Blade Surface Pressure Research Articles

Supersonic compressor cascade flow control using plasma actuation at low Reynolds number

To control the supersonic compressor cascade flow at low Reynolds numbers, this paper describes the use of nanosecond dielectric barrier discharge (NS-DBD) plasma actuation for flow control, and presents the results of large-eddy simulations conducted to investigate the corresponding flow control effects. NS-DBD plasma actuation on both the blade pressure surface and suction surface induces a distorted flow structure (DFS) within the blade passage. In the case of NS-DBD plasma actuation on the blade pressure surface, the influence of the DFS on the flow is suppressed by a shock wave. Even so, the DFS can still trigger the instability in the shear layer between the separated flow and the mainstream flow. Shock-wave-induced large-scale flow separation on the blade pressure surface is then suppressed, and the overall total pressure loss of the blade passage is reduced by 7.4%, despite the increased shock wave loss from the reduced flow blockage within the blade passage. In the case of NS-DBD plasma actuation on the blade suction surface, the DFS is less effective in suppressing the shock-wave-induced small-scale flow separation on the blade suction surface. However, the DFS on the blade suction surface enhances the shock wave oscillations within the blade passage, and this suppresses the flow separation on the blade pressure surface.

Transonic Turbine Blade Tip Heat Transfer with Pressure Side Film Cooling

Investigated are spatially resolved distributions of surface adiabatic film cooling effectiveness and surface heat transfer coefficients for a transonic turbine blade tip, with a unique and innovative film cooling arrangement, wherein a single row of five film cooling holes, located on the pressure side of the blade very near to the blade tip, provides thermal protection to the blade tip. The blade tip contains a squealer rim, and a squealer recess region. The present tip gap magnitude is 1.2% of the true blade span. When blade upper pressure side data are considered, heat transfer coefficient ratio variations are due, in part, to a horseshoe-shaped vortex structure, which forms around each film cooling jet, and then advects downstream. Spatially resolved distributions of surface adiabatic film cooling effectiveness show that the coolant advects to the upper edge of the blade pressure surface, along the pressure side rim, over the squealer recess region, and then sometimes collects in a substantial manner along portions of the suction side rim. As a result, local effectiveness values are generally higher on the suction side rim relative to pressure side rim values when compared at a particular value of blowing ratio.

Numerical simulation of the influence of mixed sand on erosion characteristics of centrifugal pump

PurposeThe purpose of the paper is to predict the erosion rate of the components of centrifugal pump under certain operating condition to identify the maximum erosion area and to discuss the factors affecting them. This helps to optimize design and estimate service life.Design/methodology/approachIn the paper, the Eulerian–Lagrangian approach method coupled with the erosion model to investigate the mixed sand characteristics on erosion characteristics of centrifugal pump flow-through wall. The hydraulic performance and wear characteristics experiment of the pump is used to verify the accuracy of the numerical simulation.FindingsThe blade erosion area mainly occurs near the blade inlet and the trailing edge of the pressure surface, the main erosion area of the impeller back shroud is near the outlet of the flow passage and the main erosion area of the volute is near the tongue and the I section. With the change of the average diameter and density of sand particles, the average erosion rate on different flow-through walls is positively correlated with the average mass concentration to a certain extent. However, for different sand shape factors, there is little correlation between the average erosion rate and the average mass concentration. In addition, compared with other erosion areas, the increase of average sand particle diameter and density has the greatest impact on the total erosion rate of blade pressure surface, while the shape of sand particles has a greater impact on the total erosion rate of each flow-through wall of centrifugal pump.Originality/valueIn this work, according to the characteristics of the mixed distribution of different sand diameters in the Yellow River Basin, the erosion characteristics of centrifugal pumps used in the Yellow River Basin are studied. The numerical calculation method for predicting the wall erosion of centrifugal pump is established and compared with the experimental results. The results can provide reference for optimizing design and increasing service life.

