Compressor efficiency variation with rotor tip gap is assessed using numerical simulations on an embedded stage representative of that in a large industrial gas turbine with Reynolds number ∼ 2 to 7×106. The results reveal three distinct behaviors of efficiency variation with tip gap. For relatively small tip gap (less than 0.8% span), the change in efficiency with tip gap is non-monotonic with an optimum tip gap for maximum efficiency. The optimum tip gap is set by two competing flow processes: decreasing tip leakage mixing loss and increasing viscous shear loss at the casing with decreasing tip gap. An optimum tip gap scaling is established and shown to satisfactorily quantify the optimal gap value. For medium tip gap (0.8%–3.4% span), the efficiency decreases approximately on a linear basis with increasing tip clearance. However, for tip gap beyond a threshold value (3.4% span for this rotor), the efficiency becomes less sensitive to tip gap as the blade tip becomes more aft-loaded thus reducing tip flow mixing loss in the rotor passage. The threshold value is set by the competing effects between increasing tip leakage flow and decreasing tip flow induced mixing loss with increasing tip gap. Thus, to desensitize compressor performance variation with blade gap, rotor should be tip aft-loaded and hub fore-loaded while stator should be tip fore-loaded and hub aft-loaded as much as feasible. This reduces the opportunity for clearance flow mixing loss and maximizes the benefits of reversible work from unsteady effects in attenuating the clearance flow through the downstream blade-row. The net effect can be an overall compressor performance enhancement in terms of efficiency, pressure rise capability, robustness to end gap variation and potentially useful operable range broadening.

Compressor efficiency variation with rotor tip gap is assessed using numerical simulations on an embedded stage representative of that in a large industrial gas turbine with Reynolds number ∼ 2 × 106 to 7 × 106. The results reveal three distinct behaviors of efficiency variation with tip gap. For relatively small tip gap (less than 0.8% span), the change in efficiency with tip gap is nonmonotonic with an optimum tip gap for maximum efficiency. The optimum tip gap is set by two competing flow processes: decreasing tip leakage mixing loss and increasing viscous shear loss at the casing with decreasing tip gap. An optimum tip gap scaling is established and shown to satisfactorily quantify the optimal gap value. For medium tip gap (0.8%–3.4% span), the efficiency decreases approximately on a linear basis with increasing tip clearance. However, for tip gap beyond a threshold value (3.4% span for this rotor), the efficiency becomes less sensitive to tip gap as the blade tip becomes more aft-loaded thus reducing tip flow mixing loss in the rotor passage. The threshold value is set by the competing effects between increasing tip leakage flow and decreasing tip flow induced mixing loss with increasing tip gap. Thus, to desensitize compressor performance variation with blade gap, rotor should be tip aft-loaded and hub fore-loaded while stator should be tip fore-loaded and hub aft-loaded as much as feasible. This reduces the opportunity for clearance flow mixing loss and maximizes the benefits of reversible work from unsteady effects in attenuating the clearance flow through the downstream blade-row. The net effect can be an overall compressor performance enhancement in terms of efficiency, pressure rise capability, robustness to end gap variation, and potentially useful operable range broadening.

N,N-dimethyltryptamine (DMT) is a psychoactive substance that has been gaining popularity in therapeutic and recreational use. This is a case of a physician who chronically took DMT augmented with phenelzine in an attempt to self-medicate refractory bipolar depression. His presentation of altered mental status, mania, and psychosis is examined in regards to his DMT use. This case discusses DMT, the possible uses of DMT, and the theorized mechanism of DMT in psychosis and treatment of depression, particularly involving its agonist activity at 5-HT1A, 5-HT2A, and 5-HT2C. It is also important to recognize the dangers of self-medication, particularly amongst physicians.

Siemens Energy has commissioned an extensive multi-year experimental and numerical (CFD) project to improve its ability to design for and predict compressor stall. The experimental test rig is a half scale six stage axial compressor. The goal of this work is to provide insight into how best to predict the compressor performance map and in particular the stall point by applying state-of-the-art multiple blade row CFD simulation tools. A preliminary CFD analysis quantified numerical, model and systematic error on the first stage of the compressor. Subsequent steady (Mixing Plane) and transient (Time Transformation) CFD simulations of the entire six stage compressor are compared to each other and to experimental data. Both the steady and transient simulations are shown to be computationally efficient and in very good agreement with the experimental data across the full performance map, up to stall inception on multiple speedlines. Physical explanations of the key flow features observed in the experiment, as well as of the differences between the predictions and experimental data, are given.