Mass Flow Rate Of Cooling Air Research Articles

Experimental Investigation of the Sensitivity of Forced Response to Cold Streaks in an Axial Turbine

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. It has already been shown that hot streaks from the combustors lead to inhomogeneity in the flow path, resulting in increased blade dynamic stress. However, not only hot streaks but also cold streaks occur in modern aircraft engines due to deterioration-induced widening of cooling holes. This work investigates this effect in an experimental setup of a five-stage axial turbine. Cooling air is injected through the vane row of the fourth stage at midspan, and the vibration amplitudes of the blades in rotor stage five are measured with a tip-timing system. The highest injected mass flow rate is 2% of the total mass flow rate for a low-load operating point. The global turbine parameters change between the reference case without cooling air and the cold streak case. This change in operating conditions is compensated such that the corrected operating point is held constant throughout the measurements. It is shown that the cold streak is deflected in the direction of the hub and detected at 40% channel height behind the stator vane of the fifth stage. The averaged vibration amplitude over all blades increases by 20% for the cold streak case compared to the reference during low-load operating of the axial turbine. For operating points with higher loads, however, no increase in averaged vibration amplitude exceeding the measurement uncertainties is observed because the relative cooling mass flow rate is too low. It is shown that the cold streak only influences the pressure side and leads to a widening of the wake deficit. This is identified as the reason for the increased forcing on the blade. The conclusion is that an accurate prediction of the blade’s lifetime requires consideration of the cooling air within the design process and estimation of changes in cooling air mass flow rate throughout the blade’s lifetime.

Film Cooling Modeling in a Turbine Working under the Unsteady Exhaust Flow of Pulsed Detonation Combustion

Pressure gain combustors (PGCs) have demonstrated significant advantages over conventional combustors in gas turbine engines by increasing the thermal efficiency and reducing the pollution emission level. PGCs use shock waves to transfer energy which contributes to the increase in outlet total pressure. One of the major obstacles in the actual implementation of PGCs in the gas turbine cycle is the exploitation of the highly unsteady flow of the combustor outlet with the downstream turbine. Because of the higher outlet temperature from the PGCs, the turbine blade cooling becomes essential. Due to the highly fluctuating unsteady flow of PGCs, 3D CFD simulation of turbines becomes very expensive. In this work, an alternative approach of using a 1D unsteady Euler model for the turbine is proposed. One of the novel aspects of this paper is to implement the turbine blade cooling in the unsteady 1D Euler model. The main parameters required for the turbine blade cooling are the cooling air mass flow rate, temperature, and pressure. Due to the introduction of coolant flow, the blades are no longer adiabatic and the mass flow rate across the turbine is not constant. Comparing the 1D Euler results against zero-dimensional calculation and 3D CFD approach showed a very good match for both steady and unsteady simulations confirming the applicability of the 1D method.

Investigation of hydrogen-enriched kerosene-fueled rotating detonation engine with multi-column film cooling

To address the thermal protection challenges associated with the rotating detonation engine (RDE) in engineering applications, this study employs a three-dimensional numerical simulation based on the Eulerian–Lagrangian model to investigate the flow field of the kerosene-fueled rotating detonation with hydrogen addition. We explore the interaction between the rotating detonation flow field and the cooling air induced by multiple columns of uniformly distributed film cooling holes and also analyze the cooling effectiveness of film cooling. In the flow field where the rotating detonation wave passes through the film hole periodically at a high frequency, an increase in the number of film hole columns can decrease the fluctuation amplitude of the cooling air mass flow rate, and the recovery time of the blockage of film cooling holes shortens within a complete rotating detonation cycle. At a low injection pressure of 0.4 MPa, the cooling jet can barely be injected into the combustor. As the injection pressure increases to 0.6 and 0.8 MPa, the mass flow rate of cooling air increases significantly with enhanced cooling efficiency; however, a further rise to 1.0 MPa may result in the detachment of cooling air from the surface, without providing additional improvements in the protection area and cooling efficiency. Along the axial direction of the RDE, film cooling holes demonstrate an enhancement in cooling efficiency, which is found to maximize near the outlet.

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.

Visualization and PIV-study of the formation of a cooling film when flowing around the leading edge of the gas turbine nozzle blade

The results of particle image velocimetry near the perforated leading edge of the nozzle vane of gas turbine are presented. Visualization of the formation of cooling film on the surface of the blade with determination of its thickness is carried out. On the basis of the obtained results, the influence of the blown cooling air mass flow rate on the formation of the film is analyzed.

