Asymmetric Flow in Vaneless Diffusers of Centrifugal Blowers

1977 ◽  
Vol 99 (1) ◽  
pp. 104-111 ◽  
Author(s):  
Yasutoshi Senoo ◽  
Yoshifumi Kinoshita ◽  
Masahiro Ishida
Keyword(s):  
Reverse Flow ◽  
Flow Behavior ◽  
Maximum Velocity ◽  
Flow Rates ◽  
Velocity Flow ◽  
Special Relations ◽  
Small Flow ◽  
Vaneless Diffusers ◽  
Momentum Integral ◽  
Large Flow

An analytical method is proposed to evaluate the flow behavior in vaneless diffusers assuming that the flow is not symmetric between the walls. In the analysis momentum integral equations are used together with some special relations for the main flow or for the maximum velocity flow. According to the authors’ experiment, for the case of a small flow rate a reverse flow is observed on one wall near the inlet of the diffuser but at a larger radius the reverse flow disappears and another reverse flow is observed on the other wall. The predictions quantitatively agree well with experiments not only in the case of large flow rates but also in the case of small flow rates where the flow pattern is very complicated.

Optimization of Inlet Ring Groove Arrangement for Suppression of Unstable Flow in a Centrifugal Impeller

2005 ◽  
Author(s):  
Masahiro Ishida ◽  
Daisaku Sakaguchi ◽  
Hironobu Ueki
Keyword(s):  
Flow Rate ◽  
The Other ◽  
Centrifugal Impeller ◽  
Shape Parameters ◽  
Unstable Flow ◽  
Ring Groove ◽  
Flow Rates ◽  
Small Flow ◽  
Specific Speed ◽  
Large Flow

An optimization of the inlet ring groove arrangement has been pursued in the present study for obtaining better impeller characteristics and a wider operation range at both small and large flow rates in a high specific speed type centrifugal impeller with inducer. The effects of the shape parameters with respect to the inlet ring groove on the impeller characteristic and the flow incidence were analyzed mainly based on numerical simulations, but also compared to the experimental results. At small flow rates, a significant improvement in the impeller characteristic is achieved due to reduction in the excessive-positive flow incidence by optimizing both location and width of the rear groove near the inducer tip throat. On the other hand, the impeller characteristic is improved at large flow rates by implementing the corner radius at the rear groove edge and by placing another front ring groove in the suction pipe. As a result, by the optimized configuration of the front and rear ring grooves, the unstable flow range of the test impeller can be reduced by about 50% without deterioration of the impeller characteristic even at the 125% flow rate.

Predicting the Rate of 222Rn Entry from Soil into the Basement of a Dwelling Due to Pressure-Driven Air Flow

1988 ◽  
Vol 24 (1-4) ◽  
pp. 199-202 ◽  
Author(s):  
W.W. Nazaroff
Keyword(s):  
Indoor Radon ◽  
Air Flow ◽  
Entry Rate ◽  
Flow Rates ◽  
Small Flow ◽  
Recommended Guidelines ◽  
Large Flow ◽  
226Ra Content ◽  
Soil Level ◽  
Pressure Driven

Abstract A combination of analytical and numerical methods is applied to the problem of computing 222Rn transport from soil into a dwelling having a basement. Transport is assumed to occur solely by pressure-driven air flow, and the basement shell is assumed to have a single dominant leak that is uniformly distributed around the perimeter at the level of the floor. The results show that for small flow rates of air through the soil, the radon entry rate into the basement increases in proportion to ?Po, the outdoor-indoor pressure difference at the soil level. For large flow rates, the entry rate increases only in proportion to ?Po2/3, due to depletion of radon concentration in the soil. A sample calculation indicates that via this transport mode, soil having ordinary 226Ra content and moderately high permeability can be responsible for indoor radon concentrations of the order of 500 Bq.m-3, greater than recommended guidelines for new housing.

