Richard J. Anthony

High Frequency Surface Heat Flux Imaging of Bypass Transition

A high-frequency surface heat flux imaging technique was used to investigate bypass transition induced by freestream turbulence. Fundamental experiments were carried out at the University of Oxford using high-density thin film arrays on a flat plate wind tunnel model. Bypass transition was induced by grid-generated turbulence with varying intensities of 2.3%, 4.2%, and 17% with a fixed integral length scale of approximately 12 mm. Unique high resolution temporal heat flux images are shown which detail significant differences between unsteady surface heat flux events induced by freestream turbulence and the classical Emmons-type spots which many turbomachinery transition models are based on. The temporal imaging technique presented allows study of unsteady surface heat transfer in detail, and helps elucidate the complex nature of transition in the high-disturbance environment of turbomachinery.

Flexible Non-Intrusive Heat Flux Instrumentation for the AFRL Research Turbine

This paper describes a large scale heat flux instrumentation effort for the AFRL HIT Research Turbine. The work provides a unique amount of high frequency instrumentation to acquire fast response unsteady heat flux in a fully rotational, cooled turbine rig along with unsteady pressure data to investigate thermal loading and unsteady aerodynamic airfoil interactions. Over 1200 dynamic sensors are installed on the 1 & 1/2 stage turbine rig. Airfoils include 658 double-sided thin film gauges for heat flux, 289 fast-response Kulite pressure sensors for unsteady aerodynamic measurements, and over 40 thermocouples. An overview of the instrumentation is given with in-depth focus on the non-commercial thin film heat transfer sensors designed and produced in the Heat Flux Instrumentation Laboratory at WPAFB. The paper further describes the necessary upgrade of data acquisition systems and signal conditioning electronics to handle the increased channel requirements of the HIT Research Turbine. More modern, reliable, and efficient data processing and analysis code provides better handling of large data sets and allows easy integration with the turbine design and analysis system under development at AFRL. Example data from cooled transient blowdown tests in the TRF are included along with measurement uncertainty.Copyright

A Review of the AFRL Turbine Research Facility

The Air Force Research Laboratory Turbine Research Facility is a transient blowdown facility that allows simultaneous measurement of unsteady heat transfer and aerodynamics on full scale engine hardware. It is unique for its size and consequent blowdown duration. Compared to engine validation testing, full scale, short duration turbine-rig testing is able to provide very large amounts of rotating turbine flowfield information using far less energy, orders of magnitude lower cost, and greater instrumentation selection.This paper provides an updated review of the facility’s history, operation, and enhancements since its initial construction over two decades ago. Historical connections to pioneering work in short-duration turbine heat transfer testing are highlighted, and an overview of past developments, features, and capabilities is given. More recent experimental and computational integration is described using a suite of in-house developed CFD design and analysis tools. Example test programs include a non-proprietary 1+ 1/2 stage research turbine rig, which is the most heavily instrumented high pressure turbine tested in the facility to date.. Recent data illustrates the character of unsteady airfoil shock interactions that may lead to large levels of resonant stress or turbine high cycle fatigue. The paper ends with a brief discussion of future work.© 2013 ASME

Comparison of Predictions From Conjugate Heat Transfer Analysis of a Film-Cooled Turbine Vane to Experimental Data

Conjugate heat transfer analysis was conducted on a 648 hole film cooled turbine vane using Code Leo and compared to experimental results obtained at the Air Force Research Laboratory Turbine Research Facility. An unstructured mesh with fully resolved film holes for both fluid and solid domains was used to conduct the conjugate heat transfer simulation on a desktop PC with eight cores. Initial heat flux and surface metal temperature predictions showed reasonable agreement with heat flux measurements but under prediction of surface metal temperature values. Root cause analysis was performed, leading to two refinements. First, a thermal barrier coating layer was introduced into the analysis to account for the insulating properties of the Kapton layer used for the heat flux gauges. Second, inlet boundary conditions were updated to more accurately reflect rig measurement conditions. The resulting surface metal temperature predictions showed excellent agreement relative to measured results (+/− 5 degrees K).Copyright

Three-Dimensional Film-Cooled Vane CFD Simulations and Preliminary Comparison to Experiments

Reynolds-Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) simulations are conducted using the Wilcox k-ω turbulence model within a code called LEO on a threedimensional fully film-cooled modern turbine inlet vane called the High Impact Technologies (HIT) Research Turbine Vane (RTV). External flows at operating conditions around the vane and their interaction with film cooling flows from the vane leading edge, pressure side (PS), suction side (SS), trailing edge, and hub and tip endwalls are modeled. The film cooling is modeled using a local source term in the governing equations for the added mass flux at the appropriate locations in the fluid domain along the vane surface. Cooled and uncooled isothermal vane simulations are conducted. Predictions of stream-wise distributions of heat flux and net heat flux reduction (NHFR) at two span locations are provided and compared to vane-only-configuration heat flux data recently obtained in the Air Force Research Laboratory (AFRL) Turbine Research Facility (TRF) short-duration blowdown facility. Details on proper matching of experimental boundary conditions for the CFD simulations are also given in order to provide a validation case for the maturing CFD code. Uncooled and cooled experimental data show appropriate relative trends, as do the uncooled and cooled predictions. However, comparing heat flux data to predictions shows disparities that require further investigation of the cooling modeling technique and appropriate assumptions going into the model.

