Optimization of a circumferential groove in a centrifugal compressor

In this work, a circumferential groove on the shroud was applied to a centrifugal compressor and optimized to improve the stability of the compressor. To reduce the number of design variables before optimization, the position of the casing groove that maximizes the stall margin of the compressor was firstly selected. The width and height of the casing groove were optimized using the RSM (Response Surface Method) and the full factorial design of experiments to increase the stall margin further. It was observed that the optimized case with the casing groove can increase the stall margin by 7.0% but the adiabatic efficiency at the design condition decreases by 0.99%, in comparison to the reference case without the groove. Finally, the flow field of both cases with and without the optimized casing groove was compared to each other to analyze effects of the casing groove on the stall margin and design efficiency. The casing groove decreases the leakage flow across the impeller tip and weakens the tip leakage vortex, consequently decreasing the blockage near the shroud and improving the stall margin. However, it was found that the spillage of the flow from the casing groove increases the mixing loss near the shroud.

Impedance modelling of acoustically treated circumferential grooves for over-tip-rotor fan noise suppression

Experimental investigation of Over-Tip-Rotor circumferential groove liners has shown potential for fan noise suppression in turbofan engines whilst providing minimal penalty in fan aerodynamic performance. The validation of Over-Tip-Rotor liner analytical prediction models against published experimental data requires the modelling of an equivalent impedance for such acoustic treatments. This paper describes the formulation of two analytical groove impedance models as semi-locally reacting liners, that is locally reacting in the axial direction and non-locally reacting in the azimuthal direction. The models are cross-verified by comparison with high-order FEM simulations, and applied to a simplified Over-Tip-Rotor configuration consisting of multiple grooves excited by a monopole point source located close to the grooved surface.

The Thermo-Hydrodynamic Analysis of the Plain Journal Bearing With Centered Circumferential Groove: Numerical Simulation vs. Experiment

In order to increase the reliability of the oil lubricated journal bearing, the thermal characteristics of the plain journal bearing are investigated and optimized. In this paper, the steady state thermo-hydrodynamic analysis of the plain journal bearing with centered circumferential groove is studied by numerical simulation and experiments. The diameter of the journal bearing is 190mm, and the load of the bearing is 6150N, which is operated with the rotating speed of 5560 r/min. The flow characteristics including the temperature distribution in the clearance of the bearing are simulated by ANSYS CFX, where the Walther viscosity temperature relation and the cavitation effect are considered. The test rig for measuring the pressure and temperature distributing in established, which is driven by electrical motor and certain bearing load can be exerted on it. In the experiments, the temperature distribution of the bearing is measured by 10 temperature sensors, which is arranged on three cross sections along the axial direction. The temperature of the lubricating oil is obtained by the sensors on the shell of the bearing, which is installed in the Babbitt metal. In order to obtain the circumferential distribution of the temperature, the sensors locate at different circumferential angles. The influence of geometrical parameters on the temperature distribution is studied, including the bearing clearance, the bearing length and the groove width by numerical simulation and experiment. The bearing clearance ratios of 1.8‰ and 2.5‰ are compared, and as the increment of the bearing clearance ratio, the temperature of the bearing decreased, which is benefit from the flow mass into the bearing increases. For the bearing length increasing from 90mm to 94mm, the maximum temperature decreases about 3K. For the groove width varying from 20mm to 19mm and 18mm, the temperature of the bearing decreases. The comparison of the numerical results and experiments are presented, and they show similar tendency for the temperature distribution, but the difference of temperature values exists. Based on the results from variation of bearing clearance ratio, bearing length and groove width, the optimized parameters of the bearing are proposed by determining the groove width with 18mm, bearing length with 94mm and the bearing clearance ratio with 2.1‰. The thermo-hydrodynamic analysis from the CFD and the experiments for the optimized bearing are carried out. The results indicate that the thermal performance of the bearing is improved. Compared with original design of the bearing, the maximum temperature is reduced by approximately 5K for optimized design of the bearing.

Numerical analysis of the effects of circumferential groove casing suction in a counter-rotating axial flow compressor

To extend the current understanding of the circumferential groove casing suction applied to a counter-rotating axial flow compressor, the impact of different axial locations of the circumferential suction groove on the characteristics of the tip leakage flow (TLF) and the corresponding physical mechanisms producing the stability enhancement have been studied based on validated numerical simulations. The results show that the optimal location for the suction groove is at around 20% axial chord, which demonstrated a high potential for reducing additional stall mass flow coefficient with about 8.4% increment in the stall margin. After the casing suction groove was applied, the interface between the incoming main flow and TLF was pushed significantly downstream in the second rotor. The blade loading in the region below the groove, the tip leakage flow angle and the reversed axial momentum flux injected into main flow passage through the tip gap were all reduced, which contributed to the stall margin improvement. Detailed analysis of the tip leakage flow structures showed that the TLF originating from different chord locations played different roles in the stall inception process. It was found to be more effective to improve stall margin and adiabatic efficiency by controlling the front part of the TLF, which was most sensitive.

