Gas Dynamics and Propulsion Laboratory (7 Projects)

1. Jet Noise-Prediction and Reduction (Funded by GE Aviation, NASA, US Dept. of Defense, ONR, Sweden DoD, NRL)
The advent of jet engine as a power plant for military and civil aircraft and its unavoidable counterpart, jet engine noise, initiated substantial research on the sources and causes of jet noise, as well as methods and devices for its reduction. The noise level of jet engines, particularly during takeoff and climb, is often a concern for people living near airports or working near airplanes. Such high noise levels can limit future airport air traffic expansion, and force new airports to occupy remote sites. It also limits the ability of personnel to work for extended times near airplanes. New requirements for lower jet noise are a continued area of interest both by governmental agencies and by neighborhoods located in close proximity to airports, flight paths and to engine and flight vehicle manufacturers. Due to these concerns a need to further jet noise reduction technology is in demand.

Various approaches have been proposed to overcome the noise issue. The optimal solution should be such that substantial noise suppression is achieved using a method that is easy to implement, low cost, reliable, and without substantial adverse effects on the engine performance. Development of such devise requires basic understanding of the noise generation mechanisms. The objectives of our research are to evaluate experimentally new concepts for jet noise reduction and to develop analytical or numerical tools for the prediction of jet noise and jet noise reduction techniques for commercial and military engines (subsonic and supersonic jets).

2. Combustion Control and Flameless Combustion (Funded by Office of Naval research, NASA, GE Aviation and UTC)

Considerable amount of work in the area of passive and active combustion control for gaseous and liquid fueled combustion has been reported during the last two decades. These studies have dealt mostly with bluff-body-stabilized combustor and dump combustors where the recirculation induced by a bluff-body or by a sudden expansion is used to stabilize the flame and were more recently extended to swirl stabilized combustors. Active control strategies have been used to suppress thermo-acoustic instabilities resulting from a coupling between the heat release and the acoustic modes in the combustor. These control strategies have generally relied on modulating the fuel injection and phase shifting it so as to decouple the pressure rise and heat release with respect to each other. Control strategies have also looked at improving fuel efficiency and reducing pollutants, and in extending flammability limits. Our research deals with the control of gas-turbine gaseous and liquid fuel combustors with swirlers, bluff body stabilizers and distributed fuel injection for rapid mixing and stabilization. It focuses on investigating the mixing patterns and flame structure in these combustors and developing control strategies for improved performance of gas-turbine combustors.

In addition, we are developing new technology of combustion, called “Flameless Combustion” for gas turbine engines. This technology provides low emissions and very stable combustion and has the potential of becoming the next generation of combustion systems for propulsion and power generation gas turbines.

3. Rotating Detonation Engines - RDE (Funded by NASA, ONR, AFOSR, and GE Aviation/GEGR)

A  pulse detonation engine (PDE) offers few moving parts, high efficiency, high thrust, low weight, low cost, and ease of scaling.  These make the PDE an attractive alternative to jet turbine engines for small disposable engines.  The near constant volume heat addition process, along with the lack of a compression cycle, lend to the high efficiency and specific impulse, simplicity, and low-cost of pulse detonation engines.  Pulse detonation engines have the potential for operation at speeds ranging from static to hypersonic, with competitive efficiencies, enabling supersonic operation beyond conventional gas turbine engine technology.  Currently, no single cycle engine exists which has such a broad range of operability.  Computational and experimental program is conducted at UC to investigate the performance of an air breathing pulse detonation engine (PDE).  This research effort involves investigating such critical issues as: detonation initiation and propagation; valving, timing and control; instrumentation and diagnostics; purging, heat transfer, and repetition rate; noise and multi-tube effects; detonation and deflagration to detonation transition modeling; and performance prediction and analysis.  Our lab has a unique hybrid engine that includes an array of 6 PDEs integrated with an axial turbine.  This system potentially can replace the entire high pressure core of a jet engine, including high pressure compressor and turbine and the combustor.

