Search

Background: Cardiac functions and support modes of left ventricular assist device (LVAD) will influence the pump inner flow field and blood damage potential. Methods: Computational fluid dynamics (CFD) method and lumped-parameter-model (LPM) were applied to investigate the impacts of cardiac functions under full (9000 rpm) and partial (8000 rpm) support modes in an axial pump. Results: The constitution of hemolysis index ([Formula: see text]) in different components of the pump was investigated. [Formula: see text] was found to be more sensitive to positive incidence angles ([Formula: see text]) compared with negative incidence angles in rotors. Negative incidence angles had little impact on [Formula: see text] both in rotors and the outlet guide vanes. The improved cardiac function made only a minor difference in [Formula: see text] (estimated average [Formula: see text] in one cardiac cycle) by 9.88%, as the flow rate expanded mainly to higher flow range. Switching to partial support mode, however, would induce a periodic experience of severe flow separation and recirculation at low flow range. This irregular flow field increased [Formula: see text] by 47.97%, remarkably increasing the blood damage potential. Conclusion: This study revealed the relationship between the blade incidence angle [Formula: see text] and [Formula: see text], and recommended negative-incidence-angle blade designs as it yielded lower [Formula: see text]. Moreover, to avoid flow range below 50% of the design point, careful evaluations should be made before switching support modes as weaning procedures in clinical applications.

The total temperature and pressure are measured as inter-stage data in axial compressor experiments. Traditional diagnosing methods of 0-dimension (0D) or 1-dimension (1D) could lead to higher errors at hub sections without the presence of the radial equilibrium equation at stator leading edges, and 3-dimensional computational fluid dynamics can hardly provide reliable results for multistage compressors. In this paper, a fast method called “Diagnosis Using Inter-stage Data” (DUID) was developed to convert experiment data into meridional flow fields, which automatically satisfies the radial equilibrium equation and provides more accurate results for axial compressors. An aeroengine fan, a 3-stage compressor and a 6-stage compressor were used to validate the DUID. Their meridional flow fields, which cannot be observed directly in test rigs, were rebuilt. Results reveal facts that hub static pressures are approximately 15% lower than the traditional 0D/1D constant assumption. Though the stator models determine the loss ratio in a single stage, the DUID can avoid the model error amplification and be robustious for multistage compressors. And the generated flow field is sensitive to changes in the total temperature. Analyses of the experiment flow fields provide more quantitative and accurate references for subsequent modifications. In conclusion, using experiment inter-stage data, the DUID can rebuild meridional flow fields, which help to improve data processing accuracy.

Tip leakage flow is an important factor affecting the efficiency and stability of compressors. It is important to study the tip leakage flow model in the design and performance prediction process of turbomachinery. This work analyzes the existing tip clearance loss prediction model and refines it to predict the tip clearance loss considering more blade geometric parameters. After analyzing the Yaras tip leakage loss model derivation process, it is found that the discharge coefficient (taken as constants by Yaras) will change with the gap geometry, namely, it is related to the maximum thickness and the gap size of the blade. In this paper the discharge coefficient of tip gap is revised to better predict the effect of gap loss with regard to the maximum thickness of the blade. In this paper, the research objects are linear cascades with NACA65 profile and numerical experiments were carried out by a CFD package Numeca under the condition of Mach number equal to 0.45, where the variables are the gap sizes (1%, 2%, 3%, 4%, 6% of the axial chord length) and the maximum thickness of blades (3%, 5%, 7%, 9%, 11% of the axial chord length). Combined with the numerical calculation results, according to Yaras loss prediction formula and using the similar characteristics to the discharge coefficient of the variation trend and the Planck blackbody radiation formula, the relationship between the discharge coefficient and the maximum thickness of the blade and the tip clearance is summarized, which is integrated with the Yaras loss prediction formula to obtain the final formula. This prediction formula fits the NACA65 blade calculation fairly. The average error of 24 calculation points is 2.59%. Then the improved model was compared with several existing models. Besides the CDA062, C4 and polynomial thickness distribution blade tip clearance loss is predicted using the refined prediction formula and the biggest prediction error is 5.46%. Therefore, the improved formula still has a good prediction effect when the blade type change. It is considered that within a certain range of maximum thickness of the blade type and tip gap sizes, the improved formula can give good predictions even though the blade type is different.

