Effect of Specific Heat Ratio, Impeller Tip Running Clearance, and Compressor Insulation on High-Pressure-Ratio Centrifugal Compressor Modeling

1975 ◽  
Vol 97 (2) ◽  
pp. 174-179
Author(s):  
J. A. Block ◽  
P. W. Runstadler
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Specific Heat ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Specific Heat Ratio ◽  
High Pressure Ratio ◽  
Air Inlet ◽  
Stage Efficiency ◽  
Isentropic Efficiency

Results are displayed which show the effect of gas specific heat ratio, impeller tip running clearance, and compressor insulation on modeling of a high-pressure-ratio compressor’s performance. The data were obtained using a low-speed-of-sound gas and a compressor previously tested extensively in air. Duplication of the air inlet specific heat ratio was found to be essential to modeling the air-equivalent flow rate accurately. Stage pressure ratio and stage efficiency were found to be less sensitive to the accurate replication of the air specific heat ratio. For the compressor tested, stage isentropic efficiency increased as impeller-to-shroud tip running clearance was reduced from 15 to 5 percent of the impeller tip axial depth. The measured stage efficiency was found to depend strongly on the heat transfer between the compressor and surroundings.

Effect of Recirculation Device With Counter Swirl Vane on Performance of High Pressure Ratio Centrifugal Compressor

2011 ◽  
Author(s):  
Hideaki Tamaki
Keyword(s):  
High Pressure ◽  
Mach Number ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Negative Slope ◽  
Tip Leakage Flow ◽  
Recirculation Flow ◽  
Operating Range ◽  
High Pressure Ratio

Centrifugal compressors used for turbochargers need to achieve a wide operating range. The author has developed a high pressure ratio centrifugal compressor with pressure ratio 5.7 for a marine use turbocharger. In order to enhance operating range, two different types of recirculation devices were applied. One is a conventional recirculation device. The other is a new one. The conventional recirculation device consists of an upstream slot, bleed slot and the annular cavity which connects both slots. The new recirculation device has vanes installed in the cavity. These vanes were designed to provide recirculation flow with negative preswirl at the impeller inlet, a swirl counterwise to the impeller rotational direction. The benefits of the application of both of the recirculation devices were ensured. The new device in particular, shifted surge line to a lower flow rate compared to the conventional device. This paper discusses how the new recirculation device affects the flow field in the above transonic centrifugal compressor by using steady 3-D calculations. Since the conventional recirculation device injects the flow with positive preswirl at the impeller inlet, the major difference between the conventional and new recirculation device is the direction of preswirl that the recirculation flow brings to the impeller inlet. This study focuses on two effects which preswirl of the recirculation flow will generate. (1) Additional work transfer from impeller to fluid. (2) Increase or decrease of relative Mach number. Negative preswirl increases work transfer from the impeller to fluid as the flow rate reduces. It increases negative slope on pressure ratio characteristics. Hence the recirculation flow with negative preswirl will contribute to stability of the compressor. Negative preswirl also increases the relative Mach number at the impeller inlet. It moves shock downstream compared to the conventional recirculation device. It leads to the suppression of the extension of blockage due to the interaction of shock with tip leakage flow.

Investigation of Self-Recycling-Casing-Treatment (SRCT) Influence on Stability of High Pressure Ratio Centrifugal Compressor With a Volute

2011 ◽  
Author(s):  
Mingyang Yang ◽  
Ricardo Martinez-Botas ◽  
Yangjun Zhang ◽  
Xinqian Zheng ◽  
Takahiro Bamba ◽  
...  
Keyword(s):  
High Pressure ◽  
Numerical Method ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Flow Distortion ◽  
Casing Treatment ◽  
High Pressure Ratio ◽  
The Stability

Large feasible operation range is a challenge for high pressure ratio centrifugal compressor of turbocharger in vehicle engine. Self-Recycling-Casing-Treatment (SRCT) is a widely used flow control method to enlarge the range for this kind of compressor. This paper investigates the influence of symmetrical/asymmetrical SRCT (ASRCT) on the stability of a high pressure ratio centrifugal compressor by experimental testing and numerical simulation. Firstly, the performance of the compressor with/without SRCT is tested is measured investigate the influence of flow distortion on the stability of compressor as well as the numerical method validation. Then detailed flow field investigation is conducted by experimental measurement and the numerical method to unveil the reasons for stability enhancement by symmetrical/asymmetrical SRCT. Results show that static pressure distortion at impeller outlet caused by the volute can make passages be confronted with flow distortion less stable than others because of their larger positive slope of T-S pressure ratio performance at small flow rate. SRCT can depress the flow distortion and reduce the slope by non-uniform recycling flow rate at impeller inlet. Moreover, ASRCT can redistribute the recycling flow in circumferential direction according to the asymmetric geometries. When the largest recycling flow rate is imposed on the passage near the distorted static pressure, the slope will be the most effectively reduced. Therefore, the stability is effectively enhanced by the optimized recycling flow device.

