The bulk viscosity μb is generally set equal to zero (Stokes’ hypothesis). For certain gases, such as CO2, μb/μ exceeds 103, where μ is the shear viscosity. In this circumstance, the bulk viscosity may substantially alter a hypersonic boundary layer. A general, nonsimilar, laminar, boundary-layer formulation is provided in which the bulk viscosity terms are included as a correction. To obtain explicit results, flow over a flat plate is considered. In addition to the heat transfer, the transverse pressure gradient inside the boundary layer is not zero, whereas the skin friction is unaltered by the bulk viscosity. This analysis is relevant to aerogravity-assisted maneuvers in planetary atmospheres that largely consist of CO2.

Theoretical and experimental knowledge of the bulk viscosity for a dilute gas is briefly reviewed. Neither area is satisfactory; the lack of experimental data for polyatomic gases over a broad temperature range is particularly acute. There is one circumstance where this deficiency is especially detrimental, namely, high-speed entry into planetary atmospheres.

Although predicted early in the 20th century, a single-phase vapour rarefaction shock wave has yet to be demonstrated experimentally. Results from a previous shock tube experiment appear to indicate a rarefaction shock wave. These results are discussed and their interpretation challenged. In preparation for a new shock tube experiment, a global theory is developed, utilizing a van der Waals fluid, for demonstrating a single-phase vapour rarefaction shock wave in the incident flow of the shock tube. The flow consists of four uniform regions separated by three constant-speed discontinuities: a rarefaction shock, a compression shock, and a contact surface. Entropy jumps and upstream supersonic Mach number conditions are verified for both shock waves. The conceptual van der Waals model is applied to the fluid perfluoro-tripentylamine (FC-70, C15F33N) analytically, and verified with computational simulations. The analysis predicts a small region of initial states that may be used to unequivocally demonstrate the existence of a single-phase vapour rarefaction shock wave. Simulation results in the form of representative sets of thermodynamic state data (pressure, density, Mach number, and fundamental derivative of gas dynamics) are presented.

A second-order accurate method-of-characteristics algorithm is used to determine the flow field and wall contour for a supersonic, axisymmetric, minimum length nozzle with a straight sonic line. Results are presented for this nozzle and compared with three other minimum length nozzle configurations. It is shown that the one investigated actually possesses the shortest length as well as the smallest initial wall turn angle at the throat. It also has an inflection point on the wall contour, in contrast to the other configurations.

Currently, the bulk viscosity μb of a gas can only be obtained with an acoustic absorption experiment. A method is proposed that is primarily applicable to a dense polyatomic gas. In this circumstance, the density-based thickness Λρ is large, consisting of many thousands of mean-free paths. Moreover, the ratio μb/μ (μ is the shear viscosity) is linear with this thickness. Consequently, shock measurements of Λρ can be used to evaluate μb. The approach is illustrated using sulfur hexaflouride.

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