Lower Total Pressure Loss Research Articles

Study of Circumferential Grooved Casing Treatment on Cascade Aerodynamic Performance

To explore the influence of circumferential grooved casing treatment on subsonic cascade performance, a numerical simulation of subsonic cascade was conducted. In contrast to traditional research on variable single parameters for casing treatment, this paper used the Latin hypercube sampling method to randomly sample multiple geometric parameters of casing treatment and compared many sample data with the total pressure loss of the cascade as a measurement standard. After selecting several typical cases of high and low total pressure loss cases for in-depth flow field analysis, it was found that casing treatment affects the strength and structure of the leakage vortex, thereby reducing the blockage of fluid in the passage of the cascade. Changes in the total pressure loss and in the margin of the cascade meant that casing treatment affected cascade performance. This prompted analysis of the correlation between the casing treatment parameters and total pressure loss of the cascade. The clearance height and groove depth had the greatest influence on the total pressure loss of the cascade.

Performance Investigation of a Large Turning Blade for Marine Gas Turbine Based on Experimental and Numerical Methods

Replacing the last-stage stator and the outlet guide vane of the low-pressure compressor of the marine gas turbine with a large turning blade can reduce the number of compressor blades and reduce the size and weight of marine gas turbines. At present, there are few studies on similar profiles, and it is necessary to verify the feasibility of this type of compressor profile with a large turning angle. The performance of this profile is investigated by combining experimental measurement with numerical simulation calculation. The analysis of the experimental and numerical results reveals that this profile has a large flow turning angle, a wide operating range, and low overall total pressure losses. The loss of the profile only suddenly increases at some large positive angles of attack due to the large separation of the suction surface. The results show that this profile can compress air and increase the turning ability at a low loss, and can play the role of both the original last-stage stator and the outlet guide vane. This research provides a reference for the design and analysis of marine gas turbines and guidance for the application of the blade to gas turbines in other fields.

Numerical Research on the Jet-Mixing Mechanism of Convergent Nozzle Excited by a Fluidic Oscillator and an Air Tab

Unsteady numerical simulations, coupled with the SST (Shear Stress Transport) k-ω turbulence model, were conducted to study the mixing-enhancement characteristics of the excited jet generated by the fluidic oscillator and the air tab in a single channel convergent nozzle with an inlet total pressure of 140–200 kPa. Compared with the steady air-tab jet, the sweeping jet generated by the fluidic oscillator has roughly the same penetration in the main flow, but it can induce streamwise vortices and planar vortices of larger scale and longer duration, which is beneficial to enhance jet mixing efficiency in the range of 1.0 DN (DN represents the diameter of the main nozzle outlet) downstream from the main nozzle. When x > 1.0 DN, the jet mixing is mainly dominated by the shear layer between the main jet and the ambient. As the sweeping jet suppresses the expansion of the main jet, which reduces the contact area between the main jet and the ambient, its mixing efficiency is less than that of the air tab in this region. With the increasing inlet total pressure of the fluidic oscillator, the influence range of the sweeping jet is increased, but its mixing efficiency does not increase significantly. In general, the fluidic oscillator can use a small jet flow (<5%) to achieve a high mixing efficiency (i.e., 60% at x = 2.0 DN) at the expense of low total pressure loss (<2.3%), which indicates that it has good engineering applicability.

The influence of mouth opening on pharyngeal pressure loss and its underlying mechanism: A computational fluid dynamic analysis.