Conjugate Heat Transfer Assessment of a 3-D Vane with Film Cooling and Comparison to Experiments

Heat transfer characteristics were predicted here on a full-scale 3-D model of a modern high pressure turbine vane with 648 film cooling holes called the High Impact Technologies Research Turbine Vane (HIT RTV). A Reynolds-Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) code called Leo simulated the internal cooling plenums, cooling hole passages, external main flow passages as well as the solid vane metal in realistic turbine-representative conditions at a typical film cooling blowing ratio using an unstructured mesh. This conjugate assessment of both the solid and fluid domains allows for a more accurate representation of the heat transfer environment for the vane. Surface data including heat flux, net heat flux reduction (NHFR), and surface temperature are computed and compared to full-scale annular blow-down rig experimental measurements from the same vane in the Turbine Research Facility (TRF) of the Air Force Research Laboratory (AFRL). Predictions from the conjugate heat transfer (CHT) CFD are compared to experimental measurements for six span locations on both the suction side (SS) and pressure side (PS) of the vane. These are also compared to CFD predictions from previous simulations that only model the external main flow and estimate the cooling influx using a transpiration boundary condition. The heat transfer information gleaned from this study helps validate the maturing CHT CFD code used, helps realize the problem areas and conduction trends on the surface of a typical modern turbine vane with film cooling in true geometry and operational conditions, and provides critical information about the level of CFD integrity required for axial turbomachinery flows. This work also provides a thorough benchmarking of a film cooling array on a modern vane design for ongoing cooling optimization studies to be reported in the future. Results show that heat flux is generally over-predicted on the vane surface, especially without film cooling but shows some areas with fair agreement for both the cooled and uncooled cases. Surface temperature is much more accurately predicted for both sides of the cooled and uncooled vanes. Prediction of NHFR is fair but inconclusive due to the limited available experimental measurements. Meanwhile, a rarely reported parameter, net temperature reduction (NTR), is more accurately predicted by the CFD. The challenges in predicting heat transfer in such a realistic environment is primarily, but not exclusively, attributed to the necessity for more heat transfer measurements on the cooling air in the rig cooling channels and inside the vane and due to the fact that the experiments may have more isothermal wall temperatures at over the run time than expected.

Modifications and Upgrades to the AFRL Turbine Research Facility

The Turbine Research Facility (TRF) at the Air Force Research Laboratory has undergone a two-year effort to enhance and modernize multiple systems for advanced study of unsteady turbine aerodynamics and heat transfer. This paper provides an overview of several concurrent projects to upgrade a number of facility hardware and software systems. A unique scalable high speed, high channel count data acquisition architecture is developed with modern hardware and software that expands capability while maintaining compatibility and synchronization with legacy hardware. The combination of both new and existing channels with custom Matlab-based data acquisition and processing code provides accurate and efficient signal processing and display for over 750 high speed data channels. Codes are integrated with a new Turbine Design and Analysis System that provides design CFD modeling, optimization, and post-test analysis. The paper describes a new 1+ 1/2 stage cooled high pressure research turbine that has been designed, instrumented, and tested. Initial cooled vs. uncooled data comparisons are given including fast response unsteady airfoil pressure and heat flux. This work further describes significant modification to the TRF rotordynamic drive system. Analysis and mechanical re-design have been completed to mitigate vibration effects. Facility monitoring and control upgrades are implemented to improve test situational awareness and safety. Updated cryogenic cooling hardware and software improve cooling flow delivery to HPT airfoils, platforms, and blade outer air seals. Future work includes continued research turbine testing, industry test rig collaboration, new instrumentation technology, and advanced modeling and simulation development.Copyright

Showerhead Film Cooling Performance of a Turbine Vane at High Freestream Turbulence in a Transonic Cascade

