A theoretical study of fluid forces on a centrifugal impeller rotating and whirling in a vaned diffuser

The fluid forces on a centrifugal impeller rotating and whirling in a vaned diffuser are analyzed on the assumption that the number of impeller and diffuser vanes is so large that the flows are perfectly guided by the vanes. The flow is taken to be two dimensional, inviscid, and incompressible, but the effects of impeller and diffuser losses are taken into account. It is shown that the interaction with the vaned diffuser may cause destabilizing fluid forces. From these discussions, it is found that the whirling forces are closely related to the steady head-capacity characteristics of the impeller. This physical understanding of the whirling forces can be applied also to the cases with volute casings. At partial capacities, it is shown that the impeller forces change greatly when the flow rate and whirl velocity are near to the impeller or vaned diffuser attributed rotating stall onset capacity, and the stall propagation velocity, respectively. In such cases the impeller forces may become destabilizing for impeller whirl

Effects of Leading Edge Sweep on the Cavitating Characteristics of Inducer Pumps

It is well known that leading edge sweep has a favorable effect on the cavitation of turbomachines. However, the mechanisms of the improvement have not been made clear. It has been shown that the lift and the drag on a cavitating swept single hydrofoil can be correlated fairly well based on the velocity component normal to the leading edge. In the present paper, such correlations for swept cascades are derived and the results are examined, neglecting the full geometrical effects of the inducer rotor. It is shown that the correlations can simulate the developments of various types of cavitation, including alternate blade cavitation, rotating cavitation, and cavitation surge. This result is based on the observation that the steady cavity length, as well as the developments of various types of cavitation, is fairly well predicted by the correlation

CPPD crystal deposition disease of the cervical spine: A common cause of acute neck pain encountered in the neurology department

Background: Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease is one of the most common forms of crystal-associated arthropathy in the elderly. However, CPPD deposition on the cervical spine is less well known, and only a limited number of cases have been reported to date. Here, we report our recent clinical experience with CPPD crystal deposition disease of the cervical spine and describe the clinical features of this disease. Methods: Fourteen patients with clinically diagnosed CPPD crystal deposition disease of the cervical spine at our department during the period from January 2005 to December 2008 were analyzed retrospectively. Results: Patients ranged in age from 54 to 92 (mean +/- SD, 77.5 +/- 8.5). Chief symptoms of patients were acute posterior neck pain and fever. All patients had markedly restricted neck rotation. Serum CRP level was highly elevated in all patients (10.16 +/- 5.35 mg/dL). Computed tomography of the cervical spine demonstrated linear calcific deposits in the transverse ligament of atlas (crowned dens syndrome) in all patients. Calcific deposits were also found in other periodontoid structures and the ligamenta flava in some patients. Posterior neck pain, fever, and increased serum inflammatory indicators were relieved within 1 to 3 weeks by nonsteroidal antiinflammatory drugs (NSAIDs) or a combination of NSAIDs and prednisolone. Most of the patients were misdiagnosed as having other diseases before consultation. Conclusions: CPPD crystal deposition disease of the cervical spine is one of the most common underrecognized causes of acute neck pain in the neurology department, especially in elderly patients.ArticleJOURNAL OF THE NEUROLOGICAL SCIENCES. 296(1-2):79-82 (2010)journal articl