Objective: During inspiration, mechanical energy generated from respiratory muscle produces a negative pressure gradient to fulfill enough pulmonary ventilation. The pressure loss, a surrogate for energy loss, is considered as the portion of negative pressure without converting into the kinetic energy of airflow. Mouth opening (MO) during sleep is a common symptom in patients with obstructive sleep apnoea-hypopnea syndrome (OSAHS). This study aimed to evaluate the effects of mouth opening on pharyngeal pressure loss using computational fluid dynamics (CFD) simulation. Methods: A total of four subjects who were morphologically distinct in the pharyngeal characteristics based on Friedman tongue position (FTP) grades were selected. Upper airway computed tomography (CT) scan was performed under two conditions: Mouth closing (MC) and mouth opening, in order to reconstruct the upper airway models. computational fluid dynamics was used to simulate the flow on the two different occasions: Mouth closing and mouth opening. Results: The pharyngeal jet was the typical aerodynamic feature and its formation and development were different from mouth closing to mouth opening in subjects with different Friedman tongue position grades. For FTP I with mouth closing, a pharyngeal jet gradually formed with proximity to the velopharyngeal minimum area plane (planeAmin). Downstream the planeAmin, the jet impingement on the pharyngeal wall resulted in the frictional loss associated with wall shear stress (WSS). A rapid luminal expansion led to flow separation and large recirculation region, corresponding to the interior flow loss. They all contributed to the pharyngeal total pressure loss. While for FTP I with mouth opening, the improved velopharyngeal constriction led to smoother flow and a lower total pressure loss. For FTP IV, the narrower the planeAmin after mouth opening, the stronger the jet formation and its impingement on the pharyngeal wall, predicting a higher frictional loss resulted from higher WSS. Besides, a longer length of the mouth opening-associated constant constrictive segment was another important morphological factor promoting frictional loss. Conclusion: For certain OSAHS patients with higher Friedman tongue position grade, mouth opening-related stronger jet formation, more jet breakdown and stronger jet flow separation might contribute to the increased pharyngeal pressure loss. It might require compensation from more inspiratory negative static pressure that would potentially increase the severity of OSAHS.

Influence of Spinner Shape on Droplet Impact over Rotating Spinners

Droplet impact affects water collection, which is the key to investigating the icing process on an aero-engine spinner. Different from a stationary spinner, droplet impact is affected by Coriolis acceleration and centrifugal acceleration on rotating aero-engine spinners, showing different impact dynamics. Based on the Eulerian method, using the rotating coordinate system we numerically investigated droplet impact characteristics on three different shapes of aero-engine spinners using ANSYS Fluent. The results indicate that the impact area covered all the windward surface on the conical spinner, and only covered the windward surface prior to the impingement limit of the elliptical spinner and the coniptical spinner. The sensitivity of water collection to inflow velocity declined in the order of coniptical the spinner, the elliptical spinner, and the conical spinner. In addition, the elliptical region could effectively improve aerodynamic performance, as shown in a lower total pressure loss through the spinner. This work is relevant to the anti-icing system of a rotating aero-engine spinner.

Film Cooling Performance Enhancement by Upstream V-shaped Protrusion/Dimple Vortex Generator

Film cooling is an effective technique to isolate the heat flux from high-temperature mainstream, but the counter-rotating vortex pair (CRVP) generated by the interaction between film jet and mainstream leads to serious jet-off and poor film coverage. To enhance film cooling performance, a v-shaped protrusion/dimple vortex generator is arranged at the upstream location of film hole for suppressing the CRVP. The flow and heat transfer characteristics of film cooling with four kinds of vortex generators, v-shaped protrusion vortex generator (VSPVG), v-shaped dimple vortex generator (VSDVG), anti-v-shaped protrusion vortex generator (AVSPVG) and anti-v-shaped dimple vortex generator (AVSDVG), are investigated in detail over the blowing ratio ranging from 0.5 to 1.5 by solving three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Realizable k-ε turbulence model. Results indicate that both the v-shaped vortex generators can generate additional anti-counter-rotating vortex pairs (ACRVP) to weaken the CRVP, while both the anti-v-shaped vortex generators will enlarge the CRVP. The arrangement of VSPVG or VSDVG is proved to enhance film cooling performance significantly, especially the VSPVG, which improves the adiabatic film cooling effectiveness by 82.3%, 187.9%, 157.7%, 162.2% and 145.2% respectively corresponding to the BR=0.5, 0.75, 1, 1.25 and 1.5 compared with Baseline case. Considering the total pressure loss, it is found that the enhancement of film cooling effectiveness comes at the cost of slightly increased total pressure loss. In further study, the effect of VSPVG height on film cooling performance is also discussed. It is observed that the adiabatic film cooling effectiveness increases with an increase of the height, and the total pressure loss also inescapably increases, but it is worth celebrating that compared with Baseline case, the higher film cooling effectiveness and lower total pressure loss coefficient is obtained when the height is lower than 0.15D.