Differences in Formation Mechanism of Static Pressure Circumferential Distribution of Centrifugal Compressor Under Different Operating Conditions

2021 ◽  
Author(s):  
Botai Su ◽  
Ce Yang ◽  
Hanzhi Zhang ◽  
Xin Shi ◽  
Li Fu
Keyword(s):  
Static Pressure ◽  
Operating Conditions ◽  
Single Peak ◽  
Double Peak ◽  
Flow Rates ◽  
Flow Balance ◽  
Impeller Outlet ◽  
Outlet Flow ◽  
Small Flow ◽  
Large Flow

Abstract The casing-wall static pressure of the centrifugal compressor behaves the double-peak distribution in the circumference at small flow rates but the single-peak distribution at large flow rates. A previous study shows that the double-peak distribution is induced by the redistribution of impeller outlet flow rates. In this paper, by using the similar simplified method of directly imposing pressure boundary to the diffuser outlet, the original reason for the formation process difference of pressure distribution in the circumference at different operating conditions is further investigated. The results show that at large flow rates, under the combined action of the specific downstream pressure distribution and the flow performance of the compressor itself, alternating low/high velocity airflow zones similar to those at small flow rates cannot be established in the diffuser when the impeller outlet flow rates are redistributed. Therefore, the static pressure can only express the single-peak distribution in the circumference. In fact, whether the static pressure exhibits the double-peak or single-peak distribution in the circumference depends on whether the impeller outlet flow mutation can destroy the original flow balance. When the flow mutation is dominant, the double-peak distribution is created, whereas when the original flow balance is prevailing, the single-peak distribution is formed.

Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers

1985 ◽  
Vol 107 (2) ◽  
pp. 514-519 ◽  
Author(s):  
Y. Kinoshita ◽  
Y. Senoo
Keyword(s):  
Flow Analysis ◽  
Rotating Stall ◽  
Experimental Results ◽  
Flow Coefficient ◽  
Critical Flow ◽  
Flow Rates ◽  
Small Flow ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Vaneless Diffusers

The limit of rotating stall was experimentally determined for three very small specific speed centrifugal blowers. The impellers were specially designed for stall-free at very small flow rates, so that the cause of rotating stall could be attributed to the vaneless diffusers. Experimental results demonstrated that the blowers did not stall until the flow coefficient was reduced to very small values, which had never been reported in the literature. The critical flow coefficient for rotating stall agreed very well with the prediction based on a flow analysis and a criterion for rotating stall in vaneless diffusers developed by the authors.

Improvements in Aerodynamic Performance and Noise Due to Low Solidity Cascade Diffuser in a Centrifugal Blower

2007 ◽  
Author(s):  
Daisaku Sakaguchi ◽  
Masahiro Ishida ◽  
Tengen Murakami ◽  
Hiroshi Hayami ◽  
Yasutoshi Senoo ◽  
...  
Keyword(s):  
Leading Edge ◽  
Aerodynamic Performance ◽  
Broadband Noise ◽  
Wake Flow ◽  
Frequency Noise ◽  
Vaneless Diffuser ◽  
Centrifugal Blower ◽  
Flow Rates ◽  
Small Flow ◽  
Large Flow

