Pre-swirl System Research Articles

Theoretical and experimental evaluation of temperature drop and power consumption in a cover-plate pre-swirl system for gas turbine cooling

The pre-swirl system has the ability to decrease the air supply temperature so as to improve the cooling performance and the operating life for turbine rotating blade. In this paper, a test rig was designed to reveal the aero-thermal characteristics in a cover-plate type pre-swirl system of gas turbine engines. Then, the theoretical derivation and experimental evaluation were conducted to reveal the variation of temperature drop and power consumption of a pre-swirl system with the mass flow rate ratio and rotating speed. Especially, the pressure and temperature on the rotating turbine disc were measured by a co-rotating data recorder. The theoretical and experimental analyses indicate that the temperature drop of pre-swirl system increases as the velocity coefficient of the pre-swirl nozzle outlet enhanced, but presenting a decrease with the increment of the rotating Mach number. Then, the ideal dimensionless temperature drop can be formally unified with the actual dimensionless temperature by defining the tangential velocity recovering coefficient, which is verified with the experimental results. Moreover, a linear relationship between the dimensionless temperature drop and the effective swirl ratio at the nozzle outlet can be deduced further. Especially, this relationship shows a good agreement between the predicted values and numerical results. Since the dimensionless temperature drop decreases with the increase of the dimensionless power consumption; an important discovery can be concluded that the algebraic sum of these two physical quantities is always equal to 1. Therefore, the results can offer a reference for the design and optimization of gas turbine cover-plate type pre-swirl system.

Effect of pre-swirl nozzle closure modes on unsteady flow and heat transfer characteristics in a pre-swirl system of aero-engine

The pre-swirl system is of great importance for temperature drop and cooling air supply. This study aims to investigate the influencing mechanism of heat transfer, nonuniform thermodynamic characteristics, and cooling air supply sensitivity in a pre-swirl system by the application of the flow control method of the pre-swirl nozzle. A novel test rig was proposed to actively control the supplied cooling air mass flow rate by three adjustable pre-swirl nozzles. Then, the transient problem of the pre-swirl system was numerically conducted by comparison with 60°, 120°, and 180° rotating disk cavity cases, which were verified with the experiment results. Results show that the partial nozzle closure will aggravate the fluctuation of air supply mass flow rate and temperature. When three parts of nozzles are closed evenly at 120° in the circumferential direction, the maximum value of the nonuniformity coefficient of air supply mass flow rate changes to 3.1% and that of temperature changes to 0.25%. When six parts of nozzles are closed evenly at 60° in the circumferential direction, the maximum nonuniformity coefficient of air supply mass flow rate changes to 1.4% and that of temperature changes to 0.20%. However, different partial nozzle closure modes have little effect on the average air supply parameters. Closing 14.3% of the nozzle area will reduce the air supply mass flow rate by 9.9% and the average air supply temperature by about 1 K.

Prediction of the sealing flow effect on the temperature drop characteristics of a pre-swirl system in an aero-engine

Abstract The sealing flow will inevitably affect the cooling airflow quality in a second air system of an aero-engine. In this study, theoretical derivation and numerical simulation were conducted to establish a modified mixing model that considers both the torque and the source of the mixing flow. Then, the effect of the sealing flow can be evaluated using the modified mixing model. The results demonstrate that the effects of the sealing outflow on the flow and temperature characteristics of the pre-swirl system are weak when the air supply mass flow rate and pressure are fixed. However, the effects of the sealing inflow are significant. When the inner sealing inflow mass flow rate is increased from 0 to 20%, the temperature drop effectiveness is decreased by 31.3%. The temperature drop effectiveness is decreased by 29.2% as the inner sealing inflow temperature rises by 37 K. Then, the temperature drop effectiveness is increased by 15.6% as the inner sealing inflow swirl ratio is increased from 0 to 0.8. The results of the modified mixing model are in satisfactory agreement with the numerical results, which show a maximum temperature drop deviation of 7.22%. Compared with the previous method, the prediction accuracy of the pre-swirl cavity temperature drop can be increased by 22.28%.