At present, researches on the discharge coefficient of the combustion chamber cooling holes are mostly based on the experimental study of the porous plates considering various geometric structures under different flow conditions. In this method, the average discharge coefficients of multiple holes are obtained. Since the discharge coefficient will be applied to the numerical simulation, it is important to obtain an accurate formula for each cooling hole. Therefore, the discharge coefficient will be associated with some local aerodynamic parameters around the cooling holes and geometric parameters of the cooling holes. In this paper, the geometric parameters consist of length-to-diameter ratio (L/d) and inclination angle (α). The aerodynamic parameters cover the Mach number of cooling flow and mainstream (Mac, Mam), characterizing the flow feature, and the pressure ratio (π) which associates the cooling flow with the mainstream. The purpose of this paper is to study the discharge coefficient of a single circular hole with variable geometries under a cold condition of a combustion chamber, which has low crossflow and low-pressure ratio on both sides of the hole. In this environment, according to the research results, the discharge coefficient is sensitive to the cooling flow Mach number, length-to-diameter ratio and pressure ratio (π ≈ 1.05). Discharge coefficient decreases with L/d linearly, conforms the quadratic function with Mac and changes complexly at π ≈ 1.05. Other parameters have little effect on the discharge coefficient. The data for discharge coefficient of the cylindrical hole considering different parameters is obtained through numerical simulation and the correlations summarized by these data are valid for the following ranges: L/d = 3∼12, α = 20°∼45°, Mac = 0.05∼0.15, Mam = 0∼0.1, π = 1.05∼1.15. Compared with the CFD data, the prediction formula has a maximum error of less than 3% and a mean absolute error of 0.78%.

Through-flow methods are widely used in turbomachinery design and performance prediction due to its fast calculation. In the past, circumferentially-averaging through-flow methods tended to ignore circumferential fluctuation source term (CFST) in the governing equations, leading to an inaccurate result when blades showed a strong three-dimensional feature. To solve this problem, CFST needs to be properly modeled. In this paper, three-dimensional numerical simulation is conducted to find the area where CFST dominates. The influence of inlet Mach number, incidence, camber angles and sweep angle on the CFST in this area is analyzed. A model for CFST is constructed. Three-dimensional verification of this model suggests that within the common scope of use of aerospace compressor designing, this model shows a good accuracy.

The seal cavity leakage flow has a considerable impact on the performance of the aeroengine, especially on the multistage compressor. Thus, a quasi-three-dimensional simulation program named CAM is developed basing on circumferentially averaged throughflow method. The program enables a rapid diagnosis for the performance degradation of multistage compressor caused by labyrinth wear. The coupling flow field between the seal cavity leakage flow and the main flow field at the root of the shrouded stator of a high-loading three-stage compressor with inlet guide vanes (IGV) was simulated by CAM and the results indicate that seal cavity leakage flow has a significant impact on the overall performance of the compressor. That is, for a 1% increase in the seal-tooth clearance-to-span ratio, the decrease in total pressure ratio was 2.6%, and the reduction in efficiency was 0.6%. Stage performance shows that the seal cavity leakage flow reduces the pressurization capacity of the current stator and the work capacity of the downstream rotor, but has little effect on the upstream blade row. Spanwise distribution of blade element performance shows that the leakage flow leads to an increased flow blockage near the hub, resulting in spanwise migration. The incidence of the stator and rear rotor then change through the entire span. The leakage flow leads to the flow blockage and migration and hence changes the incidence angle, which results in the deterioration of compressor performance.

The strategy of sweep design should be based on the inner flow field of the compressor. In this paper, a transonic centrifugal compressor within the splitter is discussed in detail, and both forward sweep and backward sweep are studied with numerical simulation for optimization. Splitter introduces extra leakage and it’s worth noting that the high-entropy region is shifted from the suction side of the main blade to the suction side of the splitter. Different from the transonic axial rotor, the leakage of the main blade mainly occurs after the passage shock and will be mixed with the leakage of the splitter in the suction side of the splitter. Therefore, the flow control on the middle and rare part of the compressor is more essential for the performance of the stage. In this regard, the backward sweep of the main blade exhibits a good effect by reducing the mixing loss of secondary leakage. Due to the redistribution of the airflow, the mainstream velocity in the tip area is accelerated in the forepart and reduced in the rare part, the aerodynamic loss in the high-entropy zone is then improved, and the flow capacity of the compressor is also increased. The best performance is achieved by an 8° backward sweep for the centrifugal compressor in this work, the pressure ratio is increased by 2.84% and isentropic efficiency is increased by 1.40%, compared to the prototype.

