R. A. Helfinstine

Bio: R. A. Helfinstine is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Potential flow & Lift coefficient. The author has an hindex of 1, co-authored 1 publications receiving 48 citations.

Potential Flow Past a Group of Circular Cylinders

Abstract: The problem of an accelerating potential flow past a group of stationary circular cylinders is considered using the method of images. The problem is formulated so that the number and location of the cylinders is arbitrary so long as there is no overlap between adjacent cylinders. Inertial and lift coefficients are determined for several different cylinder arrangements. The inertial coefficient for a cylinder can vary in either direction from its single-cylinder value of 2.0. The controlling factors on this variation are the relative geometric position of the cylinder within the group and its distance from its neighbors. These same factors determine, as is expected, the lift coefficient values. In two example configurations, there is even a drag-type force generated on an individual cylinder in the potential flow.

Effective mass and damping of submerged structures

Abstract: Various structures important for safety in nuclear power plants must remain functioning in the event of an earthquake or other dynamic phenomenon. Some of these important structures, such as spent-fuel storage racks, main pressure-relief valve lines, and internal structures in the reactor vessel, are submerged in water. Dynamic analysis must include the force and damping effects of water. This report provides a technical basis for evaluating the wide variety of modeling assumptions currently used in design analysis. Current design analysis techniques and information in the literature form the basis of our conclusions and recommendations. We surveyed 32 industrial firms and reviewed 49 technical references. We compare various theories with published experimental results wherever possible. Our findings generally pertain to idealized structures, such as single isolated members, arrays of members, and coaxial cylinders. We relate these findings to the actual reactor structures through observations and recommendations. Whenever possible we recommend a definite way to evaluate the effect of hydrodynamic forces on these structures.

A potential-flow theory for the dynamics of cylinder arrays in cross-flow

Abstract: The full linear unsteady potential-flow solution for fluid flowing across a bank of cylinders has been obtained. The potential function is expanded into a Fourier series and the boundary condition of impermeability is applied at the moving cylinder surfaces. Mutual contradictions among the various potential-flow solutions available in the literature are exposed, and it is shown that the present solution is consistent with certain basic physical checks, which some of the previous solutions could not meet. The effect of fluid viscosity is incorporated solely as a phase lag between the steady-state lift and drag coefficients on each cylinder and its respective motions. By incorporating the fluid-dynamic forces obtained from this modified potential-flow theory in a stability analysis, the threshold for fluid-elastic instability is predicted. Comparison with experimentally observed thresholds is encouraging, given the high level of idealization of the theory and the accuracy of present-day semi-empirical prediction methods.

Breakdown of doublet recirculation and direct line drives by far-field flow in reservoirs: implications for geothermal and hydrocarbon well placement

Abstract: S U M M A R Y An important real world application of doublet flow occurs in well design of both geothermal and hydrocarbon reservoirs. A guiding principle for fluid management of injection and extraction wells is that mass balance is commonly assumed between the injected and produced fluid. Because the doublets are considered closed loops, the injection fluid is assumed to eventually reach the producer well and all the produced fluid ideally comes from stream tubes connected to the injector of the well pair making up the doublet. We show that when an aquifer background flow occurs, doublets will rarely retain closed loops of fluid recirculation. When the far-field flow rate increases relative to the doublet’s strength, the area occupied by the doublet will diminish and eventually vanishes. Alternatively, rather than using a single injector (source) and single producer (sink), a linear array of multiple injectors separated by some distance from a parallel array of producers can be used in geothermal energy projects as well as in waterflooding of hydrocarbon reservoirs. Fluid flow in such an arrangement of parallel source-sink arrays is shown to be macroscopically equivalent to that of a line doublet. Again, any far-field flow that is strong enough will breach through the line doublet, which then splits into two vortices. Apart from fundamental insight into elementary flow dynamics, our new results provide practical clues that may contribute to improve the planning and design of doublets and direct line drives commonly used for flow management of groundwater, geothermal and hydrocarbon reservoirs.