| As an external combustion engine, Stirling engine is being paid more and more attention nowadays for its abroad heat sources adaption and good environmental feature. Oscillating flow is one of the important characteristics of working fluid in Stirling engine. Precise analysis and prediction are required to describe oscillating flow and heat transfer characteristics of Stirling engine heat exchangers, which are crucial for the optimization and design of Stirling engine. Based on the features of narrow space, high frequency, compressible and unsteady of oscillating flow in Stirling engine heated pipe, the theory analysis and experimental research of oscillatory pipe flow are studied in present research.Based on the existing research, an oscillating pipe flow system of two pistons is chosen as research object. A complex function is used to solve control equations, and analytical solutions of velocity and temperature in laminar fully developed oscillating flow are obtained.A numerical investigation of oscillating flow and heat transfer in pipe are solved on k-ω two equations turbulence model with dynamic mesh technology. Numerical solutions show that there is big difference among velocities or temperatures in the pipe cross section during flow period. When the wall temperature of pipe is constant, the change rule of fluid temperature along the axial direction is that it increases first and then decreases. The axial high-temperature fluid is mainly located in the cross-section of x=0.Measuring techniques of HWA and PDA are used to measure oscillating flow field in the pipe at the same time, and the experimental data is compared with analysis solutions and numerical solutions. The results show that:when oscillating flow is in low dynamic Reynolds number Reω, there is a good agreement between the complex theoretical model and experimental results, and the deviation is less than15%; while turbulence model deviates from the experimental data severely. On the contrary, when oscillating flow is in high dynamic Reynolds number Reω, there is excellent agreement between numerical solutions and experimental date, and their deviation is less than16.5%; while the complex theory model can only give qualitative descriptions. The experiment of constant temperature Tw on pipe wall was carried out. When the oscillating frequency Reω increases, it caused the velocity of fluid increased, the thickness of velocity and temperatures decreased, and higher conversion efficiency of thermal-power in Stirling engine.Complex function theory and numerical method of turbulence model are applied in oscillating flow of annular cross section pipe. The study shows that the ratio of out diameter and inner diameter c has an important influence on oscillating flow. When the value of c is high, the temporal velocity of cross section is in’annular distribution’. While the value is small, the temporal velocity is similar with parabolic. For the condition of same Reω number, as the value of c decreases, the amplitude of fluid temperature increases and the fluctuation is intensified, which cause the heat transfer efficiency of heated pipe increased. |