Instrumentation development and testing of a wind turbine blade for sub-scale wake studies

Wind turbine blade aerodynamics and the resulting wake flow are complex, and wind tunnel testing of these flows can provide critical insight. The data from such tests are also valuable for validation of numerical models. For experiments using sub-scale turbines to be useful, the blade aerodynamics and wakes must exhibit the important features observed in utility-scale turbine flows. In this work, ∼1 m blades designed to produce physics relevant to larger scale turbines were manufactured and affixed to an existing turbine. One of the blades was instrumented for blade surface pressure measurements. Time-dependent surface pressure measurements coupled with instantaneous measurements of the inflow with Cobra probes and the wake with particle image velocimetry allowed for characterization of the inflow, blade flow, and near wake. The results demonstrate that the instrumentation was effective in characterizing the blade loading and the flow field. For the one test case discussed in this paper, the measurements of inflow, blade loading, and wake properties facilitate understanding of the wake's behavior.

Influence of inlet gas volume fraction on energy conversion characteristics of multistage electric submersible pump

A local-regional power loss analysis method based on multiphase computational fluid dynamics (CFD) simulation results is proposed in this study. This method is used to investigate the energy conversion characteristics of a three-stage electric submersible pump under high inlet gas volume fraction (IGVF) conditions. Results show that the input power and effective power increase first and then decrease along the streamline. When IGVF increases from 0% to 14.5%, the total input power and total effective power decrease by 32.4% and 56.2%, respectively. In particular, the input power and effective power in R4 drop by 62% and 67%, respectively. The high gas volume fraction (GVF) area on the blade pressure surface near the impeller inlet causes the power decrease in R4. However, the input power in R6 increases by 47.5%. This condition is due to a jet flow near the impeller outlet causes the vortex and high GVF area in R6, thereby leading to a high liquid velocity area along the radial direction near the pressure surface of the impeller blade. The kinetic energy of the fluid in the jet region increases rapidly in accordance with Bernoulli equation and is converted into pressure energy in the vortex area. The total power loss increases quickly with IGVF. The power loss near the impeller outlet area at 14.5% IGVF is ten times higher than that of 0% IGVF condition and five times higher than that of 5% IGVF condition. This condition is caused by the large air pockets accompanied by vortices in the area. This work provides a theoretical basis for the design and optimization of the multiphase pump.

Numerical study on hot streak migration characteristics of micro axial turbine

The thermal load distribution and aerodynamic performance of turbine are affected by the hot streak (HS) migration characteristics. Especially in micro turbine, hot streak will show different migration characteristics affected by dimensional effect (DE). In this paper, a numerical study was employed on a micro axial turbine (MAT) to investigate the HS migration characteristics. Combining theory with numerical result, the phenomena of "heat deposition" and "heat migration" in micro turbine are revealed. The results show that: In MAT stator, the hot streak will migrate toward the hub 1.1% blade height for heat deposition, which is not obvious in conventional turbine stator. In MAT rotor, the heat streak will migrate to the blade pressure surface around 30.9% of the passage pitch, which is 4.3% more than that in conventional turbine. In addition, the hot streak transfers very complex due to the effects of the hub secondary flow and the leakage flow, and tends to be stretched into two parts. The study provides a theoretical reference for the aerodynamic and cooling design of MAT.

Spectral proper orthogonal decomposition of compressor tip leakage flow

To identify the spatiotemporal coherent structure of compressor tip leakage flow, spectral proper orthogonal decomposition (SPOD) is performed on the near-tip flow field and the blade surface pressure of a low-speed compressor rotor. The data used for the SPOD analysis are obtained by delayed-detached eddy simulation, which is validated against the experimental data. The investigated rotor near-tip flow field is governed by two tip leakage vortices (TLV), and the near-tip compressor passage can be divided into four zones: the formation of main TLV (Zone I), the main TLV breakdown (Zone II), the formation of tip blockage cell (Zone III), and the formation of secondary TLV (Zone IV). Modal analysis from SPOD shows that a major part of total disturbance energy comes from the main TLV oscillating mode in Zone I and the main TLV vortex shedding mode in Zone III, both of which are low-frequency and low-rank; on the contrary, modal components in Zones II and IV are broadband and non-low-rank. Unsteady blade forces are mainly generated by the impingement of the main TLV on the blade pressure surface in Zone III, rather than the detachment of the secondary TLV from the blade suction surface in Zone IV. These identified coherent structures provide valuable knowledge for the aerodynamic/aeroelastic effects, turbulence modeling, and reduced-order modeling of compressor tip leakage flow.

