Partial Admission Conditions Research Articles

Loss characteristics and optimization method of a compressed air energy storage radial turbine with nozzle governing

During the operation of the compressed air energy storage (CAES) system, a discrepancy exists between the air storage pressure and the turbine inlet pressure. At the same time, to ensure that the turbine operates efficiently when the system load varies, the turbine needs to be regulated reasonably. In this paper, the influence of three nozzle governing (NG) parameters on turbine performance during the NG process is investigated: the inlet pressure of the NG region, the area of the NG region, and the base pressure. The flow characteristics and loss mechanisms under partial admission conditions and NG conditions are also analyzed. Furthermore, the NG process is optimized by using a transition section. The results show that the loss under the NG condition with low inlet pressure at the NG region is similar to the partial admission loss, both of which are mainly affected by the area of the NG region. In both working conditions, vortex structures appear at the stator outlet of the NG region. At the same time, the mixing of different airflows and the flow separation phenomenon within the rotor leads to a significant increase in entropy production rate. The transition section can attenuate the leakage and reduce the entropy production rate in the radial gap between the stator and rotor, increasing turbine efficiency by up to 1.1 % at maximum when using the transition section.

Assessment of a twin-entry turbine efficiency model including momentum exchange between branches

Radial twin-entry turbines standard maps have limited data available for fitting model parameters since they usually provide information only at full and partial admission conditions. However, twin-entry turbines’ most common operation is at unequal admission conditions. A new losses-based efficiency model has been developed that takes into account the behaviour of the twin-entry turbines at unequal admission conditions considering the different losses produced in each of its parts to improve the model predictions in these conditions. The model is validated with experimental measurements of the whole range of admission conditions, and all the model parameters needed are fitted. Moreover, the model’s accuracy is compared with empirical and commercial models using a limited amount of data instead of the whole measured map, obtaining reasonable extrapolations and improving the results provided by the other models at unequal admission conditions.

Study on influence of admissions on loss generation in a twin-entry nozzleless radial turbine

Twin-entry radial turbine has an evident advantage of enhancing the output power in internal combustion engine, while it is confronted by complex inlet conditions because of the interval flow feeding into two limbs. Although the performance of twin-entry turbine is notably influenced by admission conditions, detailed flow mechanism is yet fully revealed in previous researches. This paper investigates the mechanism of the influence by different admissions on a nozzleless twin-entry turbine via experimentally validated numerical methods. Turbine performance is studied under different admission conditions and the results demonstrate that twin-entry turbine performance is notably different between two partial admission conditions, although the volute passage is symmetrically divided. Rotor decomposition methods are employed for the analysis of loss distributions to understand this performance difference. Flow separation and tornado vortex generated near the rotor inlet is confirmed as the key source for the flow loss in the rotor. The off-design incidence angle near the hub rather than the shroud is the reason for the vortex initiation in the twin-entry turbine. Moreover, the volute flow features demonstrate that volute leakage flow is the reason for the lower incidence angle near the blocked limb. Consequently, the mechanism of the asymmetric performance of the symmetric twin-entry turbine under partial admission conditions is revealed.

Real-time evaluation method of turbine rotor’s thermal stress with governing stage partial admission condition at low-load

In order to ensure the safety and stability of the new energy power system, many power units will be maintained at low-load state for a long time during peak-load regulation in China. However, the partial arc admission of the nozzle governing mode will cause uneven temperature distribution in the circumferential direction after GS, which will affect real-time thermal stress of the rotor. Toward this end, this paper proposes a real-time evaluation method of thermal stress for rotors in low-load conditions. First of all, the solution boundary conditions of thermal stress model can be obtained by designing the measuring points arrangement after GS, which comprehensively takes into account the uneven temperature distribution of GS under low-load conditions. In the meantime, various punching schemes are analyzed by ANSYS, which used to analyze the influence of cylinder structure strength caused by the new measuring point punching of each scheme. The result shows that the punching impact on the stress and deformation of cylinder is not obvious, which has a great significance to reduce minimum technical output and improve peak governing capability of thermal power unit.

