Design Mass Flow Research Articles

Experimental and numerical the effect of cavitation detection on hydraulic performance of the centrifugal pump based on different geometrical configurations

The cavitation phenomena and its experimental evaluation of hydraulic pump performance are the subjects of this study. Both qualitative and quantitative assessments of a pump's flow structure were carried out. The unsteady flow in a pump with various impeller geometry characteristics was investigated numerically. In-depth examinations of the local flow parameters for the static pressure, pump head, vapour volume variation fraction, and pressure fluctuations in the time and frequency domains were conducted. The findings showed that the low-pressure region that closed the impeller eye close to the leading edge of the blade is where the cavitation phenomena takes place. Additionally, the results showed that the blade passing frequency (BPF) and the pump's rotational frequency (RF) are two significant dominant frequencies in the device. Furthermore, the numerical results show that modest cavitation occurred at the design mass flow for Z=3, 4, 5, 6, and 7 impeller blades.

Investigation of aerodynamic effects and dominant design variables of cavity squealer-tip in three-dimensional performance of a centrifugal compressor

Enhancing the performance of turbomachines has been a longstanding area of interest, with numerous geometry modification methods proposed in the literature. One such method, historically prevalent in turbines, is the cavity squealer tip. However, its application in compressors, particularly of the centrifugal type, remains relatively underdeveloped. This study employs the Taguchi method's L-9 orthogonal array as a sensitivity analysis (utilizing Design of Experiments) to investigate the impact of cavity squealer design variables on the performance of the NASA-CC3 compressor at three key operational points: choke, design, and near stall regions. Computational fluid dynamics is utilized to derive performance parameters, and various sets of design variables result in improvements across pressure ratio, isentropic efficiency, mass flow rate, and surge margin. Notably, a significant 20 percent enhancement in surge margin is achieved in one instance. The performance at the remaining operating points varies among the nine cases, with improvements observed in some areas and declines in others. Processing the data yields three optimal geometries, with the best configuration enhancing all performance parameters (0.59% for design mass flow rate and 2.20% for efficiency, maintaining a constant pressure ratio compared to the base). As anticipated, the optimal impellers exhibit reduced flow leakage compared to the baseline.

A design method of turboexpander-compressors based on multi-objective optimization applied to reverse brayton cycle

This paper presents a new design method for turboexpander-compressors used in air refrigeration. As a key component of the reverse Brayton cycle, the efficiency of the turboexpander-compressor significantly has an impact on the overall cycle performance. The expander section is optimized for multi-objective efficiency at different flow rates using the Imperialist Competitive Algorithm to achieve high performance across all operating conditions. Regarding achieving high utilization efficiency for output power from efficient expanders, the compressor section adopts combined methods involving the jet-wake model and parameter equations. The proposed design is validated through public models, computational fluid dynamics simulations and experiments. Simulations and analysis are conducted on test cases representing comprehensive operational scenarios for both the compressor and the expander, confirming that conclusions drawn based on this method align well with underlying theoretical principles. At the design mass flow, the expander efficiency is 89%, and the compressor utilizes the output power of the expander with an efficiency of 90%. Near the design flow, the expander efficiency is more than 85%, and the compressor utilizes the output power of the expander with an efficiency exceeding 80%. This paper presents a method for turboexpander-compressors applicable to air refrigeration cycles, which achieves a reduction in design costs and an improvement in efficiency under varying loads.

Passive flow control at impeller radial bend for stall delay in centrifugal compressors with fishtail pipe diffusers

