Huanlong Chen

Effects of Boundary Layer Suction on the Performance of Compressor Cascades

The effects of boundary layer suction on the aerodynamic performance of compressor cascade are mainly determined by: (1) the location of the suction slot; (2) the suction flow rate; (3) the suction slot geometry; and (4) the aerodynamic parameters of the cascade (e.g. solidity and incidence). In this paper, an extensive numerical study has been carried out to investigate the effects of these influencing factors in a highly-loaded compressor cascade by comparing the aerodynamic performance of the cascade in order to give guidance for the application of boundary layer suction to improve the performance of modern highly-loaded compressors. The results show that boundary layer suction alleviates the accumulation of low-energy fluid at suction surface corners and enhances the ability of flow turning, and this improvement in flow behavior depends on the location of the suction slot and the suction flow rate. When the location of the suction slot and the suction flow rate are fixed, as the cascade solidity decreases from 1.819 to 1.364 and 1.091, the cascade total pressure loss is reduced at most by 25.1%, 27.7% and 32.9% respectively, and the cascade exit flow deviation is decreased by 3.1°, 4.2° and 5.0° accordingly. Moreover, boundary layer suction also has the largest effect in the cascade with smaller solidity at large positive incidences, which means that boundary layer suction is an effective way to widen the stable operating range of the highly-loaded compressor cascade. The suction slot geometry is described by the suction slot width and the suction slot angle with respect to the direction normal to the blade suction surface. The results show that the flow behavior is improved and the endwall loss is reduced further as the increase of the suction slot width. The suction slot angle has an obvious influence on the pressure inside the slot, therefore, should be considered in the design of the suction slot since the maximum pressure inside the slot is usually required.Copyright

Enhancing Aerodynamic Performances of Highly Loaded Compressor Cascades via Air Injection

This article experimentally studies the effects of air injection near the blade trailing edge on flow separation and losses in a highly loaded linear compressor cascade. Aerodynamic parameters of eight cascades with different air injection slot configurations are measured by using a five-hole probe at the cascade outlets. Ink-trace flow visualization is performed to obtain the flow details around the air injection slots. The static pressure distribution is clarified with pressure taps on the endwalls. The results indicate that air injection has little effect on the static pressure distribution on the endwalls, but improves the flow behavior at the corners between the suction surfaces and the endwalls with the decrease in losses at midspan. Slot positions have great effect on the compressor cascade performances. The optimal slot location is 25% of the blade span. The energy loss coefficient is reduced by 5.5% at most.

Effects of Air Injection on Performance of Highly-Loaded Compressor Cascades

The effects of air injection on the performance of highly-loaded straight blade compressor cascade and compound lean blade cascade were investigated numerically. Air injection was implemented via the hole/slot penetrating through the pressure and suction surfaces under the effect of the pressure difference between the two sides. Various injection configurations including one-hole, multi-hole and slot configurations were studied in the straight blade cascade first to find the optimum injection configuration in this case. Then the mechanism of the injection slot on the performance improvement of the straight blade cascade was discussed in detail. The results show that air injection provides the low-momentum fluid near the suction surface with kinetic energy, to enhance its ability to withstand the adverse pressure gradient within the compressor cascade. Among the hole/slot configurations, the slot configuration (the radial width of 4.0mm) has the most favorable results in through-flow capacity enhancement and total loss reduction, and is used in the compound lean cascade study. The effects of air injection on the performance improvement in the compound lean blade cascade are less significant than those in the straight blade cascade though the compound lean blade cascade with the injection slot has the most improvement in the aerodynamic performance when the slot is placed at an appropriate location in this study.Copyright