Numerical investigation into the structural characteristics of a hydrogen dual-swirl combustor with slight temperature rise combustion

For decades, hydrogen has been identified as the most promising potential fuel to replace fossil fuels. In order to fully implement it and to promote the rationality of the design of hydrogen combustion chamber structure, it is very essential to understand the hydrogen/air combustion mechanism based on structural variations. The structural characteristics of a novel dual-swirl burner for hydrogen-air non-premixed combustion was studied numerically in this study. The influences of air distributions, swirling directions and nozzle configurations of the dual-swirl burner were studied, and the combustion performance was evaluated from various aspects. The numerical results showed that there was a trade-off between lower total pressure loss and the risk of fusing when considering air distribution strategies. The co-rotating swirl burner exhibited better uniformity of temperature distribution at the downstream of the combustor. The multi jet orifices showed superior penetration depth than the circular seam. Efficient and stable combustion could be achieved, which was beneficial to improve gas turbine efficiency and stable operation.

Aerodynamic design optimization of a bellmouth shaped air intake for jet engine testing purposes and its experiment based validation

Jet engine ground tests are carried out with bellmouth shaped air intakes in order to measure the mass flow rate and the inlet flow quantities while supplying the engine an undisturbed flow. Although there are a variety of design standards and academic guidelines for the design of bellmouths, they can be designed to reach a lower total pressure loss coefficient, a less disturbed radial velocity profiles for the engine and a less thickened boundary layer at the engine inlet. This enhanced design can be achieved with the help of optimization algorithms and computational fluid dynamics (CFD) computations thanks to the increasing average computational power and simplicity of the flow problem. In this study, a genetic algorithm based optimization method and a RANS solver under a commercial software platform are applied to find a bellmouth design with less loss and less disturbed flow. An elliptical bellmouth lip profile with a linear extension part is defined with parametrization and a wide range of parameter space is investigated during the design work. Optimum design candidates are presented comparatively regarding the design purpose. The selected design candidate is produced and tested for CFD validation.

Performance characteristics of flow in annular diffuser using CFD

Abstract An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 105. The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery (C p = 0.76) and a lower total pressure loss coefficient of (C L = 0.12) at a 17° swirl angle.

Performance characteristics of flow in annular diffuser using CFD

Abstract An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 105. The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery (C p = 0.76) and a lower total pressure loss coefficient of (C L = 0.12) at a 17° swirl angle.

Full Three-Dimensional Inverse Design Method for S-Ducts Using a New Dimensionless Flow Parameter