This paper proposes a new strategy for extending centrifugal compressor stall margin through shroud passive flow control placed at the impeller radial bend. Relative to the usual leading-edge location, the radial bend presents fewer geometrical constraints for flow control devices and allows them to have potentially more impact on low-momentum flow structures that lead to stall. Two centrifugal compressors with fishtail pipe diffusers are chosen for study: a high-speed transonic design exhibiting diffuser stall and a low-subsonic design with exducer stall. Four passive flow control techniques placed on the impeller shroud at the radial bend are evaluated for each compressor, in terms of stall margin improvement and efficiency penalty at design mass flow, using unsteady RANS CFD simulations. These are circumferential groove, slots, impeller recirculation pipe and diffuser-impeller recirculation pipe. The results indicate that passive flow control at the impeller shroud radial bend can be significantly more effective than at the impeller leading edge. For each compressor, the flow mechanisms associated with stall initiation and its delay by the most effective studied flow control technique as well as the associated efficiency penalty are elucidated. The findings indicate that techniques having flow injection with high spanwise penetration and low relative streamwise momentum are most effective for delaying diffuser stall, while the opposite applies to exducer stall. The design point efficiency penalty is due to mixing/shear losses from the jet-in-cross flow phenomenon in the impeller and shear losses from flow redistribution in the diffuser.

Fuzzy-Genetic based Approach in Decision Making for Repair of Turbochargers using Additive Manufacturing

dditive manufacturing (AM) is an effective technology for repairing and restoring automotive components. However, the effectiveness of additive manufacturing technology in repair and restoration is highly influenced by several factors related to components and process. The objective of this paper is to improve the decision-making in repair and restoration of a turbocharger with AM. In this article, a Fuzzy-Genetic approach was presented as a decision-making tool for repairing a remanufacturable component. Fuzzy logic (FL) is deployed as the method to model the design parameters of a turbocharger, such as design complexity, failure mode, damage size, disassembleability, preprocessing, temperature, durability, pressure ratio and mass flow rate to model the relationship between the inputs and outputs using Mamdani model with their membership functions. Genetic algorithm optimization method was used to optimize the cost of the repairing process once the decision on whether the turbocharger was repairable was determined by the Fuzzy system. The FL approach applied rules affecting the process, the robustness and accuracy of the model increases with a higher number of rules. The work focuses on the dataset related to design information, which represents as a knowledge base for decision parameters on design optimization to automate repair process during remanufacturing. The results showed the effects of the design parameters on repairing and replacement decisions, and how the fuzzy model related the inputs to the outputs based on the generated rules. In conclusion, FGA method can be used to improve the repair and restoration process of a turbocharger through AM technology.

Performance enhancement of photovoltaic solar collector using fins and bi-fluid: Thermal efficiency study

This work exhibits a three-dimensional numerical investigation of a solar collector Photovoltaic Thermal (PV/T) bi-fluid based on the use of dual exchangers cooling with both water and air simultaneously. The effect of the absorber plate design and water mass flow rate (mf) of water and natural airflow has been studied according to the fins added to the system, which mainly includes a flat plate of aluminum attached to the tubes of aluminum. The objective is to analyze the effects of water mf fluctuating between 0.01 and 0.02 kg/s, fins location and number (from 20 to 40 fins), and changing solar irradiation values (100 to 1050 W/m2) on the flow structure and thermal efficiency of photovoltaic solar cells. The hybrid collectors studied are made of monocrystalline photovoltaic cells and an absorber plate of aluminum in the lower of the PV module. An evaluation was made between three configurations of bi-fluid (air and water) PV/T manifolds according to the number of fins. The first configuration is a hybrid PV/T system containing tubes without fins. The second configuration is a hybrid PV/T system containing tubes attached with 20 fins. The third configuration is a hybrid PV/T system containing tubes attached with 40 fins. The results confirm that the thermal efficiency of the PV/T system using (water and air) as a working fluid increase with increasing the number of fins (from 20 to 40 fins) and with increasing solar radiation (100 to 1050 W/m2), but it decreases a little with increasing mf of water (0.01 to 0.02 kg/s) by about 1.1%. For the mf of water equal to 0.01 kg/s, the thermal efficiency of the PVT system configurations 1, 2, and 3 are equal to 50.54%, 52.33%, and 54.25%, respectively. The optimal design for good cooling of the photovoltaic cells and higher yields of the hybrid collector is the third configuration with a water mf of 0.01 kg/s.