4. Novel Augmentor System Design (Funded by GE Aviation, AFRL, ONR)

A new and unique facility that simulates the flow conditions in an afterburner configuration is operating in our laboratory. The facility includes a combustor with an exhaust duct where innovative strategies of secondary fuel injection can be tested. It is also instrumented for advanced flow and combustion diagnostics. The facility is used to study secondary combustion dynamics in an augmentor configuration. The research emphasizes new concepts for flame stabilization, and investigation of combustion instabilities in augmentors and their prevention using passive control and acoustic liners. The research combines experimental and computational work.

5. Flight Control of Modern Shaped Wings Using Vortex and Flapping Actuators (Air Force Research Laboratory)

Lift force on modern shaped wings at a high angle of attack relies on complex set of vortices that are formed at the leading edges, flaps, and tips of the wing.  At high angle of attack these vortices loose gradually their coherence due to intrinsic flow instabilities.  At these conditions, the lift produced by the vortices is reduced and the aerodynamic moments derivatives change from stable to unstable conditions causing loss of controllability and stall.  Tests showed that small continuous, pulsating, or flapping microjets that are injected into the separated regions from certain locations on the wing surface could control the behavior of the flow over the wing.  Depending on the orientation of the injected microjets, the flow pattern over the wing can be altered to achieve the desired controllability.  The microjets injection can therefore be used for flight control without the conventional control surfaces.  Controlled actuation of different combinations of microjets based on feedback from sensors distributed over the wing surface can yield the desired pitch, yaw, and roll moments. Moreover, this method incurs little or no drag penalty.

The control system relies on rational activation of pulsating jets. Static and dynamic modeling of the flow topology, aerodynamic responses and actuator characteristics are required for closed-loop control system design.  Advanced external flow control and aircraft attitude control architectures and algorithms are needed to cope with the highly coupled, time-varying, uncertain and complex nonlinear  aerodynamics that are dynamically and structurally unstable.

The present concept is applicable to attitude control of tailless fighters, reentry vehicles and UAVs, especially micro UAVs, without requiring control surfaces such as ailerons, rudder, elevator, or flaps.  This type of controlled lift can also be used to enhance performance of lifting bodies.  The advantage of such a system lies in its aerodynamic simplicity, reduced radar cross-section and ease of miniaturization.

6. Airway, Voice, Cardiovascular Research (Funded by NIH, UC CoM, CCHMC, NCAI)

Mechanisms of voice production are not well understood.  They involve interaction between flow and structural vibrations of the vocal folds within the larynx; this is the aeroelastic aspect of the mechanism.  The interaction between the flow and vibrating folds modify the flow and produces highly vortical flow pattern.  This flow includes organizes vortices and random turbulence generates sound via mechanisms described by aeroacoustic theory.  The sound is amplified and filtered in the mouth cavity before exiting as voice.  Our jet noise research described in section 1 above has many similarities to voice generation mechanisms.  Our research investigates the relationship between the flow field and the noise produced by the jet and both experimental and computational tools are useful for the larynx applications.  The voice research is a collaborative effort between our laboratory and the Otolaryngology Department at the UC School of Medicine.  Our goal is to develop the physical understanding of voice production that will help in developing new medical treatment and surgical procedures for patients with voice pathologies.

In addition to voice research we are collaborating with the Pulmonary and ENT Departments of CCHMC (Cincinnati Children’s Hospital) in applying CFD to compute airway flow and pressure distribution for sleep apnea and airway reconstruction research.

7. Advanced Scramjet Propulsion (Air Force Office of Scientific Research and NASA)

Scramjet combustors are characterized by an extremely short residence time for the completion of fuel atomization, mixing and combustion.  It is therefore desired to develop fuel injection schemes that will accelerate the mixing process by improving penetration, achieving small-dispersed fuel droplets, and enhancing mixing. In addition, during vehicle acceleration the location of heat release in the combustor has to shift to ensure optimal performance in the entire range of Mach numbers.  This project addresses the aforementioned issues by investigating fuel injection flow control strategies.  Specially designed injectors are designed and tested in quiescent, cold cross flow, and reacting conditions.  The effect of fuel temperature, as the fuel is heat soaked for combustor cooling, would also be simulated to test the stability of the injectors. Emissions, which are a critical concern for commercial space applications, would also be used as a performance parameter in evaluating the injectors. In parallel with these experiments, numerical modeling is pursued to study the flow physics and effectiveness of the different injector configurations in cold and reacting flows.