Some Low Speed Problems of High Speed Aircraft

1962 ◽  
Vol 66 (616) ◽  
pp. 211-225 ◽  
Author(s):  
A. Spence ◽  
D. Lean
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Supersonic Speed ◽  
Jet Propulsion ◽  
Low Speed ◽  
The Past ◽  
Flight Range ◽  
The Future ◽  
Mach Numbers ◽  
Leading Edges

The high speed aircraft whose low speed aerodynamic problems are discussed in this part of the paper belong to the future rather than to the past or present. Küchemann has shown how jet propulsion and the use of a new set of aerodynamics appropriate to supersonic speed lead one from the classical aircraft to new shapes suitable for achieving a required flight range. These shapes include wing-body arrangements with wing sweepback angles of 55° or 60° suitable for a Mach number of about 1·2, and slender, neartriangular wings with sharp leading edges suitable for Mach numbers of around 2 or more, depending on the ratio of span to length.

Aeroelastic Problems in connection with High-Speed Flight

1956 ◽  
Vol 60 (547) ◽  
pp. 459-475 ◽  
Author(s):  
E. G. Broadbent
Keyword(s):  
Mach Number ◽  
High Speed ◽  
The Other ◽  
Control Surface ◽  
The Past ◽  
Other Hand ◽  
Aerodynamic Derivatives ◽  
Mach Numbers ◽  
The One

SummaryA review is given of developments in the field of aeroelasticity during the past ten years. The effect of steadily increasing Mach number has been two-fold: on the one hand the aerodynamic derivatives have changed, and in some cases brought new problems, and on the other hand the design for higher Mach numbers has led to thinner aerofoils and more slender fuselages for which the required stiffness is more difficult to provide. Both these aspects are discussed, and various methods of attack on the problems are considered. The relative merits of stiffness, damping and massbalance for the prevention of control surface flutter are discussed. A brief mention is made of the recent problems of damage from jet efflux and of the possible aeroelastic effects of kinetic heating.

Separation and Transition Control on an Aft-Loaded Ultra-High-Lift LP Turbine Blade at Low Reynolds Numbers: High-Speed Validation

2006 ◽  
Vol 129 (2) ◽  
pp. 340-347 ◽  
Author(s):  
Maria Vera ◽  
Xue Feng Zhang ◽  
Howard Hodson ◽  
Neil Harvey
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Surface Finish ◽  
High Speed ◽  
Reynolds Numbers ◽  
High Lift ◽  
Low Reynolds Numbers ◽  
Low Speed ◽  
Transition Mechanism ◽  
Low Reynolds

This paper presents the second part of an investigation of the combined effects of unsteadiness and surface roughness on an aft-loaded ultra-high-lift low-pressure turbine (LPT) profile at low Reynolds numbers. The investigation has been performed using low- and high-speed cascade facilities. The low- and high-speed profiles have been designed to have the same normalized isentropic Mach number distribution. The low-speed results have been presented in the first part (Zhang, Vera, Hodson, and Harvey, 2006, ASME J. Turbomach., 128, pp. 517–527). The current paper examines the effect of different surface finishes on an aft-loaded ultra-high-lift LPT profile at Mach and Reynolds numbers representative of LPT engine conditions. The surface roughness values are presented along with the profile losses under steady and unsteady inflow conditions. The results show that the use of a rough surface finish can be used to reduce the profile loss. In addition, the results show that the same quantitative values of losses are obtained at high- and low-speed flow conditions. The latter proves the validity of the low-speed approach for ultra-high-lift profiles for the case of an exit Mach number of the order of 0.64. Hot-wire measurements were carried out to explain the effect of the surface finish on the wake-induced transition mechanism.

The Past of the Future of Computation

2018 ◽  
Author(s):  
James A. Anderson
Keyword(s):  
Artificial Intelligence ◽  
High Speed ◽  
The Other ◽  
Cognitive Tasks ◽  
Cognitive Tool ◽  
The Past ◽  
The World ◽  
The Future ◽  
Simple Step ◽  
A Current

Hand axes, language, and computers are tools that increase our ability to deal with the world. Computing is a cognitive tool and comes in several kinds: digital, analog, and brain-like. An analog telephone connects two telephones with a wire. Talking causes a current to flow on the wire. In a digital telephone the voltage is converted into groups of ones or zeros and sent at high speed from one telephone to the other. An analog telephone requires one simple step. A digital telephone requires several million discrete steps per second. Digital telephones work because the hardware has gotten much faster. Yet brains constructed of slow devices and using a few watts of power are competitive for many cognitive tasks. The important question is not why machines are becoming so smart but why humans are still so good. Artificial intelligence is missing something important probably based on hardware differences.