Understanding of tip clearance flow structure in high speed mixed flow compressor

This paper addresses the necessity to make a physical interpretation of a highly complex three-dimensional tip clearance flow field study for high-speed mixed-flow compressor having stage exit static pressure to inlet total pressure ratio of 3.8 with 39,836 rpm rotor speed. The four different tip configurations namely the constant (λ = 0.016 and 0.019) and variable (λ = 0.011 (inlet)-0.019 (exit) and 0.019 (inlet)-0.022 (exit)) tip clearances were numerically analysed using available experimental data-set. The numerical investigation reveals that in contrast to the classic jet-wake pattern, two anomalous velocity profiles formed at the impeller exit which results in pressure losses in the vaneless diffuser. Near the impeller inlet, the tip leakage flow rolls up to discrete tip leakage vortex structure for each tip clearance configuration. This results in the formation of a region of momentum deficit, recirculation zone, which gets weakened as it moves downstream. The tip clearance configuration is observed to profoundly influence the extent and vorticity of the tip leakage vortex. In the splitter blade passage, the tip leakage flow and Coriolis flow interact with passage flow, resulting in the formation of two secondary passage vortices that move downstream along the pressure and suction surface of the splitter blade. The tip clearance configuration directly influences the impeller exit jet-wake pattern by modulating the secondary passage vortices trajectory and vorticity. Moreover, off-design analysis for tip clearances λ = 0.016 and λ = 0.019, depict distinctive tip leakage vortex characteristics. When operating near the stall conditions (80% of design mass flow rate), λ = 0.019 exhibits bubble shape tip leakage vortex breakdown occurring near the impeller inlet. This result in a substantial change in the tip leakage vortex nature; expansion of the recirculation zone and early weakening of the vorticity in the tip leakage vortex. It is observed that vortex breakdown plays a vital role in characteristics of the passage flow field structure and compressor performance near the stall conditions.

On the Nature of Transonic Shock Buffet in an Axial-Flow Fan

Transonic buffet or self-sustained shock oscillation in transonic flow is not well-understood in fans and compressors. The present work is a numerical study of transonic buffet flow using a full-annulus model of a transonic fan—the NASA rotor 67. Firstly, results obtained with steady simulations are validated with experimental and numerical data available, and shock structures from these simulations are found to exhibit distinct features as seen in experiments. Unsteady Reynolds-averaged Navier–Stokes simulations are then carried out at two operating points—near design mass flow rate and toward stall—on the fan characteristic to capture transonic shock buffet. The unsteady simulations are able to capture necessary attributes of transonic buffet flow. Further, wave propagation in an unsteady flow solution featuring transonic buffet is investigated to understand the mechanism driving shock buffet in axial turbomachines. Upstream- and downstream-propagating pressure perturbation waves are observed on the blade suction surface within a buffet cycle, while only an upstream-propagating wave is seen on the blade pressure surface. The driving mechanism of transonic buffet in this turbomachine is elucidated through a feedback loop of the upstream- and downstream-propagating waves—qualitatively and quantitatively. Besides the streamwise pressure waves, circumferential pressure waves propagating at part speed of the rotor in the spinning direction and radially outward moving pressure waves of similar speeds on the blade suction and pressure surfaces are also detected as distinct features of buffet flow for this turbomachine.

The Effect of Impeller Tip Clearance on the Performance of a MGT Mixed Flow Compressor Stage Fitted with a Crossover Diffuser

Mixed flow compressor stage designs are becoming increasingly popular for use in Micro Gas Turbine (MGT) engines. Due to manufacturing constraints and structural considerations, such compressors typically feature unshrouded impeller designs. A numeric investigation of the effect of impeller-shroud tip clearance on the performance of a MGT mixed flow compressor stage fitted with a crossover diffuser is presented. Three baseline test compressors are designed using an in-house-developed application based on one-dimensional mean line theory. These cover a wide range of design mass flow rates, design speeds, and impeller meridional exit (mixed flow) angles. The performance of each of the test compressors are evaluated at an impeller-shroud tip clearance of 0.1 mm, 0.3 mm, and 0.6 mm. Commercial CFD software is used to verify the performance results of the various test compressor configurations. It is found that an increase in impeller tip clearance negatively impacts both compressor performance (total-to-total pressure ratio and efficiency) and choke margin. Conversely, stall margin increases with an increase in impeller tip clearance.

