Blade Surface Pressure Research Articles

Variable Working Condition to the Influence of the Centrifugal Fan Impeller Wear

This paper makes use of the FLUENT to the variable working condition centrifugal fan on the gas-solid two phase flow numerical simulation, the numerical simulation adopts the whole flow field simulation, makes the use of surface source, analysis working condition changes on centrifugal fan blade pressure surface wear, finally it draws a relatively high-quality fan operation condition and takes measures to control fan wear in view of the situation.

Numerical Simulation and Experimental Research of Blade Erosion in Particulate Gas Turbine

Euler-Lagrange method is adopted to simulate 3-D viscous turbulent flow field of a one-stage gas turbine. Gas-solid two-way coupling is realized to analyze the trajectories and slip of 1000 beam particles, with diameter 5~50μm, then calculate the mass erosion rate based on the impact velocity and attack angles. Simulation exhibits: erosion wear is mainly caused by impact of larger particles (>10μm), erosion areas are mainly concentrated on the roots of pressure surface entrance of static blade and on the rear pressure surface of rotor blade. Comparing experiments are conducted between the substrate of X20Cr13 and the specimen with steel-bead injection. Experiment indicates: the attack angle corresponding to the maximal mass loss for substrate is about 40°, while the steal-bead injection is about 50°. Within the scope of the attack angle 20°~80°, the mass loss of the reinforced specimen is obviously less than that of the substrate, and under other angles of attack, the two kinds of material’s erosion tolerance are close to each other.

Numerical and experimental study on flow-induced noise at blade-passing frequency in centrifugal pumps

With the increasing noise pollution, low noise optimization of centrifugal pimps has become a hot topic. However, experimental study on this problem is unacceptable for industrial applications due to unsustainable cost. A hybrid method that couples computational fluid dynamics (CFD) with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects. Under Langthjem’s assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps, the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software. The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency (BPF) noise, and the sound pressure level (SPL) reached peaks near the cutoff that corresponded with the pressure pulsation in this region. An experiment is performed to validate this prediction. Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model. The simulation results for the noise are analyzed and compared with the experimental results. The variation in the calculated noise with changes in the flow agreed well with the experimental results. When the flow rate was increased, the SPL first decreased and reached the minimum near the best efficient point (BEP); it then increased when the flow rate was further increased. The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps. The noise simulation method in current study has a good feasibility and suitability, which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.

임펠러 형상에 따른 양흡입 원심송풍기 성능특성

This paper presents the performance enhancement of a double-inlet centrifugal blower by the shape optimization of an impeller. Two design variables, a number of blade and a length of chord, are introduced, and analyzed by a response surface method. Three-dimensional compressible Navier-Stokes equations are used to analyze the blower performance and the internal flow of the blower. Throughout the numerical simulation of the blower, blower efficiency can be increased by reducing separation flow generating from the blade leading edge of a blade pressure surface. It is noted that recirculation flow observed inside the blade passage induces low velocity region, thus increases pressure loss. Efficiency and pressure of the optimum blower are successfully increased up to 3% and 3.9% compared to those of reference blower at the design flow condition, respectively. Detailed flow field inside the blower is also analyzed and compared.

Design Work of a Compressor Stage Through High-To-Low Speed Compressor Transformation

Low-speed model testing has advantages such as great accuracy and low cost and risk, so it is widely used in the design procedure of the high pressure compressor (HPC) exit stage. The low-speed model testing project is conducted in Nanjing University of Aeronautics and Astronautics (NUAA) to represent aerodynamic load and flow field structure of the seventh stage of a high-performance ten-stage high-pressure compressor. This paper outlines the design work of the low speed four-stage axial compressor, the third stage of which is the testing stage. The first two stages and the last stage provide the compressor with entrance and exit conditions, respectively. The high-to-low speed transformation process involves both geometric and aerodynamic considerations. Accurate similarities demand the same Mach number and Reynolds number, which will not be maintained due to motor power/size and its low-speed feature. Compromises of constraints are obvious. Modeling principles are presented in high-to-low speed transformation. Design work was carried out based on these principles. Four main procedures were conducted successively in the general design, including establishment of low-speed modeling target, global parameter design of modeling stage, throughflow aerodynamic design, and blading design. In global parameter design procedure, rotational speed, shroud diameter, hub-tip ratio, midspan chord, and axial spacing between stages were determined by geometrical modeling principles. During the throughflow design process, radial distributions of aerodynamic parameters such as D-factor, pressure-rise coefficient, loss coefficients, stage reaction, and other parameters were obtained by determined aerodynamic modeling principles. Finally, rotor and stator blade profiles of the low speed research compressor (LSRC) at seven span locations were adjusted to make sure that blade surface pressure coefficients agree well with that of the HPC. Three-dimensional flow calculations were performed on the low-speed four-stage axial compressor, and the resultant flow field structures agree well with that of the HPC. It is worth noting that a large separation zone appears in both suction surfaces of LSRC and HPC. How to diminish it through 3D blading design in the LSRC test rig is our further work.

