计及叶片前缘周向不均匀源项的弯掠叶片流动机理

目前弯掠叶片被广泛应用于现代叶轮机设计,以协调高负荷、高通流、高效率和喘振裕度之间的矛盾,但同时也会引发应力、振动和稳定性等问题。因此,为更好地发挥弯掠叶片的气动优势,同时减少其空间结构复杂性,需要对弯掠空气动力学有更深的机理认识。利用周向平均降维方法,推导获得了可定量描述的周向不均匀源项,揭示出周向不均匀性会诱发叶轮机进气流场产生不同于直叶片的再平衡,进而影响弯掠叶片各基元的设计迎角,并使叶轮机内部流场和性能特性产生变化。采用数值仿真和Stereoscopic Particle Image Velocimetry(SPIV)实验的方法对弯掠叶片的这一机理进行了验证。结果表明弯掠叶片中,周向不均匀源项会打破原有的进气流场的径向平衡,导致进气流场的径向迁移,使进气流场关键参数产生展向差异,改变迎角的展向分布,进而影响整个流场性能。同时,对影响进气流场的周向不均匀源项构建解析模型及机器学习代理模型,解除叶轮机进气均匀流场的传统假设,以利于三维弯掠叶片的气动设计与分析。

Optimization of endwall contouring in axial compressor S-shaped ducts

This paper presents a numerical investigation of the potential aerodynamic benefits of using endwall contouring in a fairly aggressive duct with six struts based on the platform for endwall design optimization.The platform is constructed by integrating adaptive genetic algorithm（AGA）, design of experiments（DOE）, response surface methodology（RSM） based on the artificial neural network（ANN）, and a 3D Navier–Stokes solver.The visual analysis method based on DOE is used to define the design space and analyze the impact of the design parameters on the target function（response）.Optimization of the axisymmetric and the non-axisymmetric endwall contouring in an S-shaped duct is performed and evaluated to minimize the total pressure loss.The optimal ducts are found to reduce the hub corner separation and suppress the migration of the low momentum fluid.The non-axisymmetric endwall contouring is shown to remove the separation completely and reduce the net duct loss by 32.7%.

Investigation of Non-Axisymmetric Endwall Contouring in a Compressor Cascade

The current paper presents experimental and computational results to assess the effectiveness of non-axisymmetric endwall contouring in a compressor linear cascade. The endwall was designed by an endwall design optimization platform at 0° incidence(design condition). The optimization method is based on a genetic algorithm. The design objective was to minimize the total pressure losses. The experiments were carried out in a compressor cascade at a low-speed test facility with a Mach number of 0.15. Four nominal inlet flow angles were chosen to test the performance of non-axisymmetric Contoured Endwall(CEW). A five-hole pressure probe with a head diameter of 2 mm was used to traverse the downstream flow fields of the flat-endwall(FEW) and CEW cascades.Both the measured and predicted results indicated that the implementation of CEW results in smaller corner stall,and reduction of total pressure losses. The CEW gets 15.6% total pressure loss coefficient reduction at design condition, and 22.6% at off-design condition(+7° incidence). And the mechanism of the improvement of CEW based on both measured and calculated results is that the adverse pressure gradient(APG) has been reduced through the groove configuration near the leading edge(LE) of the suction surface(SS).

Modeling and Numerical Investigation of the Inlet Circumferential Fluctuationsof Swept and Bowed Blades

The circumferential fluctuation(CF) source terms induced by the inviscid blade force can affect the inlet distribution of flow parameters and radial equilibrium of swept and bowed blades. However, these phenomena cannot be adequately described by throughflow methods based on the axisymmetric assumption. A transport model for the CF stresses is proposed and correlated to the distribution of circulation to reflect the effect of the inviscid blade force. To investigate the effect of the inlet CFs on swept and bowed blades, the model is integrated into a throughflow model and applied to a series of cascades with different sweep and bow angles. For swept cascades, the CF source terms change the distributions of incidence angles, as well as the radial equilibrium at the inlet of the blade passage. And the influence is enhanced as the absolute value of the sweep angle increases. For bowed cascades, the distributions of incidence angles are also altered. For both cases, the model can offer a good prediction of the inlet CF source terms, and prove to exert a better prediction of blade design key parameters such as flow angles.

Numerical Investigation of Base-Setting of Stator's Stagger Angles for a 15-stage Axial-Flow Compressor

A 15-stage axial-flow compressor utilized in steel industry was studied in this paper. All the stator's stagger angles of the compressor are variable to ensure the multistage compressor operate effectively within a wide range of flow rate and meanwhile satisfy the demand for sufficient pressure ratio, adiabatic efficiency and stall margin. Three in all different base-settings of stator's stagger angles were presented and commercial CFD software was applied to obtain the overall performance characteristics. The results showed that both of the optimized base-settings improved the performances both in summer and winter conditions, although the adiabatic efficiency was somewhat decreased. Taking incidence angle and stage loading into consideration, differences among the three cases were analyzed in detail. On the basis of numerical computations, the performance could be effectively improved through adjusting the base-setting of stator's stagger angles.

