Blade Passage Research Articles

Effect of Intake Acoustic Reflection on Blade Vibration Characteristics

Recent studies in turbomachinery have shown that the phase of acoustic wave reflection within an intake can have either positive or negative effects on the aeroelastic stability of fan rotor blades. However, the typical flow structures, such as the shock wave, within rotor blade passages with acoustic wave reflection remain unclear. The aim of this research was to address this gap by investigating how these flow structures impact blade aeroelastic stabilities with acoustic wave reflections. The focus of this study was the NASA Rotor 67 blade with an extended intake. Moreover, a bump is incorporated on the shroud at different distances from the fan to reflect acoustic waves of varying phases. Utilizing the energy method, variations in the aerodynamic work density on blade surfaces were calculated under different phases of reflected acoustic waves. Analysis indicates that the spatial position of the shock wave undergoes periodic changes synchronized with the phase of acoustic reflection, marking the first instance of such an observation. This synchronization is identified as the primary factor causing variations in the aeroelastic stability of blades due to acoustic wave reflection, contributing to a deeper understanding of the mechanism behind acoustic flutter. The acoustic–vortex coupling at the blade tip leads to unpredictable variations in unsteady pressures on the blade suction surface, although its effect on blade aeroelastic stabilities is relatively limited compared to that of the shock wave.

Numerical studies on shock wave and boundary layer interaction in the high-load turbine rotor cascades

Design of transonic high-load turbine is the essential approach to improve thrust-to-weight ratio of gas turbine engines. The shock wave and boundary layer interaction (SWBLI) in high-load turbine is one of the important unsteady sources and the main source of loss in turbine stages. In order to study mechanism of SWBLI in high-load turbine, rotor blades with loading coefficients range from 1.6 to 2 were designed and Delayed Detached Eddy Simulations (DDES) were carried out. The influences of loading coefficient, exit isentropic Mach number and incidence angle on characteristics of shock wave, SWBLI as well as flow details in the blade passages were compared. Results indicated the shock wave was generated and enhanced as exit isentropic Mach numbers increased leading to the increase of 2.8% in the total pressure loss coefficient. There was not significant difference in the total pressure loss coefficient as loading coefficient increased, however the shock wave was stronger and the separation bubble was longer at the loading coefficient of 1.6. Meanwhile, the influence of strong separation near the leading edge of suction surface induced by variation of incidence angles on the characteristics of the shock wave and the loss was also obvious.

Time-Resolved Local Loss Analysis of Single- and Two-Blade Pump Flow

Abstract A method for the evaluation of time-resolved entropy production in isothermal and incompressible flow is presented. It is applied as a postprocessing of the three-dimensional (3D) flow field obtained by time-resolved computational fluid dynamics (CFD) with scale adaptive turbulence modeling. Wall functions for direct and turbulent entropy production are presented for a cell-centered finite volume method, implemented in the open-source software OpenFOAM and validated on channel, asymmetric diffuser, and periodic hill flow. Single- and two-blade centrifugal pump flow is considered for a wide range of load conditions. Results are compared to experimental data. Time-averaged analysis shows essentially the same loss density distribution among pump components for both pumps, with the impeller and volute region contributing the most, especially in off-design conditions. For both pumps, the losses exhibit significant fluctuations due to impeller–volute interactions. The fluctuation magnitude of loss density is in the same range as flowrate fluctuations and much smaller than pressure fluctuation magnitude. For the two-blade pump (2BP), loss fluctuation magnitude is smaller than for the single-blade pump (1BP). Distinct loss mechanisms are identified for different load conditions. Upon blade passage, a promoted or attenuated volute tongue separation is imposed at part or overload, respectively. In between blade passages, a direct connection from pump inlet to the discharge leads to enhanced flowrate and loss density fluctuations. Future work aims at extending this analysis to stronger off-design conditions in multiblade pumps, where stochastic cycle fluctuations occur.