The gaps between the blades and the shroud (or hub) of an axial blood pump affect the hydraulics, efficiency, and hemolytic performance. These gaps are critical parameters when a blood pump is manufactured. To evaluate the influence of blade gaps on axial blood pump performance, the flow characteristics inside an axial blood pump with different radial blade gaps were numerically simulated and analyzed with special attention paid to the hydraulic characteristics, gap flow, hydraulic efficiency, and hemolysis index (HI). In vitro hydraulic testing and particle image velocimetry testing were conducted to verify the numerical results. The simulation results showed that the efficiency and pressure rise decreased when the gap increased. The efficiency of the axial blood pump at design point decreased from 37.1% to 27.1% and the pressure rise decreased from 127.4 to 71.2 mm Hg when the gap increased from 0.1 to 0.3 mm. Return and vortex flows were present in the outlet guide vane channels when the gap was larger than 0.2 mm. The HI of the blood pump with a 0.1 mm gap was 1.5-fold greater than that with a 0.3 mm gap. The results illustrated poor hydraulic characteristics when the gap was larger than 0.15 mm and rapidly deteriorated hemolysis when the gap was larger than 0.1 mm. The numerical and experimental results demonstrated that the pressure rise, pump efficiency, and scalar shear stress decreased when the gap increased. The HI did not strictly decrease with gap increases. The preliminary results encourage the improvement of axial blood pump designs.

In this paper, the effect of the rotor–stator axial spacing is investigated in an axial pump with the working fluid of water. The pressure-rise performance was tested at a range of flow rates. Results indicate that decreased axial spacing generates improved hydraulic head, especially when the flow rate is low. Particle image velocimetry measurement was performed and flow fields for five rotor phases were obtained in a low flow rate condition. Particle image velocimetry results demonstrate that the stator inlet flow is both affected by the wake of the rotor and the existence of the stator. As the axial spacing gets close, the incidence angle of the stator decreases and the flow separation on the suction side is restrained, and therefore the pressure rise ability is improved.

Short rotor–stator axial spacing has been demonstrated to be beneficial to the aerodynamic performance of subsonic compressors. In this paper, it is further verified that this benefit partly originates from the improvement of the rotor blade lift. A tiny axial pump is investigated both numerically and experimentally with three different rotor–stator axial spacings. The time-accurate simulation indicates that both the peak and average rotor blade lifts are enhanced as the axial spacing decreases. The potential field of the downstream stator has significant effects on the pressure distribution in the rotor when the blade rows get close. The two-dimensional (2D) PIV measurement demonstrated that short axial spacing generates high circulation around the rotor blade due to the flow tube compression, which contributes to the blade lift improvement. Besides, close blade-rows axial spacing generates enhanced unsteadiness for the inlet flows of the downstream stator, which should be taken into consideration in the design process.

Through-flow method is still widely applied in the revolution of the design of a turbomachinery, which can provide not merely the performance characteristic but also the flow field. In this study, a program based on the through-flow method was proposed, which had been verified by many other numerical examples. So as to improve the accuracy of the calculation, abundant loss and deviation models dependent on the real geometry of engine were put into use, such as: viscous losses, overflow in gaps, leakage from a flow path through seals. By means of this program, the aerodynamic performance of a certain high through-flow commercial fan/booster was investigated. On account of the radial distributions of the relevant parameters, flow deterioration in this machine was speculated. To confirm this surmise, 3-D numerical simulation was carried out with the help of the NUMECA software. Through detailed analysis, the speculation above was demonstrated, which provide sufficient evidence for the conclusion that the through-flow method is an essential and effective method for the performance prediction of the fan/booster.