Experimental investigation on air-breathing continuous rotating detonation engine in the cavity-based combustor

In order to broaden the stable working range of air-breathing continuous rotating detonation engine and explore the influence of combustor configuration on the propagation characteristics of rotating detonation wave, the cavity-based annular combustor is introduced. Air-breathing rotating detonation engine experiments are conducted with non-premixed ethylene and air. A tri-propellant air-heater is used to imitate the outlet parameters of the intake of Ma4/20km. The designed mass flow is 1kg/s and the total temperature is 860K. The results show that the self-sustaining rotating detonation wave cannot be formed in the conventional annular combustor. The self-sustaining propagation of detonation wave is realized at the equivalent ratio of 0.62 to 0.72 in the cavity-based combustor, and the propagation velocity of which is about 900 m/s. It is demonstrated that the vortex zone in the cavity is conducive to the formation of rotating detonation wave, which can effectively broaden the stable working range of the engine. Feasibility of cavity-based annular combustor in rotating detonation engine is validated.

Numerical investigation on the combined effects of pinching and rotation on the performance of a high-speed centrifugal compressor with a vaneless diffuser

Computational investigations are carried out on a high-speed centrifugal compressor with the vaneless diffuser to study the combined pinch and rotation effect. The axial inlet width of the rotating vaneless diffuser is reduced at diffuser inlet, either at the hub wall or at the shroud wall, or both the walls. The reduction is varied from 0% (base case) to 20% at an interval of 5%. Numerical simulations are conducted for different speed range by varying the rotating diffuser diameter ratio from 1.25–1.75. Among all these cases, the best performance of 25% increase in pressure recovery with uniform diffusion and 2.3% increase in isentropic efficiency is obtained with 15% shroud pinch at a diameter ratio of 1.375 at the design mass flow rate.

Optimal Design and Analysis of a High-Load Supersonic Compressor Based on a Surrogate Model

To explore the internal flow mechanism and improve the performance of a supersonic compressor, an efficient global optimization design method was developed for an axial flow compressor and applied in the optimization design of a prototype supersonic compressor. Based on the multiple circular arc (MCA) blade parameters, the method can be used to parameterize the elementary stage of the blade. The optimized solution is obtained by changing the elementary stage and stacking lines of the blade during the optimization process. It has the advantages of fewer optimization variables, strong physical intuition, and a smooth surface. The optimization results show that a change in the rotor blade shape parameters has a significant effect on the compressor efficiency under design conditions, while a change in the skewed-swept parameters of the stator is the main factor that improves the compressor’s performance under near-stall conditions. Further numerical results show that the optimized rotor changes the form of the shock, weakens the degree of shock boundary layer interference, inhibits the radial migration flow of the supersonic rotor, reduces the loss of the rotor blade top, and improves the performance of the compressor under design conditions. The stator’s optimization restrains the generation of a concentrated shedding vortex at the root of the blades and greatly improves the stall margin of the compressor. Finally, the total pressure ratio and flow rate are less than 1% of the values based on the prototype operating conditions, the design mass flow of the optimized high-load supersonic compressor is increased by 0.25%, the isentropic efficiency is increased by 1.05%, and the stall margin is enhanced by 3.5%, thus verifying the effectiveness of the optimization method.

Design optimization of exit stage with diffuser passage based on NSGA-II and kriging surrogate model

In this paper, a diffuser passage compressor design is introduced via optimization to improve the aerodynamic performance of the exit stage. An in house design optimization platform is constructed based on non dominated sorting genetic algorithm II and kriging surrogate model to perform the optimization. A pareto front is obtained through optimization, from which optimal designs are selected by comprehensively considering efficiency and stability of the exit stage. The results show that application of diffuser passage design can improve the total pressure ratio by 0.79% and efficiency by 1.56% at the design mass flow rate, and the stall margin can be improved by 6.20%. The database is analyzed to investigate how different parameters affect the performance of the exit stage. The reasons for total pressure ratio increasing of the optimized compressors are expounded by analyzing the velocity triangle. Furthermore, the loss of rotor and stator region are quantized according to the local entropy generation rate model.

