WE found, on experimental grounds in Article I, that the field of air‐flow past a short body of low resistance shape, such as an aerofoil, comprises two dissimilar parts: (a) a thin boundary layer enveloping the body and dominated by viscous effects, and (b) a motion outside the boundary layer in which viscosity is much less important. It will be remembered that in the external motion occur the large pressure changes, which, transmitted through the boundary layer, account for nearly all the lift and for part of the drag. These pressures we observed to be calculable from the velocities without appreciable error by Bernoulli's equation. In the present Article we confine attention to this external flow, assuming it to be steady, incompressible, and inviscid. Its dependence upon (a), already discussed to some extent, we ignore; the boundary layer is conceived to be everywhere very thin, so that the only role it plays is to allow of relative velocity at the surface of the body. The assumptions made, excepting that of incompressibility, will appear drastic, and it will not be surprising if some of our deductions prove discordant with experimental fact. Nevertheless, they lead to a theory which finds many applications and uses in real fluid motion, and, in particular, gives an intimate view of aerofoil flow that is very close to the truth. It is convenient to develop our reasoning in analytical terms and for simplicity to restrict the flow to two dimensions (Article 1, §5). But the engineer will find special scope in this part of aerodynamics for graphical methods in the solution of particular problems.

Aerodynamics for Engineers

Understanding policy and technology responses in mitigating urban heat islands: A literature review and directions for future research

The rapid urbanization and land-use/land-cover (LU/LC) changes have resulted in the unplanned and unsustainable growth of the Indian cities. This has resulted in a number of environmental issues such as escalating the urban heat island (UHI) intensity over the cities. Therefore, this study was designed to model and quantify the UHI dynamics of Mumbai city in response to the LU/LC change during 1991–2018 using temporal Landsat datasets. The result shows a significant decline in vegetation cover from 215.8 to 129.27 km2, while the built-up areas have almost doubled, i.e., from 173.09 to 346.02 km2 in the Mumbai city during 1991–2018. As a consequence of this, a significant increase in the LST has been noticed in both urban heat island (UHI) and non-UHI zones. Although the areas under UHI zones have not increased significantly, the land surface temperature (LST) gap (difference between minimum and maximum LST) has declined in the Mumbai city from 30.04 °C in 1991 to 20.7 °C in 2018. Further, the minimum and mean LST over each LU/LC classes have also shown a significant increase. On the other hand, the regression analysis shows that the association between UHI and normalized difference built-up index (NDBI) has increased in the city, while the association of vegetation density (NDVI) and normalized difference bareness index (NDBaI) has declined in the city. The study can provide useful insights into the process of urban planning and policy makings for urban spatial planning and UHI mitigation strategies.

Urban Heat Island Dynamics in Response to Land-Use/Land-Cover Change in the Coastal City of Mumbai

Effects of lockdown due to COVID-19 outbreak on air quality and anthropogenic heat in an industrial belt of India

Urbanization creates enormous opportunities and contributes to socio-economic diversity that renovates the built environment. However, growth and development has an overwhelming impact on urban microclimate (UMC), as it modifies key environmental and meteorological parameters creating impacts like urban heat and dry islands, change in precipitation rate, frequency and intensity and so on. The current review focuses on UMC parameters like temperature, relative humidity, wind direction and speed, concentrating on reported variations and interlinkages. Although, there have been many advances in methodologies adopted for assessment of UMC, the implementation of key findings for improved urban planning is not adequately addressed. Chronology of research methodologies related to UMC assessment is compiled and reported including field observation-based studies, satellite-based observations and modeling and simulation of parameters affecting UMC. The study stresses on the gaps in research methodologies adopted and helps pave way for future research, by emphasizing implementation-oriented perspectives, such as development of frameworks, integrated assessment of parameters, development of simplistic tools for effective decision making. The study demonstrates the missing links in this reserach field and suggests action steps to take it from lab to land and further demands to focus on policy and implementation front, for coherent urban planning.

Assessment methods of urban microclimate and its parameters: A critical review to take the research from lab to land

Urbanization has resulted in many critical issues like increase in pollution levels, sudden climatic changes and the rise of temperature in the urban area, that is the formation of Urban Heat Islands (UHI). As the density of population rises, most of the land areas are being converted into cities and cities grows very rapidly. Due to the UHI effect, the cities are becoming hotter day by day. In India, all the metropolitan cities are victims of UHI effect and the severity of heat formation, necessitates research in this area. The present paper evaluates the trends of UHI studies in Indian cities and its out reach till 2018. Heat Island classification, methods of studying UHI in India and their limitation are discussed. Eventually a comparison of new trends of UHI studies in the world and where India lacks its growth in UHI research are included in this paper. One of the findings is that numerical modelling studies are very limited in India in this field and more focus in this area is required.