Numerical Study on Typical Wet Steam Flow Based on a New Two-Fluid Model

A new two-fluid model with the influence of inter-phase velocity-slip taken into account was proposed and a modified realizable k-e turbulence model was put forward as well to make the equation set of two-fluid model closed. Based on this two-fluid model, numerical simulations were conducted on typical wet steam flow in different cases. The good consistency of numerical result and the experimental result infers that this two-fluid model is provided with high accuracy and wide applicability. The flow field analysis also shows that there exist several particular positions along the flow direction. These particular positions illustrate the development mechanism of nucleation and droplet growing. In addition, further discussion on the flow in cascade then indicates that the occurrence of condensation has strong impact on the flow while the impact of inter-phase velocity-slip is relatively weaker. The composition of total pressure loss is present here, the majority of total pressure loss brought by condensation is about 8.78% of inlet total pressure while the inter-phase velocity-slip just results in a small part of about 0.42% of inlet total pressure, the rest of the total pressure loss is caused by pneumatic factors and this part is about 3.95% of inlet total pressure. In addition, discussion about the turbulence then shows that the turbulence intensity in two-phase flow is higher than that in single-phase flow.Copyright

Numerical investigation on impact of blowing control in flush-mounted S-shaped inlet to rear fan-stage performance

In this paper, numerical simulation of the whole structure of a half flush-mounted S-shaped air-intake and the rear fan stage was conducted for investigating the impact of air-intake exit distortion on the fan-stage performance. Considering substantial boundary layer ingesting, a scheme of blowing control imposed near the first bend of the inlet where the flow separation occurs was also carried out. The results show that the air intake internal separation is eliminated, and the distorted air region at its exit decreases significantly after blowing, simultaneously, the aerodynamic performance of the rear fan stage improves dramatically. The choked mass flow increases about 1.45%, and the maximum isentropic efficiency as well as the corresponding total pressure ratio at this point increases about 1.83% and 1%, respectively. In addition, the distorted fluid always covers several blade passages no matter with blowing control or not when it goes through the fan stage. Both relative total pressure and velocity of air in these distorted blade passages are lower than that in other uniform passages and have slightly increased with blowing. Under effect of the inlet flow angle increase caused by the non-uniform air admission and the adverse pressure gradient in the rear part of the flow passage, serious flow separation occurs at the stator blade suction side but mainly exists at 50% span and below and weakens after blowing control.

Numerical Investigation of Two-Phase Wet Steam Flow With Spontaneous Condensation Based on Euler S2 Calculation Method

The Euler equation suitable for the S2 stream surface calculation is derived in the arbitrary orthogonal coordinate system firstly. The numerical method for the two-phase wet steam flow with the spontaneous condensation is then developed on basis of the Euler S2 calculation code, the Eulerian/Eulerian multiphase model and the classic nucleation theory.To adapt the complex geometry of the turbine blades, the Euler equations for the S2 stream surface calculation method are derived in the body-fitted coordinate system. The mathematical model for the third order TVD scheme with the non-conservative variables is also developed for the gas phase governing equation. The 2nd order NND and the VanLeer scheme are applied to the variable reconstruction and the numerical flux calculation respectively in the liquid equations solving process. The pressure and the droplet radii distribution fit well with the experimental data for both the high pressure nozzle and the low pressure nozzle. The S2 calculation method is also employed to predict the performance of a 3-stage low pressure steam turbine with spontaneous steam condensation, and the reasonable results are obtained.The numerical method developed in the present work is able to predict the real wet steam flow with the spontaneous condensation and its impact on the flow field and the aerodynamic parameters distribution reasonably, supplying a fast and accurate technic and method to the steam turbine design.Copyright

Numerical Investigation of the Non-Axisymmetric End Wall Application to the White Cascade

A profiling method, in terms of the trigonometric function and considering about the different axial location of the non-axisymmetric end wall warping, is developed firstly. The axial and the circumferential location of the end wall warping are defined by the cosine function and the sine function respectively.To investigate the effects of the non-axisymmetric end wall on the flow property and the steam condensation, the profiling method is applied to the aft-loaded White cascade with the revised nucleation model of the two-phase wet steam flow. The results show that it has very little influence on the performance while the non-axisymmetric end wall warping is closing to the leading edge. If the non-axisymmetric end wall warping locates nearby the trailing edge, the aerodynamic loss increases significantly with a sharp flow separation on the corner of the suction side. While the crest is in the middle of the axial chord, the aerodynamic loss nearby the end wall decreases about 2.0%, implying a well improvement in the aerodynamic performance. Besides, the steam condensation nearby the end wall is restrained significantly while the non-axisymmetric end wall warping is in the middle axial chord or closing the trailing edge.The proper designed non-axisymmetric end wall, which is able to increase the pressure of the zone with the wet steam nucleation, is beneficial to improve the aerodynamic performance and control the steam condensation in the passage of the low pressure steam turbine.Copyright