In this study, a new inverse design method is proposed for the full 3-D inverse design of S-ducts using curvature-based dimensionless pressure distribution as a target function. The wall pressure distribution in a 3-D curved duct is a function of the centerline curvature and the cross-sectional profile and area. A dimensionless pressure parameter was obtained as a function of the duct curvature and height of the cross-sections based on the normal pressure gradient equation. The dimensionless pressure parameter was used to eliminate the effect of the cross-sectional area on the wall pressure distribution. Full 3-D inverse design of an S-shaped duct was carried out by substituting the 3-D duct with a large number of 2-D planar ducts. The ball-spine inverse design method with vertical spins was coupled with the dimensionless pressure parameter as a target function for the design of the planar ducts. The inverse design process was performed in two steps. First, the height of each cross-section was considered constant, and only the duct centerline was allowed to be deformed by applying the difference between the dimensionless pressure on the upper and lower lines of symmetry plane. Then, a constant curvature was considered for each centerline in the equation, and the difference between the current and the target dimensionless pressure was applied to each upper and lower line of the planar sections to correct the heights of the 2-D planar sections, separately. The method was validated by choosing a straight duct as an initial guess, which converges to the target S-shaped duct. The results showed that the method is an efficient physical-based residual-correction method with low computational cost and good convergence rate. The 3-D wall pressure distribution of a high-deflected 3-D S-shaped diffuser was modified to eliminate the separation, secondary flow, and outlet distortion. Finally, the geometry corresponding to the modified pressure was obtained by the proposed 3-D inverse design method, which revealed higher pressure recovery, lower total pressure loss, and lower outlet flow distortion and swirl angle.

An efficient approach to temporarily separate foulants using hydrocyclone with reflux function for thermal energy recovery from sewage

For municipal sewage, recoverable potential of thermal energy is at least 6–8 times higher than that of chemical energy, which is usually treated as the only recoverable energy in sewage. Accordingly, the sewage source heat pump with de-foulant hydrocyclone with reflux function was proposed and studied experimentally and numerically. To date, however, effect of the Pressure Difference between Overflow Outlet and Reflux Inlet (PDOORI) on its performance is not studied. Considering the significant influence of back pressure on performance of hydrocyclone, in this study, streamwise-periodic flow boundary, Reynolds Stress Model with low-Re stress-omega model, and Discrete Phase Model were utilized to numerically verify its feasibility under different PDOORI, which is caused by depressurization effect of the heat exchanger and pipeline and pressurization effect of the back water pump. Results indicate that, compared with designs of variable underflow diameter, optimizing the PDOORI can markedly enhance the de-foulant performance without increasing blockage risk of underflow, thereby improving the Coefficient Of Performance of sewage source heat pump. As a result, the recoverable potential of thermal energy in sewage will increase, and hence the amount of carbon emissions will decrease. Unlike the conventional hydrocyclone without reflux device, which is similar to a Y-shape branched pipe network, the de-foulant hydrocyclone with reflux function is similar to a loop pipe network. Therefore, effects of the pressure drop ratio on their pressure distribution, velocity distribution, and separation performance are different, even opposite. The optimum pressure drop ratio of the de-foulant hydrocyclone with reflux function is 82.14%–88.50%, which is markedly lower than that of the conventional hydrocyclone without reflux device (119.3%–135.3%). Because only at this moment, the small split ratio (6.49%–18.05%), high separation efficiency (83.00%–86.18%), and low total static pressure losses (hydrocyclone without reflux device: 1.39–1.55 kPa; hydrocyclone with reflux device: 1.99–2.25 kPa) can be simultaneously achieved.

Structural and thermal analysis on oblique detonation influenced by different forebody compressions in hydrogen-air mixtures

Various oblique detonation waves (ODW) structures have been investigated with the application background of ramjet engine, but effects of forebody compression have attracted little attention before. Two forebody compression models, the ESS (equal-strength-shock) compression and the SI (shock-isentropic) compression, have been introduced to study their effects on the ODW structure and thermal performance. Numerical results demonstrate that the compression method influences the ODW structure obviously, including the initiation location and the OSW–ODW transition type. Compared with the ESS compression, the SI compression leads to the downstream movement of initiation location, and the transition prefers to be abrupt rather not smooth. On the thermal features, the total pressure recovery is used to analyse the difference as the key parameter on the potential of engine impulse. The ESS compression corresponds a low total pressure loss when considering only the combustion process, while the SI compression performs better when considering the inlet–combustion whole process. Analysis on total pressure recovery gives the average total pressure recovery with flight Ma, altitude, and wedge angle. It is pointed out the SI compression has two shortcomings, including a long initiation length and a low total pressure recovery of combustion process, which should be considered in the future application.

