An Experimental Investigation to Improve the Performance of Centrifugal Compressors Operating at Off-Design Conditions

2006 ◽  
Author(s):  
Saad A. Ahmed ◽  
Dhafar S. Mohammed
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Instability ◽  
Dynamic Pressure ◽  
Critical Mass ◽  
Flow Coefficient ◽  
Flow Area ◽  
Stall Inception ◽  
Pressure Transducers

Experiments to investigate the feasibility of controlling (delaying/or suppressing) the stall in the radial diffuser of a low speed centrifugal blower were carried out. The mass flow rate of air through the blower could be gradually reduced until stall inception is accomplished. The static and dynamic pressures in the diffuser were measured along a radial or a circumferential path using static and dynamic pressure transducers. The technique was very simple and involved changing the flow area at the diffuser exit with the use of throttle rings to either diffuser shroud, or the diffuser hub. Simultaneous attachment of the throttle rings to both the diffuser shroud and the hub was also made. The diffuser exit blockage ratio varied between 0% and 75% when throttle rings were attached to the diffuser walls to reduce its exit flow area. The results showed that the flow instability in the diffuser (stall) was delayed to a lower flow coefficient (the critical mass flow rate could be reduced to 55% of its value without the blockage). The experimental data also confirmed that the throttle rings could be an effective way to control the stall in the vaneless radial diffuser.

Control of Self-Excited Oscillations in Centrifugal Blowers

2007 ◽  
Author(s):  
Saad A. Ahmed
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Industrial Applications ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Flow Area ◽  
The Stability

Centrifugal compressors or blowers are widely used in many industrial applications. However, the operation of such systems is limited at low-mass flow rates by self-excited flow instabilities which could result in rotating stall or surge of the compressor. These instabilities will limit the flow range in which the compressor or the blower can operate, and will also lower their performance and efficiency. Experimental techniques were used to investigate a model of radial vaneless diffuser at stall and stall-free operating conditions. The speed of the impeller was kept constant, while the mass flow rate was reduced gradually to study the steady and unsteady operating conditions of the compressor. Additional experiments were made to investigate the effects of reducing the exit flow area on the inception of stall. The results indicate that the instability in the diffuser was successfully delayed to a lower flow coefficient when throttle rings were attached to either one or both of the diffuser walls (i.e., to reduce the diffuser exit flow area). The results also showed that an increase of the blockage ratio improves the stability of the system (i.e., the critical mass flow rate could be reduced to 50% of its value without blockage). The results indicate that the throttle rings could be an effective method to control stall in radial diffusers.

scholarly journals Centrifugal Compressor Stall Control by the Application of Engineered Surface Roughness on Diffuser Shroud Using Numerical Simulations

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2033
Author(s):  
Amjid Khan ◽  
Muhammad Irfan ◽  
Usama Muhammad Niazi ◽  
Imran Shah ◽  
Stanislaw Legutko ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Control Method ◽  
Flow Instability ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Low Mass

Downsizing in engine size is pushing the automotive industry to operate compressors at low mass flow rate. However, the operation of turbocharger centrifugal compressor at low mass flow rate leads to fluid flow instabilities such as stall. To reduce flow instability, surface roughness is employed as a passive flow control method. This paper evaluates the effect of surface roughness on a turbocharger centrifugal compressor performance. A realistic validation of SRV2-O compressor stage designed and developed by German Aerospace Center (DLR) is achieved from comparison with the experimental data. In the first part, numerical simulations have been performed from stall to choke to study the overall performance variation at design conditions: 2.55 kg/s mass flow rate and rotational speed of 50,000 rpm. In second part, surface roughness of magnitude range 0–200 μm has been applied on the diffuser shroud to control flow instability. It was found that completely rough regime showed effective quantitative results in controlling stall phenomena, which results in increases of operating range from 16% to 18% and stall margin from 5.62% to 7.98%. Surface roughness as a passive flow control method to reduce flow instability in the diffuser section is the novelty of this research. Keeping in view the effects of surface roughness, it will help the turbocharger manufacturers to reduce the flow instabilities in the compressor with ease and improve the overall performance.

