered angle, louvered pitch and louvered length has been studied and analyzed. The results are compared to plane solar air heater (PSAH) to evaluate the effectiveness of louvered finned solar air heater (LFSAH). The exergy efficiency of LFSAH is comparatively higher for all the operating conditions except for higher mass flow rate where it may even go below that of PSAH; possibly due to the higher pressure drop and more loss of exergy at high mass flow rate. In addition, the results conclude that for louvered parameters viz., louvered angle 20°, fin pitch to louvered pitch ratio 0.75 and louvered length to louvered pitch ratio 1.25, high exergy performance of SAH is obtained as compared to other louvered parameter values.

Effect of a volute on the unsteady flow in the vane diffuser of a centrifugal compressor

2016 ◽  
Vol 230 (8) ◽  
pp. 773-791 ◽  
Author(s):  
Gong W Qi ◽  
X Hong Zhang
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
High Mass ◽  
Flow Conditions ◽  
Asymmetric Component ◽  
Unsteady Loading ◽  
Vane Diffuser

A volute is the only circumferential asymmetric component in a centrifugal compressor, and thus, it should account for the circumferential asymmetry of the flow in a vane diffuser. This study performs a transient numerical analysis to investigate the effect of a volute on the flow in the vane diffuser of a centrifugal compressor under three operating conditions (near-stall, middle, and high mass flow). We compare numerical and experimental performance of the compressor, including polytropic efficiency, total pressure ratio, and unsteady pressure on a diffuser vane. The numerical scheme is proven valid owing to the fact that the numerical and experimental results considerably agree well with each other. Under middle and high mass flow conditions, the time-averaged static pressure recovery and the total pressure loss coefficients for all the diffuser passages indicate that the performance of the passages near and upstream of the volute tongue is affected negatively by the volute, whereas that of the passages downstream of the volute tongue is less affected. Under near-stall condition, the performance of all the passages is disturbed, and the diffuser passage marked as DP 3 demonstrates the worst performance. Investigation on the time-averaged aerodynamic forces, loading, and pressure on the vanes yields results that are consistent with those of the investigation on the performance of the passages. The harmonics with 0.5 fb and fb, which are included in the unsteady loading and pressure on the pressure and suction sides of the vanes, are dominant, where fb is the impeller main and splitter blades passing frequency. Their amplitude values increase as mass flow deviates from the middle mass flow condition. Under middle and high mass flow conditions, the harmonic with 0.5 fb is affected more negatively because of the larger amplitude on the vanes near and upstream of the volute tongue than those downstream, whereas the harmonic with fb is less affected by the volute. Under the near-stall condition, the transient vorticity fields along with the harmonics of 0.5 fb and fb are investigated to evaluate the performance of the diffuser passages. DP 3, which is located at approximately 90° downstream of the volute tongue, suffers the strongest flow deterioration and is inferred to stall first. Further researches for designing more matching diffuser/volute combination will be performed by referring this study.

Numerical Research of Aerodynamic Sweep on Leading Edge in the Ram-Rotor

2017 ◽  
Author(s):  
Jian Guan ◽  
Ji-ang Han ◽  
Jingjun Zhong ◽  
Chenguang Yuan
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
High Performance ◽  
Pressure Ratio ◽  
Leading Edge ◽  
High Mass ◽  
Positive Role ◽  
Performance Curves ◽  
Flow Loss

In order to diminish the flow loss in the ram-rotor and improve its aerodynamic performance, the effect of forward and backward swept leading edge on flow field and shock pattern in the ram-rotor was investigated using 3-dimensional steady CFD. Ram-rotors with sweeping angles of −60°, −30°, −15°, 0°, 15°, 30°, 60° were modeled, and ram-rotor performance, shock pattern and leakage flow in different swept schemes were the main focuses of attention. The effect of sweeping angle was also discussed in this paper. It has been found that forward sweep makes performance curves move to high mass flow rate zone in the performance map. Meanwhile, strake tip loading decreases, and maximum adiabatic efficiency increases by 0.31% compared to baseline ram-rotor. Contrary to the forward swept scheme, performance curves of backward sweep schemes shift to small mass flow rate zone, and the tip leakage near front part of strake is enhanced. Backward sweep plays a positive role in improving pressure ratio with a maximum increment of 0.46% at peak efficiency point, but causes a high flow loss. As sweeping angle changes, there is an optimum angle value to get a high performance.

scholarly journals Cavitating Flow in the Volute of a Centrifugal Pump at Flow Rates Above the Optimal Condition

