High Pressure Ratio Research Articles

The application of support vector regression and mesh deformation technique in the optimization of transonic compressor design

With the development of modern aero-engine, the compressor is required to achieve higher performance such as transonic operation, high stage pressure ratio and efficiency. At present, the traditional blade design methods have the disadvantage of highly relying on designer's experience and heavy computational burden. In order to reduce design variables used to define blade geometry, the present work introduces the Free-Form Deformation technique. It can achieve high degree-of-freedom deformation and update mesh and geometry simultaneously. To further alleviate computational cost, the Support Vector Regression surrogate model is adopted to replace the time-consuming numerical simulation. It performs well in small sample learning problems. On this basis, a surrogate-based optimization design framework is established by combining the Advanced Latin hypercube sample and NSGA-II multi-objective genetic algorithm. Then an aerodynamic optimization of the transonic NASA Rotor 37 is conducted as a validation. The results show that the pressure ratio and isentropic efficiency are increased by 4.2% and 2.5%, respectively. The optimized shape sweeps forward with a slight increase in twist angle, and shock loss is reduced effectively. Compared with traditional optimization method, the proposed framework can improve the optimization efficiency by decreasing design variables and training samples.

Design of an Axial Transonic Rotor by Modified Spanwise Loading Distribution

Improving the aerodynamic performance of the transonic fan in a turbofan engine can be beneficial for both the fuel consumption and maneuverability of an airplane. Deep insight into the supersonic aerodynamics is needed for the simultaneous improvement of all operating parameters of a transonic rotor, including the pressure ratio, efficiency, and surge margin. A design method was developed for an axial transonic rotor by using a combination of radial equilibrium theory, the free vortex method, and a distributed span-wise diffusion factor. The loading distribution obtained by this method was the highest in the hub section and gradually decreased in the tip section. To evaluate the method, a transonic rotor was designed using the geometric parameters and operating conditions of NASA rotor 67. A code was developed to determine a geometry for the new rotor and to modify it. The code was coupled with a RANS flow solver for 3D modification of the new designed rotor. Only standard multi- and double-circular arc airfoils were applied in different radial sections of the new rotor with no blade profile optimization. The results of the RANS equations solution for the new designed rotor showed 1.5% higher efficiency, 3% higher pressure ratio, and more than 1.5 times larger operating range in comparison to NASA rotor 67. The new designed method seems to be an efficient approach that not only improved the efficiency and pressure ratio but also increased the operating range of an axial transonic rotor.

Research on improving development effect of high-saturated reservoir in the late stage of water-flooding

High-saturated reservoir is characterized by high saturation pressure and high gas-oil ratio. The effects of water flooding are easily influenced by the formation pressure and GOR, especially at the late stage. This article presents the relationship between the reasonable pressure maintenance level and GOR as well as water cut based on the actual characteristics of high-saturated reservoir. Then, the reservoir numerical simulation method is used to analyse the influence of pressure recovery rate and water cut rise under different injection-production ratios and injection-production methods. Research results show that the pressure maintenance level of high-saturated reservoir is larger than normal reservoirs. Bigger injection-production ratio results in not only faster pressure recovery rate but also higher water cut. Cyclic injection and production method under the maximum injection rate and liquid extraction amount can enhance oil recovery rate and control water cut rise at the same time, which plays a significant role in improving the development effect of water-flooding in high-saturated reservoirs at the late stage.

Research on aerodynamic characteristics through airflow clearances in compressor blades of gas turbine engine

Reducing the loss in the airflow clearance among the compressor blades of the rotor disk and stationary blades (guide vanes) is an urgent issue. Furthermore, additional losses of airflow through the clearances among the blades and airfoil losses are the main cause of reducing the efficiency of an axial flow compressor, especially the blade height is small. With a view towards the efficiency improvement of a multistage axial compressor with a high-pressure ratio, it is necessary to manufacture a highly economical compressor with a variety of compression stages. Airflow in the circulation clearances alternating among compressor blades has viscosity, unstable compression, and quite complex flow structure. This needs to be researched into the design with the assistance of modern software (ANSYS CFX, FlowER, etc.). Although this is an important step in the current design orientation, it requires additional practical elements to perform, especially the problem of optimizing the outer rim, the level, and the number of compression stages in the whole compressor. In this paper, authors have used the method of creating three-dimensional (3D) models for blade profiles in a compressor based on analyzing the flow in three-dimensional form and studying their parameters. This paper deals with the geometry problems of the row of rotating blades (cascade) by proposing the structural arrangement of stacking blades in the circular direction and the blade profile formed the S-shape. Investigating and calculating the aerodynamic properties of the airflow through clearances of compressor blades by using ANSYS is one of the new methods. The researched result showed the dependence between the camber angle as the rotating blade formed an S-shape profile rotates regarding the stagger angle of the airfoil and the incident angle of airflow. Some characteristics of aerodynamic properties are distributed according to the blade height in conducting with different curved profiles of the rotating blades on the rotor disk and stationary blades.