Compressibility effects in a turbulent annular mixing layer. Part 2. Mixing of a passive scalar

2000 ◽  
Vol 421 ◽  
pp. 269-292 ◽  
Author(s):  
JONATHAN B. FREUND ◽  
PARVIZ MOIN ◽  
SANJIVA K. LELE
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Mixture Fraction ◽  
Mixing Layer ◽  
Passive Scalar ◽  
Momentum Equation ◽  
Mixing Efficiency ◽  
Scalar Flux ◽  
Mach Numbers ◽  
Highly Correlated

The mixing of fuel and oxidizer in a mixing layer between high-speed streams is important in many applications, especially air-breathing propulsion systems. The details of this process in a turbulent annular mixing layer are studied with direct numerical simulation. Convective Mach numbers of the simulations range from Mc = 0.1 to Mc = 1.8. Visualizations of the scalar field show that at low Mach numbers large intrusions of nearly pure ambient or core fluid span the mixing region, whereas at higher Mach numbers these intrusions are suppressed. Increasing the Mach number is found to change the mixture fraction probability density function from non-marching to marching and the mixing efficiency from 0.5 at Mc = 0.1 to 0.67 at Mc = 1.5. Scalar concentration fluctuations and the axial velocity fluctuations become highly correlated as the Mach number increases and a suppressed role of pressure in the axial momentum equation is found to be responsible for this. Anisotropy of scalar flux increases with Mc, and is explained via the suppression of transverse turbulence lengthscale.

scholarly journals On active control of laminar–turbulent transition on two-dimensional wings

2011 ◽  
Vol 369 (1940) ◽  
pp. 1382-1395 ◽  
Author(s):  
Ralf Erdmann ◽  
Andreas Pätzold ◽  
Marcus Engert ◽  
Inken Peltzer ◽  
Wolfgang Nitsche
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Active Control ◽  
High Speed ◽  
Control Algorithm ◽  
Frequency Range ◽  
Wind Tunnel Experiments ◽  
Low Speed ◽  
Turbulent Transition ◽  
Mach Numbers

This paper gives an overview of drag reduction on aerofoils by means of active control of Tollmien–Schlichting (TS) waves. Wind-tunnel experiments at Mach numbers of up to M x =0.42 and model Reynolds numbers of up to Re c =2×10 6 , as well as in-flight experiments on a wing glove at Mach numbers of M <0.1 and at a Reynolds number of Re c =2.4×10 6 , are presented. Surface hot wires were used to detect the linearly growing TS waves in the transitional boundary layer. Different types of voice-coil- and piezo-driven membrane actuators, as well as active-wall actuators, located between the reference and error sensors, were demonstrated to be effective in introducing counter-waves into the boundary layer to cancel the travelling TS waves. A control algorithm based on the filtered- x least mean square (FxLMS) approach was employed for in-flight and high-speed wind-tunnel experiments. A model-predictive control algorithm was tested in low-speed experiments on an active-wall actuator system. For the in-flight experiments, a reduction of up to 12 dB (75% TS amplitude) was accomplished in the TS frequency range between 200 and 600 Hz. A significant reduction of up to 20 dB (90% TS amplitude) in the flow disturbance amplitude was achieved in high-speed wind-tunnel experiments in the fundamental TS frequency range between 3 and 8 kHz. A downstream shift of the laminar–turbulent transition of up to seven TS wavelengths is presented. The cascaded sensor–actuator arrangement given by Sturzebecher & Nitsche in 2003 for low-speed wind-tunnel experiments was able to shift the transition Δ x =240 mm (18%  x / c ) downstream by a TS amplitude reduction of 96 per cent (30 dB). By using an active-wall actuator, which is much shorter than the cascaded system, a transition delay of seven TS wavelengths (16 dB TS amplitude reduction) was reached.

scholarly journals Revaluation of Researches on the Free Rotating Vaneless Diffusor

1989 ◽  
Author(s):  
Yves Ribaud ◽  
Christian Fradin
Keyword(s):  
High Speed ◽  
Mechanical Design ◽  
Free Rotation ◽  
Vaneless Diffuser ◽  
Low Speed ◽  
Mach Numbers ◽  
High Mach

After eighteen years, an attempt is now being made to revaluate the studies performed by RODGERS-MNEW and RIBAUD-FRADIN on the rotating vaneless diffuser. These two studies are complementary. The first deals with a high speed rotating vaneless diffusor fed by a swirl generating nozzle and giving high Mach numbers. The second concerns a real compressor comprising a low speed rotor followed by a rotating vaneless diffuser. The free rotation of the vaneless diffusor reduces the friction losses by about 70%. The high speed, mechanical design of the rotating vaneless diffusor is a success. The structure of the flow at the rotor outlet seems to have an important effect on the efficiency of the rotating vaneless diffusor. New types of rotating vaneless diffusors should be experimented and new comparative experiments attempted. The application of the rotating vaneless diffusor concept to low specific speeds compressors is also proposed.

