Search

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.

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.

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.

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.

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.

A stall precursor-suppressed casing treatment is designed to enhance stall margin for both subsonic and transonic compressors. It is noted that the open area ratio of the stall precursor-suppressed casing treatment is only 4–10%, far smaller than conventional casing treatments, with over 50% open area ratio. The effect of the novel casing treatment on the stall margin and efficiency of compressors has been investigated experimentally. The results show that the stall precursor-suppressed casing treatment can improve the stall margin by about 8–18% without significantly decreasing the efficiency of the related fan/compressors. Meanwhile, the present investigation has also attempted to reveal the mechanism of stall margin improvement with such casing treatment. It is found that the stall precursor-suppressed casing treatment will delay the nonlinear development of the stall process by suppressing the propagation of the stall precursor waves, as compared with the evolution of the precursors without casing tre...

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.

A 15-stage axial-flow compressor utilized in steel industry was studied in this paper. All the stator’s stagger angles of the compressor are variable to ensure the multistage compressor operate effectively within a wide range of flow rate and meanwhile satisfy the demand for sufficient pressure ratio, adiabatic efficiency and stall margin. Three in all different base-settings of stator’s stagger angles were presented and commercial CFD software was applied to obtain the overall performance characteristics. The results showed that both of the optimized base-settings improved the performances both in summer and winter conditions, although the adiabatic efficiency was somewhat decreased. Taking incidence angle and stage loading into consideration, differences among the three cases were analyzed in detail. On the basis of numerical computations, the performance could be effectively improved through adjusting the base-setting of stator’s stagger angles.

Blood pumps have been adopted to treat heart failure over the past decades. A novel blood pump adopting the rotor with splitter blades and tandem cascade stator was developed recently. A particle image velocimetry (PIV) experiment was carried out to verify the design of the blood pump based on computational fluid dynamics (CFD) and further analyze the flow properties in the rotor and stator. The original sized pump model with an acrylic housing and an experiment loop were constructed to perform the optical measurement. The PIV testing was carried out at the rotational speed of 6952±50 r/min with the flow rate of 3.1 l/min and at 8186±50 r/min with 3.5 l/min, respectively. The velocity and the Reynolds shear stress distributions were investigated by PIV and CFD, and the comparisons between them will be helpful for the future blood pump design.

The advent of various technologies has allowed mechanical blood pumps to become more reliable and versatile in recent decades. In our study group, a novel structure of axial flow blood pump was developed for assisting the left ventricle. The design point of the left ventricular assist blood pump 25 (LAP-25) was chosen at 4 Lpm with 100 mm Hg according to our clinical practice. Computational fluid dynamics was used to design and analyze the performance of the LAP-25. In order to obtain a required hydraulic performance and a satisfactory hemolytic property in the LAP-25 of a smaller size, a novel structure was developed including an integrated shroud impeller, a streamlined impeller hub, and main impeller blades with splitter blades; furthermore, tandem cascades were introduced in designing the diffuser. The results of numerical simulation show the LAP-25 can generate flow rates of 3-5 Lpm at rotational speeds of 8500-10,500 rpm, producing pressure rises of 27.5-148.3 mm Hg with hydraulic efficiency points ranging from 13.4 to 27.5%. Moreover, the fluid field and the hemolytic property of the LAP-25 were estimated, and the mean hemolysis index of the pump was 0.0895% with Heuser's estimated model. In conclusion, the design of the LAP-25 shows an acceptable result.

A fully implantable, axial flow blood pump has been developed in our hospital. Both in vitro and in vivo tests showed that the hemolysis and thrombus characteristics of the pump were in an acceptable but not in an ideal range. Computational fluid dynamics (CFD) and in vitro test results showed that the pump worked at off-design point with a low hydraulic efficiency; CFD analysis also showed regions of reverse flow in the diffuser, which not only decreases the pump's hydrodynamic efficiency, but also increases its overall potential for blood trauma and thrombosis. To make a blood pump atraumatic and nonthrombogenic, several methods were taken to reach a final model of the optimized blood pump using CFD, which decreased the rotational speed from 9,000 to 8,000 rpm, and the design flow rate from 11 to 6 L/min. More significantly, the flow separation and recirculation in the diffuser region were eliminated, which mitigated the traumatic and thrombus effect on blood. The acceptable results of the numerical simulations encourage additional in vitro and in vivo studies.

This paper presents the relation between circumferential fluctuation and the geometric and flow parameters. The governing equations are derived by circumferentially averaging the three-dimensional (3D) Navier-Stokes equations. Different types of compressor cascades are simulated and the circumferential fluctuation terms are extracted according to the definition of circumferential average. Three different blade profiles are chosen, including CDA, C4 and NACA65 profile, respectively. The peak value of circumferential fluctuation terms often occurs at the leading or the trailing edge and increases as the radius grows. Meanwhile, the circumferential fluctuation terms exist at the inlet of the blade which can be accurately calculated. 0°, 15° and 30° camber angles are chosen to study the influence of camber angle. When the camber angle is smaller, the flow is more uniform and therefore, the value of circumferential fluctuation is lower. Different incidence angles are compared to discuss the relationship between circumferential fluctuation and incidence angle. For specific term of circumferential fluctuations, the distribution curves are different.Copyright © 2014 by ASME

