Search

Thermo-acoustic characterization of gas turbine combustion systems is crucial for a successful development of new gas turbine engines to meet emission and efficiency targets. In this context, it becomes more and more necessary to predict the limit cycle amplitudes of thermo-acoustic induced combustion instabilities in order to figure out if they can be tolerated or if they are above the critical design limit and will cause damage to the engine. For the prediction of limit cycle amplitudes, the nonlinear flame response of the combustion system is needed, which is represented in this work by the flame describing function (FDF). In this article, the identification of the FDF from a large eddy simulation (LES) is validated. The test case used was a premixed atmospheric swirl flame, for which experimental data on the FDF were available. First a steady reacting LES solution was obtained and compared to experimental data. The simulation was then excited by superimposing a mono-frequency harmonic wave on the velo...

The nonlinear heat release response of a premixed swirl flame to velocity perturbations is investigated using Large Eddy Simulation. The nonlinear heat release response is required for the prediction of thermo-acoustic limit cycle pressure amplitudes and is represented here by the Flame Describing Function (FDF). As test case a premixed atmospheric swirl flame, for which experimental data on the FDF is available, was used. First a steady reacting LES solution was obtained and compared to experimental data. The simulation was then excited by superimposing a mono-frequency harmonic wave on the inlet boundary condition. Both the frequency and amplitude of the acoustic wave were varied to obtain the FDF. The calculated FDF was in good agreement with experimental data. At a frequency of 115 Hz, the flame was found to saturate for larger excitation amplitudes. A detailed analysis of the LES results revealed that the mechanism causing the saturation was a nonlinear evolution of the area of the flame surface with increasing perturbation amplitudes. Furthermore it was shown that for the present swirl flame, the heat release and flame surface fluctuations were linearly dependent on the tangential component of velocity fluctuations upstream of the flame, while they increased nonlinearly with the axial component of velocity fluctuations.

Rats were treated acutely, ip, with saline vehicle or an antidepressant: iprindole (15 mg/kg), nortriptyline (15 mg/kg), A75200 (10 mg/kg), fluoxetine (15 mg/kg), desipramine (10 mg/kg), bupropion (20 mg/kg) or tranylcypromine (7.5 mg/kg). Mapping the neuroanatomical distribution at 64 sites of the immediate early gene, c-fos revealed several patterns: first, increased counts of Fos-like neurons were found in all but one instance; second, drugs which had dopaminergic effects (bupropion and tranylcypromine) were more likely to potentiate c-fos reactivity than were the other drugs; third, Fos-like counts were more likely to be significantly elevated in structures bordering brain ventricles; fourth, only in the central amygdala were the Fos-like counts higher in all seven drug groups relative to the saline group. It remains to be seen whether or not this shared substrate is therapeutically significant.

A prospective study of 500 consecutive patients surviving the first 24 hours following cardiac surgical procedures was undertaken to determine the prevalence, etiology and results of therapy for postoperative acute renal failure (ARF). Thirty-five patients developed either moderate or severe ARF and an additional 102 developed mild preprenal azotemia. Positive risk factors noted inthe development of postoperative renal failure included age, elevated preoperative concentrations of blood urea nitrogen (BUN), serum creatinine, and decreased 24 hour urine creatinine clearance. The duration of cardiopulmonary bypass (CPB), aortic cross-clamping, and the total duration of the operation also closely correlated with the incidence of ARF. In the early postoperative period, clinical assessment of hemodynamic change was most helpful in predicting postoperative ARF. Significant negative risk factors included type of operation performed, New York Heart Association classification, the use of preoperative diuretic therapy, and associated other chronic illnesses. During the operation itself, the lowest and mean blood pressures, flow rates on CPB and the presence of hemoglobinuria failed to correlate with subsequent ARF. The mortality rate for established ARF was extremely poor (88.8 per cent), and there were no survivors among those requiring dialysis. ARF following cardiac surgery is a highly lethal complication which arises in a setting of inadequate cardiac function and is associated with a multiple organ system failure. Therapy of this postoperative complication, therefore, appears to be better directed toward its prevention rather than treatment once established.

Appointment breaking by patients causes problems for the physician's office. Patients who neither keep nor cancel their appointments are often referred to as "no shows." Twenty variables were identified as potential predictors of no-show behavior. These predictors were applied to 291 Family Practice Center patients during a one-month study in April 1977. A discriminant function and multiple regression procedure were utilized ascertain the predictability of the selected variables. Predictive accuracy of the variables was 67.4 percent compared to the presently utilized constant predictor technique, which is 73 percent accurate. Modification of appointment schedules based upon utilization of the variables studies as predictors of show/no-show behavior does not appear to be an effective strategy in the Family Practice Center of the Community Hospital of Sonoma County, Santa Rosa, due to the high proportion of patients who do, in fact, show. In clinics with lower show rates, the technique may prove to be an effective strategy.

The clinical records from 507 adult patients surviving open-heart operations were reviewed to determine the incidence of renal dysfunction. Three hundred nine patients (61%) were considered to have maintained normal renal function throughout the postoperative period compared to 198 patients who developed a blood urea nitrogen (BUN) level of greater than 50 mg/100 ml or a serum creatinine level of greater than 2.0 mg/100 ml. The mortality in the former group was only 1.6% compared to 30.3% in the patients having abnormal renal function. Age and the mean preoperative BUN and creatinine values were substantially greater in the "abnormal" patients than in the "normal" patients. Although a cause and effect relationship between renal dysfunction and mortality cannot be made on the basis of the present study, the data suggest the prevalence of renal failure in the postoperative period and the potentially serious nature of this complication.