Characteristics of Transient Flow and Pressure Fluctuation in Impeller for Centrifugal Pump

Transient flow analyses in centrifugal pump are focused mainly on the volute, while little attention is paid on the rotating impeller. The transient flows for different operating conditions in centrifugal pump are numerically investigated using RNG k-e turbulence model and moving mesh. The computational results of pump head and efficiency show good agreement with the experimental data. Three monitor points are positioned on the blade pressure and suction surfaces. The pressure fluctuations on monitor points are analyzed and discussed. For design flow rate, the dominant frequencies on blade surface are 1 or 2 times rotating frequency. The dominant frequency equals the rotating frequency for both small and large flow rates. The amplitudes of pressure fluctuation increase gradually from the impeller inlet to outlet. The maximum amplitude of pressure fluctuation for small rate is about 5 times than that for design flow rate at the same monitor point. The relative velocity distributions in impeller are analyzed for small flow rate. The results show that the vortexes evolving with time at the impeller outlet near the pressure surface give rise to the flow non-uniformity, inducing low operating efficiency and large pressure fluctuation for centrifugal pump.

The Impeller Improvement of the Centrifugal Pump Based on BVF Diagnostic Method

Selecting one IS 150-125-250 centrifugal pump as reference model, impeller with 3D blades has been designed using two-dimensional theory. Numerical simulations using Reynolds averaged N-S equations with a RNG k-ε two-equation turbulence model and log-law wall function are used to estimate the hydraulic performance of pump and obtain BVF distributions on impeller blade pressure surfaces and suction surfaces. The results show that, compared with IS150-125-250 pump, the designed one shows better performance in a wide operation range with the maximal efficiency 2.8% increase. With the help of boundary vorticity flux diagnostic, further improvement is realized. Local defect areas on blade surfaces are identified and inlet blade angle distribution modification and wrapping angle change of designed impeller are carried out on local defect areas. The vortices that exist in designed impeller disappear after modification and it flows more smoothly in the modified impeller with slight hydraulic performance improvement than in the original designed one. BVF diagnostic can be further embedded in optimal design method to perform an automatic optimal design without manual trial-and-error procedures.

Numerical investigation of sediment erosion to the impeller in a double-suction centrifugal pump

Based on Euler-Lagrange multiphase flow model and Finnie ductile material erosion model, using phase coupled SIMPLE algorithm, k-e RNG turbulence model and Reynolds Averaged Navier-Stokes (RANS) equation, the solid-liquid two-phase flows in a double-suction centrifugal pump is simulated. The erosion rate and solid mass concentration distribution on the pressure and suction surfaces of blades were obtained in different situations, which include different solid mass concentration (2.17kg/m3, 8.66kg/m3 and 14kg/m3) and different sediment diameter (0.019mm, 0.036mm, and 0.076mm). By comparisons of the test and numerical simulation values, the reliability of numerical calculation method has been verified. The numerical simulation result obtained show that the Finnie ductile material erosion model can accurately predict the erosion rate and erosion areas on the impeller. The erosion rate is increases with solid sediment diameter or solid mass concentration increasing. The main erosion areas on the pressure surface of blades near the blade inlet and outlet and close to the hub, and on the suction surface of blades near the blade inlet and close to the hub. For different sediment diameter or solid mass concentration, the erosion rate on the pressure surface of blades is always greater than that on its suction surface.