This paper presents the design of a highly loaded transonic two-stage fan using several advanced three-dimensional blading techniques including forward sweep and “hub bending” in rotors and several bowed configurations in stators. The effects of these blading techniques on the performance of the highly loaded transonic two-stage fan were investigated on the basis of three-dimensional Navier-Stokes predictions. The results indicate that forward sweep has insignificant impact on the total pressure ratio and adiabatic efficiency of the fan. The throttling range of the fan is found to be improved by forward sweep because the shock in the forward swept rotor is expelled later upstream to the leading edge than that in the unswept one. Hub bending design technique increases the efficiency in the hub region of R1 due to the reduction of the low momentum zone in the hub region near the trailing edge. The stator vane design has a pronounced impact on the performance of the fan. The total pressure ratio, adiabatic efficiency, and stall margin of the schemes with the bowed vanes are increased significantly compared to the scheme with the straight vanes. The large corner stall in the straight S1 vane is reduced effectively by the bowed S1 vanes. Moreover, the strong corner stall in the straight S2 vane is fully eliminated by the bowed S2 vanes. Among the bowed vane schemes, the scheme with positive bowed (P. B.) hub and negative bowed (N. B.) tip vanes has the best efficiency and stall margin performances thanks to the superiority of the performance over the midspan regions of the bowed vanes.Copyright © 2011 by ASME

The heart failure patients supported by the mechanical rotary blood pumps have been validated and investigated in recent decades. A series of adult blood pumps have been investigated in our research group in the last several years and one of them is currently under clinical trials. This present paper aimed at analyzing a micro pediatric blood pump (MPBP) with Computational fluid dynamics (CFD) tool. MPBP is developed to assist the ventricular according to the practice of pediatric heart failure in Fuwai Hospital of Chinese Academy of Medical Sciences. The blade tip diameter of the MPBP is 10 mm. Some advanced structures proposed in our adult blood pumps were further improved in the MPBP and a cantilevered stator applied in the blood pump is a novel try. The results of the numerical simulation show that the MPBP can generate the flow rates of 0.74–3.21 lpm at the rotational speeds of 9,000–11,000 rpm, producing the pressure rises of 36.9–89.7 mmHg. The structural advantage, hydraulic performance and hemolytic property of the MPBP were analyzed in detail. Overall, the attempt of the cantilevered stator blade improved the performance of the blood pump effectively and the MPBP deserves a promising prospect.Copyright © 2011 by ASME

Purpose Various ventricular assist devices (VADs) have been developed for clinical use in recent years. The aim of a multidisciplinary research team at the Fuwai Hospital of the Peking Union Medical College is to design and develop an axial flow left ventricular assist device (LVAD) for adults. Methods Using Computational Fluid Dynamics (CFD), the inflow characteristics of the axial flow pump were analyzed. After CFD analysis, the axial pump was fabricated using a 5-axis, computer numerical control (CNC) milling machine. Performances of the pump both in vitro and in vivo were tested. Results This VAD, which was developed after numerous CFD analyses for the flow characteristics of the pump, is 58.5 mm long, 30 mm wide and weighs 120 g. The pump can deliver 5 lpm for pressures of 100 mmHg over 8500 rpm. The NIH value was 0.01 g/100 L. The hemolysis, which was evaluated in an in vivo test, was a bit higher than the normal value, but remained within an acceptable range. Conclusions Performance of the pump in vitro and in vivo was considered sufficient for an LVAD. Further design improvements are being undertaken in terms of hemolysis and thrombosis to improve the biocompatibility of the pump.

An experimental program was carried out to improve the flow uniformity/periodicity in a high speed compressor cascade. This program was motivated by recent compressor cascade testing conducted in the Virginia Tech high speed cascade wind tunnel, which was intended to experimentally evaluate the performances of optimized compressor stator blades. The tunnel facility was modified by adding tailboards and guide vanes as well as employing bottom wall suction. Their effects on flow periodicity were investigated through cascade testing on a modern compressor stator cascade with a large turning-angle of about 55°. The tests were conducted for different inlet Mach numbers at the same incidence angle. Experimental results show either the tailboards (always used with the guide vanes) or bottom wall suction can improve flow periodicity effectively, and when used in conjunction, they can help to further improve flow periodicity. Based on the improved tunnel facility condition, a typical series of cascade tests (loss and flow angle) on the modern compressor stator blades was performed. Experimental results show that the flow periodicity is excellent for low inlet Mach number around 0.6 and fairly good for high inlet Mach number about 0.9. This program has allowed the Virginia Tech high speed cascade wind tunnel to be used for cascade testing on modern-featured compressor blades, i.e., high speed and high turning.

The unsteady transition characteristics of rotating stall have been studied experimentally in a single-stage transonic axial compressor. Three tested conditions in the near design and below design speed range, at tip relative Mach numbers from 1.26 to 1.0, were performed. The characteristics of rotating stall were studied by its dynamic behavior on the scale of compressor circumference and also by the flow field details in the blade passage. The dynamic behavior was analyzed by the technique of successive frequency spectrum and the flow field details were studied through internal transient pressure patterns in the blade passage plotted by the dynamic pressure data measured on the compressor shroud. It has been shown that intermittent pre-stall perturbations are evident for all the tested speeds and distinct by the different time and length scale of their existence. These are also interpreted by the difference of pressure loading and shock structure visualized in the pressure plots in the blade passage during stall inception. The pre-stall perturbations, with rather scattered frequency spectra, grow into fully developed stall abruptly. Nevertheless, the frequency spectrum of rotating stall falls into constant fraction of the frequency of compressor rotation for all the tested conditions. The increasing trend of the amplitude of pressure oscillation of rotating stall while gathering at its frequency spectrum could be detected in the stage of stall inception. Based on these two observations, there is a possibility of warning the stall precursors even for the high speed transonic compressor like the one tested in this paper.Copyright © 1999 by ASME