2021 ◽  
Vol 9 (4) ◽  
pp. 446
Author(s):  
Hu Qixiang ◽  
Yang Yang ◽  
Shi Weidong ◽  
Cao Weidong ◽  
Shi Yansheng
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Flow Distribution ◽  
Leading Edge ◽  
Flow Area ◽  
Flow Rates ◽  
Blade Loading ◽  
Impeller Outlet ◽  
Optimal Value ◽  
Performance Deterioration

Cavitation is regarded as a considerable factor causing performance deterioration of pumps under off-design conditions, especially at overload conditions. To investigate the unsteady cavitation evolution around the tongue of a pump volute, and its influence on the flow field within passages of the impeller, numerical calculations and several hydraulic tests were performed on a typical centrifugal pump with a shrouded impeller. Emphasis was laid on the cavitation evolution and blade-loading distribution at flow rates above the optimal value. Results indicated that vapor is likely to first emerge from the tongue of the volute rather than at the leading edge of the blades at overload conditions. In contrast to the designed condition, the flow distribution in each passage is obviously different. The flow rate of the passage reaches a maximum just past the location of the tongue, while the minimum flow rate value is projected to appear at the passage upstream. The cavitation at the tongue squeezes the flow area at the outlet of the corresponding flow passage of the tongue, thereby causing a huge growth in the flow rate at the impeller outlet.

Numerical Investigation of Diffuser Rotating Stall and System Instability in a Centrifugal Compressor With Vaned Diffuser

2018 ◽  
Author(s):  
Yang Zhao ◽  
Guang Xi ◽  
Jiayi Zhao
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Flow Instability ◽  
Leading Edge ◽  
Rotating Stall ◽  
Vaned Diffuser ◽  
Corner Separation ◽  
Lumped Parameter

The operating range of a centrifugal compressor is often limited by the occurrence of the flow instability, such as diffuser rotating stall or system surge. In the paper, the unsteady numerical simulations are performed on a low-speed centrifugal compressor to investigate the characteristic of the rotating stall in the vaned diffuser. And also, the developed model of lumped parameter is used to predict the system instability. The flow field in the diffuser is firstly investigated at near stall condition. It is found that the leading-edge vortex and the secondary flow induce the hub-corner separation at the suction side of the diffuser blade. When the mass flow rate is reduced gradually, the fore part of the volute turns to act as a diffuser from a nozzle. Under the influence of the asymmetry induced by the volute, the hub-corner separation firstly develops into rotating stall in the passage with the lowest mass flow rate when at critical stall point. And then the diffuser rotating stall propagates along the circumferential direction at about 7% of the impeller speed. And also, the model of lumped parameter considering the effect of rotating stall is developed to analyze the system instability of mild surge. The predicted vibration frequency is within 5.8% of the measurement and the predicted transient process in mild surge matches well with the measurement. With different volume of the compressed air, the transient compressor characteristic tends to be stabilized or oscillates in a cycle along the counter-clockwise with different magnitude.

Numerical Analysis of Flow Characteristics of the Low-Speed Centrifugal Compressor Stage Comprising Wedge Diffuser

2021 ◽  
Vol 13 (4) ◽  
Author(s):  
S. Seralathan ◽  
N.S.V. Bhavaniprasad ◽  
J. Sai Krishna ◽  
S. Lakshmankumar ◽  
V. Hariram ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Grid Turbulence ◽  
Compressor Stage ◽  
Flow Rates ◽  
Low Speed ◽  
Centrifugal Compressor Stage ◽  
Mass Flow Rates

Wedge type diffusers are used generally in the highly loaded stages of smaller jet engines as it is compact in size. Low speed centrifugal compressor (LSCC) is selected for this present study as experimental details are available. A centrifugal compressor stage comprising wedge type diffuser is used in this numerical investigation in which studies are carried out at design mass flow rate (30kg/s) and off-design mass flow rates (23.64kg/s and 36.36kg/s) at constant rotational speed of 1920 rpm. Single passage approach is chosen to model the computational domain which is meshed with unstructured grid. Turbulence model chosen is kω-SST. The investigation revealed the jet-wake structure along the pressure side and suction side of the impeller and its subsequently mixing at impeller exit vaneless diffuser region. Diffusion process in the LSCC is observed to be effective as the outlet values of absolute velocity are lesser compared to its inlet values. Highest static pressure rise is observed for design mass flow rate and followed by below and above off-design mass flow rates.

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