Study on the erosive wear of the gas-solid flow of compressor blade in an aero-turboshaft engine based on the Finnie model

In this study, a Ti-6Al-4V alloy erosive wear test bench was designed and built. Particle velocities were tested using particle image velocimetry (PIV) at different air pressures. A Finnie wear model for the compressor blade materials was parameterized, and the gas–solid flow of a turboshaft engine pre-1.5 stage compressor blade was analyzed. The results showed that there were areas of wear concentrated on the pressure surface of the rotor blade and the suction and pressure surfaces of the stator blade. The maximum wear rate concentration appeared near the leading edge of the 80% span and near the leading and trailing edges of the 95% span on the rotor blade.

Flow characteristics of a low-solidity cantilevered stator embedded in a 4-stage low-speed research compressor

This research presents the influence of the low-solidity design on the loss and stability of the cantilevered stator and the evolution of the hub leakage vortex. The highly loaded 4-stage low-speed research compressor (LSRC) with an embedded cantilevered stator (CS) of Stator 3 (S3) was experimentally measured at the blade row outlet and in the S3 passage, respectively, and the URANS simulation method was calibrated accordingly. Then, the prototype CS blade number was reduced, namely low-solidity cantilevered stator (LSCS), to increase the blade loading. The diffusion factor ( DF) of LSCS at the midspan at the design working condition is 5.2% higher than that of CS. The URANS results show that LSCS provides higher efficiency for the 1.5 stage compressor with a consistent stall margin. For S3, the total pressure loss of LSCS is lower than CS at the design point (DP) working condition, but it is the opposite at the near stall (NS) working condition. For LSCS at the NS point, the blockage region becomes large and occupies the lower half of the fore blade passage because the low-solidity stator could not provide the enough flow turning ability, and the core of the hub leakage vortex (HLV) moves forward and the intensity is strengthened. The high loss region of LSCS at the near stall condition is consistent with the size of two hub leakage vortices. The first HLV breakdown is caused by unsteady mixing flow, and then it twists downstream and contacts with the trailing edge of the adjacent blade pressure surface. The study of the hub leakage flow characteristics of the low-solidity cantilevered stator can help designers to control flow better.

Analysis of vortex cooling fluid-structure interaction under different vortex chamber curvature

The vortex cooling with cascade channel and blade leading edge solid region is established. The flow and heat transfer properties of vortex cooling region, and the stress and displacement properties of blade solid region are analyzed by the fluid-structure interaction method. The ellipses edges with vertical axis to horizontal axis ratio a/b of 0.48, 0.72, 1.00, 1.31 and 1.73 are utilized to form the vortex chamber with different curvature. Influences of vortex chamber curvature on the vortex cooling fluid-structure interaction characteristics are researched to reveal the vortex cooling high heat transfer mechanism deeply. Results show that, for a/b decreasing from 1.73 to 0.48, the overall average Nusselt number and comprehensive heat transfer factor will first increase and then decrease, and the drag coefficient will gradually decrease. As a/b decreases, the high Nusselt number region moves from the target wall next to the nozzle to the target wall under the nozzle and at the vortex chamber bottom. With decreasing a/b, the thermal stress and thermal displacement on the blade pressure surface gradually decrease, while on the blade suction surface the thermal stress first decreases and then increases, and the thermal displacement first increases, then decreases and finally increases. In this study, compared with a/b = 1.73, the heat transfer performance for a/b = 0.72 has been enhanced by 21.00% and can provide the best protection for the blade.

