Turbine Innovation and Energy Research

Current Projects

Sample Publications

Current Students

CURRENT PROJECTS

INTERNAL COOLING OF TURBINE BLADES

Micro-Heat Exchangers for Turbine Blade Cooling (DARPA):
Simulation of fluid flow and heat transfer in proposed high efficiency micro-heat exchangers is performed via a commercial computer code. Simulation results are checked against actual experimental results of the configurations studied. Eventually, it is hoped that the simulations will be able to drive the direction of future experiments by selecting the most promising set of heat exchanger parameters to be varied in tests.

Direct Numerical Simulation are also being performed for the above geometry, and the results below show the unsteady temperature distributions as a function of time.

Improved Turbulator/Dimple Designs for Internal Cooling of Turbine Blades (DOE):
Work is ongoing at exploring improved rib turbulator configurations and alternative strategies to rib turbulators such as dimples. These measurements are being undertaken in a rotating facility that permits mass transfer measurements to be performed. Two specific examples of such activities are described below.

In one project, the effect of ribs with different cross-stream profiles are investigated through detailed, surface mass (heat) transfer distributions along four active walls of a square duct containing a sharp 1800 bend. The duct simulates two passes of an internal coolant channel in a gas turbine engine with ribs mounted on two opposite walls. Mass (heat) transfer measurements, taken using the naphthalene sublimation technique, are presented for Reynolds numbers of 30,000, and rotation number of 0.3. Comparisons are made with conventional ribs having a rectangular cross-section. It is shown that the use of certain profiled ribs provides considerable heat transfer enhancements over conventional ribs with the same blockage ratio in the duct. These enhancements are attributed to the generation of longitudinal vorticity (or secondary flows) by the profiled ribs in the channel.

In the second project, mass/heat transfer measurements are made in dimpled (hemispherical depressions) inlet and outlet coolant flow passages using the naphthalene sublimation method. The leading and trailing surfaces are dimpled, while the side walls are kept smooth. Measurements are made at a Reynolds number of 21,000 and for Rotation numbers of 0 and 0.2. The measurements indicate that dimples enhance surface mass/heat transfer. This enhancement is stronger in the inlet passage than in the outlet passage. Peak mass/heat transfer occurs immediately downstream of the dimples, while the minimum mass/heat transfer occurs in the dimple region itself. Higher mass/heat transfer is also observed along the lateral edges of the dimple. The location of the Sherwood number peaks suggest the existence of streamwise vortical structures generated from the leading and lateral edges of the dimples.

FILM COOLING OF TURBINE BLADES (NASA)

Large Eddy Simulations of Film-cooling Flows in Gas Turbines:
Various fluid dynamics and heat transfer problems related to film cooling of gas turbine blades were studied. The influence of freestream turbulence intensity, turbulence length scale, hole geometry and jet injection angle were studied to understand the flow physics in jets-in-crossflow configuration. Heat transfer predictions are also done for the circular jet injected at 358 into the crossflow. The jet Reynolds number is 22200 and the blowing ratio is 1.0.

Development of Turbulence Models using DNS/LES in Complex Turbulent Flows:
The current models fail to perform in complex, non-equilibrium flows. DNS/LES produce temporally and spatially reliable and extensive information about flow field and scalar fields. Therefore, an improved understanding of current models, corrections to existing models and entirely new formulations can be obtained from these simulations. The construction of low-order systems for the flow-control purposes is also possible. As an illustration, the eddy viscosity is computed using LES data for a jets-in-crossflow case at some downstream station from jet injection hole. Clearly, any isotropic eddy viscosity model will fail to produce such effect.

GAS TURBINE COMBUSTION

Active Control of Combustion Instability (ONR):
Instabilities in the combustor can lead to significant performance degradation, possible blowout, structural vibrations, and even catastrophic failure. At LSU, we have been working for several years in developing active and passive control systems and methodologies for combustion control. We have achieved demonstrated success with feedback-loop active control and passive devices such as non-circular coaxial geometries. Both adaptive and robust controllers have been shown to be successful in reducing instabilities. Successful application to gas-turbines is hampered by large sensors/actuators of limited bandwidth, their susceptibility to harsh environments, and the use of wire-based communications. Furthermore, robust control is usually difficult to achieve in combustion systems due to limited information obtainable with macro-sensors. Research in these areas is ongoing with support from ONR.

Trapped Vortex Combustion (AFOSR):
The performance of a liquid-fueled trapped vortex (TV) combustor is analyzed both experimentally and computationally. The TV cavity, formed between a forebody and an afterbody, is placed coaxially inside a combustor shell. Fuel and primary air are injected from the inside face of the afterbody. The flame holding capability of this trapped vortex configuration is evaluated for different primary equivalence ratios. Very low overall lean-blow-out (LBO) equivalence ratios are obtained for the TV combustor over a wide range of annular and primary airflow rates. It is found that by injecting the primary air with a tangential velocity component the circumferential mixing is improved without disrupting the vortex trapped in the cavity. The performance of the TV combustor is also evaluated through emissions measurements at the exit of the combustor and temperature distribution inside the cavity. Numerical simulations are performed for the TV configuration with a k-e turbulence model coupled with a PDF combustion chemistry model for simulating liquid spray combustion. The predicted results are in reasonable agreement with the measurements and provide an assessment of the flow distribution in the cavity region.