Design and performance analysis of a cryofan for helium closed loop cooling systems

Cryofan is the most vital component for helium closed loop cooling systems, which can provide the circulatory force of the gaseous helium. Thus, it is essential to develop a high efficiency cryofan in order to improve the energy efficiency of the cooling system. In this paper, a cryofan is designed for a helium closed loop cooling system of superconducting magnets. The design inlet temperature and total pressure ratio are 80 K and 1.1 respectively. The design mass flow rate is 17.5 g·s−1. A novel empirical model for incidence loss is proposed to calculate the incidence flow loss. A mean-line design and analysis model based on flow loss models is established to design and predict the performance of the cryofan. Based on the mean-line design results, a 3D design approach is proposed to design the detailed 3D geometry of the cryofan. Furthermore, 3D CFD simulations are conducted in order to predict the performance in design condition and off-design conditions, and further verify the accuracy of the mean-line model. The results indicate that the proposed novel empirical model for incidence loss is accurate and reliable, and an efficient cryofan can be designed and analyzed conveniently through applying the proposed mean-line model and 3D design method.

Aerodynamics of Sweep in a Tandem-Bladed Subsonic Axial Compressor Rotor

Abstract The present numerical investigation aims to understand the effect of the chordwise sweep on the performance of a tandem rotor. In a tandem compressor rotor, diffusion is achieved through two smaller airfoils, which are positioned in a particular fashion to nullify the effect of the boundary layer separation. The forward and aft rotor blades have different blade setting angles from the hub to the tip. Executing a chordwise sweep turns out to be an invalid tandem configuration due to the intersection of the forward and the aft rotor. To overcome this, a certain amount of lean is provided to the aft rotor. Therefore, the configurations selected for the current investigation are blades with a combination of sweep and lean. Two different forward sweep configurations and one backward sweep configuration are investigated. A significant improvement in the stall margin is observed for the forward-swept rotor configuration. However, the stage loading and efficiency of the unswept rotor are found to be higher than the forward-swept rotor case. Forward sweep reduces the tip loading of the forward rotor, which delays the tip stall. Backward sweep appears to be more detrimental in terms of the operating range of the tandem rotor, causing a substantial drop in the stall margin. The performance of the swept and the unswept rotor is compared at the design mass flow and near the stall mass flow rate. The pay-off derived from the chordwise sweep is elucidated with the help of blade loading, tip leakage vortices, blockage, skin friction lines, and various vortex interactions.

Performance testing and temperature fluctuations of a 4.5 K@150 mW Joule-Thomson closed cycle cryocooler for space applications

To meet future space applications, the Shanghai Institute of Technology Physics, Chinese Academy of Sciences (SITP, CAS) has developed a closed cycle Joule-Thomson (JT) cryocooler with a prospect of providing more than hundred milliwatts at liquid helium temperatures. The JT cryocooler is driven by staged efficient valved linear compressors with a pressure rate of 18 (low pressure of 0.1 MPa and high pressure of about 1.8 MPa). The designed mass flow is more than 14.8 mg/s. The preliminary experiment is carried out. A two-stage precooler capable of providing a pre-cooling capacity of about 15 K is used to verify the developed JT cryocooler. The test results show that the cryocooler successfully reached 4.5 K with a cooling power of more than 150 mW. A temperature fluctuation test is carried out. A long-term temperature fluctuation of more than 12 h has been tested. There exists a strong reaction among the temperatures of 4.5 K cold head, the precooling stages, and the ambient environment. The temperature fluctuation at 4.5 K cold head is within 5 mK/10 mins because of the large temperature fluctuation of the selected pre-cooler. The quantitative analysis of the temperature fluctuation of each temperature is discussed. By substituting the pre-cooler to a two-stage pulse tube cryocooler developed in our lab, the expected temperature fluctuation can be restrained to 1 mK@10 min and 5 mK@12 h, which can meet the requirement of future applications.