Investigation of the Relative Performance of Vaned and Vaneless Mixed Flow Turbines for Medium and Heavy-Duty Diesel Engine Applications with Pulse Exhaust Systems

<div class="section abstract"><div class="htmlview paragraph">This paper details results of a numerical and experimental investigation into the relative performance of vaned and vaneless mixed flow turbines for application to medium and heavy-duty diesel engines utilizing pulse exhaust systems. Previous investigations into the impact of nozzle vanes on turbine performance considered only open turbine housings, whereas a majority of medium and heavy-duty diesel engine applications are six-cylinder engines using pulse exhaust systems with divided turbines. The two turbine stages for this investigation were carefully designed to meet the constraints of engines with pulse exhaust systems and to control confounding factors that would undermine the vaned vs vaneless performance comparison. Detailed CFD analysis and turbine dynamometer test results confirm a significant efficiency advantage for the vaned turbine stage under both full and partial admission conditions.</div></div>

Using a CFD analysis of the flow capacity in a twin-entry turbine to develop a simplified physics-based model

The current paper presents a flow behaviour analysis of twin-entry radial turbines by means of experimental measurements and computational fluid dynamics (CFD) simulations. The experimental data were measured at partial, unequal and full admission conditions, and was used to globally validate CFD simulations. The experimental results hinted towards considering twin-entry turbines as two separated single-entry turbines working in parallel when used in simplified physics-based models such as in one-dimensional simulations. After analysing the CFD results, a simple flow capacity model was developed, exploiting some of the observed characteristic phenomena to reduce the number of fitting parameters to their minimum while keeping its accuracy and extrapolation capabilities.

A reduced-order model of twin-entry nozzleless radial turbine based on flow characteristics

Twin-entry radial turbine has evident advantages on energy recovery of internal combustion engine because of better utilization of exhaust pulse energy. One-dimensional performance prediction plays an important role in automobile industry because of the cost-effective feature. However, as twin-entry turbine is confronted by out-of-phase pulses, to capture the flow distortion by twin-entry turbine model is challenging, especially under partial admission conditions. This paper establishes a reduced-order parallel-rotor model for performance prediction of twin-entry nozzleless radial turbine based on internal flow characteristics. Firstly, twin-entry turbine experiment and 3D simulation are applied to analyze the different flow features under partial admission conditions. The flow distortions in the spanwise and circumferential directions are both demonstrated. Based on these flow characteristics, a reduced-order twin-entry turbine model with parallel rotor passages is established for predicting the rotor at distorted flow field. Finally, the model is carefully validated against the results of CFD. The results show that satisfied consistency can be obtained and the maximum discrepancy of turbine performance is 3.8% and the performance difference and flow distortion under partial admissions can be captured, thus prove the credibility of the model. This investigation provides a reliable methodology for performance prediction and behavior analysis of twin-entry turbine.

Finding an optimal blade-profile to improving the performance of partially admitted turbines

Purpose This paper aims to present the designing and investigating various types of impulse blade profiles to find the optimal profile that has better performance than the first or original blade. The studied model is a turbine with an output power below 1 MW and a large pressure ratio up to 20, which is used to gain relatively high specific work output. As a result of its low mass flow rate, the turbine is used under partial-admission conditions. The turbine’s stator is a group of convergence–divergence nozzles that provide supersonic flow. Design/methodology/approach More than 10 types of two-dimensional blade profiles were designed using the developed preliminary design calculations and numerical analysis. The numerical results are validated using the existing experimental results. Finally, the case with improved performance is introduced as the final optimum case. Findings It was found that the performance parameters such as efficiency, power and torque are increased by more than 8% in the selected best model, in comparison with the original model. Moreover, the total pressure loss is 12% decreased for the selected model. Finally, the selected profile with superior performance is proposed. Originality/value Simultaneous numerical tests are conducted to examine the interaction of different supersonic blade profiles with the partially injected flow to the rotor.