Numerical Investigation of Equilibrium Wet Steam Flow Property Based on S2 Calculation Code

Though it is non-equilibrium wet steam flow in steam turbine, the droplets with micron dimension are usually not considered in the primary design of the steam turbine in the industrial application because the global properties of steam are concerned mostly. Two calculation models of equilibrium wet steam property are proposed and applied to the performance prediction of a one stage low pressure (LP) steam turbine with superheated vapor and a 1.5-stage LP steam turbine with superheated and saturation steam by the using of the central S2 stream surface calculation code developed in this paper.Different from the ordinary S2 stream surface calculation code, the three-dimensional Euler equations are adopted to count the influence of the cascade spatial structure on the flow field parameters in this S2 calculation method. The non-conservative variables are used to avoid the non-uniqueness of density. The implicit time marching method and the upwind-diagonal implicit approximate factored format are applied to improve the calculation stability. The high-order TVD scheme is applied to increase the calculation accuracy. The Riemann problem is utilized to solve the discontinuity of variables transition at grid interface.Two models of wet steam property computation are developed to adapt the numerical calculation in this paper. The first one is the “Ideal Steam” model, using the ideal gas properties formulations to calculate the steam parameters with the given cp(T)-T relationship obtained from the evaluated enthalpy-entropy curve and the IAPWS-IF97 formula. The second one is the “IF97 Table” model, calculating the steam properties with the inerratic multi-variables combination tables generated by the IAPWS-IF97 formulations and the fast interpolation method.Furthermore, both the models are added to the S2 calculation code to predict the performance of the steam turbine respectively. The results show that the S2 code developed in this paper can predict the performance of steam turbine with high precision. The results of the one stage LP steam turbine imply that the two models are almost the same and are similar to the 3D results, indicating that both the models can be applied to the superheated vapor flow with high precision. Compared to the full 3D results, the error of the mass flow rate and efficiency with the “IF97 Table” model is 0.83% and 0.46% respectively, indicating a higher accuracy than the “Ideal Gas” model with 1.00% and 1.54%. The distribution of primary parameters shows that both the steam calculation models are well applied to the aerodynamic performance prediction. The distribution of temperature and moisture imply that the “IF97 Table” model can predict the aerodynamic parameters better than the “Ideal Gas” model. The S2 calculation method with the “IF97 Table” method or the “Ideal Gas” saves most of the time compared to the full 3D calculation, supplying an effective and fast calculation method in the primary design and the performance prediction of steam turbine.Copyright

Numerical Investigation on Impact of a Flush-Mounted Airintake Exit Distortion to the Rear Fan Performance

For the sake of investigating impact of inlet distortion on the fan stage performance, numerical simulation of the whole structure of a flush-mounted S-shaped inlet and the rear fan stage was conducted in this paper. The single fan stage with uniform air admission was researched at the same time for comparison. Considering substantial boundary layer ingesting, a scheme of suction control imposed at the first bend of the inlet was also carried out. The results show that the total pressure ratio as well as the efficiency of the fan stage decreases dramatically and the choked mass flow has a reduction about 1.20% as compare with the uniform air condition. With suction control, aerodynamic performance of the fan stage improves slightly, the choked mass flow and total pressure ratio at the maximum isentropic efficiency point increase about 0.28% and 0.25% respectively, and the stable operation range is extended. With effect of rotating rotor, the significant low energy region at bottom of the airintake exit decrease continually as it travels downstream to the rotor and covers nearly three flow passages at the front-edge rotor blade, moreover, the high-energy fluid mixes with the low-energy fluid.Copyright