Large Eddy Simulations of Trapped-Vortex Combustor:
High combustor inlet temperatures and airflow velocities, as well as near-stoichiometric combustion, impose very stringent requirements for the development of new, affordable, robust, lightweight, compact combustor systems with improved operability. The Trapped Vortex Combustor (TVC) is a unique turbine engine combustor concept that offers reduced emissions and improved performance in a small, simple, low cost package. The TVC has proven to be a great advancement in combustor technology. Mixing of fuel and stability of a trapped vortex in realistic combustor geometry are analyzed in order to improve the current design. These are critical issues from the perspective of reduction of the NOX emissions and increase in the range of operation from small to large air to fuel ratios.

Simulation of Gas Turbine Combustion (ONR, AFOSR):
Numerical simulations are being performed for a swirl-stabilized spray combustor housed in the gas turbine combustion laboratory. The ultimate goal of the simulations are to reproduce the unsteady behavior (combustion instability) measured in the combustor. The experimental facility consists of an enclosed spray combustion reactor. The combustion air pass through a 12-vane swirl cascade, that imparts the angular momentum necessary to stabilize the flame, and flows around the nozzles before entering the reactor. The simulations are performed using FLUENT (computational fluid dynamics software), using the k-e model for turbulence and the PDF model for chemistry.

Flow and Mixing Characterisitcs of Asymmetric Fuel Injectors (NASA):
Several studies have shown that gaseous jets issued from asymmetric nozzles are an effective method of passive flow control that allows significant improvements of performance at a relatively low cost because noncircular jets rely solely on changes in the geometry of the nozzle. These jets produce increased jet spreading and mass entrainment as compared to jets issued from an axis-symmetric nozzle. It has been shown that the overall spreading rate of a jet issued from an elliptic nozzle was significantly greater than that of a jet issued from a circular nozzle. It is the goal of this work to determine if these mechanisms will produce similar mixing enhancements for a liquid spray issued from asymmetric nozzles. Such mixing enhancements in a gas turbine spray combustor application are likely to result in a more uniform temperature distribution and lower emissions. Improved large and small scale mixing in low speed flows enhances combustor performance, by improving combustion efficiency, and reducing combustion instabilities and undesired emissions in reacting flows. In the present work, the liquid spray from a Parker Hannifin Research Simplex Atomizer (RSA) Nozzle is to be studied for different nozzle geometries. The conventional "holder" piece of the RSA nozzle has a circular orifice and is used as a baseline in the current experiments. Two additional holder pieces have been modified with rectangular and elliptical shaped orifices. Each of these modifiedpieces has a 2 to 1 aspect ratio (length of major diameter to minor diameter) and the same hydraulic diameter as the circular nozzle. The jets issued from the different nozzles are characterized using a TSI 3-D Phase Doppler Particle Anemometry (PDPA) system. Velocity and size measurements of the particles in the spray are made at different radial and axial locations. These measurements are used to quantify the mixing enhancements achieved and the mechanisms associated with these enhancements.

OTHER ROTATING MACHINERY RESEARCH

Flow and Mixing in Impeller-Stirred Vessels (DOW Chemical):
The numerical simulation of turbulent flow in stirred tank reactors has attracted the attention of many researchers ( Kresta and Wood, 1991; Ranade and Joshi, 1990; Distelhoff and Marquis, 2000). This is due to the need for better reactor design for improved mixing. Smith (1991) reported that the poor understanding of the processes in stirred tanks cause losses of the order of $10 billion dollars per year. Through the use of CFD a detailed analysis of the flow field and mixing characteristics may be obtained to give needed insight for improved design and scale-up.

The need for speedy results has influenced industry to primarily rely on two-equation k-e models for predicting turbulence. These models are known to inaccurately predict turbulence in complex swirling flows such as the flow in a stirred tank. The use of LES for predicting stirred tank flows has been limited due to the complex geometry and large computational domain associated with stirred tanks. The motivation of our research is to develop improved turbulence models that can accurately predict the turbulence in stirred tanks without extensive computational resources.

Large Eddy Simulations of Stirred-Tank Reactor:
The complex flow generated due to an impeller in a cylindrical tank is of great importance to chemical industries. The geometry of a Ruston impeller is modeled using immersed boundary method. The flow dynamics and scalar mixing in a stirred-tank reactor are currently under investigation. Large eddy simulations can capture the unsteady dynamics of coherent structures in this non-equilibrium flow where most of the current RANS models fail.

MEMS for Rotating Machinery (DARPA, AFOSR):
Pumps, compressors, and turbines are particularly important to the petrochemical process industries that form one of the legs of the Louisiana economy. Gas turbines are used for power generation and propulsion of aircraft, ships, and ground vehicles around the world. Our goals are: Development of "intelligent" gas turbines using distributed sensor and actuator modules to control thermo fluid performance and vibration Application of microstructures over large areas to enhance heat transfer, such as on mechanical seals. Using HARM (high-aspect ratio micromachining) fabrication technology, modules can be produced in a range of materials, including ceramics,functionally graded materials, and high temperature alloys, suitable for harsh environments.

See http://www.cmm.lsu.edu for more details on MEMS research.