A Robust Adiabatic Model for a Quasi-Steady Prediction of Far-Off Non-Measured Performance in Vaneless Twin-Entry or Dual-Volute Radial Turbines

The current investigation describes in detail a mass flow oriented model for extrapolation of reduced mass flow and adiabatic efficiency of double entry radial inflow turbines under any unequal and partial flow admission conditions. The model is based on a novel approach, which proposes assimilating double entry turbines to two variable geometry turbines (VGTs) using the mass flow ratio ( MFR ) between the two entries as the discriminating parameter. With such an innovative approach, the model can extrapolate performance parameters to non-measured MFR s, blade-to-jet speed ratios, and reduced speeds. Therefore, the model can be used in a quasi-steady method for predicting double entry turbines performance instantaneously. The model was validated against a dataset from two different double entry turbine types: a twin-entry symmetrical turbine and a dual-volute asymmetrical turbine. Both were tested under steady flow conditions. The proposed model showed accurate results and a coherent set of fitting parameters with physical meaning, as discussed in this paper. The obtained parameters showed very similar figures for the aforementioned turbine types, which allows concluding that they are an adequate set of values for initializing the fitting procedure of any type of double entry radial turbine.

Effects of nozzle arrangement angle on the performance of partially admitted turbines

This paper presents the experimental and numerical evaluations of the effects of a supersonic Nozzle arrangement angle (NAA) on the performance of an impulse axial turbine. The studied model is a small turbine with a large pressure ratio that is used to gain high specific work output. As a result of its low mass flow rate, the turbine is used under partial admission conditions. The turbine stator is a group of convergence–divergence nozzles that provide supersonic flow. Five stators with different NAAs are modeled and tested. Results show that NAA exerts considerable impact on the performance of the turbine. In this work, suggestions for achieving a decent design process for partly arranged nozzles are offered, and the proposed model and numerical analysis are validated using experimental tests.

Effects of rotor solidity and leakage flow on the unsteady flow in axial turbine

Partial admission turbine plays an important role in power control, which strengthens the unsteady flow. The effects of rotor solidity at partial admission condition can be more complicated, and leakage flow deeply strengthens the unsteadiness. Hence, the investigations of rotor solidity and leakage flow on the unsteady flow are of great significance for turbine designs. Turbines including five kinds of solidity at full and partial admissions are modeled based on 3D viscous compressible NS equation. In addition, the leakage flow model including tip leakage, inlet and outlet cavity is investigated. The results show that the solidity effects on partial admission turbine are not exactly the same as that on full admission turbine. The differences are identified, especially the axial unsteady aerodynamic force. Moreover, the attack angle tends to be negative with rotor solidity increasing; meanwhile, the low pressure region varies with solidity due to flow separation or throat area reduction. Leakage flow model is more able to reveal the unsteady flow, and the comparative analysis of flow phenomenon under the combined effects of leakage flow and partial admission flow is conducted. The change of rotor inlet parameters is smoothed down for leakage model and the axial exciting force is relative lower.

Experimental Comparison of Axial Turbine Performance Under Steady and Pulsating Flows

The performance of an axial turbine is studied under close-coupled, out-of-phase, multiple-admission pulsed air flow to approximate turbine behavior under pulsed detonation inflow. The operating range has been mapped for four frequencies and compared using multiple averaging approaches and five formulations of efficiency. Steady performance data for full and partial admission are presented as a basis for comparison to the pulsed flow cases. While time-averaged methods are found to be unsuitable, mass-averaged, work-averaged, and integrated instantaneous methods yield physically meaningful values and comparable trends for all frequencies. Peak work-averaged efficiency for pulsed flow cases is within 5% of the peak steady, full admission values for all frequencies, in contrast to the roughly 15–20% performance deficit experienced under steady, 50% partial admission conditions. Turbine efficiency is found to be a strong function of corrected flow rate and mass-averaged rotor incidence angle, but only weakly dependent on frequency.