Numerical modeling of core compressor discharge for a windmilling aero engine

A gas turbine engine's ability to relight in flight depends heavily on the combustion chamber's inlet conditions. These conditions are dictated by the core compression system located immediately upstream of the combustor, but such conditions during windmill have not been thoroughly investigated and are not commonly available in the literature. In this paper, an entire high pressure ratio axial compressor is modeled using scale adaptive simulation. Real windmilling inlet conditions extracted from altitude test facility data are used as boundary conditions. The implications of steady vs. unsteady modeling and the use of different interface modeling approaches are investigated. A description of the discharge flow-field is given in terms of flow statistics, turbulent quantities, and dominant dynamic modes. The discharge flow-field is dominated by small scale structures resulting from leading edge separation in the last stator (OGV), with little influence of the upstream stages on the stator flow-field dynamics. The study has shown that, while an unsteady analysis is required, reduced order models allowing for a decoupled analysis of the last stage flow dynamics may be sufficient in future studies seeking to characterize combustor inlet conditions for inflight relight.

Electricity storage based on coupled thermochemical reactions: The Thermochemical Battery

Thermochemical reactions are under investigation for a wide variety of applications. However, the system of two coupled gas-solid reactions exchanging both thermal energy and gas solely with each other has not been investigated yet. This approach allows realizing a compact thermochemical unit with two gas reservoirs at different pressure levels at approximately the same temperature. In this work, such a system is fundamentally analyzed and its technical potential as an energy storage component is investigated. While any two thermochemical gas-solid system can be used, this work exemplarily focusses on metal hydrides. Based on a thermodynamic analysis, it can be shown that the system is feasible, as the intrinsic difference in the reaction enthalpies of the metal hydrides can be compensated with heat integration of the compression unit. Following these findings, a thermochemical battery is investigated in more detail including an energetic analysis of efficiencies and potential storage densities. It is deduced that a higher pressure ratio between the hydrides yields in higher storage density but lower efficiency. Co-generation of cooling energy during discharging is feasible.

Investigation on the Optimal Design and Flow Mechanism of High Pressure Ratio Impeller with Machine Learning Method

The optimization of high-pressure ratio impeller with splitter blades is difficult because of large-scale design parameters, high time cost, and complex flow field. So few relative works are published. In this paper, an engineering-applied centrifugal impeller with ultrahigh pressure ratio 9 was selected as datum geometry. One kind of advanced optimization strategy including the parameterization of impeller with 41 parameters, high-quality CFD simulation, deep machine learning model based on SVR (Support Vector Machine), random forest, and multipoint genetic algorithm (MPGA) were set up based on the combination of commercial software and in-house python code. The optimization objective is to maximize the peak efficiency with the constraints of pressure-ratio at near stall point and choked mass flow. Results show that the peak efficiency increases by 1.24% and the overall performance is improved simultaneously. By comparing the details of the flow field, it is found that the weakening of the strength of shock wave, reduction of tip leakage flow rate near the leading edge, separation region near the root of leading edge, and more homogenous outlet flow distributions are the main reasons for performance improvement. It verified the reliability of the SVR-MPGA model for multiparameter optimization of high aerodynamic loading impeller and revealed the probable performance improvement pattern.

Flow Control Effect of Spanwise Distributed Pulsed Arc Discharge Plasma Actuation on Supersonic Compressor Cascade Flow

To achieve efficient control of supersonic compressor cascade flow, a type of spanwise distributed pulsed arc discharge plasma actuation (PADPA) was designed. To simulate the influences of PADPA on the flow field, a phenomenological model was established. Then, the flow control effects of PADPA on supersonic compressor cascade flow were researched numerically. The results show that under low static pressure ratio condition, the compressive wave induced by PADPA reduced the intensity of the passage shock wave, which eventually reduced shock wave loss. It was also found that PADPA produced an adverse pressure gradient (pre-compression effect) around the actuation location, which reduced the strength of the high adverse pressure gradient induced by the passage shock wave. The airflow on both sides of the actuation location was accelerated by PADPA owing to the spanwise distributed layout. Thus, it improved the ability of the boundary layer to resist the effect of the adverse pressure gradient and reduced the separation zone. Consequently, the total pressure loss was reduced by 6.8%. Under high pressure ratio condition, the effect of PADPA on the suction side controlling the large separation of the boundary layer was insignificant. The total pressure loss also increased slightly.