Purge–Mainstream Interactions in a Turbine Stage With Rotor Endwall Contouring

Abstract Purge flows are prevalent in modern gas turbine design, allowing for increased turbine entry temperatures. The purge flow passes through a rim seal and interacts with the mainstream flow, modifying the blade secondary flow structures and reducing stage efficiency. These structures may be controlled using end wall contouring (EWC), though experimental demonstration of their benefit is seldom reported in the literature. The optically accessible turbine at the University of Bath was designed to directly measure and visualize the flow field within the blade passage for a rotor with EWC. The single-stage turbine enables phase-locked flow field measurements with volumetric particle image velocimetry (PIV). Purge flow was supplied to investigate a range of operating conditions in which the secondary flow structures were modified. The modular turbine rotor allowed for expedient change of a bladed ring, or bling, featuring non-axisymmetric EWC. The identified secondary flow structures were the pressure-side leg of the horse shoe vortex (PS-HSV) and an egress vortex (EV) of concurrent rotational direction. An increase in purge flowrate monotonically shifted the EV toward the suction-side (SS) of the adjacent blade. The migration of the PS-HSV toward the SS caused the two aforementioned vortices to merge. The EWC rotor design included a leading-edge (LE) feature to alter the PS-HSV and a trough to guide the EV low spanwise in the passage and maintain displacement from the adjacent suction-side. The EWC rotor was found to be effective at altering the formation and positioning of the secondary flow structures at a range of purge flow conditions.

Analysis of Ingress Into the Downstream Wheel Space of a 1.5-Stage Turbine By Full Circumference and Single Blade Passage Large-Eddy Simulations

Abstract The flow in a 1.5-stage axial turbine is investigated by large-eddy simulations. The focus is on the ingress in the downstream wheel space. Two setups are considered. In the first, the full 360 deg annulus is included on a computational mesh with approx. 1 billion mesh cells. The second setup includes a single blade passage in a 22.5 deg segment. The computational mesh has approx. 75 million mesh cells accordingly. The flow fields in the downstream wheel space differ strongly. In the 22.5 deg setup, the disk pumping effect is much more pronounced than in the 360 deg setup and the fluid bulk rotates in the direction of the rotor rotation. In the 360 deg setup, the fluid rotates in the opposite rotor direction and the velocities feature a deflection at intermediate radii. The differences are caused by the instantaneous flow fields. In the upstream wheel space of the 360 deg setup, two large-scale rotating vortex structures are predicted, which create four pressure peaks that propagate downstream. They interact with the second stator and create a rotating flow structure in the downstream wheel space, which generates alternating ingress and egress. Due to their spatial extent, none of these structures can exist in the 22.5 deg setup. The results show that for the investigated combination of turbine geometry and operating condition, the analysis of the downstream wheel space requires the detailed prediction of the unsteady flow phenomena in the upstream wheel space, i.e., it cannot be performed using the 22.5 deg setup.

Simulation research on aerodynamic noise characteristics of a compressor under different working conditions.

The shear stress transport turbulence model is employed to conduct a detailed study of flow characteristics at the highest efficiency point and near-stall point in a full-channel 1.5-stage compressor in this paper. The simulation results for the compressor's total pressure ratio and efficiency exhibit good agreement with experimental data. Emphasis is placed on examining the internal flow structure in the tip area of the compressor rotor under near-stall conditions. The results reveal that significant differences in flow structure primarily occur in the tip area as the compressor approaches stall. Specifically, a reduction in turbulent kinetic energy is observed in a region spanning approximately 20%-60% of the chord length on the rotor suction face near-stall conditions. Two additional peak frequencies, at 0.8 and 1.6 times the blade passage frequency, are observed, and the intricate flow phenomena are elaborated at the near-stall point. The near-stall point exhibits greater noise levels than the highest efficiency point, where the intensity of the surface source increases by more than 10 dB, peaking at 20 dB. This additional peak serves as a significant supplementary noise source near the stall point, leading to a maximum increase of 33.3 dB in the free radiated sound power. The acoustic response within the duct indicates that the compressor operating at the near-stall point continues to produce substantial noise on the actual test bench, showing an average increase of 6 dB in noise levels, and the distribution of the additional peak single-tone noise at the entrance significantly differs from that observed at the highest efficiency point.