Reducing the influence of partial admission on unstable synchronous vibration of turbines by bearing elevation optimization

To investigate the rotor-bearing dynamics and solve the unstable synchronous vibration problem under partial admission conditions in axial steam turbines, a three-dimensional computational fluid dynamics model of the governing stage for a 350 MW turbogenerator unit was established. Steam force under different partial admission cases was calculated. Results show that the uneven steam force in the horizontal direction was fairly as strong as that in the vertical direction. The maximal horizontal steam force was about 40% of the high intermediate pressure cylinder rotor weight. Synchronous vibration faults caused by partial admission may occur in practice. The finite element model was further built to analyze the rotor-bearing dynamics under partial admission conditions. Large fluctuation of the synchronous vibration was observed during the variation of control valve sequence. Finally, the effect of bearing elevation on the rotor-bearing dynamics was studied. The sensitivity of bearing load varies for different bearing elevations. An effective solution to the unstable synchronous vibration faults caused by partial admission was achieved by optimizing the distribution of bearing elevation. A relevant case was presented through practical test.

Experimental and numerical investigation of design optimization of a partial admitted supersonic turbine

To obtain a high specific work output, the large pressure ratios across the turbine are required. This can be achieved using a supersonic turbine. When the fluid mass flow is low, the impulse kind of one or two stages supersonic turbine is employed. To prevent losses due to low blade aspect ratio and issues related to manufacturing and industrial problems, the turbine is used in partial admission conditions. Studies show that the turbine efficiency is highly dependent on the amount of partial admission coefficient. The turbine efficiency in full admission is high, but the use of partial admission lowers the additional losses. Therefore, there will be a degree of partial admission in which the turbine will have the highest efficiency. The aim of this work is to achieve the optimum partial admission for a special impulse turbine as a case study. Therefore, in the beginning, an appropriate model of losses is presented. Then, using a nonlinear design optimization code, the partial admission of an impulse supersonic turbine is optimized. This code is written using a genetic algorithm. Then, using three-dimensional numerical analysis, the optimal model will be selected. In the optimization problem, the turbine efficiency is the objective function. The amount of design parameters and constraints used in this process are ten and eight, respectively. After the optimization process, prototypes of designed and modified turbines are made and tested. Test results were compared and analyzed. The results showed that the turbine efficiency is improved between 2.5% and 3% depending on various operation conditions.

Understanding the Twin Scroll Turbine: Flow Similarity

The current study investigates the flow conditions of a twin scroll asymmetric turbine. This is motivated by the operating conditions of the turbine at a heavy-duty reciprocating internal combustion engine with exhaust gas recirculation. The flow conditions of the turbine at the engine can be described best with the turbine scroll interaction map. Standard hot gas measurements of a turbocharger turbine are presented and discussed. Due to the strong interaction of the turbine scrolls, further hot gas measurements are performed at partial admission conditions. The turbine inlet conditions are analyzed experimentally, in order to characterize the turbine performance. The turbine scroll pressure ratio is varied, leading to unequal twin turbine admission conditions. The flow behavior is analyzed regarding its ability for further extrapolation. Beyond scroll pressure ratio variations, unequal temperature admission conditions were studied. A way of characterizing the representative turbine inlet temperature, regarding the reduced turbine speed, is presented. The different scroll parameter ratios are evaluated regarding their capability of describing flow similarity under different unequal turbine admission conditions. In this content, turbine scroll Mach number ratio, velocity ratio and mass flow ratio are assessed. Furthermore, a generic representation of the turbine flow conditions at the engine is presented, based on standard turbine performance maps.