Preliminary Investigations of an Opposed Rotary Piston Compressor for the Air Feeding of a Polymer Electrolyte Membrane Fuel Cell System

Automotive polymer electrolyte membrane fuel cell systems are attracting much attention, driven by the requirements of low automotive exhaust emissions and energy consumption. A polymer electrolyte membrane fuel cell system provides opportunities for the developments in different types of air compressors. This paper proposed an opposed rotary piston compressor, which had the merits of more compact structures, less movement components, and a high pressure ratio, meeting the requirements of polymer electrolyte membrane fuel cell systems. Preliminary performance evaluations of the opposed rotary piston compressor were conducted under various scenarios. This will make a foundation for optimizations of outlet pipe layouts of the compressor. A three-dimensional numerical simulation approach was used; further, in-cylinder pressure evolutions, fluid mass flow rates, and P–V diagrams were analyzed. It indicated that the cyclic period of the opposed rotary piston compressor was half of reciprocating piston compressors. The specific mass flow rate of the compressor is in the range of 0.094–0.113 kg·(s·L)−1 for the given scenarios. Outlet ports 1 and 2 dominated the mass flow in the discharge process under scenarios 1, 3, and 4. In-cylinder pressure profiles show multipeaks for all of these scenarios. In-cylinder pressure increased rapidly in the compression process and part of the discharge process, which led to high energy consumption and low adiabatic efficiency. The maximum adiabatic efficiency is approximately 43.96% among the given scenarios.

A comparative study of laser-induced gas breakdown ignition and laser ablation ignition in a supersonic combustor

Cavity ignition was achieved in a supersonic combustor by laser-induced gas breakdown (LIGB) and laser ablation (LA). High-speed photography and schlieren imaging were employed to characterize the ignition processes. schlieren imaging was also applied to visualize LIGB and LA in quiescent air. The input energy was approximately 200 mJ. The distance between the focal point of the convex lens and the target plate (d) varied from 10 mm above the target plate (d = 10 mm) to 5 mm below the target plate (d = −5 mm). The experiments performed in quiescent air indicated that the plasma of LA (d = −5 mm) was relatively small. Compared to LIGB, the expansion of the hot plume resulting from LA was less significant because the plate prevented the formation of the third lobe. The primary shock wave of LA propagated faster than that of LIGB because of high pressure ratio between the plasma and the ambient air. In the supersonic combustor with d = 5 or 10 mm, the laser induced a plasma by LIGB at the focal point and induced another plasma by LA at the cavity floor. These two tests were the combination of LIGB ignition and LA ignition. LA ignition was achieved in the test with d = −5 mm. The ignition process of the test with d = 10 mm was the slowest because of severe plasma quenching at the focal point. For the early stage of ignition, the flame kernels of the tests with d = 5 and −5 mm were different. However, the differences gradually vanished after the flame kernels reached the cavity leading edge. The ignition times of these two tests were almost the same. Therefore, the plasma resulting from LA was as effective as the plasma generated by LIGB in terms of ignition. Laser ablation ignition was a promising ignition method in a supersonic combustor.

Numerical assessment of a very high pressure ratio centrifugal impeller

The paper focuses on studying the influence of mesh size, numerical discretization schemes and different turbulence models on radial impeller performances. The chosen impeller is a 14:1 pressure ratio novel design for use in the TIDE pulse detonation engine architecture. In preparation for the experimental research, numerical studies were performed for five steady-state analysis and one unsteady, single passage with a fully structured solver. A grid sensitivity study was conducted over four grid resolutions, starting from a coarse to dense mesh (0.7 mil, 1.5 mil, 5 mil and 9 mil), in order to determine the influence of mesh points, numerical stability and reduce interpolation errors. Another problem in a CFD study is the selection of a proper turbulence model, thus six RANS models were investigated: k-ε, v2-f, k-ω Shear Stress Transport (both steady and unsteady), Spalart – Allmaras and an Explicit Algebraic Reynolds Stress Model. Results show that global parameters such as pressure ratio and efficiency predictions remain unchanged above 1.5 mil cells/passage, while above 5 mil cells/passage, RANS models become unstable and lead to poor convergence. The most conservative model proved to be the SST with minimalistic values for both pressure ratio and isentropic efficiency.