CFD and experimental investigation into a non‐intrusive method for measuring cooling air mass flow rate through a synchronous generator

This study presents a detailed methodology for non-intrusive measurement of cooling air mass flow rate that enables an overall machine evaluation. This approach enables the simultaneous measurement of air mass flow with shaft torque at differing operating points while minimising the change in air flow introduced by the measurement system. The impact of geometric parameters in the designed system is investigated using a detailed 180° computational fluid dynamics (CFD) model. Special attention was paid to minimising their influence on pressure drop, the mass flow rate through the machine, and measurement uncertainty. Based on the results of this investigation, the system was designed and manufactured, and the experimentally measured data was used to validate the CFD predictions. For the as optimal identified configuration, the flow rate is predicted to decrease by 2.2% relative to unrestricted operation. The achieved measurement uncertainty is ± 2.6% at synchronous speed.

Thermal performance enhancement of vapor chamber by coating mini-channel heat sink with porous sintering media

This paper have been investigated on the thermal performance enhancement of air cooling vapor chamber by coating mini-channel heat sink inside with porous sintering wick sheet. The results obtained from experiments are considered and compared with without porous sintering wick sheet. The effects of power input, amount of filled working fluid into the vapor chamber and mass flow rate of air on the cooling performance and thermal resistance characteristics are considered. It can be found that the porous sintering wick sheet has significant effect on the increment of the capillary force which results in higher heat transfer rate. Therefore, the thermal performance of air cooling vapor chamber with porous sintering wick sheet inside mini-channel shows 20% maximum higher than that without porous sintering wick sheet. In addition, the increasing of power in put and cooling air mass flow rate have significantly increased thermal performance of the vapor chamber. The passive cooling device with vapor chambers is favorable technique that can enhanced thermal performance and reduce heat accumulate on the electronic component.

Experimental investigation on air-side flow-field and water-side heat exchange performance of radiator based on matrix fans

This paper investigated the effect of four different fan matrix configurations on the air-side flow-field and water-side heat exchange performance of a radiator. With the introduction of fan matrix configurations, the wake region behind bumper beam is enlarged, and the vortex pair breaks up much rapidly, thus enhancing the turbulence intensity of wake. The vorticity reaches the minimum level under the fan matrix N = 6, which could reduce the energy loss of the airflow upstream of radiator. The fan matrix configuration can increase the velocity uniformity of the airflow passing through the radiator, especially for the fan matrix N = 6. Furthermore, due to the fan matrix N = 6 achieves the maximum heat dissipation uniformity of radiator, and it also achieves the best heat exchange performance. Consequently, to achieve the maximum cooling air mass flow rate and heat exchange performance, it should carry out an optimization process during the design phase of fan matrix.

An approach to the analysis of heat and mass transfer characteristics in indirect evaporative cooling with counter flow configurations

Indirect evaporative cooler (IEC), regarded as a zero pollution, inexpensive and energy efficient cooling device, has been used in many occasions. This paper aims at developing a new approach for analyzing the coupled heat and mass transfer characteristics in indirect evaporative cooling with counter flow configurations. Firstly, a two-dimensional computational fluid dynamics (2-D CFD) model is used to simulate the coupled heat and mass transfer processes. Then, a one-dimensional (1-D) model is used to analyze the fluid stream side average Nusselt number and the cooling air side average Nusselt and Sherwood numbers based on the numerical results of the 2-D model. Thus, the 1-D model can be used to retrieve the 2-D model results using those average Nusselt and Sherwood numbers obtained. This improved accuracy will help to promote the control technologies based on an electronic control unit (ECU) for the processes in similar indirect evaporative cooling devices involved. Further, a similarity analysis is presented to deduce the 2-D model equations into dimensionless forms with the purpose of obtaining the minimum set of grouped dimensionless factors affecting the average Nusselt and Sherwood numbers. Finally, the effects of the ratio of liquid water film to cooling air mass flow rate, cooling air inlet Reynolds number, cooling air inlet dimensionless temperature, fluid stream inlet Reynolds number, liquid water film inlet dimensionless temperature, the ratio of channel length to half width of cooling air channel and the ratio of fluid to cooling air channel width on the average Nusselt and Sherwood numbers are examined in detail.