Enhancement of pollutants hydrocyclone separation by adjusting back pressure ratio and pressure drop ratio

To solve the long-term restrictions on the development of hydrocyclones (i.e., underflow diameter is difficult to flexibly and stably control, and underflow orifice and pipe are easy to be blocked), in 2017, researchers enhanced the hydrocyclone separation by using the underflow pumping to adjust the back pressure ratio, namely, ratio of the absolute underflow pressure to absolute overflow pressure. However, the effect of back pressure ratio may be affected by overflow pressure, whereas the pressure drop ratio, i.e., ratio of overflow pressure drop (pressure difference between inlet and vortex-finder outlet) to underflow pressure drop (pressure difference between inlet and underflow orifice), may be more reliable for monitoring the hydrocyclone-separation performance. Therefore, in this study, Discrete Phase Model and low-Re stress-omega Reynolds Stress Model, with which the near-wall sub-layer can be resolved, were employed to numerically and comprehensively compare their effects on the hydrocyclone-separation performance. Results indicate that, compared with back pressure ratio, pressure drop ratio is a more reliable parameter monitoring the hydrocyclone-separation performance. The reason is that, unlike the back pressure ratio, the effect of pressure drop ratio is basically not affected by the increase of overflow pressure. The optimum pressure drop ratio of the simulated hydrocyclone is within 119.3–135.3%. Because only at this time, the high separation efficiency (86.25–98.96%), small split ratio (0–16.07%), and the low total static pressure loss (2569.83–2951.58 Pa) can be simultaneously obtained. With increase of the pressure drop ratio, the split ratio linearly decreases, whereas the total static pressure drop decreases slower in general. This is consistent with the experimental results obtained by other researchers. The pressure drop ratio is proportional to the self-rotation speed of inertia-free particles in upper part of the hydrocyclone, whereas is inversely proportional to that in lower part of the hydrocyclone, especially that near the apex.

Role of the backward-facing steps at two struts on mixing and combustion characteristics in a typical strut-based scramjet with hydrogen fuel

Scramjet is one of the most promising propulsion systems for the new generation supersonic/hypersonic air-breathing flight vehicles. To achieve sufficiently high combustion efficiency and relatively low total pressure loss, developing a new strut is an attractive approach. In this study, we focus on the backward-facing steps and investigate the geometry parameters of the backward-facing steps of the two struts. In this work, Reynolds-averaged Navier-Stokes equation coupled with the one-step H2-air reaction finite-rate/eddy-dissipation model is adopted to simulate all the two-strut cases, then this code is validated by the available experimental data. Next, we investigate the effects of different lengths and heights of the backward-facing steps on the two-strut based scramjet performance. For cold flow, enhancing the length of the backward-facing step can promote partly the mixing process with few extra total pressure losses. Further, the mixing process is weakened with increasing the height of the backward-facing steps to certain content, meanwhile, the total pressure loss is increased. In terms of reacting flow, increasing the length enhances the combustion efficiency, whereas the total pressure loss relatively decreases and thereafter increases. Enhancing the height of the backward-facing steps makes the combustion efficiency relatively decreases and thereafter increases, moreover, the total pressure loss increases as a result.

Preliminary engine design and inlet optimization of the MULDICON concept

In this study, aspects of the propulsion design for a highly swept wing configuration with military application are presented. These include the design of the thermodynamic cycle and the automated optimization of the inlet geometry. First, the thermodynamic design process of a conventional turbofan engine is described, which is intended to meet the requirements of a generic UCAV configuration. In addition to the thrust requirements derived from the mission profile, other constraints such as maximum fuel consumption, available installation space and aerodynamic and structural limits dimension the model in preliminary design. The resulting engine data are used as boundary conditions for the CFD simulation of the associated engine intake. This CFD calculation is part of an optimization process chain for determining the inlet duct geometry with low total pressure loss and low engine visibility. In order to estimate the effects of the different total pressure losses on the mission fuel consumption, the results obtained using CFD calculations are fed back into the performance simulation. This allows quantifying the influence of the inlet geometry on the global engine parameter. Based on the investigations and obtained results, the final configurations for the engine and intake are selected.

