Quantifying Optical Tip-Timing Probe Error With Laboratory Apparatus

Detection of airfoil time of arrival with optical probes has been evolving since the 1980s. Time of arrival data are used to infer airfoil stresses caused by vibration through a sequence of manipulations. The data conversion begins by converting arrival time to blade position, so blade deflection can be determined from the expected non-vibrating position. Various methods are used in the industry to convert deflection data to frequency, amplitude, and stress, which is beyond the scope of this paper. Regardless of the analytical approach used, producing accurate stress information relies on the precise detection and measurement of time of arrival, which equates to blade position. Recent improvements have been made in time of arrival system accuracy by running faster clocks to increase temporal resolution of the measurement. Greater timing resolution, afforded by clock speed, will have diminishing returns when probe and blade-tip interactions begin producing dominant errors. In the case of optical probes, the blade-tip needs to be treated as a curved reflector in the optical system that is capable of introducing dynamic errors. In engine operation the blade-tip moves axially under the probe from untwist, static deflection, and vibration, causing the light to reflect from different parts of the blade-tip. This relative movement between the probe and blade-tip cause the arrival time to change dynamically. Neglecting the dynamic arrival errors caused by the blade-tip’s optical properties will result in blade deflection-errors that propagate into the stress information. This paper presents a laboratory study that quantifies time of arrival errors due to optical interaction with tip radii. The study reports measured arrival position error as a function of location and optical signal power levels. The work is presented in terms of arrival position, producing information that is independent of rotational speed, and vibratory mode.

Integrated Optimization Design for a Radial Turbine Wheel of a 100kW-Class Microturbine

The aerodynamic performance, structural strength and wheel weight are three important factors in the design process of the radial turbine. This paper presents an investigation on these aspects and develops an optimization design approach for radial turbine with consideration of the three factors. The aerodynamic design for the turbine wheel with inlet diameter of 230mm for 100kW-class microturbine unit is carried out firstly as the original design. Then, the cylinder parabolic geometrical design method is applied to the wheel modeling and structural design, but the maximum stress predicted by Finite Element Analysis greatly exceeds the yield limit of material. Furthermore, the wheel weight is above 7.2kg thus bringing some critical difficulties for bearing design and turbine operation. Therefore, an integrated optimization design method for radial turbine is studied and developed in this paper with focus on the wheel design. Meridional profiles and shape lines of turbine wheel are optimized with consideration of the whole wheel weight. Main structural modeling parameters are reselected to reduce the wheel weight. Trade-off between aerodynamic performance and strength performance is highly emphasized during the optimization design. The results show that the optimized turbine wheel gets high aerodynamic performance and acceptable stress distribution with the weight less than 3.8kg.

Passive Absorption/Emission Spectroscopy for Gas Temperature Measurements in Gas Turbine Engines

A novel technique is developed to simultaneously measure hot surface and gas temperatures based on passive absorption/emission spectroscopy (PAS). This non-intrusive, in situ technique is the extension of multi-wavelength pyrometry to also measure gas temperature. The PAS technique uses hot surface (e.g., turbine blade) as the radiation source, and measures radiation signals at multiple wavelengths. Radiation signals at wavelengths with minimum interference from gas (mostly from water vapor and CO2) can be used to determine the hot surface temperature, while signals at wavelengths with gas absorption/emission can be used to determine the gas temperature in the line-of-sight. The detection wavelengths are optimized for accuracy and sensitivity for gas temperature measurements. Simulation results also show the effect of non-uniform gas temperature profile on measurement results. High pressure/temperature tests are conducted in single nozzle combustor rig to demonstrate sensor proof-of-concept. Preliminary engine measurement results shows the potential of this measurement technique. The PAS technique only requires one optical port, e.g., existing pyrometer or borescope port, to collect the emission signal, and thus provide practical solution for gas temperature measurement in gas turbine engines.

Functional Analysis and Exergoeconomic Evaluation for the Combined Production of Electromechanical Power and Useful Heat of a Cogeneration Power Plant

In the Ecuadorian electrical market, several sugar plants, which significantly participate in the local electricity market, are producing their own energy and commercializing the surplus to the electrical market. This study evaluates the integral use of the sugar cane bagasse for productive process on a Cogeneration Power Plant in an Ecuadorian Sugar Company [8]. The electrical generation based on biomass requires a great initial investment. The cost is around US$ 800/kW installed, twice the US$ 400/kW initial investment of conventional thermoelectric power plant and almost equal to the US$ 1,000/kW initial cost of hydroelectric power plant [5]. A thermoeconomic study was carried out on the production of electricity and the sales of the surplus of 27 MWe average produced by the power plant. An operational analysis was made using instantaneous values from the estimated curves of demand and generation of electricity. From the results, it was concluded that the generated electricity costs are 0.0443 US$/kWh, while the costs of the electricity from Fossil Power Plants (burning fuel oil, diesel fuel and natural gas) are in the range 0.03–0.15 US$/kWh and from Hydroelectric Plants are about 0.02 US$/kWh. Cogeneration power plants burning sugar cane bagasse could contribute to the mitigation of climatic change. This specific case study shows the reduction of the prospective emissions of greenhouse gases, around 55,188 ton of CO2 equivalent yearly for this cogeneration power plant.

