Low-solidity Cascade Diffuser Research Articles

Improvement of Unstable Flow in a Low Solidity Cascade Diffuser of Centrifugal Compressor by Multi-Objective Optimization

A compressor for turbochargers is commonly required improving efficiency and expanding the operating flow rate range. Though an aerofoil type diffuser shows better pressure recovery than conventional vaneless diffuser, it is difficult to design the aerofoil type diffuser under conditions of wide change of the flow angle. An innovative design of a Low Solidity circular cascade Diffuser (LSD) was proposed for flow range enhancement of cascade diffuser¸ and an interesting function of the LSD is introduced. At small flow rate conditions, low energy fluid near the diffuser side wall spread between the diffuser blade, and low energy fluid moves to the leading edge of the adjacent blade, then low energy fluid merged with main flow and suppress the flow separation. The phenomena spread to circumferential direction, and whole of the LSD blades show high stability for separation under a large angle of attack. In this study, LSD is designed for compressors of turbocharger by using a Genetic Algorithms (GA) with meta-model of an Artificial Neural Networks (ANN). The final goal of this study is to optimize the LSD with having secondary flow effect under low flow rate conditions.

Performance improvement of a centrifugal compressor stage by using different vaned diffusers

The vaneless diffuser (VLD) is usually adopted in the traditional design of the multi-stage centrifugal compressor because of the stage's match problem. The drawback of the stage with vaneless diffusers is low efficiency. In order to increase the efficiency and at the same time, induce no significant decline in the operating range of the stage, three different types of vaned diffusers are designed and numerically investigated: the traditional vaned diffuser (TVD), the low-solidity cascade diffuser (LSD) and the partial-height vane diffuser (PVD). These three types of vaned diffusers have different influences on the performance of the centrifugal compressor. In the present investigation, the first part investigates the performance of a centrifugal compressor stage with three different vaned diffusers. The second part studies the influences of the height and the position of partial height vanes on the stage performance, and discusses the matching problem between the PVD and the downstream return channel. The stage investigated in this paper includes the impeller, the diffuser, the bend and the return channel. In the process of numerical investigation, the flow is assumed to be steady, and this process includes calculation and simulation. The calculation of 3-D turbulent flow in the stage uses the commercial CFD code NUMECA together with the Spalart-Allmaras turbulence model. The simulation of the computational region includes the impeller passages, the diffuser passages and return channel passages. The structure and surrounding region are assumed to have a perfect cyclic symmetry, so the single channel model and periodic boundary condition are applied at the middle of the passage, that is to reduce the calculation region to only one region. The investigation showed that the low-solidity cascade diffuser would be a better choice as a middle course for the first stage of the multistage centrifugal compressor. Besides, the influences of the height and the position of partial height vanes on the stage performance are intensively investigated and concluded at the design point, the isentropic efficiency and the static pressure ratio of the stage are improved with the increasing of the partial vane's height, and that installing the half-height vanes on the shroud side the stage would obtain a more uniform diffuser outflow and a better aerodynamic performance.

0417 小弦節比翼列ディフューザの多目的最適化 (翼先端隙間による二次流れの安定化)(OS4-4 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

0417 小弦節比翼列ディフューザの多目的最適化 (翼先端隙間による二次流れの安定化)(OS4-4 流体機械の研究開発とそれに関連した複雑流動現象,OS4 流体機械の研究開発とそれに関連した複雑流動現象)

小弦節比翼列ディフューザにおける二次流れの挙動解析 : 第2報,前縁近傍翼端溝の影響(流体工学,流体機械)

A low solidity cascade diffuser (LSD) shows features of a wide operating range and a high pressure ratio, however, a high level of noise. The first objective of the present study is to show that the noise can be reduced effectively without deterioration of the LSD performance by means of a small tip-groove located at the shroud side alone, and the second one is to clarify the mechanism being able to achieve high blade loading without stall even under the large attack angle of 15 degrees. By analyzing the flow in the diffuser numerically, the effect of a small tip-groove on the stagnation area near the LSD blade leading edge, the vortex generated in the tip-groove and the secondary flow behavior were investigated. It was found that the formation of circumferentially moving secondary flow generated by the vortex in the shroud tip-groove is a key factor of the high LSD performance. Finally, an optimum tip-groove configuration was proposed.

小弦節比翼列ディフューザにおける二次流れの挙動解析 : 第1報,翼前縁位置の影響(流体工学,流体機械)

小弦節比翼列ディフューザにおける二次流れの挙動解析 : 第1報,翼前縁位置の影響(流体工学,流体機械)

Noise characteristics of centrifugal blower with low solidity cascade diffuser (Noise reduction by means of small groove located at LSD blade leading tip)

This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blower characteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near the leading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reduce the noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondary flow formed additionally by the tip-groove were investigated experimentally as well as numerically, especially analyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD blade and the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of the LSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, the noise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove located only at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced without deteriorations of the LSD performance and the blower characteristics as well.

