Improve performance centrifugal fan impeller

Centrifugal fan as an important type of fluid machinery, widely used in various sectors of the national economy, is one of the major energy-consuming machinery, energy saving is an important area of ​​research. The study showed that: improve the centrifugal fan impeller design level, it is to improve the efficiency of centrifugal fan, to expand its working range of the key. This article from the centrifugal fan impeller design and the use of boundary layer control technology to improve performance centrifugal fan impeller these two aspects of the research proposed in recent years to improve the performance centrifugal fan ways and means of inductive analysis.

1 impeller centrifugal fan design approach outlined

How to design efficient and simple process centrifugal fan has been a major problem researchers study design efficiency impeller blades is the main way to solve this problem.

The fan impeller is the core pneumatic components, the impeller internal flow directly determine the performance and efficiency of the machine. So scholars to understand the real situation inside the impeller flow and improved impeller design to improve performance and efficiency of the impeller, we made a lot of work.

In order to design a highly efficient centrifugal impeller, researchers have studied from various angles, the gas flow pattern within the impeller, find the best impeller design. The earliest use of an element design [1], through a lot of statistical data and theoretical analysis, the law of centrifugal fans get to select key sections of each aerodynamic and structural parameters. In the early one element method to use, simply by key sections of the average speed of each fan calculations to determine the key parameters of the centrifugal impeller and volute, and generally blade profile with a simple single-arc shape. This method is very rough, the fan performance design requires designers to have a very rich experience, sometimes you can get a good performance of the fans, however, in most cases, the low efficiency of the design fans. In order to improve, the researchers impeller cover meridional surface profile using excessive flow cross section of the design concept [2-3], so designed centrifugal impeller wheel cover to two or more segments arc, designed in this way impeller although slightly higher than the former one element design approach is inefficient, but the designed fan wheel covers difficult process, high cost, it is difficult for large fans and fans of non-standard production. Another important aspect is to improve blade design, for improved methods for the introduction of the binary leaves and other major deceleration method and the like dilation method [4], and the average flow line using a given impeller along the relative velocity W m distribution [5 ] Methods. Etc. deceleration method loss from the viewpoint of airflow relative velocity in the impeller flow process within the channel to the same rate of uniform changes, can reduce flow loss and further increase the impeller efficiency; etc. dilation method is to avoid the local area too large expansion angle The proposed method. Given the impeller relative velocity W m along the distribution line is the mean flow velocity relative to the average variation along the flow line m by controlling, by simple geometry, it can get distributed along the blade profile radius. The above method is simple, but it requires more complex numerical calculations.

With the rapid development of numerical computation and computer, you can use a more sophisticated approach to design centrifugal fan blades. Miao Miao and other water use & ldquo; Controllable Eddy & rdquo; concept [6], the establishment of a design method Impeller designed with streamline curvature of the impeller meridian plane, which has now extended to the engineering sector and it has achieved remarkable results [7]. However, this method determines the key to the success of the impeller design, namely, how to give a reasonable distribution of the meridional flow surface of the blade vortex. This aspect needs to have a wealth of design experience; on the other hand also in the design process needs to continue to improve design results to match the distribution of blade vortex with a view to the final design of efficient turbomachinery. For the entire meridian plane controllable vortex determination can rCu, can be determined by linear interpolation method along roulette wheel cover of a given use rCu distribution throughout the meridian plane [8-9], or by the empirical formula OK controllable vortex distribution [10], but also the use of a given blade loading method [11] centrifugal fan blade design. The above methods are adopted streamline curvature method, design a ternary centrifugal blade, For binary centrifugal fan blade can not be directly applied. But numerical display, Dual flow centrifugal fan blades inside the structure is more complex three-dimensional flows. Therefore, the calculation method of how to use the three-dimensional flow field further to design efficient binary centrifugal impeller centrifugal fan design technology is the key to improvement.