Three compressors with fore-loaded, uniformly loaded and aft-loaded rotor blades are designed via streamline curvature method coupled with blade generation that uses arbitrary camber lines so as to study the effect mechanism of rotor axial blade loading distributions on compressor performance. The rotor blade loading design is achieved by modifying the flow circulation in the rotor region on the basis of ensuring the total rotor work unchanged during the through-flow solving. Based on global linear stability analysis, a stall inception prediction model is established and integrated into the compressor design process as an assessment tool of flow stability. The predicted stall inception of the fore-loaded compressor validates the model precision by comparing with experimental measurements. Steady numerical simulations show that the pressure rise and efficiency of aft-loaded compressor are the best at the mass flow rates less than design point, followed by the uniformly loaded compressor, and those of the fore-loaded compressor are the worst. Steady blade loading analysis indicates that the peak loading positions of the three types of rotors move towards the leading edge accompanying with the throttling process. The comparison of predicted stall inception points among the three compressors presents that the fore-loaded compressor is the first to enter instability state, followed by the uniformly loaded compressor, while the aft-loaded compressor is the last. The steady and unsteady flow fields show that the maximum tip loading of rotor and stator blades becomes larger at the near-stall point as the rotor becomes more fore-loaded. This finding combined with the unsteady tip clearance flow explains the flow stability distinction of the three compressors to some extent.

The current paper presents experimental and computational results to assess the effectiveness of non-axisymmetric endwall contouring in a compressor linear cascade. The endwall was designed by an endwall design optimization platform at 0o incidence (design condition). The optimization method is based on a genetic algorithm. The design objective was to minimize the total pressure losses. The experiments were carried out in a compressor cascade at a low-speed test facility with a Mach number of 0.15. Four nominal inlet flow angles were chosen to test the performance of non-axisymmetric Contoured Endwall (CEW). A five-hole pressure probe with a head diameter of 2 mm was used to traverse the downstream flow fields of the flat-endwall (FEW) and CEW cascades. Both the measured and predicted results indicated that the implementation of CEW results in smaller corner stall, and reduction of total pressure losses. The CEW gets 15.6% total pressure loss coefficient reduction at design condition, and 22.6% at off-design condition (+7o incidence). And the mechanism of the improvement of CEW based on both measured and calculated results is that the adverse pressure gradient (APG) has been reduced through the groove configuration near the leading edge (LE) of the suction surface (SS).

The circumferentially averaged equation of the inlet flow radial equilibrium in axial compressor was deduced. It indicates that the blade inlet radial pressure gradient is closely related to the radial component of the circumferential fluctuation (CF) source item. Several simplified cascades with/without aerodynamic loading were numerically studied to investigate the effects of blade bowing on the inlet flow radial equilibrium. A data reduction program was conducted to obtain the CF source from three-dimensional (3D) simulation results. Flow parameters at the passage inlet were focused on and each term in the radial equilibrium equation was discussed quantitatively. Results indicate that the inviscid blade force is the inducement of the inlet CF due to geometrical asymmetry. Blade bowing induces variation of the inlet CF, thus changes the radial pressure gradient and leads to flow migration before leading edge (LE) in the cascades. Positive bowing drives the inlet flow to migrate from end walls to mid-span and negative bowing turns it to the reverse direction to build a new equilibrium. In addition, comparative studies indicate that the inlet Mach number and blade loading can efficiently impact the effectiveness of blade bowing on radial equilibrium in compressor design.

Pump thrombosis potential exists in most blood pumps and limits their clinical use. To improve the pump thrombosis performance of blood pumps, a method for emulating the platelet deposition on the flow passage component surfaces inside blood pumps was presented and tested. The method emulates the blood platelet deposition, employing laser-induced fluorescence tracing technology. The blood pump was rotated in a mock circulation loop with deionized water filled with fluorescent particles. The component surfaces were then explored via laser. The fluorescent particles were induced by laser and imaged in a charge-coupled device (CCD) camera to show the distribution of fluorescent particles gathering on the blood pump component surfaces. The activated platelet deposition was emulated by fluorescent particle gathering. The experiment showed obvious particle gathering on the interface surfaces and cross-sectional surface (perpendicular to the flow). This platelet deposition estimation (PDE) method can be easily incorporated in the in vitro testing phase to analyze and decrease a pump's thrombosis potential before animal experimentation, thereby reducing the cost of blood pump development. This methodology of emulating blood platelet deposition indicates its potential for improving flow passage component structure and reducing device thrombosis of blood pumps.