Analysis on the blade inlet pressure fluctuation of the centrifugal pump based on LES

In order to study the characteristics of the blade inlet pressure fluctuation under unsteady flow in centrifugal pump, a three-dimensional model of a pump ns=50 was built. Based on large eddy simulation (LES), the inner flow field of the pump was simulated by the flow field simulation software Fluent in design condition and off-design conditions. The pressure fluctuation of the monitored points was obtained at the blade suction surface and pressure surface at impeller inlet, which was analyzed by time and frequency domain with Fast Fourier Transformation (FFT). The results show that the pressure fluctuation of inlet and outlet in large flow rate is more obvious than low flow rate. It is easily found that the static pressure of outlet in 1.2Qd condition has five peaks and five valleys, but this phenomenon does not exist in 0.6 Qd condition. In the time domain spectrums, the static pressure curve has five peaks and five valleys that the maximum pressure is positive number and the minimum pressure is negative number. In the frequency domains spectrums, the frequency of FFT factors peak is lower than the blade passing frequency 241.65Hz.

Study on Application of CAE in a Centrifugal Compressor Impeller

CAE technology is the most common method to study properties of impeller in a centrifugal compressor. The fluid field was numerically simulated by CFX program to obtain the distribution rules of pressure, turbulence intensity and erosion wear. Based on fluid-solid interaction, stress and deformation were analyzed by Ansys program. According to the simulation results, the maximum deformation and equivalent stress of the impeller are all located on the junction between the blade trailing edge and the shroud. The most serious damaged part by erosion wear in impeller is on the pressure surface of long blade. The erosion wear area on blade pressure surface caused by particles impact primarily locates on blade trailing edge root and middle part. In the flow field, the turbulent intensity on suction surface is greater than that on pressure surface in the corresponding position and the greatest turbulent intensity is located on the leading edge of suction surface. There is backflow phenomenon around the suction surface of long blade and the short blade has significant effect to reduce backflow. The results of numerical simulation explain some actual impeller failure cases and can be applied to anti-wear impeller design and repair.

Analysis of inner flow in low specific speed centrifugal pump based on LES

To investigate unsteady flow in the low specific speed centrifugal pump, a three-dimensional model of a pump that n s is equal to 50 is modeled with the software Pro/E. With standard k-ɛ, SST k-ω and RNG k-ɛ turbulence model, the testing performance of pump is compared with the simulated results. Based on the result of steady flow, the unsteady flow of RNG k-ɛ turbulence model and large eddy simulation (LES) are calculated at both design and off-design conditions. The time domain of pressure fluctuation value of indicator points, which are located interfaces between volute and impeller, has been investigated numerically. The unsteady flow characteristic of pump with RNG k-ɛ turbulence model is compared with LES. The distribution of vortex in the volute is discovered. The results show that in steady flow, an error of 2.6% of RNG k-ɛ is the lowest, SST k-ω of 3.65% is second and the worst is standard k-ɛ of 4.78% at design condition. The calculated precision using RNG k-ɛ model is highest in steady condition. Because of the interaction of relative movement between volute and impeller, the pressure fluctuation can clearly be observed. The flow separation of the blade pressure surface and the stall channels in off-designed condition is the reason that the efficiency of pump operating under off-design condition is low. The vortex intensity is obviously different in the eight sections of the volute and is gradually increasing from first section to eighth section. Large eddy simulation can discover the unsteady flow of the centrifugal pump effectively.

An investigation on the effects of irregular airfoils on the aerodynamic performance of small axial flow fans

In this paper, the effects of airfoils on the aerodynamic performance of small axial flow fans were investigated to reduce airflow turbulence on the blade surface and to improve the aerodynamic performance of small axial flow fans. Irregular airfoils where several convex grooves are bound in the blade pressure surface of the fans have two kinds. The wave-shaped edge is bound to the blade trailing edge of the fans and is designed from the smooth airfoil of the fans. The filtered N-S equations with the finite volume method and the standard k-ɛ turbulence model were adopted to carry out the steady simulation calculation. The large eddy simulation and the FH-W noise models were adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation are in good agreement with the tests, which proves that the numerical calculation method is feasible. The spectrum characteristics of aerodynamic noise of the smooth airfoil and the two kinds of irregular airfoils were analyzed. Although the fans of the three airfoils are regarded as noise sources, the vortex distribution features in the unsteady flow field are also described. Noise reduction mechanisms of the irregular designs of the airfoils were also discussed. The results of this research may provide proof of the parameter optimization and the structural design of small axial flow fans with low noise.