With the continuous development of computer technology, three-dimensional viscous flow field obtained very great progress, thus, some researchers have proposed approximation model methods. This method is for when the project is completely random class optimization problem of excessive optimization calculation, methods of applied statistics, a small amount of calculation proposed, to some extent, to ensure the accuracy of the method of design. In the approximate model turbomachinery aerodynamic optimization method is applied to the design of domestic and foreign researchers have done a considerable part of the work [12-14], in which the response surface and artificial neural network applications majority. How to effectively approximate model method is applied to multi-disciplinary, multi-condition optimization problem, and cover a larger design space with fewer actual design parameters, it is an important issue.

2010, Xi light, etc. An approximate model of optimization methods in turbomachinery aerodynamic design application [15]. Approximate model building process include: (1) Select test design and layout sample points generated design variables and design goals corresponding sample data in the sample points; (2) Select the model expressed as a function of sample data above; (3 ) choose a method, fit the sample data model function above to establish an approximate model. Each of the above step to select different methods or models to produce a variety of appropriate approximation model methods. This method not only contribute to a more accurate insight into the relationship between the amount of design and design goals, and calculate approximate model to replace the time-consuming calculation and analysis program to assess the objective function can be optimized for the engineering design space exploration provides rapid analysis tools reduce the computational cost. In the aerodynamic optimization design process, by using the model of precision replace time-consuming computational fluid dynamics analysis, it can speed up the design process and reduce design costs. Based on statistical theory of approximation model, which effectively balance the turbomachinery aerodynamic computational fluid dynamics analysis based on the optimization of the design of cost and accuracy of computing this contradiction. The approximate model of test design method, based on the response surface method, Kriging method and artificial neural network technology successfully applied to optimize the design of turbomachinery components, the centrifugal compressor diffuser blades, mixed flow impeller and pump impeller design and other issues has been successfully applied to show the broad prospect of engineering application. Currently, the group has established a seat light components and pump impeller centrifugal compressor optimization design system, and played an important role in engineering design.
In 2011, Li Jing and silver on the basis of the approximate model of the proposed method of controlling the relative centrifugal impeller average speed optimization method [16], the approximate model method used in the earlier centrifugal fan impeller design. This method gives the average velocity in the flow channel airflow along the lines of the design average flow distribution, design a set of centrifugal fan parameters, according to an orthogonal criteria, taking full account of the impeller efficiency factors based on orthogonal optimization method optimization combinations and numerical simulation of fluid dynamics analysis software based on the successful development of the final product and the country to promote the same design parameters 9-19 and the size of the centrifugal fan impeller model to calculate the total pressure efficiency is improved by more than 4%. The method is simple, reasonable and reliable, has been the design and development of high efficiency.

With the increasing deepening of theoretical research and design methods for reducing the impeller aerodynamic losses, improve impeller aerodynamic performance of measures to improve the efficiency of research centrifugal fan, it will be better used in engineering practice.

2 ways to improve the flow of a centrifugal impeller fan

Centrifugal fan impeller is the heart of the internal flow centrifugal fan is a very complex process of reverse voltage, high-speed rotation of the impeller and leaves road complex geometry all their internal flows into a very complex three-dimensional turbulent flow. Because of pressure, generally there will be pressure for the blade within the blade passage secondary flow suction surface, and because the airflow 90 & deg; turn, led to the roulette wheel cover pressure is greater than the pressure to form a secondary flow, which generally results in the impeller wheel lid and blade suction surface low velocity zone appears even separation, forming a jet & mdash; wake structure [17]. Since the jet & mdash; the presence of wake structure, resulting in decreased efficiency centrifugal fan noise increases. In order to improve the liquidity situation centrifugal impeller, improve efficiency impeller, an important research direction is the use of boundary layer control mode to improve performance centrifugal impeller, which is a hot research direction in recent years.

In 2009, 刘小民, who used active boundary layer control technology in compressor inlet, selectively arranged vortex generators, thereby changing the impeller inlet flow field numerical calculation of centrifugal compressor performance under different configuration parameters were analyzed [18 ʱ?? This article applies to a centrifugal impeller vortex generator flow control effect a preliminary verification and research, numerical analysis shows that this method can indeed improve the internal flow impeller, the impeller to improve performance results. However, the complex structure of the active control technology, and the need for additional control equipment and energy, the requirements of economic and durable centrifugal fan products are not competitive.