A high efficiency and a wide operating range are required in recent centrifugal compressors and blowers. Low solidity circular cascade diffuser (LSD) was proposed in place of vaned diffuser and channel diffuser for achieving both higher pressure ratio and wider operating range. In the present study, aerodynamic performance and noise characteristics of LSD were investigated changing a radial location of LSD leading-edge. It is known that an interaction occurs between jet-wake flow discharged from the rotating impeller and the LSD leading edge, however jet-wake flow pattern is almost uniformalized until the radial position of R = 1.20 in the vaneless diffuser. Aiming at reducing the noise generated by the interaction mentioned above, the LSD leading edge was moved from RLSD = 1.10 to 1.15 and 1.20 in a centrifugal blower with low specific speed. The frequency spectra of noise were analyzed and the noise due to LSD were discussed from the view point of overall noise, discrete frequency noise and broadband noise. In order to clarify the relationship between the flow field and the noise, flow behavior in the impeller as well as in the diffuser was simulated using a Navier-Stokes solver ANSYS-CFX. According to the present experimental results, about 40% improvement in diffuser performance and about 11% improvement in unstable flow range were achieved in small flow rates by the LSD compared with the vaneless diffuser except for a small deterioration in diffuser performance at the large flow rate. On the other hand, the noise increased clearly in the case of RLSD = 1.10 at the large flow rate and the small flow rates as well. By locating the LSD blade leading edge downstream farther from the impeller exit, a remarkable reduction in overall noise was achieved without deterioration of diffuser performance. It is found that the noise increase due to LSD is mainly dependent on the broadband noise based on the jet-wake flow, the interaction between the reverse flow and the impeller blades results in the discrete frequency noise defined by the frequency of cross product of the rotational speed of the impeller and the number of LSD blade, and a significant reduction in noise is achieved by uniformalization of the jet-wake flow.

Prediction of Flow Behavior and Performance of Squirrel-Cage Centrifugal Fans Operating at Medium and High Flow Rates

1997 ◽  
Vol 119 (3) ◽  
pp. 639-646 ◽  
Author(s):  
R. J. Kind
Keyword(s):  
Reverse Flow ◽  
Flow Behavior ◽  
Design Flow ◽  
Flow Rates ◽  
Factors Affecting ◽  
Squirrel Cage ◽  
Centrifugal Fans ◽  
Flow Phenomena ◽  
And Performance ◽  
Inlet Zone

This paper describes a method for predicting flow behavior and performance for centrifugal fans of the squirrel-cage type. The work is directed at improving under standing of the factors affecting performance of these fans. A simulation approach has been adopted. That is, the fan is subdivided into a number of zones (inlet zone, blading zone, volute zone) and the zones are divided into elements. Flow behavior in the zones and elements and interactions between them are modeled using appropriate equations and correlations. The blading correlations make use of new experimental data for high-solidity cascades of bent sheet metal blades, typical of squirrel-cage fans. Predicted fan performance characteristics are in reasonable agreement with experimental results for flow rates at and above the best-efficiency operating point. Although relatively simple, the method recognizes the main flow phenomena and interactions that occur in squirrel-cage fans and it thus represents a substantial advance over what is currently available in the literature. Together with earlier experimental work, development of the method has provided considerable insight into the relative importance of various aspects of flow behavior. The ability to deal with extensive reverse flow through the rotor blading has not yet been incorporated and it is evident that this ability is essential for realistic prediction of flow behavior and performance at below-design flow rates.

scholarly journals Limits of Rotating Stall and Stall in Vaneless Diffuser of Centrifugal Compressors

1978 ◽  
Author(s):  
Y. Senoo ◽  
Y. Kinoshita
Keyword(s):  
Flow Behavior ◽  
Rotating Stall ◽  
Critical Conditions ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Flow Rates ◽  
Vaneless Diffusers

Based on the theory in Reference (3), the flow behavior is predicted in four vaneless diffusers with different geometries at the flow rates just before rotating stall and just before stall, which have been experimentally determined. Since the predicted velocity distributions at the critical conditions are physically reasonable for rotating stall and for stall are tentatively set so that the critical conditions are predictable using the theory. Prediction is made for two cases for backward leaning blade impellers and three cases for radial blade impellers in the literature in addition to the authors’ experiments. Satisfactory results are obtained except one example.