Experimental and CFD analysis on the pressure ratio and entropy increment in a cover-plate pre-swirl system of gas turbine engine

The pre-swirl system can offer cooling air to improve the extreme thermal shock to the rotating turbine blades in a gas turbine engine. This study focuses on theoretical, experimental, and numerical analyses about the flow and entropy increment for a pre-swirl system at the high-speed test conditions (up to 10000 rpm). Especially, the pre-swirl system entropy increment was firstly measured in the experiment. Then, the experimental test and CFD analysis are conducted to reveal the pressure ratio characteristics and loss mechanism. Research suggests that the non-dimensional temperature drop and the rotating Mach number are major determinants for the ideal pressure ratio. However, the ratio of the actual system pressure ratio to the ideal pressure ratio only depends on the entropy increment. For a given rotating Mach number, the actual system pressure ratio decreases with the non-dimensional temperature drop increasing. The increment of mass flow rate results in an enhancement in the entropy increment. In addition, the entropy increment of the receiver hole can be minimal for the swirl ratio of pre-swirl nozzle outlet close to 1. Therefore, this study can provide the basis for designing and optimizing the pre-swirl system at a high rotation speed.

Design optimization of a vane type pre-swirl nozzle

Pre-swirl system is installed to minimize energy loss between the stationary and rotating parts of turbine secondary air system. Although various optimization studies were conducted to increase the pre-swirl efficiency, most of the studies were focused on a hole type pre-swirl nozzles. In this study, a vane type pre-swirl nozzle was optimized to increase mass flow rate and temperature drop for given boundary conditions. The system performance was analyzed by 3D CFD and the objective functions were used to maximize the discharge coefficient and the adiabatic effectiveness. After sensitivity analysis, seven design variables were chosen on the three planes of nozzle span-wise direction. The OLHD method was used to obtain the initial scattered test points, and the additional ones were supplied by the ALHD method. The Kriging model was constructed as the surrogate one, and refined iteratively until satisfying the convergence criteria between the estimated point and the CFD result. The optimized model improved the span-wise uniformity of the flow path and the discharge coefficient was increased by 2.57%, whilst the adiabatic effectiveness remained nearly constant. The performance was also analyzed for pressure ratio and off-design points, with the optimized model showing better performance at all boundary conditions.

The effect of rotating receiver hole shape on a gas turbine pre-swirl system

The life assessment and the efficiency of turbine cooling blades and vanes are seriously affected by the cooling air delivery system of a gas turbine. The pre-swirl system in a gas turbine plays an important role between the stationary and rotating parts to supply enough cooling air at the appropriate temperature at the expense of pressure drop. In the stationary part, the pre-swirl nozzle creates the flow angle in advance of the rotating orifice, called the receiver hole, to minimize energy loss. However, because of the sudden change of direction and area of the flow path, an energy loss occurs at the inlet of the receiver holes. The circumferential velocity at the receiver hole inlet decreases even though the circumferential velocity at the pre-swirl outlet is equal to the tangential velocity of the turbine rotor system. To reduce the energy loss at the pre-swirl system, various shape parameters can be applied to the receiver hole, and the area ratio between the pre-swirl nozzle throat area and the receiver hole cross-sectional area can also be varied considering the structure problem, mass flow rate, and pressure drop. In this study, the shape of the receiver holes and its effects were analyzed using a 3D CFD method that was validated by previous studies including experimental data. The edge shape, inclined angle, area ratio, and number of receiver holes were analyzed with the discharge coefficient, adiabatic effectiveness, and pressure drop. The pre-swirl system perform-ance increased as the area ratio increased, and under fixed area ratio, a large number of smalldiameter receiver holes showed better performance. The receiver hole edge fillet was the most influential shape parameter in pre-swirl performance.