Ways to enhance the use of boundary layer control performance centrifugal impeller Another approach is to use an adaptive boundary layer control technology. In 1999, 黄东涛 et al proposed a centrifugal fan impeller design uses slotted blade length method [19-20], the method used tandem cascade technology that combines the advantages of both technologies blowing leaves and the length of the boundary layer using boundary layer blowing technique to suppress the growth of the boundary layer, increase efficiency, and the test results showed that [20], this method can effectively improve fan efficiency design and large flow rates, but small flow ineffective. [21] With this thinking to solve the centrifugal impeller fouling problems. Although the tandem cascade technology in a centrifugal compressor impeller efficiency did not get the results [20] inside, but the document content, the estimate is due to the authors of a major study series phase effects of the blade, but not studied the series leaves the impact of changes resulting from the radial position.

Theory and experiment have shown that the structure of the jet wake flow decreases as the centrifugal impeller is more intense, and a small flow, wake in the suction side, the design flow, the wake in the suction side of the junction and the wheel cover. In order to improve design efficiency and low flow centrifugal fan, 2008, Tian et al proposed blade slit technique [22], the technology proposed between the impeller vane wheel cover and the tail of the slit, the reference blade pressure surface The high-pressure gas to blow the suction side of the low-wake zone, directly to the low flow in the impeller to provide energy. Finally get at the design flow rate and low flow conditions, the impeller blade slotted surface of the separation area is reduced, the entire interior of velocity and impeller relative velocity distribution is more uniform, and the result is the absolute maximum speed is significantly reduced. This approach improves the flow conditions inside the impeller flow field, to improve the overall performance centrifugal impeller performance and results, and the formation of the jet can blow fouling addition to the suction side of the blade, in favor of gas-solid flow impeller work.
In 2011, Li Jing, who proposed method silver centrifugal fan wheel cover close to the blade suction surface of the aperture [23], the use of high-pressure gas volute generation jet, giving low or separation of a fluid impeller to provide energy directly to weakened by the secondary jet stream caused by the impeller - wake structure, and can be used when the centrifugal impeller fouling problem or part of the solution to eliminate load, often it occurs. Through the centrifugal fan machine numerical experiments found that after the wheel cover openings in the fan near the design pressure increased by about 2%, efficiency is improved by more than 1 percent, small flow pressure increased 1.5% efficiency is improved by 2.1 ʱ?? In the design flow and low flow, since the jet openings formed in the wheel cover, can significantly improve the separator outlet flow impeller, reducing low-speed region, reducing the maximum speed and velocity gradient at the outlet of the impeller, thereby weakening the centrifugal impeller exit Jet & mdash; wake structure. In addition, flow separation along the blade surface area decreases, the pressure increases more regular. Wheel cover openings closed centrifugal impeller method can improve the performance and overall performance design flow and small flow rates, if combined with centrifugal impeller boundary layer control tandem cascade of adaptive technology, it is possible to improve the performance of a centrifugal impeller.

3 Conclusion

In summary, recent studies on the internal flow impeller centrifugal fan made significant progress, some research has been applied to the actual design and get satisfactory results. Currently, the study of the internal flow impeller centrifugal fan is still one of the more active areas of research, I believe that further studies can be carried out in the following areas:

(1) How will the approximate model in the fan aspect of a deeper study, combined with the existing blade design technology and explore more rapid and efficient optimization method;

(2) How to tandem cascade, wheel covers and other openings and slotted blade centrifugal impeller boundary layer adaptive control technology combine to improve the performance of centrifugal fan impeller in the whole operating range, improve efficiency centrifugal fan;

(3) to consider research design methods unsteady characteristics. At present, centrifugal fan impellers are still unsteady flow calculation based, with the development of dynamic tests and numerical simulation, people unsteady phenomena and mechanisms turbomachinery flow will become increasingly clear that the unsteady The research results to design work is very important aspect.