A combined application of micro-vortex generator and boundary layer suction in a high-load compressor cascade

In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.

CFD Investigation on the Application of Optimum Non-Axisymmetric Endwall Profiling for a Vaned Diffuse

In order to improve the performance of a transonic centrifugal compressor stage, non-axisymmetric endwall profiling optimization was conducted for the diffuser under design condition, Artificial Neural Network (ANN) and Genetic Algorithm (GA) were used to execute the optimization with the objective of maximizing the isentropic efficiency of the compressor stage. The influence mechanism of non-axisymmetric endwall profiling on flow field and performance was discussed. Results show non-axisymmetric endwall profiling is an effective way to significantly reduce the flow loss in the diffuser. The total pressure loss of the diffuser decreases by 9.31% and 20.29% for NA0.70 and NA1.40 respectively. The profiled endwall suppresses the flow separation through accelerating the low-energy flow and reducing lateral pressure gradient. The corresponding high vorticity within the flow separation zone is reduced, which delays the formation and development of the flow separation. The diffuser becomes more fore-loaded, the overall blade loading is not affected, and the pressure ratio of the compressor stage is improved as well. At the outlet of the diffuser, the more uniform flow angle and much lower total pressure loss along spanwise are obtained. However, the backflow with high velocity gathering near the shroud of the diffuser makes the mass flow rate decrease and easily induce the stall, which results in the smaller operating range for both profiled endwall.

Study of the flow characteristics in multi-row vaned diffusers of a centrifugal compressor stage

The vaned diffuser has a significant impact on the performance and operating range of a centrifugal compressor stage, and multi-row vaned diffusers are applied to improve the compressor characteristics in this article. In order to validate the effectiveness of the present calculation method, the calculation results of the centrifugal compressor with the conventional diffuser have been verified by the experimental data. The simulation results reveal that, compared with the original model at design point, the isentropic efficiency increases by 2.8% and 4.1%, and the total pressure ratio increases by 1.9% and 3.4%, for the compressor stage with the two-row vaned diffuser and the three-row vaned diffuser, respectively. The models with multi-row vaned diffusers also give higher static pressure recovery coefficient and lower total pressure loss coefficient. A pressure gradient formed on vane suction surface near vane leading edge develops the flow separation in the conventional diffuser. The pressure gradient thus causes the secondary flow from hub to shroud on vane suction surface, aggravating the separation in the rear part of the conventional diffuser. The analysis of flow characteristics in diffuser passages also shows that using multi-row vaned diffusers can alleviate flow separation appearing in the diffuser passages.

Unsteady Study on the Effects of Matching Characteristic of Tandem Cascade on the Performance and Flow at Large Angle of Attack

To investigate the effects of matching characteristics of tandem cascade on the performance and flow at large angle of attack, the unsteady numerical simulation has been implemented. The influences of different turning angle ratio (TR) and chord length ratio (CR) of two blades and the relative angle of attack of rear blade (Delta) are analyzed. The numerical results indicated that the tandem cascade can obtain overall performance improvement including higher static pressure ratio and lower total pressure loss with the matching parameters in the range of TR=3~5, CR=0.5~1.2, and Delta=-15°~-5°. The separation on the front blade has more prominent impact than that on the rear blade, so the performance improvement of tandem cascade is significantly dependent on the reduction of front-blade separation and loss. Regarding the rear blade, the gap injection effect can periodically control the separation. Temporal and spatial analysis of the flow field shows that the optimal-performance cases generally have much smaller wake loss for both two blades, but the unsteady characteristics of the wake loss is more apparent than that of the poor performance cases.