Study on the application of 3D imaging based on the γ-photon silk thread method for visualisation and detection of flow fields

As a flow display technique, the silk thread method can clearly show the state of the flow field. However, displaying the state of the flow field in industrial closed metal cavities is impossible, and results of the traditional silk thread method fail to present depth information. To address these limitations, we propose a display method based on γ-photon silk thread 3D imaging. Firstly, a flow field visualization experimental platform applicable for industrial closed metal cavity was designed. Then, aiming at the shortcomings of insufficient γ-photon scanning data and limited imaging quality in flow field visualization, an adaptive sinogram interpolation-iterative filtering reconstruction algorithm was proposed to expand the data via the adaptive interpolation processing of the sinogram in image reconstruction. Beltrami filtering was also embedded in the iterative algorithm to effectively reduce noise and artifacts in the imaging image. Finally, the internal flow field inspection of the NACA0018 airfoil and the industrial confinement turbine were used as examples to visualise the wing upper surface flow and turbine blade passage secondary flow, respectively, and the results were consistent with those of the numerical simulation analysis. As the angle of attack of the wing increased, laminar flow separation occurred, and the silk thread structure state changed to the point where the aircraft stalled. After the imaging map analysis, the stall angle ranged between (15°,19°), which is consistent with the simulation results. In the turbine blade passage secondary flow detection, the imaging map formed a horseshoe vortex with airflow separation at the central saddle point and silk threads clearly presenting the structural state of the flow field along different directions.

Investigation of Transonic Flow Features in an Axial Flow Compressor Rotor

Numerical investigation of an axial flow rotor is carried out for its performance characterization and aerodynamic behavior during the design and off-design operating conditions. The study focuses on capturing the transonic flow features from the choke point (CP) to the near stall (NS) point in the rotor. This includes the analysis of passage shock structure, its movement in the blade passage with varying back-pressure, shock boundary layer interaction, tip leakage flow structure, and resulting losses. The study is carried out from 60 % to 100 % of the design speed using steady and unsteady RANS simulations. Three turbulence models, namely; SST, k-ε, and Reynolds stress models, are employed. The SST model predicted the closest approximation to the experimental data. The rotor aerodynamic performance is predicted in terms of total pressure ratio, efficiency, and flow contours. Unsteady analysis revealed that the primary and secondary tip leakage vortices, combined with the suction side tip corner separation, are the major instabilities near the stall region.

Numerical analysis of aero-hydrodynamic wake flows of a floating offshore wind turbine subjected to atmospheric turbulence inflows

The influence of atmospheric turbulence inflow on coupled dynamic behaviors and wakes of floating offshore wind turbine (FOWT) is pronounced, especially as blade size increases. In this study, we explore the effects of atmospheric inflow on aero-hydrodynamics and wake characteristics of a spar-type FOWT. A well-validated in-house computational fluid dynamic (CFD) solver, FOWT-UALM-SJTU, is utilized to conduct the numerical simulations. To generate the realistic atmospheric inflow condition, the large eddy simulation (LES) with long-duration is employed. Two other cases involving uniform inflow and shear inflow are conducted to provide some comparable results. Compared to uniform inflow and shear inflow, the power and thrust of FOWT under atmospheric inflow display greater instability, with their power spectrums exhibiting higher intensity in high frequency region. The variation of yaw moment in atmospheric scenario is significantly drastic, leading to a remarkable response in platform yaw motion. Notably, the dominant frequency in this scenario is the blade passage frequency, as opposed to the incident wave frequency observed in the uniform and shear scenarios. The atmospheric inflow promotes the manifestation of wake breakdown and wake meandering, resulting in the faster wake recovery of FOWT. Besides, the meandering in the far wake is more significant compared to uniform and shear scenarios. The absence of vortex rings in atmospheric scenario is observed, along with the presence of more complex and smaller vortices in far wake. Our findings highlight the remarkable impacts of atmospheric inflow on dynamic responses and wake evolution of FOWT, and it is recommended that the atmospheric inflow be taken into account when assessing wake interactions between multiple FOWTs.

MATHIMATICAL MODEL TO PREDICT THE DESIGN ANI) PERFORMANCE OF HIGH.SPEED TURBOPUMPS

In this work a high-speed turbopumps of (22000 rpm) rotational speed, which are oxidizer and fuel turbopumps, are designed. The design requirement for mass flow rate and outlet pressure are (12.5 kg/s) and (113×10 Pa) respectively for the oxidizer turbopump, and (3.5 kg/s) and (95x10 Pa) respectively for the fuel turbopump. The design work of centrifugal pump is divided into impeller and volute design works. The impeller design work is performed by the streamline curvature and quasi-orthogonal technique based on hub-to-shroud mean stream surface between two blades with assistance of experimental design coefficients and relations for first prediction. The volute is designed by using the method of constant angular momentum, where in this method the tangential and radial velocities are considered uniform around the impeller. The numerical results are compared with experimental data of the actual pumps, and it is found that these results agree well with the real designs. The output of the design program is used as an input to the performance program. The performance prediction is achieved by three dimensional, steady, incompressible and viscous flow analyses through the blade passage. The ANSYS program has been employed to solve these equation in order to predict the flow characteristics at design and off-design conditions. The analysis is done at many operation conditions, which have the range of flow coefficient ratio (ФФ) from (0.4) to (1.8), and the results are compared with experimental results for previous work to make sure the validity of the analysis program at design and off-design conditions.

