Nearly all hypersonic tunnels have turbulent nozzle-wall boundary layers that radiate acoustic noise, generating high freestream noise levels that are an order of magnitude above flight levels. A new Mach-6 quiet tunnel has been developed to provide quiet flow at high Reynolds number with low noise levels, comparable with flight. Laminar nozzle-wall boundary layers and the resulting quiet flow have now been achieved to high Reynolds numbers of 3:5 10 6 =ft (11 10 6 =m), after five years of shakedown. The Mach-6 quiet tunnel is the first operational hypersonic quiet tunnel with low operating costs and good optical access.
SUMMARYLow-dimensional models have proven essential for feedback control and estimation of flow fields. While feedback control based on global flow estimation can be very efficient, it is often difficult to estimate the flow state if structures of very different length scales are present in the flow. The conventional snapshot-based proper orthogonal decomposition (POD), a popular method for low-order modeling, does not separate the structures according to size, since it optimizes modes based on energy. Two methods are developed in this study to separate the structures in the flow based on size. One of them is Hybrid Filtered POD method and the second one is 3D FFT-based Filtered POD approach performed using a fast Fourier transform (FFT)-based spatial filtering. In both the methods, a spatial low-pass filter is employed to precondition snapshot sets before deriving POD modes. Three-dimensional flow data from the simulation of turbulent flow over a circular cylinder wake at Re = 20 000 is used to evaluate the performance of the two methods. Results show that both the FFT-based 3D Filtered POD and Hybrid Filtered POD are able to capture the large-scale features of the flow, such as the von Karman vortex street, while not being contaminated by small-scale turbulent structures present in the flow.
The runner design is the most challenging part of the turbine design process. Several parameters determine the performance and cavitation characteristics of the runner: the metal angle (flow beta angle), the alpha angle, the blade beta angle, the runner inlet and outlet diameters, and the blade height. All of these geometrical parameters need to be optimized to ensure that the head, flow rate and power requirements of the system are met. A hydraulic designer has to allocate time to optimize these parameters and should be experienced in carrying out the iterative design process. In this article, the turbine runner parameters that affect the performance and cavitation characteristics of designed turbines are examined in detail. Furthermore, turbines are custom designed according to the properties of hydroelectric power plants; this makes the design process even more challenging, as the rotational speed, runner geometry, system head and flow rate vary for each turbine. The effects of the design parameters are examined for four different turbine runners specifically designed and used in actual power plants in order to obtain general results and generalizations applicable to turbine design aided by computational fluid dynamics (CFD). The flow behavior, flow angles, head losses, pressure distribution, and cavitation characteristics are computed, analyzed, and compared. To assist hydraulic designers, the general influences of these parameters on the performance of turbines are summarized and empirical formulations are derived for runner performance characterization.
ABSTRACT:The methods and outcome of a senior undergraduate project related to the control of a turbulent cylinder wake flow using plasma actuators are summarized in this article. The study integrates computational fluid dynamics (CFD) with experimentation and combines fluid mechanics with flow control research, crossing the boundaries between engineering disciplines.Comput. Appl. Eng. Educ. ß
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