Field Experiment of Blade Surface Pressure of a HAWT

Field experimental study is performed on a 33 kW horizontal axis wind turbine with rotor diameter of 14.8 m. The distribution of pressure is gathered by disposed 191 taped pressure sensors span-ward on seven particular sections of a blade. The results will provide a comparative basis to wind tunnel experiment and numerical calculation of the flow of the wind turbine.

Experimental investigation into the impact of crossflow on the coherent unsteadiness within film cooling flows

Film cooling is regularly used to cool the surface of components within the turbine stage of an aero engine. This enables them to withstand the high air temperatures that are required for maximising aero engine cycle efficiency. It is known that the mixing of a film cooling flow with the main high temperature air flow through a turbine passage is an unsteady process, with coherent unsteady features occurring across a range of blowing ratios. Upon an aero engine the cooling holes on a turbine blade commonly have a crossflow at the hole inlet. Previous work has shown that crossflow at the hole inlet modifies the time-mean flowfield downstream of a cooling hole compared to the case without crossflow.The current paper investigates the impact of spanwise orientated crossflow on the coherent unsteadiness within film cooling flows. Both cylindrical and shaped cooling holes, located on a blade pressure surface, are studied. The range of blowing ratios considered is 0.7–1.8 and the crossflow velocity is up to 0.8 times the bulk jet velocity. High Speed Photography and Hot Wire Anemometry are used to observe the presence of coherent unsteadiness, both immediately downstream of the hole exit and within the cooling hole tube.The results show that the coherent unsteadiness downstream of the hole exit is persistent and its occurrence is not significantly affected by the magnitude of spanwise crossflow. Within the cooling hole tube the existence of coherent unsteadiness is presented for the first time, inside both cylindrical and shaped holes, with a Strouhal number of 0.6–1.2. The pattern of this in-hole coherent unsteadiness is seen to change with increasing the crossflow velocity.

Numerical study on the influence of boss cap fins on efficiency of controllable-pitch propeller

Numerical simulation is investigated to disclose how propeller boss cap fins (PBCF) operate utilizing Reynolds-averaged Navier-Stokes (RANS) method. In addition, exploration of the influencing mechanism of PBCF on the open water efficiency of one controllable-pitch propeller is analyzed through the open water characteristic curves, blade surface pressure distribution and hub streamline distribution. On this basis, the influence of parameters including airfoil profile, diameter, axial position of installation and circumferential installation angle on the open water efficiency of the controllable-pitch propeller is investigated. Numerical results show: for the controllable-pitch propeller, the thrust generated is at the optimum when the radius of boss cap fins is 1.5 times of propeller hub with an optimal installation position in the axial direction, and its optimal circumferential installation position is the midpoint of the extension line of the front and back ends of two adjacent propeller roots in the front of fin root. Under these optimal parameters, the gain of open water efficiency of the controllable-pitch propeller with different advance velocity coefficients is greater than 0.01, which accounts for approximately an increase of 1%–5% of open water efficiency.

0413 半径方向吐出斜流ファンの内部流動に関する研究 (翼先端もれ渦と正圧面はく離)(OS4-3 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)

In order to clarify the relationship between performances and internal flows in a low specific-speed diagonal flow fan, the experimental and numerical investigations ware carried out. The test fan is radial-outflow type diagonal flow fan similar to centrifugal fan and its specific-speed is 670[min^<-1>, m^3/min, m]. The velocity fields at rotor outlet were measured using a slant hotwire probe and the wall pressure on the outer casing was found out using a highly responded pressure transducer. The numerical simulations were carried out at the same flow condition. As results, the fan performance was very good near the design point. Near design flowrate, it is found that tip leakage vortex was occurred. At excessive flowrate, it is found that separated flow was occurred on blade pressure surface.