Stall Warning Using the Rotor Tip Pressure in a Transonic Axial Compressor With Circumferential Grooves

2018 ◽  
Author(s):  
Byeung Jun Lim ◽  
Tae Choon Park ◽  
Young Seok Kang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Single Stage ◽  
Stall Inception ◽  
Casing Treatment ◽  
Stall Warning ◽  
Transonic Axial Compressor

In this study, characteristics of stall inception in a single-stage transonic axial compressor with circumferential grooves casing treatment were investigated experimentally. Additionally, the characteristic of increasing irregularity in the pressure inside circumferential grooves as the compressor approaches the stall limit was applied to the stall warning method. Spike-type rotating stall was observed in the single-stage transonic axial compressor with smooth casing. When circumferential grooves were applied, the stall inception was suppressed and the operating point of the compressor moved to lower flow rate than the stall limit. A spike-like disturbance was developed into a rotating stall cell and then the Helmholtz perturbation was overlapped on it at N = 80%. At N = 70 %, the Helmholtz perturbation was observed first and the amplitude of the wave gradually increased as mass flow rate decreased. At N = 60%, spike type stall inceptions were observed intermittently and then developed into continuous rotating stall at lower mass flow rate. Pressure measured at the bottom of circumferential grooves showed that the level of irregularity of pressure increased as flow rate decreased. Based on the characteristic of increasing irregularity of the pressure signals inside the circumferential grooves as stall approaches, an autocorrelation technique was applied to the stall warning. This technique could be used to provide warning against stall and estimate real-time stall margins in compressors with casing treatments.

Axial Turbine Tip Desensitization by Injection From a Tip Trench: Part 1 — Effect of Injection Mass Flow Rate

2004 ◽  
Author(s):  
Nikhil M. Rao ◽  
Cengiz Camci
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Total Pressure ◽  
Large Scale ◽  
Dynamic Pressure ◽  
Coolant Injection ◽  
Gap Height ◽  
Tip Desensitization ◽  
Injection Rates

An experimental study of a turbine tip desensitization method based on tip coolant injection was conducted in a large-scale rotating turbine rig. One of twenty-nine rotor blades was modified and instrumented to have a tip trench with discrete injection holes directed towards the pressure side. Time accurate absolute total pressure was measured 0.3 chord lengths downstream of the rotor exit plane using a fast response dynamic pressure sensor in a phase-locked manner. The test cases presented include results for tip gap heights of 1.40% and 0.72% of the blade height, and coolant injection rates of 0.41%, 0.52%, 0.63%, and 0.72% core mass flow rate. At a gap height of 1.40% the leakage vortex is large, occupying about 15% blade span. A reduction in gap height causes the leakage vortex to reduce in size and move towards the blade suction side. The minimum total pressure measured, for the reduced gap, in the leakage vortex is about 4% greater. Coolant injection from the tip trench is successful in filling in the total pressure defect originally resulting from the leakage vortex without injection. At the higher tip injection rates the leakage vortex is also seen to have moved towards the blade tip. The high momentum associated with the tip jets affects the total pressure distributions in the neighboring passages.

Effects of Burner Diameter and Fuel Type on Smoke Point and Radiation Characteristics of Diffusion Flames

2002 ◽  
Author(s):  
S. F. Goh ◽  
S. Kusadomi ◽  
S. R. Gollahalli
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Smoke Point ◽  
Fuel Type ◽  
Fuel Flow Rate ◽  
Flame Radiation ◽  
Fuel Mass ◽  
Fuel Flow

The main purpose of this study was to comprehend the effects of burner diameter and fuel type on smoke point characteristics of a hydrocarbon diffusion flame and its radiation emission. The critical mass flow rate of pure fuel at this smoke point was measured. At nine different fractions of the critical mass flow rate, nitrogen gas was supplied along with the fuel to achieve smoke point. At each condition, flame radiation and flame height were measured. The axial radiation profile at the critical fuel mass flow rate for one burner was also measured. Three fuels of differing sooting propensities were used: ethylene (C2H4), propylene (C3H6), and propane (C3H8). Three different burners with inner diameters of 1.2 mm, 3.2 mm and 6.4 mm were used. Results showed that propylene had the highest critical fuel flow rate and the highest nitrogen dilution required to suppress smoking and total flame radiation, followed by ethylene and propane. For all fuels, the curves of nitrogen flow rate required for smoke suppression versus fuel flow rate exhibited a skewed bell shape. The variation of Reynolds number at the critical fuel mass flow rate with the burner diameter showed a linear relation. On the other hand, the variation of total flame radiation with burner diameter was nonlinear.

