Unsteady Flow in Cavitating Turbopumps

Unsteady flow in a cavitating axial inducer pump is analyzed with the help of a simple two-dimensional cascade model. This problem was motivated by a desire to study the effect of unsteady cavitation on the so-called POGO instability in the operation of liquid rocket engines. Here, an important feature is a closed loop coupling between several different modes of oscillation, one of which is due to the basic unsteady characterisitcs of the cavitation itself. The approaching and leaving flow velocities up- and downstream of the inducer oscillate, and the cavity-blade system participates dynamically with the basic pulsating flow. In the present work, attention is focused on finding a transfer matrix that relates the set of upstream variables to those downstream. This quantity, which is essentially equivalent to cavitation compliance in the quasistatic analyses, is found to be complex and frequency dependent. It represents the primary effect of the fluctuating cavity in the system. The analysis is based on a linearized free streamline theory

A Note on the Unsteady Cavity Flow in a Tunnel

The unsteady internal cavitating flow such as the one observed in a pump or a turbine is studied for a simple two-dimensional model of a base-cavitating wedge in an infinite tunnel and it is shown how the cavitation compliance can be calculated using the linearized free streamline theory. Numerical values are obtained for the limiting case of a free jet. Two important features are: First, the cavitation compliance is found to be of complex form, having additional resistive and reactive terms beyond the purely inertial oscillation of the whole channel in "slug flow." Second, the compliance has a strong dependence on frequency

Viscous Effects in the Inception of Cavitation on Axisymmetric Bodies

Cavitation inception and development on two axisymmetric bodies was studied with the aid of a Schlieren flow visualization method developed for that purpose. Both bodies were found to exhibit a laminar boundary layer separation; cavitation inception was observed to occur within this region of separated flow. The incipient cavitation index was found to be closely correlated with the magnitude of the pressure coefficient at the location of flow separation on one of the bodies. There is also experimental evidence that events at the site of turbulent reattachment of the separated flow may also greatly influence cavitation inception

Dynamics of cavitating cascades

Brief accounts of the theoretical research conducted on the unsteady cavitation characteristics of liquid rocket engine turbopumps are reported. The objective is to produce estimates of the cavitation compliance and other unsteady characteristics which could then be used in analysis of the pogo instability. Blade cavitation is the particular pheonomenon which is investigated and line arized free streamline methods were employed in both quasistatic and complete dynamic cascade analyses of the unsteady flow. The simpler quasistatic analysis was applied to particular turbopumps but yielded values of compliances significantly smaller than those indirectly obtained from experiments. Reasons for this discrepancy are discussed. The complete dynamic analysis presents a new problem in fundamental hydrodynamics and, though the basic solution is presented, numerical results have not as yet been obtained

Extending the Aircraft Availability Model to a Constrained Depot Environment Using Activity-Based Costing and the Theory of Constraints

The Aircraft Availability Model (AAM) assists managers in the selection of an optimal list of items to repair in order to attain the best aircraft availability rate. The model considers procurement or repair costs for the components as if the costs were unit variable as a price, instead of a repair cost representing a mix of both fixed and variable cost. This research used the AAM in conjunction with Activity Based-Costing (ABC) and The Theory of Constraints (TOC) methodologies to investigate the relationships between price, product mix, Aircraft Availability (AA) and total cost. This approach explicitly recognizes that the Air Force Material Command uses its own resources in repairing components, and that it is always operating in a constrained environment in which resources practical capacities are exceeded by requirements that limit the attainable AA. The results of this investigation shows that the choice of the optimal mix of reparable items is sensitive to the pricing method used as well as environmental factors like repair cycle time, fleet size, and the intensity and balanced of shop resource load. In addition, the research found that the performance of the repair center should be evaluated under the metric Aircraft Availability per System Total Cost, following the rationale under the TOC methodology that considers labor costs as operational expenses, fixed in the period, and only raw materials as variable costs

A Rare Family: Exploring Genetic Literacy in an Online Support Group

Healthy People 2020 and the Institute of Medicine (IOM) define health literacy as the “degree to which individuals have the capacity to obtain, process and understand basic health information and services needed to make appropriate health decisions.” Essential components of health literacy include oral and print literacy, numeracy, and cultural and conceptual knowledge; the latter is influenced by sociodemographic factors and cultural understandings and approaches to concepts such as healthcare. Genetic literacy, a form of health literacy, may be defined as the knowledge, skills and attitudes necessary to individual understanding of genetic information, and genetic-based health, behavior, technology and services, making it a vital component of sexual and reproductive decision-making. The current qualitative research study employed holistic-content and narrative analysis of secondary data (electronic or e-mail posts) from an online support group for individuals affected by a genetic disorder in order to to gain additional insights into specific psychosocial and environmental variables that affect individual genetic literacy, related perceptions of genetic risk, and sexual and reproductive decision-making. Findings from the study indicate that online health-related support groups can evolve into a socially-constructed “family” of individuals affected by specific disorders. Within this online family, members find others who can identify with their feelings and experiences. Like biological families of origin, this “familial” context may then exert particularly strong influences on members’ social and health decision-making via co-constructed cultural and conceptual knowledge of the disorder. Further qualitative research needs to be performed to understand the positive and negative impact that participation in a collective consciousness might have on individual genetic literacy necessary for making sensitive decisions such as those involved in sexual and reproductive health. Implications for education and counseling are discussed

Cavitation Inception on the I.T.T.C. Standard Head Form

Cavitation inception measurements were made on the I.T.T.C. Standard Head Form over a range of speeds and dissolved air content. The results were similar to those observed in other water tunnels with resorbers. Cavitation inception indices were observed as low as 0. 4 as compared with the minimum calculated pressure coefficient of O.6. As in previous measurements a pronounced velocity scale effect was observed