The axial blood pump body primarily contains the Inlet Guide Vane (IGV), Rotor Impeller (RI), Outlet Guide Vane (OGV) and pump casing. There must be gaps between rotor blade tip and pump casing or between OGV blade root and rotor hub for the impeller rotating in the pump. The flow characteristics inside an axial blood pump with different blade gaps were numerically simulated and analyzed. Hydraulics experiments were conducted to verify the numerical results. The results show that the pump efficiency decreased slowly when the OGV blade gap increased from 0.1 mm to 0.3 mm, but quickly when the rotor blade gap increased from 0.1 mm to 0.3 mm. The hydraulics characteristic results indicate that the pressure rise and efficiency are mainly influenced by the rotor blade gap. The OGV blade root gaps have little influence on the decrease of pressure rise and efficiency. The novel configuration with uneven blade gaps inside the pump result in improved hydraulics and hemolytic performance compared with the similarly sized configuration with even blade gaps.

A fully implantable axial left ventricular assist device LAP31 was developed for Chinese or other heart failure patients who need partial support. Based on the 5-Lpm total cardiac blood output of Chinese without heart failure disease, the design point of LAP31 was set to a flow rate of 3 Lpm with 100-mmHg pressure head. To achieve the required pressure head and good hemolytic performance, a structure that includes a spindly rotor hub and a diffuser with splitter and cantilevered main blades was developed. Computational fluid dynamics (CFD) was used to analyze the hydraulic and hemodynamic performance of LAP31. Then in vitro hydraulics experiments were conducted. The numerical simulation results show that LAP31 could generate a 1 to 8 Lpm flow rate with a 60.9 to 182.7 mmHg pressure head when the pump was rotating between 9,000 and 12,000 rpm. The average scalar shear stress of the blood pump was 21.7 Pa, and the average exposure time was 71.0 milliseconds. The mean hemolysis index of LAP31 obtained using Heuser's hemolysis model and Giersiepen's model was 0.220% and 3.89 × 105% respectively. After adding the splitter blades, the flow separation at the suction surface of the diffuser was reduced. The cantilever structure reduced the tangential velocity from 6.1 to 4.7–1.4 m/s within the blade gap by changing the blade gap from shroud to hub. Subsequently, the blood damage caused by shear stress was reduced. In conclusion, the hydraulic and hemolytic characteristics of the LAP31 are acceptable for partial support.

The circumferential fluctuation (CF) source terms induced by the inviscid blade force can affect the inlet distribution of flow parameters and radial equilibrium of swept and bowed blades. However, these phenomena cannot be adequately described by throughflow methods based on the axisymmetric assumption. A transport model for the CF stresses is proposed and correlated to the distribution of circulation to reflect the effect of the inviscid blade force. To investigate the effect of the inlet CFs on swept and bowed blades, the model is integrated into a throughflow model and applied to a series of cascades with different sweep and bow angles. For swept cascades, the CF source terms change the distributions of incidence angles, as well as the radial equilibrium at the inlet of the blade passage. And the influence is enhanced as the absolute value of the sweep angle increases. For bowed cascades, the distributions of incidence angles are also altered. For both cases, the model can offer a good prediction of the inlet CF source terms, and prove to exert a better prediction of blade design key parameters such as flow angles.

The ventricular assist pumps do not always function at the design point; instead, these pumps may operate at unfavorable off-design points. For example, the axial ventricular assist pump FW-2, in which the design point is 5 L/min flow rate against 100 mm Hg pressure increase at 8,000 rpm, sometimes works at off-design flow rates of 1 to 4 L/min. The hemolytic performance of the FW-2 at both the design point and at off-design points was estimated numerically and tested in vitro. Flow characteristics in the pump were numerically simulated and analyzed with special attention paid to the scalar sheer stress and exposure time. An in vitro hemolysis test was conducted to verify the numerical results. The simulation results showed that the scalar shear stress in the rotor region at the 1 L/min off-design point was 70% greater than at the 5 L/min design point. The hemolysis index at the 1 L/min off-design point was 3.6 times greater than at the 5 L/min design point. The in vitro results showed that the normalized index of hemolysis increased from 0.017 g/100 L at the 5 L/min design point to 0.162 g/100 L at the 1 L/min off-design point. The hemolysis comparison between the different blood pump flow rates will be helpful for future pump design point selection and will guide the usage of ventricular assist pumps. The hemolytic performance of the blood pump at the working point in the clinic should receive more focus.