반경방향 분사방식 프리스월 시스템의 프리스월 노즐과 리시버 홀의 상대적 위치에 따른 시스템 성능변화

프리스월 노즐과 리시버 홀의 상대적 위치가 반경방향 분사방식 프리스월 시스템의 성능에 미치는 영향을 분석하였다. 본 연구에서는 5개의 프리스월 노즐 위치와 4개의 리시버 홀 위치 조합을 통해 20개의 설계점에 대한 분석을 진행하여 유량계수와 온도 강하 효율 변화 경향성을 연구하였다. 시스템 유량계수는 프리스월 노즐의 압력비와 비슷한 경향을 보였다. 캐비티 내부의 유동이 벽면의 영향을 크게 받을수록 시스템 성능 변화가 발생하였으며 회전면보다 정지면의 영향력이 더 큰 것을 확인하였다. 형상변수 변화에 따라 기준 설계점 대비 유량계수는 -1.39%~1.25%, 온도강하 효율은 –5.41%~2.94% 변화하였다.

가스터빈 프리스월 시스템의 외기 온도와 터빈 부하 조건에 따른 탈설계점 특성 분석

가스터빈 프리스월 시스템의 외기 온도와 터빈 부하 조건에 따른 탈설계점 특성 분석

가스터빈 프리스월 시스템의 유량계수 및 온도강하 효율 향상을 위한 리시버 홀 최적화 전산해석 연구

가스터빈 프리스월 시스템의 유량계수 및 온도강하 효율 향상을 위한 리시버 홀 최적화 전산해석 연구

Optimization of pre-swirl nozzle shape and radial location to increase discharge coefficient and temperature drop

Hole-type pre-swirl nozzle was optimized using CFD analysis and experiments. CFD methodologies were validated by comparing the CFD results with experiments. Four design variables were considered in the optimization process: Nozzle inlet length (L), outlet length (l), inlet diameter (D), and radial location (rp). The optimization process included the optimal Latin hypercube design sampling method with the Kriging surrogate model and genetic algorithm. The single-objective optimization was performed to maximize the discharge coefficient. Results showed that the optimized nozzle reduced total pressure losses and increased mass flow rate. Total temperature drop effectiveness was increased from 0.07 to 0.29. The total temperature in pre-swirl system could be characterized as the reduction in temperature by nozzle acceleration and elevation by aerodynamic losses due to friction and viscous effects in the system. The optimized model showed a discharge coefficient of 0.846, which was 31.7 % higher than the baseline condition. By improving the discharge coefficient the pre-swirl system reduced aerodynamic losses, and the mass flow rate was increased at certain pressure ratios or satisfied the pressure margin for blade cooling.

Design and Numerical Analysis of a Vane Shaped Receiver Hole in a Cover-Plate Preswirl System

In a cover-plate system, rotating receiver hole is an important component, because its structure and characteristics directly influence the aerodynamic loss and cooling performance in the preswirl system. A new type of vane shaped (VS) receiver hole was designed and presented in this paper. Numerical simulations were carried out to compare the performances among high-radius direct transfer system (model-A), low-radius cover-plate system with simple drilled (SD) receiver holes (model-B), and low-radius cover-plate system with VS receiver holes (model-C). Results indicate that for the operating conditions simulated here, temperature drop effectiveness of the high-radius preswirl system is much better compared to the low-radius system with SD receiver hole. With VS receiver hole, the aerodynamic loss in model-C is the lowest. The nondimensional static pressure at preswirl nozzle exit is only 0.93, around 10% lower than model-B. Moreover, it has a more remarkable cooling performance. The temperature drop effectiveness of model-C can be as high as 0.52, around 67.7% higher compared to model-A. The system with VS receiver hole could not only realize the advantage of low leakage flow as a low-radius system, but also could achieve higher temperature drop compared to high-radius system.

