Effects of plasma actuation and hole configuration on film cooling performance

In this paper,plasma actuators are arranged asymmetrically downstream the wall to improve film cooling performance.Effects of blowing ratio,hole configuration and applied voltage on flow characteristics and film cooling effectiveness were investigated numerically on a flat plate.Results show that highest film cooling effectiveness distribution is obtained both in the spanwise and streamwise directions under blowing ratio of 0.5.Average wall film cooling effectiveness of cylindrical hole increases by 251.9%under blowing ratio of 0.5 compared to that under blowing ratio of 1.5.The scale of the counter rotating vortex pairs(CRVP)from fan shaped hole and sister hole are significantly reduced compared to that from cylindrical hole.The console hole has an anti-counter rotating vortex pair(Anti-CRVP),which weakens the entrainment of the CRVP to the coolant air near the wall.Compared with the cylindrical hole,average wall film cooling effectivenesses for fan shaped hole,sister hole and console hole increase by 73.1%,97.5%and 119.9%.The adherent performance of the coolant air is enhanced after applying plasma actuator.The aerodynamic actuation of the plasma results in the rebound of the fluid close to the wall at 24 kV applied voltage.Average wall film cooling effectiveness of the console hole at 12 kV applied voltage is 10.6%higher than that without plasma.

Heat transfer behaviors of some supercritical fluids: A review

Supercritical fluids(e.g.,hydrocarbon fuels,water,carbon dioxide,and organic working medium,etc)have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion,and have been used or selected as the working fluids in engineering fields such as aerospace,nuclear power,solar energy,refrigeration,geothermal energy,chemical technology,and so on.To better understand the interesting characteristic or abnormal behaviors of supercritical fluids,most valuable research works(including experimental results and numerical studies)from domestic and abroad have been documented.As such,this paper presents a comprehensive review on heat transfer behaviors of some supercritical fluids in engineering applications.This review focuses on recently available articles published mainly from 2016 up to the present time.The common problems(i.e.,heat transfer enhancement and heat transfer deterioration particularly for the supercritical hydrocarbon fuels)in the supercritical field are summarized and some perspectives on future prospects are also included.

Special Issue dedicated to the 1^(st) International Conference on Supercritical CO_2 Power System(ICSCPS 2018)

This Special Issue of Journal of Thermal Science(JTS)contains a selection of peer-reviewed papers from the ICSCPS 2018,held in Beijing,China during June 29^th to July 1^st,2018.The conference was chaired by professor Jinliang Xu from the North China Electric Power University and sponsored by the Ministry of Science and Technology of China based on the National Key Research&Development Project“Fundamental studies and key technology development of high-efficiency carbon dioxide coal-fired power system”.

Optimization of cooling structures in gas turbines:A review

Attempts for higher output power and thermal efficiency of gas turbines make the inlet temperature of turbine to be far beyond the material melting temperature.Therefore,to protect the airfoil in gas turbine from hot gas and eventually prolong the lifetime of the blade,internal and film cooling structures with better thermal performance and cooling effectiveness are urgently needed.However,the traditional way of proceeding involves numerous simulations,additional experiments,and separate trials.Optimization of turbine cooling structures is an effective way to achieve better structures with higher overall performances while considering the multiple objectives,disciplines or subsystems.In this context,this paper reviews optimization research works on film cooling structures and internal cooling structures in gas turbines by means of various optimization methods.This review covers the following aspects:(A)optimization of film cooling conducted on flat plates and on turbine blades or vanes;(B)optimization of jet impingement cooling structures;(C)optimization of rib shapes,dimple shapes,pin–fin arrays in the cooling channels;(D)optimization of U-bend shaped cooling channels,and internal cooling systems of turbine blades or vanes.The review shows that through a reliable and accurate optimization procedure combined with conjugate heat transfer analysis,higher overall thermal performance can be acquired for single-objective or multi-objectives balanced by other constrained conditions.Future ways forward are pointed out in this review.

Film cooling performance and flow structure of single-hole and double-holes with swirling jet

This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance.Some combined-hole designs with swirling coolant flow entering the delivery hole are proposed and analyzed.Adiabatic film cooling effectiveness values for cases with various blowing ratios are compared.Detailed flow structures and underlying mechanisms are discussed.The results show that film cooling effectiveness is improved with jet swirl at high blowing ratios,and that swirl strength has significant influence on film cooling performance.Combined-hole designs can further improve film cooling performance using swirling jets due to mixing of coolant flows and interaction of vortices.The largest improvements of area-averaged film cooling effectiveness for a single-hole swirl case and a combined-hole swirl case over corresponding non-swirling case results are 157%and 173%,respectively.

Comparisons of Heat Transfer Enhancement of an Internal Blade Tip with Metal or Insulating Pins

Cooling methods are needed for turbine blade tips to ensure a long durability and safe operation.A common way to cool a tip is to use serpentine passages with 180-deg turn under the blade tip-cap taking advantage of the threedimensional turning effect and impingement like flow.Improved internal convective cooling is therefore required to increase the blade tip lifetime.In the present study,augmented heat transfer of an internal blade tip with pin-fin arrays has been investigated numerically using a conjugate heat transfer method.The computational domain includes the fluid region and the solid pins as well as the tip regions.Turbulent convective heat transfer between the fluid and pins,and heat conduction within pins and tip are simultaneously computed.The main objective of the present study is to observe the effect of the pin material on heat transfer enhancement of the pin-finned tips.It is found that due to the combination of turning,impingement and pin-fin crossflow,the heat transfer coefficient of a pin-finned tip is a factor of 2.9 higher than that of a smooth tip at the cost of an increased pressure drop by less than 10%.The usage of metal pins can reduce the tip temperature effectively and thereby remove the heat load from the tip.Also,it is found that the tip heat transfer is enhanced even by using insulating pins having low thermal conductivity at low Reynolds numbers.The comparisons of overall performances are also included.