Adverse events caused by flow-induced thrombus formation around the bearing/shaft of an axial blood pump remain a serious problem for axial blood pumps. Moreover, excessive anticoagulation with thrombosis around the bearing potentially increases the risk of postoperative gastrointestinal bleeding. The purpose of this study is to analyze the influence of the bearing structure on the thrombosis potential of an axial blood pump. The bearing/shaft structure was embedded into an axial blood pump numerical model. The numerical simulation and analysis are focused on the low wall shear stresses, recirculation, and residence time close to the bearing region to evaluate the potential for thrombosis around the bearing. Then, the flow field near the blood pump bearing was tested via in vitro particle image velocimetry experiments to verify the numerical results. The simulation results showed that after embedding the bearing/shaft structure a recirculation zone appeared in the outlet guide vane bearing/shaft region, the residence time increased 11-fold in comparison to the pump without the bearing/shaft structure, the scalar shear stress in the shaft surface was less than 7.8 Pa, and the stress accumulation was less than 0.10 Pa s. The numerical results showed that platelets that flow through the bearing region are exposed to significantly lower wall shear stress and a longer residence time, leading to activated platelet adhesion. The reduced stress accumulation and increased time in the bearing region lead to increased platelet activation.

Multistage compressor’s experiment performance often differs from its numerical simulation, because the real flow field is much more complicated than the CFD’s assumption of steady and uniform cascade inlet flow. While CFD cannot provide a reliable prediction for multistage compressor, analyzing experiment’s data could possibly be the only way to directly diagnose the compressor’s flow field and performance. Using the testing data between rotors and stators, this program can solve the S2 stream surface field which is hard to directly observe in the compressor test rig. By calculating meridian field with experimental and formulated model, the solution reveals the essential performance parameter of each stage and each element such as flow coefficient, loading coefficient, efficient, etc. These solutions are the base of figuring out the weakest design of the compressor flow field, and the result reveals the subsequent modification quantitatively. Compressors performance can hardly reach the design goal without several such trial and error iterations.

The most progressive liner cooling technology for modern combustion chambers is represented by effusion cooling (or full-coverage film cooling), which is based on the use of several inclined small diameter cylindrical holes. However, as to simulation of the gas turbine combustion chamber, meshing of these discrete holes needs too much computer resource and demanding calculation time. The homogeneous boundary condition was attempted to apply in the throughflow method for the simulation of the full-scale combustion chamber. The verification of this uniform condition was performed through the model of two straight channels. Obtained results were compared with detailed LES simulations, highlighting well accordance and accurate flow structure around the plate. Furthermore, the modelling was used in the simulation of a loop combustion chamber with throughflow method on isothermal state. Performance characteristic and flow fields from this method were then contrasted with the details from the FLUENT simulation upon high geometric fidelity, and prove that the homogeneous boundary condition exerts a good prediction of the performance characteristics and flow field in the combustion chamber.

Swirl inlet distortion is usually encountered in modern flight vehicles since their inlet ducts usually consist of one or two bends, such as S-inlet duct. An experimental device is first designed to simulate the swirl inlet distortion and then used to test the effectiveness of a novel casing treatment (CT) on a low-speed compressor under the swirl distortions of various intensities. The influences of co- and counter-rotating swirl inlet distortion on the test compressor and the stabilization ability of this novel CT are well demonstrated by the illustrations of static pressure rise curves and efficiency curves. The dynamic prestall pressure signals are also captured to reflect the perturbation energy in the flow field through which the mechanism of the novel CT will be indicated. The relevant results show that counter-rotating swirl distortion in small intensity could increase the compressive ability of compressor with small efficiency loss, and the co-rotating swirl distortion always brings about detrimental effects on compressor performance. At the same time, the distortion of twin swirls can cause nonuniform total pressure profile which can seriously damage the compressor performance. Besides, the stall precursor-suppressed (SPS) CT shows a good capability of stall margin (SM) enhancement no matter what swirl inlet distortions are encountered in the test compressor.

This paper presents a numerical investigation of the potential aerodynamic benefits of using endwall contouring in a fairly aggressive duct with six struts based on the platform for endwall design optimization. The platform is constructed by integrating adaptive genetic algorithm (AGA), design of experiments (DOE), response surface methodology (RSM) based on the artificial neural network (ANN), and a 3D Navier–Stokes solver. The visual analysis method based on DOE is used to define the design space and analyze the impact of the design parameters on the target function (response). Optimization of the axisymmetric and the non-axisymmetric endwall contouring in an S-shaped duct is performed and evaluated to minimize the total pressure loss. The optimal ducts are found to reduce the hub corner separation and suppress the migration of the low momentum fluid. The non-axisymmetric endwall contouring is shown to remove the separation completely and reduce the net duct loss by 32.7%.