Analysis of Secondary Flow Behavior in Low Solidity Cascade Diffuser of a Centrifugal Blower

2010 ◽  
Author(s):  
Masahiro Ishida ◽  
Tengen Murakami ◽  
Daisaku Sakaguchi ◽  
Hironobu Ueki ◽  
Hiroshi Hayami ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Flow Behavior ◽  
Vortex Formation ◽  
Leading Edge ◽  
Centrifugal Blower ◽  
Flow Rates ◽  
Noise Characteristics ◽  
Small Flow ◽  
Blade Tip ◽  
Low Solidity Cascade Diffuser

Aiming at reducing noise without deterioration of diffuser performance in a low solidity cascade diffuser (LSD) of a centrifugal blower, the authors have proposed to locate a shallow and short groove or a slot between the diffuser wall and the LSD blade tip limiting to near the blade leading edge. The effect of the LSD blade tip-groove on the blower characteristics and the noise characteristics were investigated experimentally as well as numerically. The mechanism being able to maintain the high LSD blade loading even at small flow rates was pursued in view points of the vortex formation and the induced secondary flow. In addition, the effect of the tip-groove length on the vortex formation in the shroud tip-groove and the secondary flow behavior in the LSD were analyzed numerically and an optimum tip-groove configuration was proposed. It is concluded that formations of the stable and intense vortex in the shroud tip-groove and the recirculating secondary flow along the shroud wall toward the impeller exit are the key factors for achieving a high LSD performance and reducing noise simultaneously at small flow rates.

scholarly journals Investigation of Separation Phenomena in a Radial Pump at Reduced Flow Rate by Large-Eddy Simulation

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Antonio Posa ◽  
Antonio Lippolis ◽  
Elias Balaras
Keyword(s):  
Reverse Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Secondary Flows ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Radial Pump ◽  
Reduced Flow

Turbopumps operating at reduced flow rates experience significant separation and backflow phenomena. Although Reynolds-Averaged Navier–Stokes (RANS) approaches proved to be usually able to capture the main flow features at design working conditions, previous numerical studies in the literature verified that eddy-resolving techniques are required in order to simulate the strong secondary flows generated at reduced loads. Here, highly resolved large-eddy simulations (LES) of a radial pump with a vaned diffuser are reported. The results are compared to particle image velocimetry (PIV) experiments in the literature. The main focus of the present work is to investigate the separation and backflow phenomena occurring at reduced flow rates. Our results indicate that the effect of these phenomena extends up to the impeller inflow: they involve the outer radii of the impeller vanes, influencing significantly the turbulent statistics of the flow. Also in the diffuser vanes, a strong spanwise evolution of the flow has been observed at the reduced load, with reverse flow, located mainly on the shroud side and on the suction side (SS) of the stationary channels, especially near the leading edge of the diffuser blades.

Numerical Analysis on the CO-NO Formation Production near Burner Throat in Swirling Flow Combustion System

2014 ◽  
Vol 69 (2) ◽  
Author(s):  
Mohamad Shaiful Ashrul Ishak ◽  
Mohammad Nazri Mohd Jaafar
Keyword(s):  
Swirling Flow ◽  
Reverse Flow ◽  
Flow Behavior ◽  
Recirculation Region ◽  
Mixing Enhancement ◽  
Ansys Fluent ◽  
Pressure Losses ◽  
No Formation ◽  
Swirl Angle ◽  
Air Mixing

The main purpose of this paper is to study the Computational Fluid Dynamics (CFD) prediction on CO-NO formation production inside the combustor close to burner throat while varying the swirl angle of the radial swirler. Air swirler adds sufficient swirling to the inlet flow to generate central recirculation region (CRZ) which is necessary for flame stability and fuel air mixing enhancement. Therefore, designing an appropriate air swirler is a challenge to produce stable, efficient and low emission combustion with low pressure losses. A liquid fuel burner system with different radial air swirler with 280 mm inside diameter combustor of 1000 mm length has been investigated. Analysis were carried out using four different radial air swirlers having 30°, 40°, 50° and 60° vane angles. The flow behavior was investigated numerically using CFD solver Ansys Fluent. This study has provided characteristic insight into the formation and production of CO and pollutant NO inside the combustion chamber. Results show that the swirling action is augmented with the increase in the swirl angle, which leads to increase in the center core reverse flow, therefore reducing the CO and pollutant NO formation. The outcome of this work will help in finding out the optimum swirling angle which will lead to less emission.  

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