A novel method for computation of temperature profile of turbine disk

A novel temperature computation method of turbine disk is proposed according to theoretical analysis, where the coupling analysis of the outer surface in disk and fluid relative to this outer surface was carried out, instead of the segregation condition (constant wall temperature or constant wall heat flux condition). The selected correlations, numerical and experimental data of the heat transfer coefficient are presented and compared, so are the theoretical and simulated temperature profiles. The results show that: The maximum temperature deviation coefficient (φT) between the theoretical results and simulation data is less than 8.7% while ReΦ = 4.65×105, Cw = 7520, Rem = 5×105. The convective heat transfer coefficient distributions at the disk outer surface exhibited the influence of region A and region B. The convective heat transfer is dominated by the mass flow rate of cooling air in region A, while dominated by the mainstream mass flow rate in region B. The temperature of the turbine disk decreases with the mainstream mass flow rate increasing, especially at the high radius of turbine disk, while the overall temperature of turbine disk decreases with the increase of cooling air mass flow rate. Both the hr and hz increase with the ReΦ increasing, leading to a minor increase in temperature of turbine disk eventually.

Steady State Model of Cooling Tower Used in Air Conditioning

To predict the performance of cooling tower used in air conditionings in variable operating conditions, a steady state model of cooling tower suitable for variable conditions simulation was built and tested. Comparison between the prediction value and the experimental value shows good agreement. The results show that this model is suitable for calculation of cooling capacity of cooling tower used in air conditionings at variable inlet temperature or mass flow rate of condensing water, and at variable inlet wet-bulb temperature or mass flow rate of cooling-air. This model is useful for simplifying performance test, equipment selection and running control.

Performance prediction of an improved air-cooled steam condenser with deflector under strong wind

For an air-cooled steam condenser (ACSC), environmental wind can cause a large flow rate reduction in the axial fans mainly near the windward side of the air-cooled platform due to cross-flow effects, resulting in a heat transfer reduction. This leads to an increase of turbine back pressure, and occasional turbine trips occur under extremely gusty conditions. A new method is proposed in this paper to remove the strong wind effect by adding deflecting plates under the air-cooled platform, which contributes to forming a uniform air mass flow rate in the axial fans by leading enough cooling air to the fans in the upwind region. Numerical simulation is made of the thermal-flow characteristics and heat transfer performance of the improved ACSC with deflectors. A heat exchanger model is used for simulating the flow and heat transfer in the ACSC, in which the heat exchanger is simplified to a porous medium and all flow losses are taken into account by a viscous and an inertial loss coefficient. A fan model is used for reaching the flow condition at the heat exchanger inlet with the actual performance curves of the fan. It is found that the improved ACSC with deflector shows a significant enhancement in both the cooling air mass flow rate and the heat rejection rate compared with the conventional ACSC. The higher the wind speed is, the larger the heat transfer enhancement of the improved ACSC is. The effect of the plate inclination is also investigated, and the inclination angle of 45° is found to be the optimum value for the arrangement of the deflector.

J0501-2-4 トランスピレーション冷却を有するタービン翼列内の流れの数値解析(流体機械の研究開発におけるEFD/CFD(2))

The further improvement of gas turbines requires the development of cooling technique with reduction of cooling air mass flow rate as well as the increase of the turbine inlet temperature. The theoretically most effective air cooling method is the transpiration cooling, which will be expected to reduce the cooling air mass flow rate. In the present study, the two-dimensional flow within the turbine cascade made by the porous media was analyzed numerically by the commercial CFD code. The calculations were performed in order to examine the influence of parameters on the cooling efficiency, such as the porosity, the mean diameter of particles of the porous media and the blowing ratio. The results revealed that the cooling efficiency was strongly influenced by these parameters.

Numerical Investigation of Flow around the Leading Edge of a Turbine Blade with Transpiration Cooling (1st Report, Properties for Fundamental Parameters)

The further improvement of gas turbines requires the development of cooling technique with reduction of the cooling air mass flow rate as well as the increase of the turbine inlet temperature. The theoretically most effective air cooling method is the transpiration cooling, which will be expected to reduce the cooling air mass flow rate. In the present study, the two-dimentional flow simulating the flow around the leading edge of a turbine blade model (LEM) are analyzed numerically by the CFD code. The calculations are performed in order to examine the influence of parameters on the flow through the LEM, such as the porosity and the mean diameter of perticles of the porous media and the blowing ratio. The results reveal the effects of those parameters on the temperature inside the porous media and the cooling air pressure. Furthermore, the effects of the variations of the viscosity and the fluid density inside the porous media are also clarified.