Numerical Analysis of Flow Characteristics of the Low-Speed Centrifugal Compressor Stage Comprising Wedge Diffuser

Wedge type diffusers are used generally in the highly loaded stages of smaller jet engines as it is compact in size. Low speed centrifugal compressor (LSCC) is selected for this present study as experimental details are available. A centrifugal compressor stage comprising wedge type diffuser is used in this numerical investigation in which studies are carried out at design mass flow rate (30kg/s) and off-design mass flow rates (23.64kg/s and 36.36kg/s) at constant rotational speed of 1920 rpm. Single passage approach is chosen to model the computational domain which is meshed with unstructured grid. Turbulence model chosen is kω-SST. The investigation revealed the jet-wake structure along the pressure side and suction side of the impeller and its subsequently mixing at impeller exit vaneless diffuser region. Diffusion process in the LSCC is observed to be effective as the outlet values of absolute velocity are lesser compared to its inlet values. Highest static pressure rise is observed for design mass flow rate and followed by below and above off-design mass flow rates.

Design and evaluation of a conical hypersonic vehicle with an overturned aerodynamic layout

A conical hypersonic vehicle with an overturned aerodynamic layout was accomplished and its aerodynamic performances were evaluated. In this work, the aerodynamic design methodology was addressed firstly, and then the conical vehicle integrated with an overturned inlet was obtained. The mass flow capture performance and the total pressure recovery performance were evaluated under design and off-design conditions. Results show that the mass flow capture increases and the total pressure recovery decreases as the inflow Mach number increases. The total pressure recovery decreases when the inflow Mach number increases. After that, the self-starting performance of the inlet was obtained by simulating an accelerating process. The initial inlet self-starts at Mach 5.2 on attack angle 6∘ situation. Furthermore, an improvement of the inlet self-starting performance was achieved with keeping the designed mass flow capture almost constant. By altering the 3-D shape of the inlet leading edge, the inlet self-starting Mach number decreases from Mach 5.2 to Mach 4.6 on attack angle 6∘ situation.

Effect of nozzle angle, turbine inlets and mass flow rate on the performance of a bladeless turbine

A comprehensive experimental study on the effects of different operating parameters on the efficiency of tesla turbine is reported. A bladeless turbine with nine discs and up to four turbine inlets was used, with water as the working fluid. The parameters investigated are the nozzle angle, number of turbine inlets and mass flow rates. Contrary to earlier studies, an effort was made to determine the performance under varying loading conditions, and hence identify the complete performance characteristics. The study revealed that efficiency of the turbine increases at lower nozzle angles and higher number of turbine inlets. It was observed that the nozzle angle becomes a significant parameter when the number of turbine inlets is increased. Efficiencies up to 78% were achieved when the working fluid entered the turbine through two nozzles at an angle of 7°. It was also noted that the turbine is most efficient at the designed mass flow rate, and the efficiency reduces appreciably if lower mass flow rates are fed to the turbine. The results obtained are an important contribution to the available knowledge and can be used as design references for further studies.

Parametric optimization of supercritical power plants using gradient methods

Gradient nonlinear optimization methods are among the most effective approaches to determine the optimal parameters of thermal power plants. These methods allow us to consistently optimize a large number of thermodynamic and design parameters and mass flow rates of actuation fluids and of heat-transfer fluids. This paper proposes an original gradient method to optimize the parameters of a 660 MW supercritical coal-fired power unit. The specific feature of the method is that it can start from a point where there is no solution of the combined equation defining the plant. The exact solution of the nonlinear combined equation is achieved only at the optimal point, consequently the calculation time is reduced. The method provides better convergence and greater accuracy of solving the nonlinear combined equation defining the processes in the power unit. Optimization is carried out according to the criterion of maximum efficiency, minimum specific plant investments and minimum cost of electricity at different fuel prices. The austenitic and nickel alloys are considered for superheater and reheater tubes of a steam generator. Co-optimization of the thermodynamic and design parameters of the power unit by the criterion of the minimum cost of electricity allowed us to get original solutions that combine the high temperature (615–622 °C) and low pressure (16.7–18.1 MPa) of live steam.