An analysis of prop-fan/airframe aerodynamic integration

An approach to aerodynamic integration of turboprops and airframes, with emphasis placed upon wing mounted installations is addressed. Potential flow analytical techniques were employed to study aerodynamic integration of the prop fan propulsion concept with advanced, subsonic, commercial transport airframes. Three basic configurations were defined and analyzed: wing mounted prop fan at a cruise Mach number of 0.8, wing mounted prop fan in a low speed configuration, and aft mounted prop fan at a cruise Mach number of 0.8

Trace-level speculative multithreaded architecture

This paper presents a novel microarchitecture to exploit trace-level speculation by means of two threads working cooperatively in a speculative and non-speculative way respectively. The architecture presents two main benefits: (a) no significant penalties are introduced in the presence of a misspeculation and (b) any type of trace predictor can work together with this proposal. In this way, aggressive trace predictors can be incorporated since misspeculations do not introduce significant penalties. We describe in detail TSMA (trace-level speculative multithreaded architecture) and present initial results to show the benefits of this proposal. We show how simple trace predictors achieve significant speed-up in the majority of cases. Results of a simple trace speculation mechanism show an average speed-up of 16%.Peer ReviewedPostprint (published version

Compiler analysis for trace-level speculative multithreaded architectures

Trace-level speculative multithreaded processors exploit trace-level speculation by means of two threads working cooperatively. One thread, called the speculative thread, executes instructions ahead of the other by speculating on the result of several traces. The other thread executes speculated traces and verifies the speculation made by the first thread. In this paper, we propose a static program analysis for identifying candidate traces to be speculated. This approach identifies large regions of code whose live-output values may be successfully predicted. We present several heuristics to determine the best opportunities for dynamic speculation, based on compiler analysis and program profiling information. Simulation results show that the proposed trace recognition techniques achieve on average a speed-up close to 38% for a collection of SPEC2000 benchmarks.Peer ReviewedPostprint (published version

Laser velocimeter measurements of the flowfield generated by an advanced counterrotating propeller

Results are presented of an investigation to measure the flowfield generated by an advanced counterrotating pusher propeller model similar to the full-scale Unducted Fan demonstrator engine. A laser Doppler velocimeter was used to measure the velocity field in several planes normal to the centerline of the model at axial stations upstream and downstream of each rotor. During this investigation, blades of the F4/A4 type were installed on the model which was operating in a freestream Mach 0.72 regime, with the advance ratio of each rotor set at 2.80. The measured data indicate only a slight influence of the potential field of each front rotor blade on the flowfield upstream of the rotor. The data measured downstream of the front rotor characterize the tip vortices, vortex sheets and potential field nonuniformities generated by the front rotor. The unsteadiness of the flow in the rotating frame of reference of the aft rotor is also illustrated

Symbiotic Subordinate Threading (SST)

Integration of multiple processor cores on a single die, relatively constant die sizes, increasing memory latencies, and emerging new applications create new challenges and opportunities for processor architects. How to build a multi-core processor that provides high single-thread performance while enabling high throughput through multi-programming? Conventional approaches for high single-thread performance use a large instruction window for memory latency tolerance, which requires large and complex cores. However, to be able to integrate more cores on the same die for high throughput, cores must be simpler and smaller. We present an architecture that obtains high performance for single-threaded applications in a multi-core environment, while using simpler cores to meet the high throughput requirement. Our scheme, called Symbiotic Subordinate Threading (SST), achieves the benefits of a large instruction window by utilizing otherwise idle cores to run dynamically constructed subordinate threads (a.k.a. {\em helper threads}) for the individual threads running on the active cores. In our proposed execution paradigm, the subordinate thread fetches and pre-processes instruction streams and retires processed instructions into a buffer for the main thread to consume. The subordinate thread executes a smaller version of the program executed by the main thread. As a result, it runs far ahead to warm up the data caches and fix branch miss-predictions for the main thread. In-flight instructions are present in the subordinate thread, the buffer, and the main thread, forming a very large effective instruction window for single-thread out-of-order execution. Moreover, using a simple technique of identifying the subordinate thread non-speculative results, the main thread can integrate the subordinate thread's non-speculative results directly into its state without having to execute their corresponding instructions. In this way, the main thread is sped up because it also executes a smaller version of the program, and the total number of instructions executed is minimized, thereby achieving an efficient utilization of the hardware resources. The proposed SST architecture does not require large register files, issue queues, load/store queues, or reorder buffers. In addition, it incurs only minor hardware additions/changes. Experimental results show remarkable latency-hiding capabilities of the proposed SST architecture, outperforming existing architectures that share similar high-level microarchitecture

Computational Aeroacoustic Analysis of Propeller Installation Effects

In line with the goal of cleaner and quieter aircraft, this paper investigates propeller acoustics aiming to improve turboprops noise emissions, as they represent the best choice for short and medium range flights in terms of fuel efficiency. CFD is used to analyse the propeller-airframe interaction physics, and assess propeller installation effects, for a full scale twinengined aircraft. The employed propellers represent advanced designs currently used in modern aircraft and the cases of co-rotating and counter-rotating top-in layout are considered. The URANS approach is used on grids of up to 195 M points aiming to directly extract from CFD the noise tonal content. Numerical results are first validated against modelscaled experimental data. A comparison between results of the full aircraft and a propeller in isolation is also carried out. Full aircraft predictions show significant differences in the external acoustics between port and starboard sides for the co-rotating case, with a louder noise generated by the inboard-up propeller. The counter-rotating layout shows a more regular distribution of overall noise, with on average slightly higher noise levels towards the front and the rear of the cabin. Acoustic predictions from an isolated propeller in axial flight significantly underestimate noise levels even on the fuselage sides where the aircraft masks the other propeller, showing the relevance of the propeller-airframe interactions in the evaluation of actual sound pressure levels in flight

Propeller installation effects on turboprop acoustics

Propeller installation options for a twin-engined turboprop aircraft are evaluated at cruise conditions, aiming to identify the quieter configuration. Computational fluid dynamics is used to investigate the near-field acoustics and transfer functions are employed to estimate the interior cabin noise. Co-rotating and counter-rotating installation options are compared. The effect of propeller synchrophasing is also considered. The employed method captures the complexity of the acoustic field generated by the interactions of the propeller sound fields among each other and with the airframe, showing also the importance of simulating the whole problem to predict the actual noise on a flying aircraft. Marked differences among the various layouts are observed. The counter-rotating top-in option appears the best in terms of acoustics, the top-out propeller rotation leading to louder noise because of inflow conditions and the occurrence of constructive acoustic interferences. Synchrophasing is shown to be beneficial for co-rotating propellers, specially regarding the interior noise, because of favorable effects in the interaction between the propeller direct sound field and the noise due to the airframe. An angle closer to the maximum relative blade shift was found to be the best choice, yielding, however, higher sound levels than those provided by the counter-rotating top-in layout