Separation and Transition Control on an Aft-Loaded Ultra-High-Lift LP Turbine Blade at Low Reynolds Numbers: High-Speed Validation

2005 ◽  
Author(s):  
Maria Vera ◽  
Xue Feng Zhang ◽  
Howard Hodson ◽  
Neil Harvey
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Surface Finish ◽  
High Speed ◽  
Reynolds Numbers ◽  
High Lift ◽  
Low Reynolds Numbers ◽  
Low Speed ◽  
Transition Mechanism ◽  
Low Reynolds

This paper presents the second part of an investigation of the combined effects of unsteadiness and surface roughness on an aft-loaded ultra high lift low pressure turbine (LPT) profile at low Reynolds numbers. The investigation has been performed using low-speed and high-speed cascade facilities. The low speed and the high speed profiles have been designed to have the same normalized isentropic Mach number distribution. The low speed results have been presented in Part 1 of this paper. The current paper examines the effect of different surface finishes on an aft-loaded ultra-high-lift LPT profile at Mach and Reynolds numbers representative of LPT engine conditions. The surface roughness values are presented along with the profile losses under steady and unsteady inflow conditions. The results show that the use of a rough surface finish might reduce the profile loss. In addition, the results show that the same quantitative values of losses are obtained at high and low speed flow conditions. The latter proves the validity of the low speed approach for ultra high lift profiles for the case of an exit Mach number of the order of 0.64. Hot wire measurements were carried out to explain the effect of the surface finish on the wake induced transition mechanism.

The Effects of Unsteadiness and Compressibility on the Interaction Between Hub Leakage and Mainstream Flows in HP Turbines

2011 ◽  
Author(s):  
I. Popovic´ ◽  
H. P. Hodson ◽  
E. Janke ◽  
T. Wolf
Keyword(s):  
Mach Number ◽  
Relative Motion ◽  
High Speed ◽  
Leakage Flow ◽  
Linear Cascade ◽  
Low Speed ◽  
Present Test ◽  
Blade Row ◽  
Time Average ◽  
Unsteady Effects

This paper investigates the effects of compressibility and unsteadiness due to the relative blade row motion and their importance in the interaction between hub leakage (purge) and mainstream flows. First, the challenges associated with the blade redesign for low-speed testing are described. The effects of Mach number are then addressed by analyzing the experiments in the low-speed linear cascade equipped with the secondary airflow system and computations performed on the low- and high-speed blade profiles. These results indicate that the compressibility does not significantly affect the interaction between the leakage and mainstream flows despite a number of compromises made during the design of the low-speed blade. This was due to the fact that the leakage-mainstream interaction takes place upstream of the blade throat where the local Mach numbers are still relatively low. The analysis is then extended to the equivalent full-stage unsteady computations. The periodic unsteadiness resulting from the relative motion of the upstream vanes appreciably affected the way in which the leakage flow is injected and the rotor flowfield in general. However, the time-average flowfield was still found to be dominated by the rotor blade’s potential field. For the present test arrangement, the unsteady effects were not very detrimental, and caused less than a 10% increase in the losses due to the leakage injection relative to the steady calculations.

Power Plants for High–Speed Aircraft

1951 ◽  
Vol 55 (490) ◽  
pp. 642-650 ◽  
Author(s):  
A. D. Baxter
Keyword(s):  
Mach Number ◽  
Shock Waves ◽  
High Speed ◽  
Power Plants ◽  
Ground Level ◽  
Jet Propulsion ◽  
Supersonic Aircraft ◽  
Ordinary Power ◽  
The Difference ◽  
Transonic Region

A few years ago when high–speed aircraft were mentioned, speeds of 300 to 400 m.p.h. came to mind. The advent of jet propulsion has made those figures 100 per cent, out of date and today speeds are discussed more and more in terms of Mach number; for example, high–speed subsonic aircraft fly at Mach numbers of 0.85 to 0.90, aircraft are flying in the transonic region and supersonic guided missiles are proposed for speeds anywhere between M=1.5 and 2.5, i.e. ground level speeds up to 2,000 m.p.h.It is proposed to review very broadly the suitability of propulsion units for these transonic and supersonic applications. What is the difference between ordinary power plants and those for high speed? The answer might be contained in another question—why are supersonic aircraft different from conventional types? The aerodynamicist will give an involved explanation concerned with compressibility, drag rise, shock waves, and so on.

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