Stanford University-Thermosciences Division, Department of Mechanical Engineering

The Division has a full-time faculty of 16 with about 100 Ph.D. students, in two groups: Heat Transfer and Turbulence Mechanics (HTTM), and High Temperature Gas Dynamics Lab (HTGL: a major interest is optical diagnostic techniques for reacting or nonreacting flows). The Division houses the NASA Ames/Stanford Center for Turbulence Research, which funds and hosts over 20 professional researchers annually. This report covers only research related to gas turbine technology.

• 3D flows and heat transfer .
• Streamwise vortices in 2D and 3D boundary layers.
• 2D layers abruptly skewed sideways – project complete: three journal papers available.
• Boundary layers on rotating disks – flowfield measurements complete, heat-transfer measurements in progress.
• Cascade and end-wall layers – first stage complete, PhD thesis in draft.
• Limits of the law of the wall – analysis of turbulence simulation data shows large deviations from the “standard” law.
• 3D boundary layer data review – in ASME FED vol. 184, p.1.
• Heat transfer with high free-stream turbulence (FST).
• Heat transfer augmentation caused by end-wall horseshoe vortices, with and without simulated combustor FST of 15-20%.
• A recently-completed study of the effects of strong convex surface curvature and FST (up to 12%) on blade suction-surface film-cooling heat transfer, effectiveness and flowfield structure.
• Surface heat transfer with very high FST using a moving belt as a wind-tunnel floor-FST can be arbitrarily high percentage of the relative flow speed.
• Flow and heat transfer with moderate FST over flat and concave surfaces.
• Effects of blade-wake turbulence on flow and heat transfer in boundary layers.
• Flow control
• Acoustic control of jet mixing.
• Augmented mixing in backstep combustors and supersonic mixing layers.
• Vortex generator jets
• Active surface elements as vortex generators. The jets or surface elements are actuated only when needed and have negligible drag penalty at other times.
• Basic studies of flow control, using neural networks and other advanced control algorithms – simulations have shown drag reduction of up to 30 percent.
• Turbulence simulations (time-dependent Navier-Stokes solutions).
• Large-eddy simulations (using a model for the small eddies only) are being carried out for isolated airfoils, using unstructured grids. Extension to cascades is just a gridding problem.
• Techniques
• Surface temperature measurement by thermochromic liquid crystals. These can be calibrated to indicate a range of temperature contours rather than one transition. We routinely achieve +/- ¼ deg. absolute accuracy and 0.1 deg. repeatability, as good as a precision-grade thermocouple. A transient technique is used in Project (9) above: the fall in surface temperature of the moving belt downstream of a fixed steady heat (light) source is due partly to conduction into the solid, which we can calculate, and partly to convective heat transfer to the airstream, which we can deduce.
• Conductive heat transfer in electronic micro- and nanostructures. These include sensors – such as infrared imaging arrays – and actuators, as well as conventional circuits. The thermal conductivity of thin layers differs from that of the bulk material, and interfacial thermal resistances are substantial. In a new facility, temperature fields are measured with sub-microsecond temporal, resolution.
• Planar laser induced fluorescence (PLIF). This can be used for 2D and 3D imaging of species concentration, temperature, velocity and pressure, and has wide potential applications in turbomachinery research. HGTL has made several major contributions. In-house applications include very hot supersonic jets, flames, shock tunnel flows, detonation waves and ram accelerator flowfields.