尾缘S3面积比梯度对涡轮后机匣的影响

针对整流叶栅与支板融合设计中难以采用三维叶片造型对二次流进行控制的情况,开展对涡轮后机匣内部整流叶栅尾缘S3面积比梯度的研究。以某1.5级涡轮为例,通过数值模拟的方法,对比三种设计的内部流场和气动性能,验证了降低尾缘S3面积比梯度控制角区二次流的方法。结果显示:尾缘S3面积比梯度从0.01降低到-0.05时,整流叶栅总压恢复系数从0.979升高到0.991,5%展高处S参数从0.011降低到0.005,吸力面和轮毂端壁处的回流区消失,角区分离得到有效控制;尾缘S3面积比梯度从-0.05降低到-0.10时,吸力面角区流动速度增加,5%展高处S参数不再变化、堵塞程度降低、轴向密流比(AVDR)升高、总压恢复系数升高。

Investigation and Verification of the Aerodynamic Performance of a Fan/Booster with Through-flow Method

Through-flow method is still widely applied in the revolution of the design of a turbomachinery, which can provide not merely the performance characteristic but also the flow field. In this study,a program based on the through-flow method was proposed, which had been verified by many other numerical examples. So as to improve the accuracy of the calculation, abundant loss and deviation models dependent on the real geometry of engine were put into use,such as: viscous losses,overflow in gaps, leakage from a flow path through seals. By means of this program, the aerodynamic performance of a certain high through-flow commercial fan/booster was investigated. On account of the radial distributions of the relevant parameters, flow deterioration in this machine was speculated. To confirm this surmise, 3-D numerical simulation was carried out with the help of the NUMECA software. Through detailed analysis, the speculation above was demonstrated, which provide sufficient evidence for the conclusion that the through-flow method is an essential and effective method for the performance prediction of the fan/booster.

Effect of blade sweep on inlet flow in axial compressor cascades

This paper presents comparative numerical studies to investigate the effects of blade sweep on inlet flow in axial compressor cascades. A series of swept and straight cascades was modeled in order to obtain a general understanding of the inlet flow field that is induced by sweep.A computational fluid dynamics（CFD） package was used to simulate the cascades and obtain the required three-dimensional（3D） flow parameters. A circumferentially averaged method was introduced which provided the circumferential fluctuation（CF） terms in the momentum equation.A program for data reduction was conducted to obtain a circumferentially averaged flow field.The influences of the inlet flow fields of the cascades were studied and spanwise distributions of each term in the momentum equation were analyzed. The results indicate that blade sweep does affect inlet radial equilibrium. The characteristic of radial fluid transfer is changed and thus influencing the axial velocity distributions. The inlet flow field varies mainly due to the combined effect of the radial pressure gradient and the CF component. The axial velocity varies consistently with the incidence variation induced by the sweep, as observed in the previous literature. In addition, factors that might influence the radial equilibrium such as blade camber angles, solidity and the effect of the distance from the leading edge are also taken into consideration and comparatively analyzed.

Numerical Investigation of the Load Distribution between the Main Blade and the Splitter Blade in a High-Loading Centrifugal Compressor

In the traditional design of the centrifugal compressor,the splitter blade and the main blade always keep the same shape.However,to enable high efficiency of the high-loading centrifugal compressor,the matching of design parameters of the splitter blade and the main blade needs to be optimized.In this paper,the influence of the load distribution between the main blade and the splitter blade on the aerodynamic performance,the flow field,and the internal vortices of a high-loading centrifugal compressor were studied by means of CFD prediction.Four cases with different values of the variable CR which is defined as the load-ratio of splitter blade to main blade were set up.In each case,the splitter blade and the main blade were shaped according to different laws of circulation distribution(_(r)V_(u))while the average circulation of the splitter blade and the main blade at any meridional position were consistent with that of the prototype.The results showed that a proper reduction of the load-ratio of splitter blade to main blade is beneficial to suppress the leakage vortex of the splitter blade and reduce the scale of the wake in the channel near the suction-side of the splitter blade,which consequently improves the flow uniformity at the impeller outlet and enhances the aerodynamic performance of both the stage and the component.The stage isentropic efficiency of the optimal case was found to be 0.7%higher than that of the prototype and the stage total pressure ratio was also improved.The optimal value of CR,which in this investigation is 94%,is supposed to be the result of the trade-off between the development of the wake and the leakage vortices in adjacent two channels.The optimization of the load distribution between the main blade and the splitter blade provides an opportunity to further improve the high-loading centrifugal compressor performance.