Numerical Characterization of Flow and Heat Transfer in Preswirl Systems

This paper deals with a numerical study aimed at the validation of a computational procedure for the aerothermal characterization of preswirl systems employed in axial gas turbines. The numerical campaign focused on an experimental facility which models the flow field inside a direct-flow preswirl system. Steady and unsteady simulation techniques were adopted in conjunction with both a standard two-equation Reynolds-averaged Navier–Stokes (RANS)/unsteady RANS (URANS) modeling and more advanced approaches such as the scale-adaptive-simulation (SAS) principle, the stress-blended eddy simulation (SBES), and large eddy simulation (LES). Overall, the steady-state computational fluid dynamics (CFD) predictions are in reasonable good agreement with the experimental evidences even though they are not able to confidently mimic the experimental swirl and pressure behavior in some regions. Scale-resolved approaches improve the computations accuracy significantly especially in terms of static pressure distribution and heat transfer on the rotating disk. Although the use of direct turbulence modeling would in principle increase the insight in the physical phenomenon, from a design perspective, the trade-off between accuracy and computational costs is not always favorable.

가스터빈 프리스월 시스템의 유량계수 향상을 위한 베인형 프리스월러의 형상 최적화

가스터빈 프리스월 시스템의 유량계수 향상을 위한 베인형 프리스월러의 형상 최적화

가스터빈 이차 냉각 유로에 적용되는 프리스월러 노즐의 분사 방식 차이에 따른 시스템 특성 연구

가스터빈 이차 냉각 유로에 적용되는 프리스월러 노즐의 분사 방식 차이에 따른 시스템 특성 연구

Effect of splitter location on the characteristics of a vane-type pre-swirl system

The current study proposes a new pre-swirler configuration with a splitter for gas turbines. The pre-swirl vane with low aspect ratio results in strong secondary flows and high endwall loss. The splitter concept is demonstrated to reduce aerodynamic loss and improve swirl ratio. The discharge coefficient and swirl ratio increase after the distance between the vane and the splitter is adjusted. Numerical simulations are conducted to validate the performance of the pre-swirler with a splitter. The total pressure loss at the exit of the pre-swirler is reduced by 14 % to 17 % when the splitter is installed. The exit yaw angle increases when the space between the upper vane and the splitter is reduced. Consequently, the increased exit yaw angle increases the tangential velocity at the exit of the pre-swirler and the swirl ratio of the pre-swirl system. A vane-type pre-swirler with splitter is recommended to improve the performance of the pre-swirl system.

Pre-swirl system의 유량계수 향상을 위한 Pre-swirl nozzle의 형상 최적화 전산해석 연구

Optimization process of pre-swirl nozzle geometry was conducted to improve the discharge coefficient of pre-swirl system by using CFD. The optimization of pre-swirl nozzle shape covered the converging angle and the location of the converging nozzle. Optimization process included Optimal Latin Hyper-cube Design method to get the experimental points and the Kriging method to create the response surface which gives candidate points. The process was finished when the difference between the predicted value and CFD value of candidate point was less than 0.1%. This paper compared the Reference model, Initial model which is the first model of optimization and Optimized model to study flow characteristics. Finally, the discharge coefficient of Optimized model is improved about 17 % to the Reference model.

A new design of vane-shaped hole pre-swirl nozzle

Theoretical analysis shows that the temperature drop of a pre-swirl system directly relates to the pre-swirl effectiveness of the pre-swirl nozzle. Besides, increasing the discharge coefficient and reducing the actual flow angle are the main ways to increase the pre-swirl effectiveness. A new design of pre-swirl nozzle called vane-shaped hole nozzle was introduced and analyzed in this paper. By keeping the throat area, the radial location and the pre-swirl angle (15°), numerical comparisons were carried out between the vane-shaped hole nozzle and other three typical nozzles, widely used in industry: simple drilled nozzle, aerodynamic nozzle and cascade vane nozzle. In order to involve the mixing and rotating effects in the pre-swirl cavity downstream of the nozzles, the rotating pre-swirl cavity and receiver hole were included in the computational models. Numerical results show that aerodynamic nozzle could alleviate the rapid acceleration and deflection at nozzle inlet, which results in 13.7% higher discharge coefficient than the simple drilled nozzle. The discharge coefficient of the cascade vane nozzle can be as high as 0.97 due to the aerodynamical design; however, the pre-swirl effectiveness is only 0.86 because of a large deviation angle (2.4°). For the vane-shaped hole nozzle, the vane height/pitch ratio could be flexibly adjusted to an appropriate value, which makes its performance better than that of the traditional ones. Higher vane height/pitch ratio and close to zero trailing edge radius lead to a small deviation angle (0.56°). Consequently, the pre-swirl effectiveness of the vane-shaped hole nozzle is about 8% higher than that of the cascade vane nozzle, though the discharge coefficient is about 5% lower. Additionally, the volume of the solid block in the vane-shaped hole nozzle is larger than that in the cascade vane nozzle, which could reduce the difficulty in manufacturing but increase the total weight.

