Gerald W. Recktenwald, James W. Ramsey, and Suhas V. Patanakar
Presented at the AIAA/ASME Thermophysics and Heat Transfer Conference, 18-20 June 1990, Seattle, WA.
Appears in Numerical Heat Transfer American Society of Mechanical Engineers, HTD-Vol. 130, K.Vafai and J.L.S. Chen (eds.), pp. 95-105.
Flow and heat transfer inside gas springs are analyzed with a control-volume finite-difference technique based on the SIMPLER algorithm. The model is used to simulate operation of a Helium-filled gas spring over a range of speeds spanning the laminar and turbulent flow regimes. Turbulence closure is obtained with a version of the k-epsilon model, and the heat flux and shear stress at solid boundaries are calculated by wall functions. At low speeds no turbulence model is needed, and the exact ensemble-averaged equations for the fluid mass, momentum, and energy conservation are solved. Details of the velocity, temperature and turbulence fields are presented at crank speeds of 10 and 500 RPM, which are representative of laminar and turbulent flow, respectively. At both speeds the flow field deviates from a uniform expansion and compression only at top dead center and bottom dead center where changes in piston velocity create recirculating flow patterns. The recirculation zones are quickly annihilated by the subsequent piston stroke. The calculated hysteresis loss is in very good agreement with available experimental data. The results of the calculations suggest that the ensemble averaged flow field does not explain the apparent breakdown in the correlation of Kornhauser and Smith (1987, 1988) at intermediate values of oscillating Peclet number.