Unsteady characteristics of pressure on wind turbine blade surface in the field

Field experiments are carried out to investigate the fluctuation characteristics of pressure on wind turbine blade surface in real operating environments. The tested wind turbine positioned pressure tapes along the blade span to obtain the dynamic pressure of seven airfoil sections over six rotation periods, and analyzed its time-domain, frequency domain, and standard deviation. The results show that the pressure on blade surface presents highly unsteady characteristics, and rotation of the wind turbine is one of the main factors that causes pressure fluctuations on the blade surface. The standard deviation of pressure near the leading edge of each airfoil section is relatively larger, indicating that the leading edge is the most sensitive to field wind conditions. Compared with the pressure surface, the blade suction surface contributes more to wind turbine power fluctuation and is more sensitive to various unsteady sources. Moreover, the standard deviation of the pressure on the blade pressure surface is largest at the tip, and the standard deviation of the pressure on the blade suction surface is clearly divided into two regions along the chord direction with different scales at different spanwise sections.

Investigation on pressure pulsation and modal behavior of the impeller in a nuclear reactor coolant pump

AbstractAs the unique rotating component, the impeller is the core component of a nuclear reactor coolant pump (RCP), the dynamic properties of the impeller are critical for the safe operation of the whole reactor. The purpose of this study was to shed comprehensive light on the pressure pulsation and modal properties of a scaled RCP impeller via experimental and numerical methods. The numerical model was validated by an experiment connecting the pressure pulsation signals at the diffuser inlet, and a good agreement was obtained between the numerical and experimental results. Pressure pulsation acting on the impeller's blade is mainly dominated by the impeller rotating frequency, the vane passing frequency, and the double blade‐passing frequency, and the pressure pulsation acting on the blade's pressure surface is more intense than on the suction surface. The modal properties were obtained via the modal test and numerical methods with the impeller suspended as a free body in the air and submerged inside water. The reduction in the impeller natural frequencies was between 31.63% and 37.77% for the corresponding mode shape due to the added mass effect of the fluid. Based on the pressure pulsation characteristics acting on the impeller and the natural frequency of the impeller, it is considered there is no risk of resonance in the impeller. Finally, it is expected that the present work can provide scientific guidance to avoid hydraulic resonance in nuclear reactor coolant pumps.

The Effects of Different Splitter Blades Number on Characteristics of Miniature Super-Low Specific Speed Centrifugal Pump

Splitter blades are often used to improve the performance parameters of super-low specific speed centrifugal pumps, while the number of splitter blades is the most important influencing factor of head and efficiency. In order to study the effect of different number of splitter blades between long blades on the external characteristics and internal flow field of centrifugal pumps, the numerical simulation of four impeller models has been carried out by Fluent. The results show that splitter blades can raise head and efficiency of the centrifugal pump, so that the performance curve moves toward large flow rate area. The low speed area on the pressure surface of the long blade reduces with the slip and separation inhibited. When the number of splitter blades increase gradually, the head of the centrifugal pump has not much increase while the efficiency decreases. Most of the medium flow out through the runner on the pressure surface leaving the others blockage due to the backflow and vortexes, resulting in large hydraulic loss.

Intermittent breakdown of the tip leakage vortex and the resultant flow unsteadiness in the tip-region of a subsonic compressor cascade

In axial-flow compressor rotors, the breakdown of the tip leakage vortex (TLV) occurs in an intermittent manner under some conditions. In order to gain better knowledge of this unsteady phenomenon, a numerical investigation of the tip-region flow field in a subsonic compressor cascade has been conducted using unsteady Reynold-averaged Navier-Stokes simulations. First of all, the reason why TLV breakdown exhibits intermittency has been clarified through the analysis of time-resolved flow fields. It was found that the switch between the breakdown and no-breakdown states is triggered by a feedback mechanism: when the TLV breaks down, either an unsteady induced vortex or a backflow vortex forms and induces low-pressure on the pressure surface of the adjacent blade, which unloads the blade tip and subsequently suppresses the TLV breakdown; as the unsteady induced vortex or backflow vortex migrates downstream, the pressure on the pressure surface increases again so that the loading at the blade tip is increased again and the TLV breakdown is re-established. The amplitude and frequency characteristics of the unsteadiness associated with the intermittent TLV breakdown have been analyzed and presented. It was found that the backflow vortex-dominant breakdown induces much stronger flow fluctuation and has a much lower characteristic frequency than the unsteady induced vortex-dominant breakdown. The underlying flow physics responsible for this difference have been discussed based on the understanding of the feedback mechanism for the intermittent TLV breakdown.