Optimization and experimental study of stationary endwall of stator labyrinth cavity in a low-speed research compressor

Controlling the leakage flow of the labyrinth seal cavity is very important for the efficiency and aerodynamic matching design of aero-engine high-pressure compressor. However, due to the complexity of the geometry and internal flow of the labyrinth seal cavity, the design optimization of the labyrinth seal cavity is rarely studied. In this paper, a multi-objective design optimization method was used to optimize the stationary endwall of the shrouded stator labyrinth cavity, and the optimal endwall shape was obtained. Based on the optimal geometry, the 3D printing and aerodynamic testing of experimental parts were carried out, and the aerodynamic performance and flow field details of the optimal geometry were analyzed by unsteady numerical simulation. The experimental results show that for the optimal geometry, it has a little effect on the total pressure ratio, but the efficiency at the design point is increased by 1.4 %. The numerical results show that the optimal cavity shape reduces low-energy fluid, thus reduces the total pressure loss of S3. At the near stall point, the optimal S3 still has a better performance, which means that the optimal shape is not limited to the design point. From the result, an engineering design criterion can be concluded. It is suggested that the labyrinth seal cavity should be designed to match the velocity components of the leakage flow with the mainstream of the stator properly to make the leakage flow go evenly in the blade passage instead of gathering to the suction side.

Experimental Investigation on the Aerodynamic Instability Process of a High-Speed Axial-Centrifugal Compressor

Abstract Aerodynamic instability plays an important role in compressor design and may cause performance degradation and fatigue damage. In this paper, an experimental study on the evolution of aerodynamic instability is carried out on a compressor that combines the performance benefits of an axial stage and centrifugal stage. The spatiotemporal characteristics of unsteady wall pressure were obtained using fast-responding pressure transducers over a range of operating conditions. The results show that the axial stage works on the positive slope of the performance characteristic curve from choke to stall at low-speed operating conditions, and mainly features rotating instability. Rotating stall is also observed in the impeller (IMP) and diffuser passages. At medium-speed operating conditions, the centrifugal stage suffers a high-frequency mild surge, alternating with rotating stall. With the increase in back pressure, the mild surge diminishes, and rotating stall persists. This behavior is similar to a two-regime-surge, which has been reported for centrifugal compressors. At high-speed operating conditions, the compressor directly reaches surge without other instabilities. Further analysis of the spatial pattern of the rotating stall revealed the existence of a high-pressure region near the volute tongue, resulting in obvious pressure distortion along the circumferential direction at the volute inlet. This induced the amplitude difference of stall cells in corresponding diffuser passages. The disturbance caused by stall cells propagates upstream through the blade passage, and the largest pressure disturbance induced by the stall cell propagation appears in a circumferential position 45 deg downstream of the volute tongue at the impeller inlet and the axial stage inlet.

Multirotor broadband noise modulation

Rotor broadband noise spectra are typically analyzed over time scales on the order of one or more rotor periods. However, modulation of the broadband noise spectrum with the blade passage frequency (BPF) has been shown to be significant for noise levels and perception of wind turbines and helicopters. In contrast, time-varying broadband noise has not been extensively studied for aircraft with many rotors, such as unmanned aerial vehicles (UAVs) or advanced air mobility aircraft. In this work, significant broadband noise modulation was measured in flight and anechoic chamber tests of hexacopter UAVs at various observer angles. This modulation is aperiodic with the BPF such that the modulation amplitude varies substantially between blade passages, even when the BPFs are controlled to be nearly constant between all rotors at all times. Furthermore, the azimuthal phasing between rotors greatly affects the measured modulation, such that the modulation of multiple rotors may be less than or greater than for a single rotor, depending on the phase offsets. The effects of phase variations on acoustic interactions between rotors is studied by comparing the sum of the modulation of individual rotors to the modulation of those rotors operating simultaneously. This is done not only using measurements, but also noise predictions made using PSU-WOPWOP. These results contribute understanding to how the noise modulation of rotors sum together, including the resulting directivity and aperiodicity.

