Computational Study of the Wake and Contaminant Transport of a Walking Human

The unsteady aerodynamic wake of a human is studied using a time-accurate computational fluid dynamics simulation. Transport of a scalar contaminant, which originates on the body, is also considered. An existing Reynolds-averaged Navier-Stokes solver is modified to include energy, scalar-transport, and thermal buoyancy effects. Structured overset grids are used to discretize the geometry and the flow field. Results indicate two distinct wake regions: an unsteady bluff-body wake behind the torso which is characterized by a mean recirculation zone, and a region of unsteady vortex shedding behind the legs which is dominated by a “jet” of air formed between the legs. A significant downwash occurs behind the body which has the effect of laterally spreading the lower portions of the wake. The magnitude of the scalar contaminant is shown to decay exponentially within the wake and is found to be highly dependent upon the source location. DOI: 10.1115/1.2013291 The aerodynamics of the human wake has received little attention in the engineering community. This work is intended to contribute to the physical understanding of the dynamics of the human wake using computational fluid dynamics simulations. The transport of a scalar contaminant from the surface of the body and the subsequent mixing by the wake is also studied. This information may be of interest to many areas of the engineering community such as homeland defense and cleanroom design, as well as the broader medical community. The current work focuses on the aerodynamic wake behind a simplified human form, neglecting the small scale details of the human body which tend to vary from person to person. The flow about the human body can be classified as a bluffbody flow. Literature regarding bluff-body flows indicate that instabilities arising in the separating boundary layer will cause the wake to be unsteady 1‐3. Studies of three-dimensional bluff bodies, such as finite cylinders mounted on flat plates and the three-dimensional flow around tall buildings 4‐7, can provide insight into the dynamics of the wake that may be expected from the human body. These studies indicate that a downwash occurs behind three-dimensional structures. The study of circular cylinders of various aspect ratios by Okamoto and Sunabashiri 4 show that cylinders with an aspect ratio of 3, which is similar to the human geometry of this study, will have a recirculation region extending four diameters downstream. Their results also show that a cylinder with an aspect ratio of 3 is at the transition between symmetric and anti symmetric vortex shedding. While the human form definitely differs from the geometries used in these studies, it is clear that we should expect a recirculation zone in the wake that is on the order of four body widths in length. No expectations regarding symmetric or anti symmetric vortex shedding can be drawn from the studies as our geometry is close to the aspect ratio associated with transition between these two modes. The gap between the legs provides a significant geometrical difference with the three-dimensional bluff bodies studied in the literature. Several studies have been performed on twodimensional circular cylinders in side-by-side configurations 8,9 which is similar to the two legs of our human model. These studies have identified three different regimes for the wake structure, with the first regime occurring when the cylinders are placed closely together. In a closely spaced configuration, the wake is similar to that of a single bluff body with a width equivalent to the two cylinders. This regime occurs for cylinder gaps of up to 20% of the cylinder diameters. Gap widths larger than 20% of the cylinder diameter are associated with the second regime and are characterized by individual wakes behind each cylinder. These wakes strongly effect one another until the gap width reaches 120% of the cylinder diamter. Gap widths greater than 120% of the diameter allow each cylinder to act as an independent bluff body, although some synchronization between the vortex streets was noted. These studies show us that the wake behind the legs, which have a gap width of 50% of the leg diameter, will likely behave similar to the wakes observed in the second regime of the previous studies. Each leg will likely have an independent wake that is heavily influenced by the neighboring wake. The actual