In this chapter, we will consider particle–particle interactions. Here we distinguish two kinds of interactions. The first is direct interaction between particles in the form of collisions. When two particles collide, the time history of force exchange between them is controlled by the solid mechanics of elastic and plastic deformation between the colliding particles. In the context of multiphase flow computations, such collisions are simplified and treated using either a hard-sphere or a soft-sphere collision model, which will be discussed in this chapter. As a special case we will also consider the problem of particle–wall collisions.

In Chapter 4, we started with a rigorous derivation of force on a spherical particle in the limit of zero Reynolds number in a time-dependent uniform ambient flow, which led to the BBO equation. We then extended the analysis to spatially varying flows in the Stokes limit and obtained the MRG equation. At finite Reynolds number, due to the introduction of fluid inertia, we saw how difficult a complete solution of the hydrodynamic force on a particle can become. In this chapter, we plan to boldly venture into the difficult topic of interaction between a particle and a turbulent flow.

The Euler–Lagrange (EL) approach is also often referred to as the point-particle approach, since the particles are taken to be point masses, as far as their interactions with the surrounding continuous phase are concerned. In the particle-resolved approach, the presence of the particles was fed back to the surrounding continuous phase through the no-slip, no-penetration, isothermal or adiabatic, and other boundary conditions. These boundary conditions, without additional closure assumptions, directly controlled the mass, momentum, and energy exchanges between the particles and the surrounding fluid. Furthermore, these exchanges, which are in the form of tractional force, heat, and mass transfer, are properly distributed around the surfaces of the particles, and they accurately account for the presence of boundary layers, wakes, and other microscale features around the particles.

Multiphase flow is a branch of fluid mechanics that has grown rapidly over the past few decades. The term phase in “multiphase” refers to the solid, liquid, or gaseous state of matter. Thus, a multiphase flow is one that involves more than one phase. Multiphase flow can be a gas–solid flow, as in the case of a sand storm or pneumatic transport of powder.

Media Arts in the Global Souths

Traditional artistic and cultural sound practices in South Asia have a tenuous relationship with modernist media such as sound recording, photography, film, and radio exported from the colonial West. In the realm of sound practices, for example, recording technology’s invasion of South Asia and many parts of the colonized Global Souths had a mutating effect on traditional practices and indigenous technologies (e.g., pre-colonial instruments and tuning systems). From the earliest days of sound recording, modernist technologies shared a fraught relationship with pre-colonial South Asian cultures: local practitioners strongly resisted against their voices and sounds being recorded. Their contention and collective resistance to media imperialism and colonization was first recognized in the early-1970s when so-called developing countries began to criticize the dominance developed countries still held over their media and use of media technologies, a continuation of the control used to quantify and surveil colonial subjects.

And yet, a cultural melange has also had mutually beneficial aspects: the two spheres have become entangled, coalescing, and adjusting to one another, rather than having a binary and temporally linear relationship (e.g., tradition versus modernity, pre-modern versus modern). If we study the introduction of media technologies to the Global Souths, for example in India, modernist media did have a mutating influence, but colonial interventions also created transformative contexts in which inter and cross-cultural confluences could take place, and hybrid forms of art and aesthetic expressions emerged.

Artists constantly redefine the traditional categories of arts and crafts by incorporating emerging technologies into their artworks. Media art, which flourished in the early twentieth century, often depends on new technological components.

Social Resurgence

Hindi cinema’s so-called Golden Age, from the late 1940s to the late 1960s, was a resurgent period of film production across the Indian subcontinent after independence from colonial rule in 1947. The era’s films possessed quality and quantity in equal measure. They resonated with the hope, enthusiasm, and collective commitment to nation building based on the newfound sense of freedom that had beaten the spectre of oppressive colonial censorship. Many of the film directors and practitioners who pushed the industry towards its new heights were dedicated followers of India’s anticolonial movements and struggle for independence. The emergence of a modern, post-colonial India with nationalist aspirations galvanized their work, despite the harsh reality of grappling with a dwindling economy after 150 years of British exploitation. The fervor bled into regional film industries, which centred on local language film-works with distinctive provincial character. The technological means and sonic methods adapted in regional and state cinemas across the country were often similar to those used in Bombay’s large-scale industry, making the case for a legitimately subcontinent-wide national cinema that could be called ‘Indian Cinema’.

Several popular Hindi-language classics such as Mother India (Khan, 1957), Pyaasa (‘Thirsty’, Dutt, 1957), Kaagaz Ke Phool (‘Paper Flowers’, Dutt, 1959), Awara (‘The Vagabond’, Kapoor, 1951), Shree 420 (‘Mr. 420’, Kapoor, 1955), and Mughal-E-Azam (‘The Great Mughal’, Asif, 1960) come from this period. Global lists, forums, festivals, and screenings regularly featured some of these films as representative of Indian cinema. Indeed, these films influenced the development of a distinctive cinematic language on the subcontinent for decades to come.

Optical Recording and Direct Sound

The earliest sound recordings in India were registered in 1902, when London’s Gramophone and Typewriter Ltd. sent its recording engineers for an ethnographic expedition in South Asia to gather music and sound recordings. The intention of the company was to set up a sound industry in the colony in order to export the profit back to Britain through the exploitation of local resources, labour, and materials. Indian films were still silent when these developments took place. The gramophone had a separate trajectory of technological transmission in India, as did radio. Whereas the era of ‘talkies’ began in the United States with the release of The Jazz Singer in 1927, sound came to the still nascent Indian film industry only after investors and studio owners travelled to the United States to experience this new phenomenon. Once these producers, such as Jamshedji Framji Madan of the Madan Theatre, experienced sound film, they committed to bringing this technology to India. By 1931, the first Indian sound film, Alam Ara (Ornament of the World), directed by Ardeshir Irani, was released along with a large number of other films in Bombay, Kolkata, and elsewhere – all talkies.

The gramophone, and later film and radio, all modern inventions imported from the West, irrevocably altered sound practices in India in the early twentieth century. With the coming of sound recording technology, major unsettling transitions took place, and filmmaking moved from the hand of amateurs to the bigger studios that could afford the technologies of sound recording and reproduction.