Gas Turbine and Driven Machinery Management and Diagnostics

The size and complexity of gas turbines has evolved tremendously over the years and the controls, instrumentation and diagnostics tools have kept pace with the advances. This paper discusses the progress of the tools to keep these complex machines running for continued reliability, efficiency, emissions compliance and power output. The technology to enable the user to manage their machinery on site and remotely will be discussed in this paper along with the benefits added by the technologies.

Correlation Measure-Based Stall Margin Estimation for a Single-Stage Axial Compressor

This paper presents a method for estimating compressor stall margin and the results of applying the estimation technique to an axial compressor rig. Stall margin estimation is accomplished through the use of a compressor stability detection parameter called the “correlation measure.” The correlation measure captures the periodicity of the pressure in the rotor tip region of the compressor. The downcrossing frequency of the correlation measure across some preset threshold is measured while operating the compressor rig at various steady-state points along the design speed characteristic line. These measurements are used to generate a relationship with stall margin as a function of downcrossing frequency. The estimation technique is evaluated by applying it while dynamically ramping the operating point of the compressor up the design speed line towards surge. A brief investigation on the effects of inlet distortions on the correlation measure-based estimation system is also given.

A Competitive Market Approach to Gas Turbine Technology Portfolio Selection

Heavy duty gas turbine developments are major endeavors which use significant resource for development. Optimization of the technology portfolio is critical to yield a competitive product-line which is robust enough to compete in a dynamic market where vantage positions bring large profits but quickly erode over time. The current research addresses some of these challenges by proposing a transparent and integrated method aimed at investigating technology portfolio selection for future gas turbine-based power plants. The value-driven methodology analyzes technology investments, and is the foundation for a strategic decision framework that facilitates the formulation of robust and competitive technology portfolio solutions. A three-step process is proposed in this paper. A market response analysis is first carried out to estimate market penetration. A technology impact and readiness level analysis is performed next and augmented with a portfolio optimization. Finally, “what-if” scenarios are investigated to assess the robustness of selected technology portfolio candidates against a set of market conditions.

Combined Cycle Off-Design Performance Estimation: A Second-Law Perspective

A combined cycle power plant (or any power plant, for that matter) does very rarely — if ever — run at the exact design point ambient and loading conditions. Depending on the demand for electricity, market conditions and other considerations of interest to the owner of the plant and the existing ambient conditions, a CC plant will run under boundary conditions that are significantly different from those for which individual components are designed. Accurate calculation of the “off-design” performance of the overall combined cycle system and its key subsystems requires highly detailed and complicated computer models. Such models are crucial to high-fidelity simulation of myriad off-design performance scenarios for control system development to ensure safe and reliable operability in the field. A viable option in lieu of sophisticated system simulation is making use of the normalized curves that are generated from rigorous model runs and applying the factors read from such curves to a known design performance to calculate the “off-design” performance. This is the common method adopted in the fulfillment of commercial transactions. These curves, however, are highly system-specific and their broad applicability to a wide variety of configurations is limited. Utilizing the key principles of the second law of thermodynamics, this paper describes a simple, physics-based calculation method to estimate the off-design performance of a combined cycle power plant. The method is shown to be quite robust within a wide range of operating regimes for a generic combined cycle system. As such, a second law based approach to off-design performance estimation is a highly viable tool for plant engineers and operators in cases where calculation speed with a small sacrifice in fidelity is of prime importance.

Application of a Miniature Telemetry System in a Small Gas Turbine Engine

For the purpose of assessing combustion effects in a small gas turbine engine, there was a requirement to evaluate the rotating temperature and dynamic characteristics of the power turbine rotor module. This assessment required measurements be taken within the engine, during operation up to maximum power, using rotor mounted thermocouples and strain gages. The acquisition of this data necessitated the use of a telemetry system that could be integrated into the existing engine architecture without affecting performance. Due to space constraints, housing of the telemetry module was limited to placement in a hot section. In order to tolerate the high temperature environment, a cooling system was developed as part of the integration effort to maintain telemetry module temperatures within the limit allowed by the electronics. Finite element thermal analysis was used to guide the design of the cooling system. This was to ensure that sufficient airflow was introduced and appropriately distributed to cool the telemetry cavity, and hence electronics, without affecting the performance of the engine. Presented herein is a discussion of the telemetry system, instrumentation design philosophy, cooling system design and verification, and sample of the results acquired through successful execution of the full engine test program.

Integrating Systems Engineering Into the USAF Academy Capstone Gas Turbine Engine Course

This paper is intended to serve as a template for incorporating technical management majors into a traditional engineering design course. In 2002, the Secretary of the Air Force encouraged the USAF Academy to initiate a new interdisciplinary academic major related to systems engineering. This direction was given in an effort to help meet the Air Force’s growing need for “systems” minded officers to manage the development and acquisition of its ever more complex weapons systems. The curriculum for the new systems engineering management (SEM) major is related to the “engineering of large, complex systems and the integration of the many subsystems that comprise the larger system” and differs in the level of technical content from the traditional engineering major. The program allows emphasis in specific cadet-selected engineering tracks with additional course work in human systems, operations research, and program management. Specifically, this paper documents how individual SEM majors have been integrated into aeronautical engineering design teams within a senior level capstone course to complete the preliminary design of a gas turbine engine. As the Aeronautical engineering (AE) cadets performed the detailed engine design, the SEM cadets were responsible for tracking performance, cost, schedule, and technical risk. Internal and external student assessments indicate that this integration has been successful at exposing both the AE majors and the SEM majors to the benefits of “systems thinking” by giving all the opportunity to employ SE tools in the context of a realistic aircraft engine design project.