Investigation of the Matching Relation Between Impeller and Flow Channel of Regenerative Flow Pumps

Abstract As a specific radial flow pump, the regenerative flow pump (RFP) usually has a low efficiency. In this study, in order to explore the matching mechanism, three cases with various matching relations were investigated by the methods of theoretical calculation, computational fluids dynamics (CFD) simulation, and experiment test. The results illustrate that the theoretical prediction, numerical simulation, and experimental data are in good agreement. Furthermore, when the matching relation expressed by a ratio of the channel's and blade's radial length is equal to 1, the geometrical profiles of RFP can well guide the circulation flow into the channel at large radii and into the impeller at small radii, forming intense longitudinal vortex. The steady, strong exchange flow is characterized by the inflow and outflow regions approximately half of the isosurface. The axial vortex motion without apparent flow separation and irregular flow is observed in the impeller, a low velocity annulus exists in the medium radii of the impeller without other distinct velocity clouds, and a low velocity strip and a high velocity annulus in the channel are, respectively, performed along the blade's pressure surface and the channel's outer radii. All of this corresponds to the best pump's performance and the largest efficiency of the impeller and channel. This work promotes a systematical understanding of the matching mechanism between impeller and flow channel in the RFP and could provide some reference for the design and performance optimization for RFP.

Numerical study on film cooling characteristics of BESA hole with water mist/air two-phase flow

In view of a new type of film cooling hole, the backward-expanding shoulder arm(BESA) hole proposed by the author, a numerical model of two-phase flow film cooling with water mist is established. The numerical simulation of water mist / air two-phase flow film cooling characteristics shows that the comprehensive performance of water mist / air two-phase flow film cooling is significantly improved compared with pure air film cooling. For the round hole plate model, when the blowing ratio is 0.5, the film cooling efficiency of two-phase flow film cooling with 2% water spray is 37.5% higher than that of pure air film cooling (20D from the film hole outlet), When the blowing ratio is 1.0, the film cooling efficiency of the flat two-phase flow with 2% water spray is 49.0% higher than that of the pure air film cooling (20D away from the film hole outlet). When the spray amount of water is the same, the film cooling efficiency of the BESA hole is higher than that of the round hole, the expanding hole and the shoulder arm hole. For the flat film cooling model of the BESA hole, When other factors remain unchanged, the cooling efficiency of the two-phase flow film increases monotonously from 2% to 5%. The cooling characteristics of the two-phase flow film on the pressure surface of the turbine blade of the BESA hole are similar to those of the flat model, and the film coverage effect is better than that of the round hole, the expanding hole and the shoulder arm hole.

Influence of Impeller Gap Drainage Width on the Performance of Low Specific Speed Centrifugal Pump

The centrifugal pump is one of the most important pieces of energy-consuming equipment in various hydraulic engineering applications. This paper takes a low specific speed centrifugal pump as the research object. Based on the research method combining numerical calculation and experimental verification, the influence of the gap drainage structure on the performance of the low specific speed centrifugal pump and its internal flow field distribution were investigated. The flow field inside the low specific speed centrifugal pump impeller under different gap widths was studied. The comparison between the numerical calculation results and the experimental results confirms that the numerical calculations in this paper have high accuracy. It was found that the gap drainage will reduce the head of the low specific speed centrifugal pump, but increase its hydraulic efficiency. Using a smaller gap width could greatly improve the performance of the low specific speed centrifugal pump on the basis of a slight reduction in the head. The high-pressure leakage flow at the gap flows from the blade pressure surface to the suction surface can effectively suppress the low-pressure area at the impeller inlet. The flow rate of the high-pressure leakage flow increases with the gap width. Excessive gap width may cause a low-pressure zone at the inlet of the previous flow passage. These results could serve as a reference for the subsequent gap design to further improve the operating stability of the low specific speed centrifugal pump.