Flow-induced Noise Calculation of Centrifugal Pumps Based on CFD/CA Method

A hybrid algorithm combination computational fluid dynamics(CFD) with computational acoustics(CA) based on the Lighthill equation theory is adopted to calculate the sound field. Based on Reynolds-averaged equations closed by SST k-ω turbulence model, the three-dimensional unsteady flow is numerically calculated. Acoustic boundary element method is adopted to solve the acoustic radiation of dipole source caused by blade and volute surface pressure. Vibro-acoustic interaction effect on centrifugal pump sound field is analysed and flow induced noise test rig of centrifugal pumps is built to verify the calculation results. The results show that blade passing frequency and multiple are the main frequency of the flow-induced noise, and the pressure fluctuation is strongest near the tongue. It would be improper to ignore the vibro-acoustic interaction influence in sound field simulation especialy at mode frequency. Sound pressure level at pump outlet is higher than inlet, displays largest at blade pass frequency and least at maximum efficiency point. Simulation value tallies the test in the trend, maximum difference 3.1%, which is validated the forecast function of numerical simulation. This provides some useful reference for hydraulic design of centrifugal pump with low noise.

Flow in a Low Specific Speed Centrifugal Pump Using PIV

The interflow plays important roles in centrifugal pump design. In order to study the effect of rotation and z-axis on internal flow, two-dimensional particle image velocimetry (PIV) measurements have been performed to measure the steady velocity field on three planes in all impeller passages of a low specific-speed centrifugal pump. The results show that the relative velocity flows in blade passages are obviously different in terms of the positions of the blade relative to the tongue. The interaction between the impeller and tongue changes the occurrence and development of low velocity region with time. From shroud to hub, the relative velocity gradually increases, and the minimum value moves toward the suction surface. On the midplane, the magnitude increases with increased flow rate from pressure surface to suction surface, while at the shroud and hub, the measured velocity first increases with decreased flow rate from the blade pressure surface to nearly ζ = 0.5 to 0.6.

Research of performance prediction to energy on hydraulic turbine

Refer to the low specific speed Francis turbine blade design principle and double-suction pump structure. Then, design a horizontal double-channel hydraulic turbine Francis. Through adding different guide vane airfoil and and no guide vane airfoil on the hydraulic conductivity components to predict hydraulic turbine energy and using Fluent software to numerical simulation that the operating conditions and point. The results show that the blade pressure surface and suction surface pressure is low when the hydraulic turbine installation is added standard positive curvature of the guide vane and modified positive curvature of guide vane. Therefore, the efficiency of energy recovery is low. However, the pressure of negative curvature guide vane and symmetric guide vane added on hydraulic turbine installations is larger than that of the former ones, and it is conducive to working of runner. With the decreasing of guide vane opening, increasing of inlet angle, flow state gets significantly worse. Then, others obvious phenomena are that the reflux and horizontal flow appeared in blade pressure surface. At the same time, the vortex was formed in Leaf Road, leading to the loss of energy. Through analyzing the distribution of pressure, velocity, flow lines of over-current flow in the the back hydraulic conductivity components in above programs we can known that the hydraulic turbine installation added guide vane is more reasonable than without guide vanes, it is conducive to improve efficiency of energy conversion.

Experimental study on the flow of a mixed flow pump impeller

Mixed flow pump is wildly used in many field, the performance of the whole pump is affected by the flow in the impeller to a great extend. To make clear the flow phenomena in the mixed flow impeller at design and off-design flow rate condition, a mixed flow unshrouded impeller was manufactured and the flow in the impeller at design and off-design flow rate was experimental measured by Particle Image Velocimetry (PIV) in this paper. In the experiment test device, the volute was specially design and manufactured by transparent material. According to the experimental result, the distribution of time-average relatively velocity showed the velocity near blade pressure surface at design flow rate decreases and then increases from inlet to outlet of the impeller, and that near blade suction surface increase and then decreases. The velocity near the suction surface decrease from hub to casing, and the minimal velocity appears near the casing and suction surface. Near the impeller outlet, the relative velocity near blade pressure surface varies a little alone the span direction; Back-flow phenomena were found at passages outlet near casing and mid-span sections at partial flow rate. To clarify the effect of volute geometry on the velocity distribution, the flow in different impeller passages relatively to the volute tongue was test and the result showed that the velocity distribution in different passages was similar.