Condensation-Induced Water Hammer in Horizontal Refrigerant Pipe With Warm Gas Entry

2003 ◽  
Author(s):  
C. Samuel Martin
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
High Speed ◽  
Fast Response ◽  
Ammonia Gas ◽  
Pressure Transducers ◽  
High Speed Data Acquisition ◽  
High Speed Data ◽  
Liquid Depth

Careful experiments have been conducted for the purpose of investigating the phenomenon of condensation-induced waterhammer in an ammonia refrigeration system. To initiate a waterhammer event warm ammonia gas was introduced over static subcooled ammonia liquid placed in a horizontal 146.3 mm diameter carbon steel pipe 6.0 m in length. By means of fast response piezoelectric pressure transducers and a high speed data acquisition system rapid dynamic pressures were recorded whenever a shock event occurred. The occurrence of condensation-induced waterhammer depended upon three major variables; namely, (1) initial liquid depth, (2) liquid temperature, and (3) mass flow rate of warm gas. For given liquid depth and temperature, once the warm gas threshold conditions were exceeded shocks occurred with greater magnitude as the mass flow rate of gas input was increased. With adequate subcooling condensation-induced waterhammer occurred for initial liquid depths ranging from 25% to 95% of internal pipe diameter. The threshold mass flow rate of warm gas necessary to initiate waterhammer was greater as the initial liquid was lowered.

Experimental Investigation of Flow Instability in a Supersonic Inlet

2010 ◽  
Author(s):  
Mohammad Reza Soltani ◽  
Mohammad Farahani
Keyword(s):  
Mach Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Instability ◽  
Wind Tunnel Test ◽  
External Flow ◽  
Pressure Data ◽  
Supersonic Inlet ◽  
Shock Oscillation

An extensive wind tunnel test series were conducted on an axisymmetric supersonic inlet. The model was tested at Mach numbers from 1.8 to 2.2 and at different values of mass flow rate. Shadowgraph flow visualization was used to capture the external shock structure in front of the inlet. The goal of this study is to find out the general characteristics of the inlet buzz. Frequencies of the buzz have been achieved from the analysis of the pressure data as well as the shadowgraph pictures. The amplitude of the shock waves motion has been measured from the visualization pictures too. In the some large value of mass flow rate, the frequency of shock oscillation increased versus Mach number. Also in each Mach number due to the mass flow rate decrement, the buzz frequency decreases and its amplitude increases conversely. Also buzz instability affects the external flow by the same frequency of the internal one.

scholarly journals The Effects of Diffuser Geometry on Rotating Stall Behavior

1988 ◽  
Author(s):  
M. V. Otugen ◽  
R. M. C. So ◽  
B. C. Hwang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Rotating Stall ◽  
Radius Ratio ◽  
Impeller Speed ◽  
Vaneless Diffuser ◽  
Room Condition ◽  
Inlet Opening

Experiments were carried out in a model vaneless diffuser rig to investigate the rotating stall phenomenon and its relation to diffuser geometry. The experimental rig consisted of an actual impeller which was used to deliver the flow to the vaneless diffuser. Mass flow rate through the system could be adjusted by varying the rotational speed of the impeller at a fixed inlet opening or by changing the inlet opening at a fixed impeller speed. The flow exited to room condition. As such, the rig was designed to investigate the fluid mechanics of vaneless diffuser rotating stall only. Attention was focused on the effects of diffuser width and radius on rotating stall. Three diffuser widths and three outlet radii were examined. The width-to-inlet radius ratio varied between 0.09 and 0.142 while the outlet-to-inlet radius ratio varied between 1.5 and 2. Results showed that the critical mass flow rate for the onset of rotating stall decreases with decreasing diffuser width. The critical mass flow rate is affected also by the diffuser radius ratio; larger radius ratios resulted in smaller critical mass flow rates. The ratio of the speed of rotation of the stall cell to impeller speed is found to decrease with increasing number of stall cells. This relative speed also decreases with increasing diffuser radius ratio, but it is largely independent of the diffuser width.

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.

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