This paper presents comparative numerical studies to investigate the effects of blade sweep on inlet flow in axial compressor cascades. A series of swept and straight cascades was modeled in order to obtain a general understanding of the inlet flow field that is induced by sweep. A computational fluid dynamics (CFD) package was used to simulate the cascades and obtain the required three-dimensional (3D) flow parameters. A circumferentially averaged method was introduced which provided the circumferential fluctuation (CF) terms in the momentum equation. A program for data reduction was conducted to obtain a circumferentially averaged flow field. The influences of the inlet flow fields of the cascades were studied and spanwise distributions of each term in the momentum equation were analyzed. The results indicate that blade sweep does affect inlet radial equilibrium. The characteristic of radial fluid transfer is changed and thus influencing the axial velocity distributions. The inlet flow field varies mainly due to the combined effect of the radial pressure gradient and the CF component. The axial velocity varies consistently with the incidence variation induced by the sweep, as observed in the previous literature. In addition, factors that might influence the radial equilibrium such as blade camber angles, solidity and the effect of the distance from the leading edge are also taken into consideration and comparatively analyzed.

For a compressor stage, the mechanism of wake recovery leads the rotor wakes to decay in a reversible process through the stator passage. Based on this theory, the rotor-stator axial spacing is believed to be a significant factor bound up with the wake mixing loss. In this paper, the wake decay processes in a tiny axial pump with varied rotor-stator axial spacings are studied using particle image velocimetry (PIV) measurement. PIV results indicate that the rotor wakes interact with the stator blade and generate flow regions with elevated turbulence. This interaction is enhanced when the axial spacing is close. The attenuation process of the disturbance kinetic energy (DKE) and the relative wake depth demonstrate that the axial spacing significantly affects the proportion of the wakes that decay in the stator passage. Close rotor-stator axial spacing is proposed to increase the recovery rate of the rotor wakes. Supplementary CFD computation is conducted to certify that the experimental results are universal for pumps with and without splitters.

Throughflow method has the limitation inherited from the axisymmetric assumption. With this assumption, the effects induced by three-dimensional blade shaping, such as sweep, cannot be sufficiently described. To conquer these shortcomings, a transport model for the circumferential fluctuation (CF) stresses is developed and integrated into a throughflow model. Three subsonic rotors are selected to validate the transport model and investigate the effect of the CF source terms on the flow fields. The results show that the CF source terms can affect the prediction of mass flow, and redistribute the radial distribution of blade loading. Besides, the radial equilibrium at the inlet of the blade passage is also altered by the CF source terms. Moreover, the CF source terms may have different effects for different swept blades.

The outlet guide vane in a turbine rare frame plays a vital role in de-swirling the flow as well as load-bearing. This paper numerically simulates the performance of the single stage turbine with different airfoil profile design in the outlet guide vane. The result shows that the outlet guide vane with NACA65 profile has the best performance. The pressure growth in the suction side is steady and no obvious separation is found in the flow field.

For the axial fan used in air-assisted sprayer, it always requires a good outlet flow field. In addition to ensuring that the outlet flow field has sufficient dynamic pressure, it is also necessary to ensure that the outlet flow direction is close to the axial direction. In this paper, the influence of the profile load distribution and the solidity of the outlet guide vane on outlet flow field was studied with numerical simulation. The results indicates that increasing the solidity or using the fore-load distribution profile can effectively reduce the outlet flow angle, and result in increasing the spraying distance of the water droplet. This result can provide reference for the design of the guide vane for axial fan used in air-assisted sprayer.

This paper conducts an experimental research of rotating inlet distortion on a low-speed large size test compressor with emphasis on the stability problem of axial fan/compressors, and the stall margin enhancement with a kind of stall precursor-suppressed (SPS) casing treatment. Some results on compressor stall margin and prestall behavior under the restriction of rotating inlet distortion are presented. The experimental results show that whether the inlet distortion is co-rotating or counter-rotating, the SPS casing treatment can still improve the stall margin without leading to additional efficiency loss caused by such configuration. The experiment results also show that the mechanism of the stall margin improvement with such casing treatment is associated with delaying the nonlinear development of the stall precursor waves and weakening the unsteady flow disturbances in a compression system.