Urban Heat Island studies: Current status in India and a comparison with the International studies

Gas turbines are widely used in the areas of air propulsion, electric power generation, ship propulsion, external driving units, and other industrial applications. Efficient coating and cooling methods are often essential for the gas turbine surfaces to further achieve higher turbine inlet temperature and output efficiency. The thermal barrier coating (TBC) is the type of multilayered coating applied on rotating and stationary surfaces of the gas turbine components to safeguard them against the attack of high stream thermal loads and pressure gradients of the hot mainstream flows. TBC can also assist in surface-modified film cooling of gas turbine components. In this paper, the thermal barrier coated surface-modified film cooling methods for gas turbine components, viz. leading edge, pressure side, suction side, end wall, flat surfaces of stator guide vane and rotor blade, were reviewed and discussed in detail. The surface-modified film cooling methods for gas turbine components are grouped into three broad categories based on their geometric appearance. Each group was reviewed in detail for geometric and flow parameters, measurement techniques, flow characteristics, and performance parameters. Further, this study provides an overview of geometric and flow parameters of the compound angled film hole. Finally, the areas required for future research on the application of surface-modified film cooling methods are recommended in this review.

Thermal barrier coated surface modifications for gas turbine film cooling: a review

This paper presents the study of the overall aerodynamic performance of road vehicles and suggests a method to reduce the drag force and also to find the optimum location for placing basebleed in a car using aerodynamic principle. The overall aerodynamic drag force is reduced by eliminating wake region at the rear side of the car and reducing pressure in the front region of the car by delaying the flow separation. This improves the overall aerodynamic performance of the car thereby reducing fuel consumption, as well as improving stability and comfort by the attachment of basebleed. The wind tunnel tests are conducted for a subscale model of car with the basebleed at various locations along the front and rear side of the car in both X and Y directions. The coefficient of drag (CD), the coefficient of lift (CL) and coefficient of side force (CS) for the car is measured to interpret the effect of flow conditions on the car model. The experimental result reveals that the attachment of base bleed at an optimum position in the front and rear side of the car improves its performance and decreases drag coefficient by 6.188 %.

https://jafmonline.net/JournalArchive/download?file_ID=47553&issue_ID=252

Reduction of Aerodynamic Drag Force for Reducing Fuel Consumption in Road Vehicle using Basebleed

The present study explores the possibility of increasing the efficiency of the small horizontal axis wind turbine rotor by adding winglets at the tip of the blade. The effects of changing the winglet configuration with the blade on the power performance of small wind turbine rotor models were investigated experimentally. The blades with four different configurations of winglets are fabricated using Glass Fibre Reinforced Plastic materials and are used for the study. Experiments were conducted for all the rotor models with and without load conditions in the wind tunnel for various conditions. The power output is measured for the rotor models with load conditions. The maximum power coefficient obtained for an effective winglet configuration is about 0.43. It is observed that presence of winglet at the tip of the wind turbine blade will improve the power coefficient for low wind speed regions. It is recommended that the smaller curvature radius with sufficient winglet height added to the wind turbine rotor captures more wind energy in low wind speed region as against wind turbine rotors without winglets.

Experimental Investigation on Small Horizontal Axis Wind Turbine Rotor Using Winglets

Wind energy is one of the most significant renewable energy sources in the world. It is the only promising renewable energy resource that only can satisfy the nation’s energy requirements over the growing demand for electricity. Wind turbines have been installed all over the wind potential areas to generate electricity. The wind turbines are designed to operate at a rated wind velocity. When the wind turbines are exposed to extreme wind velocities such as storm or hurricane, the wind turbine rotates at a higher speed that affects the structural stability of the entire system and may topple the system. Mechanical braking systems and Aerodynamic braking systems have been currently used to control the over speeding of the wind turbine at extreme wind velocity. As a novel approach, it is attempted to control the over speeding of the wind turbine by aerodynamic braking system by providing the chord wise spacing (opening). The turbine blade with chord wise spacing alters the pressure distribution over the turbine blade that brings down the rotational speed of the wind turbine within the allowable limit. In this approach, the over speeding of the wind turbine blades are effectively controlled without affecting the power production. In this paper the different parameters of the chord wise spacing such as position of the spacing, shape of the spacing, width of the spacing and impact on power generation are analyzed and the spacing parameters are experimentally optimized.

K. M. Parammasivam

Papers

Urban Heat Island studies: Current status in India and a comparison with the International studies

Thermal barrier coated surface modifications for gas turbine film cooling: a review

Reduction of Aerodynamic Drag Force for Reducing Fuel Consumption in Road Vehicle using Basebleed

Experimental Investigation on Small Horizontal Axis Wind Turbine Rotor Using Winglets

Wind Turbine Aerodynamic Braking System Analysis Using Chord Wise Spacing