Numerical Investigation on the Aerodynamic and Aeroacoustic Characteristics in New Energy Vehicle Cooling Fan with Shroud

The cooling fan is one of the important noise sources for new energy vehicles, and the research on its aerodynamic and aeroacoustic characteristics is of great help to improve the noise, vibration and harshness performance of new energy vehicles. However, most of these studies focus on the impeller, and little consideration has been given to the study of the shroud. Based on the coupling calculation method of large eddy simulation and the Ffowcs-Williams and Hawkings acoustics model, the aerodynamic and aeroacoustic characteristics in a cooling fan with the shroud are investigated at flow rates from 0.623 kg/s to 1.019 kg/s (where 0.865 kg/s is the flow rate corresponding to the best efficiency point). The accuracy of numerical simulation results is verified by the grid independence verification and the comparison of experimental data. Research shows that several large-scale vortex structures are observed in the clearance between the impeller and the shroud. The maximum peak-to-peak values of pressure fluctuation at different flow rates occur in the intermediate section or outlet section of the shroud. Although the shroud contributes relatively less to the far field noise, its different distribution may change the position of the maximum sound pressure level. The dominant frequency of pressure fluctuation equals the blade passage frequency (BPF) and the maximum SPL is around the BPF, both of which are independent of flow rates. The maximum SPL and the amplitude of the dominant frequency decrease as the flow rate increases.

An Aerodynamic Investigation of the Last-Stage Turbine in an Upgraded Gas Turbine

Abstract Due to the lengthy certification process for newly designed turbine blades, product upgrading of industrial gas turbine units is often performed solely on compressor and combustor. Since their inlet conditions are significantly changed, the entire four-stage turbine operates far away from its original design point, leading to decreased efficiency, and increased flutter risk. This investigation first performs numerical simulations to study the flow field change of the last-stage turbine in a gas turbine before and after product upgrading. To reduce the load of the last-stage turbine without reducing the power output of the whole turbine, the enthalpy drops of turbine are reallocated to the front three stages. After modifying the blade profile based on S1 stream surface analysis, a CFD simulation is carried out on the modified three-dimensional blade passage. It is shown that the modified blade design greatly reduces the Mach number at the tip outlet of the last-stage blade, thus possibly reducing flutter risk and improving the aerodynamic efficiency of the turbine. This paper also attempts to redesign the blade geometry by different radial blade stacking of both forward sweep and backward sweep. It is found that the backward-swept blade modification can effectively reduce the endwall flow loss. This work presents the improvements of the aerodynamic efficiency of last-stage through a series of improvement methods and provides a reference for future detailed optimization of this last-stage turbine.

Separation-induced transition on a T106A blade under low and elevated free stream turbulence

The separation-induced transition on the suction surface of a T106A low pressure turbine blade is a complex phenomenon with implications for aerodynamic performance. In this numerical investigation, we explore an adverse pressure gradient-dominated flow subjected to varying levels of free stream excitation, as the underlying separation-induced transition is a critical factor in assessing blade profile loss. By comprehensively analyzing the effects of free stream turbulence (FST) on the transition process, we delve into the various mechanisms which govern the instabilities underlying bypass transition by studying the instantaneous enstrophy field. This involves solving the two-dimensional (2D) compressible Navier–Stokes equation through a series of numerical simulations, comparing a baseline flow to cases where FST with varying turbulent intensity (Tu=4% and 7%) is imposed at the inflow. Consistent with previous studies, the introduction of FST is observed to delay flow separation and trigger early transition. We explore the different stages of bypass transition, from the initial growth of disturbances (described by linear stability theory) to the emergence of unsteady separation bubbles that merge into turbulent spots (due to nonlinear interactions), by examining the vorticity dynamics. Utilizing the compressible enstrophy transport equation for the flow in a T106A blade passage, we highlight the various routes of bypass transition resulting from different levels of FST, emphasizing the relative contributions from baroclinicity, compressibility, and viscous terms.