Separation of Water Film From Last Stage Guide Blades of 1000 MW Steam Turbine

The paper deals with experimental research of water and steam flow through the grooves in hollow stator blades of the steam turbine last stages with the support of CFD calculations. Also the amount of water sucked by the circumferential groove in the upper limiting wall between the last stage rotor and stator blade was experimentally measured. Measuring took place on a steam turbine with nominal output 1000 MW. With gradual increase of the turbine output it was possible to measure parameters of hollow blades suction for outputs 205, 460, 730, 870 and also 1006 MW. Before starting turbine a complex measuring system was installed consisting of cyclone separator, set of measuring tanks, orifice and pressure sensors and transducers. This measuring system was connected to one hollow stator blade near the horizontal joint. After the measurement the extraction of steam water mixture from this blade was transferred to the condenser via the diffuser chamber in the same way as other non-measured blades. Based on measured data, i.e. the pressure in the hollow stator blade and the flow rate of water captured by the hollow stator blade, it is possible to define the efficiency of suction tract from the viewpoint of total wetness in the inter-stage channel and from the viewpoint of rough liquid phase. The rough liquid phase means water films that flow near the draining grooves and sucked inside to the grooves. The main part of the submitted paper is an analysis of the measured data. Among the analysis results are, besides the flows of rough water phase along the blade surface, the above mentioned efficiency of total wetness suction and of water film suction. For the needs of the analysis there are certain input data, e.g. the value of static pressure and wetness on the blade surface close to the slots that must be defined theoretically using flow path calculations or using CFD methods. In this case, in order to obtain input data, CFD simulations were used when the whole last stage was calculated with the diffuser and exhaust hood. Boundary conditions for CFD were taken from experimental measurements that took place simultaneously with measurement of separated water phase. Numerical simulations were not running for all outputs, but only for three of them — 460, 730 and 1006 MW. For this reason there are no sufficient data for CFD calculations for all outputs and input data of other cases had to be extracted and, based on experience, extrapolated. On the circumferential groove only a part of 30 mm of length was measured, again near the horizontal joint. Due to a short measured groove length it was not possible to obtain the water flow data which would describe suction properties for the whole circumference. The results of experimental measurements provide very important information about the whole suction tract behaviour and its ability to remove liquid water films from the stator blades surface. As very good qualities of the suction tract were confirmed by the measurement, it could be stated that hollow stator blades combined with the circumferential groove on the upper limiting wall is still a suitable technical solution for lowering erosion loading of the last stages. When using a properly dimensioned and correctly working suction system, erosion loading of LSB leading edges on the tip can be lowered by almost a half.

Numerical Investigation of Circumferential Groove Casing Treatment on a Low Speed Contra-Rotating Fan

This study is aimed at understanding the effects of circumferential groove casing treatment on the performance of a low speed contra-rotating fan. Three dimensional, transient simulations are carried out using the open source CFD library Open-FOAM. The numerical results are validated with experiments for the smooth casing, which show a good agreement. Three treated casing configurations are investigated: 1) grooves at the top of the first rotor, 2) grooves at the top of the second rotor, and 3) grooves at the top of both rotors. Two operating points are simulated for all configurations. Flow inside the grooves is highly dominated by the main and blade passage flows. Grooves increase fan performance at near-stall flow conditions by up to 3 % and reduce pressure fluctuations significantly. Furthermore, they have a larger impact on fan performance when placed on top of the first rotor compared to placing them on top of the second rotor.

Numerical Investigations on the Sealing Effectiveness of Turbine Groove Radial Rim Seal

This paper presents a numerical comparison of sealing performance between conventional radial rim seal and seven different kinds of groove radial rim seal with three coolant flow rates. Three-dimensional unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, coupled with a fully developed shear stress transport (SST) turbulent model from ANSYS-CFX, are utilized to investigate the sealing effectiveness of rim seal and flow characteristics in the wheel-space cavity of gas turbines. The numerical method for the pressure distributions on the vane hub and sealing effectiveness of rim seal is validated on the basis of published experimental data. The seven kinds of groove rim seals designed in this work include four circumferential groove structures, one axial groove structure and two oblique groove structures. The sealing effectiveness of conventional and seven different groove rim seals are compared. Then the flow field in the disc cavity of conventional and groove rim seals is simulated and analyzed. Compared with conventional radial rim seal, the groove rim seals can increase the sealing effectiveness obviously. It is shown that the groove structures improve the damping dissipation of invading gas. The number of grooves has an obvious effect on sealing effectiveness of circumferential groove rim seals. The axial groove case results in less minimum sealing flow rate than oblique groove cases. In addition, the flow pattern of rim seal and disc cavity is used to describe rim seal gas ingestion flow characteristics.