The Effect of Specific Heat Ratio on the Performance of Compressible Flow Turbo-Machines

2008 ◽  
Author(s):  
Theodor W. von Backstro¨m
Keyword(s):  
Specific Heat ◽  
Compressible Flow ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Centrifugal Impeller ◽  
Specific Heat Ratio ◽  
Total Temperature ◽  
Similar Density ◽  
Density Ratios ◽  
Stage Efficiency

The paper presents a method of determining the pressure ratio characteristic of a compressible flow turbo-machine when the specific heat ratio of the gas flowing through it is changed. It is shown that Mach number scaling in efficient machines running at low fractional increases in total temperature could tolerate limited variations in specific heat ratio. A method of finding the scaled operating conditions for the achievement of similar density ratios in scaled and prototype machines operating with gases with different specific heat ratios is presented. The method achieved very good accuracy in scaling the performance of a centrifugal impeller working with argon to its performance with carbon dioxide. The stage polytropic efficiencies were chosen to agree with measured data, although analysis indicated that polytropic stage efficiency should be independent of specific heat ratio. Further investigation and validation may lead to a standardised method of scaling turbo-machinery performance between gases with varying properties, which includes the effect of specific heat ratio.

Experimental Investigation of High Pressure Ratio Centrifugal Compressor With Axisymmetric and Nonaxisymmetric Recirculation Device

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Hideaki Tamaki ◽  
Xinqian Zheng ◽  
Yangjun Zhang
Keyword(s):  
High Pressure ◽  
Pressure Drop ◽  
Flow Rate ◽  
Average Distance ◽  
Pressure Ratio ◽  
Low Flow ◽  
Blade Loading ◽  
Recirculation Flow ◽  
High Pressure Ratio ◽  
Compressor Efficiency

Centrifugal compressors used for turbochargers are required to have a wide operating range. A recirculation device, which consists of a bleed slot, an upstream slot, and an annular cavity connecting both slots, is often used with them. It improves the incidence angle of the impeller leading edge, i.e., the blade loading of the inducer, at low flow rates due to the recirculation flow supplied to the compressor inlet. However, the compressor efficiency drops when there is a recirculation flow from the bleed slot to the upstream slot. A one dimensional analysis in the first section of this paper showed that the reduction in the compressor efficiency can be lowered by decreasing the pressure drop or reducing the recirculation flow rate within the recirculation device. This study examined the possibility of improvement in the compressor efficiency by the use of a recirculation device with an asymmetric bleed slot. An impeller of a turbocharger compressor is normally contained in a volute. Since the geometry of the volute is not axisymmetric, the impeller is surrounded by an asymmetric flow field. Hence each impeller passage, which is formed by two adjacent full blades, is operated at a different operating point. This means that some of the passages need the improvement in the blade loading by the recirculation device but others do not. There is a possibility that this is realized by a recirculation device with an asymmetrically distributed bleed slot, called a nonaxisymmetric recirculation device in this paper. If the asymmetric bleed slot shortens the average distance between the bleed slot and upstream slot or reduces the area of the bleed slot, it can reduce the pressure drop or recirculation flow rate within the recirculation deviceand, hence, can improve the compressor efficiency. This study discusses the characteristics of high pressure ratio compressors for turbochargers without the recirculation device and those with the recirculation device with an axisymmetric bleed slot. Furthermore, the effects of nonaxisymmetric recirculation devices on the compressor characteristics are experimentally investigated. Two types of nonaxisymmetric recirculation devices were tested. One had the bleed slot of a sine wave pattern. The other had the bleed slot partially channeled in the circumferential direction. There were appropriate positions relative to the volute for both nonaxisymmetric recirculation devices. The compressor efficiency with nonaxisymmetric recirculation devices was higher than that with axisymmetric recirculation devices and the surge lines of the compressor with nonaxisymmetric recirculation devices were located at a flow rate lower than or equal to those with the axisymmetric recirculation devices.

Inlet Duct Treatment for Stability Improvement on a High Pressure Ratio Centrifugal Compressor

2013 ◽  
Author(s):  
Mingyang Yang ◽  
Ricardo Martinez-Botas ◽  
Yangjun Zhang
Keyword(s):  
High Pressure ◽  
Flow Control ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Control Method ◽  
Pressure Ratio ◽  
Operating Range ◽  
High Pressure Ratio ◽  
Wide Range ◽  
Inlet Duct

The operating range of a centrifugal compressor, determined by surge and choke flow rate, is a key issue for turbocharging since a vehicle internal combustion engine (ICE) is usually operated across a wide range. In this paper a new flow control method is developed and validated numerically, in which an array of circumferentially distributed holes is designed in the inner wall of the inlet duct of a high pressure ratio centrifugal compressor of a turbocharger. Firstly the numerical method is validated by experimental results of the original turbocharging centrifugal compressor with a pressure ratio of 4. Next the validated method is used to investigate the new flow control method and its effect on the compressor’s performance. Results show that the method can enhance the compressor stability and widen the operating range effectively at all investigated speeds. At meantime, the choke flow reduces slightly. The flow details in the compressor are further analysed according to the CFD results. It is found that the flow near the blade tip at inlet is pre-swirled by the method as the conventional IGV does while the flow in the middle span or near the hub remains in an axial direction. As a result, the stability of the compressor is enhanced by the pre-swirl effect at the tip while minimally sacrificing the choke flow rate, thus the map is extended effectively by the flow control method.

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