Aerodynamic development of a high-pressure ratio compressor for an advanced microturbine powerplant

Microturbine engines are increasing in popularity both for small poly-generation power plants and unmanned aerial vehicle; however, their overall efficiency is severely limited by their thermodynamic cycle and component efficiency. This compressor allows the real cycle of the engine to operate with lower specific fuel consumption, extending the rage of the vehicle and lowering pollutant emissions. Optimization methods were implemented in the compressor design, in order to increase the aerodynamic efficiency. A 4.5:1 pressure ratio was selected in order to keep the exhaust jet subsonic. Linear models were used to optimize the speed and gross geometry while the TEIS and later fully viscous 3D models were used successively to optimize the end walls and blade shapes. For all numerical simulations, the Menter SST turbulence model was used. In order to minimize modelling errors, the rotor-stator interface was placed as far as possible downstream of the impeller.

Robust adaptive backstepping active control of compressor surge based on wavelet neural network

Surge active control can extend the stable operating range of the compressor. Most of the previous active control algorithms can only work on the basis that compression characteristics are known, which limits the engineering application of it. The robust control can alleviate the negative effects brought by uncertain system characteristics, however its designed control law is too conservative that active control can't give full play to its benefits. To overcome the weakness of the former active controllers, this paper comes up with the idea of active surge control, which assumes that the characteristics of the compression system are unknown. And it uses the wavelet neural network algorithm, a kind of algorithm with the nature of approaching any linear and nonlinear functions, to approach the unknown compressor steady-state characteristics asymptotically. Then, by applying backstepping on the second-order MG compressor surge dynamic model with CCV, a robust adaptive active controller of compressor surge is designed, which makes the control law effective to a larger extent, and greatly improve its performance in tracking and anti-interference. From the simulation results, it can be seen that the designed controller displays the strong robustness against un-modeled dynamics, flow and pressure disturbances, and in the meanwhile achieves near to zero asymptotical tracking error. The method proposed in this paper allows compressors to operate stably with high-pressure ratio and high-efficiency beyond the surge boundary, namely greatly expands its operating range. Thus, this paper has significant guidance for future development, theoretical research, and engineering application of surge active control of the compressor.

Stability Improvement of a High-Pressure Ratio Centrifugal Compressor by Flow Injection

AbstractHigh-pressure ratio centrifugal compressors are required in modern turboshaft engines with the requirements of a high power-to-weight ratio and low fuel consumption. The reduction of the st...

Experimental and numerical investigations on the acoustic characteristics and unsteady behaviors of a centrifugal compressor for fuel cell vehicles

Compared to other air compressors, high-speed centrifugal compressors are considered a more suitable choice for a mid-to-high-power fuel cell system due to its high-pressure ratio. As the centrifugal compressor is the most intensive noise source in the fuel cell vehicle, its acoustic characteristics become a major concern in the passenger comfort experience. Unlike the turbocharger compressor, the centrifugal compressor in a fuel cell vehicle tends to operate at near-surge conditions, which leads to flow instabilities and increases the noise level. In this paper, the acoustic characteristics of a centrifugal compressor for a fuel cell vehicle were measured on a compressor test rig covering the full range of the compressor map. The experimental results show that the lowest sound pressure level at the compressor inlet occurs in the design operating area, while the highest level occurs near the mild-surge line. Experimental work was complemented by numerical simulations. Time-averaged flow fields were compared between the near-choke and mild-surge conditions and the detached eddy simulations (DES) were performed at mild-surge conditions. Sparsity-promoting dynamic mode decomposition (SPDMD) was employed as a post-processing method to extract the flow structures associated with corresponding noise features. It was observed that the rotating stall of the impeller inducer is the main cause of the narrow-band whoosh noise near the mild-surge line. The location, number, and speed of the stall cells were identified by SPDMD in rotational and stationary frames.

Turboexpander wheel design for helium liquefaction plant

AbstractA turboexpander wheel, that is, turbine, is one of the critical components for a helium liquefaction plant. It helps to provide the cooling effect required for the liquefaction. The percentage of liquefaction depends upon the effective design of the turbine. The present work includes the design of a radial turbine for the intended power output of approximately 1.5 kW, with input conditions of 40‐g/s mass flow rate at inlet, inlet total pressure of 14 bar, inlet temperature of 40 K, and outlet static pressure of 6 bar. The pressure values are taken to be absolute. Inlet conditions are selected on the basis of required refrigeration effect of approximately 1 kW. The outlet static pressure of 6 bar is maintained to avoid the turbulence, which may occur due to expansion for high pressure ratios. The present work involves the design and optimization of a turbine on the basis of the mean line analysis, initiating with the assumption of values for total‐to‐static efficiency. As per mean line design concept, a one‐dimensional flow is considered for this analysis and the mean values of different parameters are considered at different sections. Losses are considered as the main constraint in design and it is desirable to get optimum net power. Besides, it is also desirable to achieve values for other design parameters in a specified range.