Numerical investigation on the flow and heat transfer characteristics in radial pre-swirl system with different fillet radius at the junction of inlet cavity and nozzle

This paper conducts a numerical study to investigate the effect of the fillet radius at the junction of inlet cavity and nozzle on the flow and heat transfer characteristics of a radial pre-swirl system. The Reynolds-averaged Navier-Stokes equations, coupled with SST turbulence model, are adopted and solved. In this paper, four fillet radii at three nozzle length to diameter ratios are selected to study the flow dynamics of the radial pre-swirl rotor-stator system. The results obtained in this paper indicate that considering the effect of the ratio of fillet radius to nozzle diameter, rf/D, on the adiabatic effectiveness, the discharge coefficient of the receiver hole and the total pressure loss in the pre-swirl nozzle and the pre-swirl cavity, there is an optimum value of rf/D which can provide the best performance of the pre-swirl system. The effect of rf/D on the heat transfer coefficient h is also conducted. Numerical results clearly show that h on the rotor wall at low radius increases with rf/D. The uniform distribution of h on the rotor wall at receiver hole radius can be observed as synchronous rotation between the receiver hole and the cooling air occurs.

Numerical investigation of the flow and heat transfer characteristics for a pre-swirl rotor–stator system with center inflow

The effects of the center inflow on the flow and heat transfer characteristics in a pre-swirl rotor–stator system are numerically investigated using the CFD software ANSYS-CFX. The investigation of the pre-swirl system without center inflow is also conducted to be served as a contrast and these results are compared with experimental measurements to verify the computational method. In this paper, five mass flow rate ratio of the center flow to the pre-swirl flow, mf, four dimensionless mass flow rate of pre-swirl flow, Cw, and five rotation speeds, n, are selected to study the flow dynamics of the pre-swirl system in terms of the flow structure, the air swirl ratio, the total pressure loss coefficient, the discharge coefficient of the receiver holes and the adiabatic effectiveness. It shows that the maximum value of the discharge coefficient occurs as swirl ratio in the core at the receiver-hole radius equals 1 and mf reaches as a high value as possible, and the adiabatic effectiveness decreases as mf increases. In addition, the relation between the Nusselt number, Nu, and mf, Cw as well as n is also illustrated and discussed.

Numerical investigation of flow and heat transfer characteristics in radial pre-swirl system with different pre-swirl nozzle angles

The effect of pre-swirl nozzle angle (θ) on the flow and heat transfer characteristics of a radial pre-swirl system is numerically investigated using the CFD software ANSYS-CFX. In this paper, six pre-swirl nozzle angles are selected to study the flow dynamics of the radial pre-swirl system in terms of the flow structure, the nozzle exit flow angle, the air swirl ratio at nozzles outlet and receiver holes inlet, the total pressure loss coefficient in the nozzle and the cavity, the discharge coefficient of the nozzles and receiver holes and the adiabatic effectiveness. It is shown that the case of θ=20° exhibits the best performance in adiabatic effectiveness and total pressure loss in this system, while the case of θ=60° provides a maximum in discharge coefficient of receiver holes that is slightly higher than that of θ=20°. Comparatively, the case of θ=20° provides the best performance of the radial pre-swirl system. In addition, the effect of pre-swirl nozzle angle on the heat transfer characteristics is also presented. Results show that the heat transfer on the rotor disk is dominated by the flow structure and tangential velocity differential, and the peak in heat transfer coefficient can be observed near the receiver hole.