This paper experimentally investigates the effect of blowing ratio and exit Reynolds number/Mach number on the film cooling performance of a showerhead film cooled first stage turbine vane. The vane midspan was instrumented with single-sided platinum thin film gauges to experimentally characterize the Nusselt number and film cooling effectiveness distributions over the surface. The vane was arranged in a two-dimensional, linear cascade in a heated, transonic, blow-down wind tunnel. Three different exit Mach numbers of Mex = 0.57, 0.76 and 1.0—corresponding to exit Reynolds numbers based on vane chord of 9.7 × 105 , 1.1 × 106 and 1.5 × 106 , respectively—were tested with an inlet free stream turbulence intensity (Tu) of 16% and an integral length scale normalized by vane pitch (Λx /P) of 0.23. A showerhead cooling scheme with five rows of cooling holes was tested at blowing ratios of BR = 0, 1.5, 2.0, and 2.5 and a density ratio of DR = 1.3. Nusselt number and adiabatic film cooling effectiveness distributions were presented on the vane surface over a range of s/C = −0.58 on the pressure side to s/C = 0.72 on the suction side of the vane. The primary effects of coolant injection were to augment the Nusselt number and reduce the adiabatic wall temperature downstream of the injection on the vane surface as compared to no film injection case (BR = 0) at all exit Mach number conditions. In general, an increase in blowing ratio (BR = 1.5 to 2.5) showed noticeable Nusselt number augmentation on pressure surface as compared to suction surface at exit Mach 0.57 and 0.75; however, the Nusselt number augmentation for these blowing ratios was found to be negligible on the vane surface for exit Mach 1.0 case. At exit Mach 1.0, an increase in blowing ratio (BR = 1.5 to 2.5) was observed to have an adverse effect on the adiabatic effectiveness on the pressure surface but had negligible effect on suction surface. The effectiveness trend on the suction surface was also found to be influenced by a favorable pressure gradient due to Mach number and boundary layer transition in the region s/C = 0.28 to s/C = 0.45 at all blowing ratio and exit Mach number conditions. An increase in Reynolds number from exit Mach 0.76 to 1.0 increased heat transfer levels on the vane surface at all blowing ratio conditions. A large increase in Reynolds number adversely affected adiabatic effectiveness on the pressure surface at all blowing ratio conditions. On the suction surface, a large increase in Reynolds number also affected adiabatic effectiveness in the favorable pressure gradient and boundary layer transition region.Copyright

Determination of Cooling Parameters for a High Speed, True Scale, Metallic Turbine Vane Ring

Film cooling technology has been around for many decades and many significant advances in cooling effectiveness have been made at many different facilities using several different methods. A large proportion of film cooling research is successfully carried out using simplified scaled-up models in wind tunnels coupled with novel measurement techniques. These tests have been very effective in assessing basic film cooling parameters for many cooling hole geometries, patterns, and blowing ratios. In real engines, however, film cooling designs are ultimately subjected to highly unsteady 3-D secondary flows and rotational effects. Few film cooling experiments have quantified these effects on real, true scale turbine hardware in a rotating test environment. The Turbine Research Facility (TRF) at the Air Force Research Laboratory has been acquiring uncooled heat transfer measurements on full scale metallic airfoils both with and without rotation for several years. The addition of cooling flow to this type of facility has provided new capability, and new challenges. The primary two issues being that the film temperature is unknown and that the airfoil is no longer semi-infinite. This makes it more difficult to extract the adiabatic effectiveness and the heat transfer coefficient from the measurements of surface temperature and surface heat transfer since conventional methods used in most other experiments are not valid in this case. In contrast another cooling parameter, the overall effectiveness, is readily obtained from measurements of surface temperature, internal coolant temperature, and mainstream temperature. The overall effectiveness is a normalized measure of metal surface temperatures expected for actual operating conditions. It is the goal of this paper to evaluate how measurements, obtained from a transient blowdown facility like the TRF, can be used to quantify the expected performance of a film cooled turbine airfoil. Additionally, it is imperative to properly correlate these experimental results to the true engine conditions. The data required for this analysis has been collected using an array of surface mounted thermocouples and thin film gauges in a series of experiments where freestream temperatures and coolant temperatures and mass flow rates were varied. The airfoil used in this investigation was a thin walled metallic airfoil with a showerhead cooling scheme and several rows of normal holes on both the pressure and suction sides of the airfoil. The flow is typical of that seen in a modern high pressure turbine — that is an inlet Mach number of about 0.1 accelerating toward sonic at the throat with a high inlet freestream turbulence level of about 20%.

What is Needed in Experimental Methods Instruction - Perspectives from a Government Laboratory

This paper offers a perspective from researchers at a government laboratory on what skills are needed in Experimental Methods Instruction in order to better prepare students for graduate research and future careers in aerospace laboratories. The paper starts with a limited overview of experimental facilities and techniques used in the Turbine Branch of the Air Force Research Laboratory, Propulsion Directorate. This brief overview includes a few general examples ranging from basic scientific research to large scale turbine research facilities. The paper then identifies skills and procedures the authors feel are needed when students leave the classroom and begin work in a research laboratory. Conclusions are stated along with a few recommendations that instructors may find helpful.