Advances in Centrifugal Compressors

Multiple-Stage compression through the use of two or more centrifugal compressors operating in series has been the approach to achieving high-pressure ratios. The complexity, inefficiency and cost of such systems are not ideal for most applications. We discuss here three recent innovations in centrifugal compressor multiple-stage systems in series. The first two are my patents, US 6,589,013 B2 and US 7600961 B2 and the third patent is Honeywell US7,568,883 B2 . Our approach is to draw parallels between centrifugal and axial compressors flow paths and relate them to the threepatent theories. Although axial and centrifugal compressors differ in many ways, they have many characteristics in common

Centrifugal turbo chiller using water as refrigerant and lubricant

Water refrigerant heat pump system with a water vapour turbo compressor is developed. Water (R718) is an ideal refrigerant that is considered perfectly environment friendly. Although water refrigerant heat pump is studied extensively, the development of turbo compressors of high pressure ratio is still a technical challenge, in terms of both aerodynamics of the impellers and high-speed rotordynamics. In this study, the high-speed rotor is supported by journal bearings lubricated with water refrigerant. Additionally, other system components such as sprayed direct intercooler heat exchanger and anti-cavitation flow control valve have to be designed and developed with the new requirements as well. An experimental test rig of closed-loop heat pump is constructed which achieves the cooling capacity of 100 kW on the rated condition with COP = 5. The experimental results and the experienced challenges and their undertaken solutions are discussed in terms of the efficiency and the vibrations of the turbo compressor and the heat pump system.

Novel Simplified Blade Hub Line Optimization of High-Pressure Ratio Centrifugal Compressor Design Using Numerical Simulations

The focus of this research is to numerically investigate the effect of blade hub line variation on the performance (Total pressure-ratio and Isentropic-Efficiency) of centrifugal compressor from stall to choke to study the operating range and stall margin. An optimization technique is carried out in which the meridional profile hub line is modified and compared with the high Mach number SRV2 compressor designed and fabricated by DLR (German Aerospace Center). Numerical simulations showed significant increase in the stall margin and operating range by bargaining on pressure ratio and isentropic efficiency. Reynolds Averaged Navier Stokes (RANS) based k-ε model is used to predict turbulence using numerical simulations. The value of Y plus for the structured mesh near the boundaries is kept 35. Blade hub line being the important parameter, has substantial performance improvement of centrifugal compressor. The novel design improved the stall margin by 44 percent while operating range from stall to choke has been upgraded by 7.5 percent.

Rake impact on turboshaft compressors, a numerical study

PurposeTurboshaft engines usually include one centrifugal compressor due to its high-pressure ratio, stability and compactness. Many designers rely on positive raking to decrease tip gap flow and therefore losses. However recent optimization studies revealed geometries contradicting this canonic view. Hence, this paper aims to investigate how the rake angle alone can influence performance and to which extent.Design/methodology/approachA turboshaft representative impeller was chosen and altered for null and +/−30° rake angles. Menter's shear stress transport model is used for steady computational fluid dynamics simulations, sweeping the nominal speedline at various tip clearances. Backsweep distribution is identical in all cases, isolating rake influence.FindingsPressure ratio was lowered for the both positively and negatively raked blades, but through distinct aerodynamic mechanisms. Although the flow through the tip gap was lower for the positive rake, this is due to lower blade loading. Splitter comparison reveal that these effects are more pronounced in the radial regions.Practical implicationsSome of the findings may extend beyond turboshaft engines, into turbochargers, home appliances or industrial blowers. However, all extrapolations must consider specific differences between these applications. Turboshaft compressors designers can benefit from this study when setting up their free parameters and penalty functions in the early concept stages.Originality/valueOnly few similar studies can be found in the literature to date, none similar to turboshaft applications. Also, this impeller is designed to eliminate leading edge shocks and suction side boundary layer separation, which makes it easier to isolate the tip gap flow effects. The authors also provide a framework on which semi-empirical design equations can be further developed to incorporate rake into 1D design tools.