Large eddy simulation of a linear turbine cascade with a trailing edge cutback

In this work, the effects of trailing edge (TE) cutback on the turbulent flow field and the aerodynamic loss of a turbine blade are investigated by Large-Eddy-Simulation (LES). A high-fidelity LES code was first developed based on a high-order finite difference method and applied to the simulation. The effects of the TE cutback on the blade surface boundary layer, pressure distribution, and loss generation are then discussed on the basis of time-mean flow fields of LES. The results represent that the cutback changed the boundary layer thickness just upstream of the TE and the base pressure around the TE, resulting in larger aerodynamic loss. Next, the time-dependent flow dynamics in the cascade is investigated. The results indicate that the dominant pressure fluctuation after the blade was influenced by the cutback. Furthermore, the phase-locked flow field is analyzed to reveal the flow dynamics responsible for the pressure fluctuation. Finally, the LES approach could clarify the underlying mechanisms of performance degradation of a turbine blade that caused by TE cutback.

An experimental study of the integral characteristics of the intrachannel liquid film suction in a turbine stator blades cascade

This paper presents the results of an experimental study of the integral characteristics of the intrachannel liquid film suction in a flat cascade of turbine stator blades. Two slots for removing the liquid film from the interblade channel were arranged on the pressure surface of the stator blade. The experiments were carried out with initial steam wetness y 0 = 3 ÷ 9.5 % and theoretical Mach number downstream the cascade M lt = 0.6 ÷ 0.78. The operation mode of the moisture removal system was determined by the relative pressure drop on the moisture-removing slots and varied over a wide range. The investigations were carried out for both the operation of the moisture-removing slots one at a time and the combined suction of the liquid film simultaneously through both slots. The measurement system used in the experiments allowed separately determining the mass flow rates of steam and liquid removed from the interblade channel. The obtained integral characteristics served to evaluate the influence of various factors on the efficiency of the intrachannel moisture removal system. Based on the analysis of the research results, recommendations on the design and operation of intrachannel moisture removal systems have been formulated.

Evolution Characteristics of Separated Vortices and Near-Wall Flow in a Centrifugal Impeller in an Off-Designed Condition

Flow separation is undesirable and lowers the efficiency of centrifugal impellers. In this study, the evolution characteristics of separated vortices in a centrifugal impeller are studied under the off-designed flow rate condition. Unsteady Reynolds-Averaged Navier–Stokes (URANS) with standard k-ε turbulent model is applied to simulate the alternating stall in the six-blade centrifugal impeller. We present and analyze the distributions of pressure gradient (either adverse or favorable) and skin friction coefficients on both sides of the blade for the stalled and unstalled passages to study the relationship between pressure gradient and separation of boundary layer flow. The evolution of skin friction coefficient is also presented at various axial cross sections. Numerical results reveal that, for the stalled passage, the increase in adverse pressure gradient on the pressure surface near the middle of the blade (S/S0 = 0.4) is much larger than that of the suction surface during a vortex formation cycle. The skin friction coefficient on the pressure surface also increases in magnitude sharply and the variation shows a peak-valley trend, while the coefficient on the suction surface increases slowly. Comparing the distribution of skin friction coefficient on the pressure surface of the same blade at different axial cross sections, it is found that the skin friction coefficient notably increases at S/S0 = 0.6 on the middle axial cross section (Z/b2 = 0.5). For the unstalled passage, both the pressure and suction surfaces produce favorable pressure gradients. The skin friction coefficient on the pressure surface shows an increasing trend around S/S0 = 0.5, and a large vortex can be seen at the exit of the impeller. The variation of skin friction coefficient on the suction surface is relatively mild; thus, the flow is relatively stable. It is clarified that the effect of adverse pressure gradient and wall shear stress jointly cause separation of the boundary layer; thus, the separated vortices are generated in the rotating impeller and deteriorate the performance of the impeller.