B22 小弦節比翼列ディフューザを有する遠心送風機の騒音特性 : 局所的翼端溝による二次流れ制御(B2 流体工学(流体機械))

B22 小弦節比翼列ディフューザを有する遠心送風機の騒音特性 : 局所的翼端溝による二次流れ制御(B2 流体工学(流体機械))

J0501-1-1 小弦節比翼列ディフューザにおける二次流れの挙動解析(流体機械の研究開発におけるEFD/CFD(1))

A low-solidity cascade diffuser was proposed for achieving a wide operating range as well as a high pressure ratio. However, noise increased by means of LSD due to vortex shedding from the LSD blade surface. The objectives of the present study are to show that the noise can be reduced effectively by means of a small tip-groove located at the shroud side alone without deterioration of the LSD performance, and to clarify the mechanism of high blade loading of the LSD blade with the shroud side tip-groove limited near the LSD blade leading edge. The effect of a small groove on the stagnation area, the vortex generated in the tip groove and the secondary flow behavior on the suction surface of the LSD blade and the diffuser walls as well are analyzed numerically. It is found that the formation of the recirculating secondary flow generated additionally and significantly by the shroud tip-groove is a key point of the high LSD performance.

C14 環状溝および小弦節比翼列ディフューザによる遠心送風機失速特性の改善(C1 流体工学(空気機械))

C14 環状溝および小弦節比翼列ディフューザによる遠心送風機失速特性の改善(C1 流体工学(空気機械))

E21 小弦節比翼列ディフューザを有する遠心送風機の騒音特性 : 局所的翼端溝によるLSD騒音の低減(流体工学II)

E21 小弦節比翼列ディフューザを有する遠心送風機の騒音特性 : 局所的翼端溝によるLSD騒音の低減(流体工学II)

G602 入口環状溝および小弦節比ディフューザの組合せによる遠心送風機低流量域不安定流動の抑制(1)(GS6 翼,渦,一般セッション)

G602 入口環状溝および小弦節比ディフューザの組合せによる遠心送風機低流量域不安定流動の抑制(1)(GS6 翼,渦,一般セッション)

G602 入口環状溝および小弦節比ディフューザの組合せによる遠心送風機低流量域不安定流動の抑制(2)(GS6 翼,渦,一般セッション)

G602 入口環状溝および小弦節比ディフューザの組合せによる遠心送風機低流量域不安定流動の抑制(2)(GS6 翼,渦,一般セッション)

Comparison of Two Diffusers in a Transonic Centrifugal Compressor

Flow mechanisms suppressing the flow separation in two diffusers, a low-solidity cascade diffuser and a vaned diffuser with additional small vanes near the inlet, were compared mainly by numerical simulation. As the superiority of the low-solidity cascade diffuser was expected, a series of experiments was conducted using a transonic centrifugal compressor with a maximum pressure ratio of 7. The performance of the compressor with the vaned diffuser was comparable to that of the low-solidity cascade diffuser only between the surge point and the design flowrate at a pressure ratio of 3.5. The maximum flowrate of the vaned diffuser was lower than that of the low-solidity cascade diffuser. At higher rotational speeds, the pressure ratio at the surge point, the efficiency, and the flow range of the low-solidity cascade diffuser exceded those of a vaned diffuser at a pressure ratio of 3.5.

Application of pressure sensitive paint measurement to a low-solidity cascade diffuser of a transonic centrifugal compressor

A pressure sensitive paint (PSP) measurement has been known as a pressure field measurement technique based on the oxygen quenching phenomenon of luminescence of specific luminophores. A PSP measurement was applied for pressure field measurement in a low-solidity circular cascade diffuser of a single-stage transonic centrifugal compressor with 5 in pressure ratio for HFC134a gas. The oxygen concentration was about 500 ppm. Ru (bath-phen) was adsorbed on a silica-gel thin-layer chromatography sheet, and the sheet was pasted onto the side-wall between the cascade vanes. A drastic change in luminescent intensity was recognized during a surge condition. Also the pressure variations based on luminescent intensity agreed well with the pressure fluctuations measured using a semiconductor pressure sensor with high-frequency-response. It was shown that a PSP measurement worked well to investigate the unsteady pressure fields in a circular cascade diffuser of a transonic centrifugal compressor. Moreover, the time response of PSP becomes clear as a problem to be overcome for the present.

Comparison of Anti-Stall Effect of Two Diffusers in a Centrifugal Compressor.

The anti-stall effects in two diffusers, a vaned diffuser with fixed small vanes and a low-solidity cascade diffuser, were compared in a centrifugal compressor with suction damper. These diffusers had the same outer diameter. The surge limit flow rate did not differ, however, the stability differed. To clarify the difference of stability, pressure measurement and numerical simulation were carried out. In the vaned diffuser, the flow guided by the small vane pushed back the flow from down stream of throat. This mechanism suggests instability near surge point. In the low-solidity cascade diffuser, there observed no backflow on the whole suction surface. This suggests the more stable character.

Effects of Camber of Inducer on Performance of a Transonic Centrifugal Compressor.

Two types of transonic centrifugal impellers with a slight variation in the inducer blade camber were tested to clarify their effects on the stall and the choke. Regarding choke, the inducer-throat blockage decreased and the choke flow rate increased in spite of a smaller throat area for the lower cambered inducer blade. Regarding inducer stall, the inducer blade camber affected the critical incidence angle against the inducer tip especially at low rotor speeds. Two impellers were also tested in combination with a low-solidity cascade diffuser, and the lower cambered blade impeller realized a wide compressor operating range especially at high rotor speeds.