Bryan E. Kaiser

Validation of a closing procedure for fourth-order RANS turbulence models with DNS data in an incompressible zero-pressure-gradient turbulent boundary layer

Among factors affecting the accuracy of flow simulations with Reynolds-Averaged Navier-Stokes turbulence models is modeling turbulent diffusion processes. With the use of the Gram-Charlier series expansions, the turbulent diffusion in fourth-order one-point statistical closures of the Reynolds-Averaged Navier-Stokes equations can be modeled without introducing unknown model coefficients and without assuming turbulence being Gaussian. Terms representing turbulent diffusion processes in transport equations for second- and third-order velocity correlations do not require any modeling in such closures. In this regard, fourth-order closures are a more accurate alternative to lower-order closures where turbulent diffusion is modeled on semi-empirical or Gaussian turbulence assumptions. In the current paper, the accuracy of the closing procedure based on the Gram-Charlier series expansions is evaluated using data of direct numerical simulations in an incompressible zero-pressure-gradient turbulent boundary layer over a flat plate. One-point third-, fourth-, and fifth-order velocity moments were extracted for this purpose from the dataset collected by the Fluid Dynamics Group at the Universidad Politécnica de Madrid at two streamwise locations Reθ= 4101 and 5200 that correspond to channels and pipes at δ+= 1331 and 1626. Results demonstrate that the truncated Gram-Charlier series expansions are an accurate approximation of the fifth-order velocity moments in the considered flow.

Computational Analysis of a Tip Vortex Structure Shed from a Bio-inspired Blade

This study analyzes the effects that a bio-inspired blade shape has on the size and structure of a tip vortex. The blade prototype was selected based on the analysis of various insect orders with the purpose of finding wing profiles most suitable for the design of small rotorcraft propellers. Flow simulations are conducted around the bio-inspired blade and in its near wake using commercial CFD software Star-CCM+. Results are compared with those for a rectangular blade. A vortical structure is captured downstream of both blades. Flow data related to these structures is used to show that the bio-inspired shape produces weaker vortices, making it more desirable for rotorcraft implementation.

Survivability Analysis of the Satellite Electrical Power Subsystem Architecture

Satellites are costly to operate and difficult to repair once in use. A failure of the satellite electric power subsystem (EPS) may result in the loss of a satellite. Analysis of the EPS ability to continue to deliver power to loads in the presence of multiple faults in its elements (or survivability) may assist in designing a more reliable EPS. The current paper analyses the EPS survivability which is due to its topology from the perspective of individual loads. The UoSAT-12 mini-satellite EPS is chosen as a testbed for conducting computational analysis of its survivability.

Application of the “Selfish” Algorithm for the Survivability Analysis of Systems with Multiple Loads

The goal of our research is the development of analytical and computational tools for quantifying the survivability of engineering systems with sources and sinks due to the system’s topology. An example of such a system is a satellite power subsystem with multiple power sources and loads. In our previous work, we developed and validated a probabilistic approach for evaluating the topological survivability of systems with multiple sources and a single sink. We also proposed the “selfish” algorithm for reducing the computational cost of survivability analysis of systems with multiple sinks. The current paper reports on a computational implementation of the “selfish” algorithm and its verification.

Near-Wake Flow Simulations for a Mid-Sized Rim Driven Wind Turbine

A relatively high free stream wind velocity is required for conventional horizontal axis wind turbines to generate power. This requirement significantly limits the area of land for viable onshore wind farm locations. To expand a potential for wind power generation onshore, new wind turbine designs capable of wind energy harvesting at low wind speeds are in development. The aerodynamic characteristics of such wind turbines are notably different from industrial standards. The optimal wind farm layout for such turbines is also unknown. Accurate and reliable simulations of a flow around and behind new wind turbine designs are required. The current paper investigates the performance of a mid-sized Rim Driven Wind Turbine (U.S. Patent 7399162) developed by Keuka Energy LLC.