The Effects of Rotation and Solidity on the Aerodynamic Behavior of Low-Pressure Axial Flow Fans

Abstract Implicit axial flow fan models are commonly used for the numerical analysis of industrial heat exchanger systems. However, these fan models perform poorly within the often complex off-design flow environments characteristic of these systems, as their low-order formulations lose applicability under highly 3D flow conditions. At off-design flow conditions, rotation and blade solidity effects cause physical fan blade behavior to deviate from the anticipated 2D behavior characterized by the implicit models. Physical fan blade behavior at off-design flow conditions, however, remains uncertain and the specific effects of rotation and solidity are not yet widely understood. This study investigates off-design fan blade behavior by presenting explicit 3D computations of two low-pressure axial flow fans. The effects of rotation and blade solidity are then identified through a side-by-side comparison of the computed 3D fan blade data against isolated 2D airfoil data. The rotating fan blade lift characteristics are shown to be distinct from the comparative 2D airfoil trends. At low-flow (off-design) operating conditions, rotation establishes large radial flow movements, and the high blade solidities cause standing vortices to develop within the rotating blade passages. The radial outflow energizes the blades' boundary layers, and the vortices inhibit the flow from separating from the blades' surfaces. Consequently, blade stall is avoided and high lift coefficient values are realized. The presented fan blade lift characteristics are unique relative to literature on other turbomachines of lower blade solidity, highlighting the importance of considering solidity effects in implicit rotor model developments.

Effect of rotor blade position on Vertical Axis Wind Turbine performance

In this paper a numerical study is presented with the aim of evaluating the performance output of three Vertical Axis Wind Turbine (VAWT) configurations. Here using Computational Fluid Dynamics (CFD) a two-dimensional Multi Reference Frame (MRF) approach has been used to perform steady state simulations. For this purpose an inlet velocity of 4m/s has been used along with rotor blade tip speed ratios (λ) in the range of 0 to 0.6. The effects of varying rotor blade position on the global and local flow fields have been quantified. Furthermore, the influence of rotor blade position on performance has been computed. It has been found that within a typical rotor blade passage, maximum torque is obtained at a unique rotor angle. It can be seen that the torque output of the turbine decreases with an increase in rotor tip speed ratio (λ) for all rotor blade positions. From the data obtained it can be concluded that the VAWT power curve characteristics vary with relative rotor blade position.

Surface Characterization of Metallic Materials in the Case of the Turning Process of NiTi Alloy.

A study was made of the machinability of NiTi alloy in turning, under conditions resulting in a small cutting layer. The experiment involved cutting with variable feeds ranging from 0.01 to 0.1 mm/rev. The cutting conditions were carefully chosen, considering the rounding radius of the cutting edge. The machined surface was examined and measured in 3D using a confocal microscope and in 2D with a contact profilometer. These measurements were used to estimate hmin, leading to the development of a surface formation model that considers both the lateral material flow due to hmin and the lateral material flow due to altered thermodynamic conditions from the previous blade pass. A method for evaluating the surface and selecting its characteristics was proposed based on analyses derived directly from surface features: PCA (Principal Component Analysis) and EMD (Empirical Mode Decomposition) with the Hilbert transform (Hilbert-Huang transform). PCA analysis facilitated the examination of individual surface component variances, while analysis of the IMF components enabled the assessment of surface component energy combined with instantaneous frequencies.

Experimental Investigation of Additional Loss Associated With Incoming Wakes in Low-Pressure Turbine Cascades

Abstract The present paper aims to experimentally investigate the influence of wake-passing frequency, Reynolds number, and suction surface diffusion rate on the additional loss due to incoming wakes to the profile loss in the low-pressure turbine (LPT) cascades and discuss a design guide for reducing the additional loss. Using a moving-bar mechanism, the unsteady effects of incoming wakes were measured in a low-speed linear turbine cascade facility. The wake-passing frequency was varied by adjusting the moving-bar speed. The different airfoils with different surface velocity distributions were tested to examine the effect of suction surface diffusion rate. For each test case in an unsteady flow condition, the additional loss due to incoming wakes was derived by subtracting the profile loss from the measured total pressure loss across the cascade. Here, the profile loss was estimated by using the friction drag force, which was calculated by the measured surface velocity distribution, and the pressure drag force, which was calculated by the measured surface pressure distribution and the predicted base pressure. The resultant additional loss includes all kinds of losses associated with incoming wakes, such as mixing loss of incoming wakes enhanced in the blade passage and unsteady interaction loss between incoming wakes and surface boundary layers. It was demonstrated that in an unsteady flow condition, a substantial performance improvement was obtained in the entire Reynolds number range by applying the surface velocity distribution with no laminar separation to a low-solidity blade row.