An audit of aerodynamic loss in a double entry turbine under full and partial admission

The current study investigates the sources of loss inside a mixed flow, double entry turbocharger turbine under steady inlet conditions in both full and partial admission. Under normal on-engine operation, it is likely that both limbs in a double entry device will be fed by exhaust pulsations which are out of phase meaning that the turbine will spend most or all of the time with unbalanced flow through each limb. In the extreme case one limb will be flowing whilst the other is stagnant, this is the partial admission condition. Even under steady state inlet conditions, unequal admission is an important effect to study on the way to fully understanding pulsed operation of a double entry device.This paper presents 3D computational analyses of the flow inside a double entry turbine under both full and partial admission. The computational results are compared to experimental results of Copeland (2009) and Copeland et al. (2010). The distribution of loss within the turbine is evaluated for each computational condition by means of entropy production. In the full admission case the most significant area of loss was found to be in the tip region. Under the partial admission condition the flow regime is very different. In this case the rotor wheel was found to be acting in a fully unsteady manner, with the flow being unable to reach a fully developed state throughout the flowing section of the volute. The most significant area of entropy generation in the partial admission case was associated with interaction of the flows in each sector of the volute, this occurred in the interspace between the nozzle exit and the rotor passage inlet.

Flow and performance characteristics of twin-entry radial turbine under full and extreme partial admission conditions

This paper presents numerical and experimental investigation of the performance and internal flow field characteristics of twin-entry radial inflow turbines at full and extreme partial admission conditions. The turbine is tested on a turbocharger test facility, which was developed for small and medium size turbochargers. Experimental results show that the lowest efficiency corresponds to extreme conditions. Therefore, flow field analyzing is employed to consider these conditions. The flow pattern in the volute and impeller of a twin-entry turbine is analyzed using an in-house fully three-dimensional viscous flow solver. The computational performance results are compared with the experimental results and good agreement is found. The flow field at the outlet of the turbine is investigated using a five-hole pressure probe; the numerical results are also compared with experimental measurements at the outlet of the rotor. For the volute, results show that lowest entropy gain factor corresponds to the extreme conditions, particularly when shroud side entry is fully closed. At the inlet of the rotor for equal admission conditions, the incidence angle is mostly in the optimum values. However, large variation in the incidence angle is seen in the extreme conditions, which lead to larger incidence losses and consequently a lower efficiency. In addition, entropy distribution contours corresponding to the exit plane are considered. For full admission, the location of low entropy gain factor at this plane occupies a region near the shroud side of suction surface as well as near the hub side of the pressure surface that corresponds to a region of high absolute flow angle. However, for the extreme cases, the low entropy gain factor occupies a relatively larger region near the shroud side than full admission. So, higher loss generation is noted at the extreme cases. Moreover, this entropy gain factor region is increased when shroud side entry is fully closed.

Study on Stability of High Pressure Turbine (Effect of Partial Admission)

Subsynchronous vibration of high-pressure steam turbine is one of the difficult problems to improve the reliability of power plant. Extensive work has been done to prevent the low frequency vibration of high-capacity steam turbine and most of the problems were practically solved (1). In the future, we must build up theoretical approach to design a new turbine operating under the steam condition of high-temperature and high-pressure. To design such an advanced steam turbine, it is necessary to solve the effect of partial admission on control stage of the steam turbine. This paper describes the experimental results from the scale model of the steam turbine and theoretical analysis of destabilizing forces. In theoretical analysis, destabilizing forces that take partial admission into consideration were analyzed. As a result, it was clarified that large destabilizing force was generated in partial admission condition and the destabilizing force varied periodically by the instant rotor position. In experimental study, we designed the new inlet seal for the prevention against the vibration. From the experimental result that increase of total flow rate leads the system stable, we showed the effectiveness of new inlet seal. And we paid attention to the step-up that is the step between blade and nozzle. As a result, it was experimentally proved that the step-up had a large influence on the rotor stability.

308 高圧蒸気タービンの不安定振動に関する研究(OS-3 振動基礎(2))

308 高圧蒸気タービンの不安定振動に関する研究(OS-3 振動基礎(2))

817 シールの不安定化力に及ぼす部分送入の影響 : その2:フラットシールとラビリンスシールの比較(GS-10 回転機)

Subsynchronous vibration of high pressure turbines has been investigated for many years. It was found that the phenomenon was related to the partial admission condition of the control stage. One of the causes of the destabilizing force is considered to be the labyrinth seal of the control stage. In this study, the partial admission effect was tested using a small seal model. It was found that partial admission increases the destabilizing force.