Vortex breakdown and control experiments in the Ames-Dryden water tunnel

Flow-field measurements have been made to determine the effects of core blowing on vortex breakdown and control. The results of these proof-of-concept experiments clearly demonstrate the usefulness of water tunnels as test platforms for advanced flow-field simulation and measurement

Control of forebody three-dimensional flow separations

Some experiments involving the development of the turbulent symmetric vortex flow about the lee side of a 5 deg semiangle conical forebody at high relative incidence are discussed. The cone was immersed in a Mach 0.6 airstream at a Reynolds number of 13.5 million based on the 1.4 - m axial length of the cone. Novel means of controlling the degree of asymmetry using blowing very close to the nose were investigated. Small amounts of air injected normally or tangentially to the cone surface, but on one side of the leeward meridian and beneath the vortex farthest from the wall, were effective in biasing the asymmetry. With this reorientation of the forebody vortices, the amplitude of the side force could be reduced to the point where its direction was reversed. This phenomenon could be obtained either by changing the blowing rate at constant incidence or by changing incidence at constant blowing rate. Normal injection was more effective than tangential injection. An organized and stable flow structure emerged with the jet vortices positioned above the forebody vortices

Symmetrical and asymmetrical separations about a yawed cone

Three dimensional flow separations about a circular cone were investigated in the Mach number range 0.6 - 1.8. The cone was tested in the Ames 1.8 by 1.8 m wind tunnel at Reynolds numbers based on the cone length from 4,500,000 to 13,500,000 under nominally zero heat transfer conditions. Results indicate that: (1) the lee-side separated flow develops from initially symmetrically disposed and near-conical separation lines at angle of incidence/cone semiangle equal to approximately 1, with the free shear layers eventually rolling up into tightly coiled vortices at all Mach numbers; (2) the onset of asymmetry of the lee-side separated flow about the mean pitch plane is sensitive to Mach number, Reynolds number, and the nose bluntness; and (3) as the Mach number is increased beyond 1.8, the critical angle of incidence for the onset of asymmetry increases until at about M = 2.75 there is no longer any significant side force development

On the evolution of U.S. foreign-exchange-market intervention: thesis, theory, and institutions

Attitudes about foreign-exchange-market intervention in the United States evolved in tandem with views about monetary policy as policy makers grappled with the perennial problem of having more economic objectives than independent instruments with which to achieve them. This paper—the introductory chapter to our history of U.S. foreign exchange market intervention—explains this thesis and summarizes our conclusion: The Federal Reserve abandoned frequent foreign-exchange-market intervention because, rather than providing a solution to the instruments-versus-objectives problem, it interfered with the Federal Reserve’s ability to credibly commit to low and stable inflation. This chapter also provides a theoretical discussion of intervention, background on U.S. institutions for conducting intervention, and a roadmap to the remainder of our book.Foreign exchange market ; Monetary policy - United States

Bretton Woods and the U.S. decision to intervene in the foreign-exchange market, 1957-1962

The deterioration in the U.S. balance of payments after 1957 and an accelerating loss of gold reserves prompted U.S. monetary authorities to undertake foreign-exchange-market interventions beginning in 1961. We discuss the events leading up to these interventions, the institutional arrangements developed for that purpose, and the controversies that ensued. Although these interventions forestalled a loss of U.S. gold reserves, in the end, they only delayed more fundamental adjustments and, in that respect, were a failure.Foreign exchange administration ; Bretton Woods Agreements Act

A brief empirical history of U.S. foreign-exchange intervention: 1973-1995

This paper assesses U.S. foreign-exchange intervention since the inception of generalized floating. We find that intervention was by and large ineffectual. We first identify which interventions were successful according to three criteria. Then, we test whether the number of observed successes significantly exceeds the amount that would randomly occur given the near-martingale nature of daily exchange-rate changes. Finally, we investigate whether the various characteristics of an intervention - its size, frequency, or coordination - can increase the probability of success. We find that intervention did tend to moderate same-day exchange-rate movements relative to the previous day, but this effect is not robust across subperiods or currencies and it occurs infrequently. Increasing the size of an intervention increases the probability of success, but no other variable consistently makes a difference, including coordinating interventions with other central banks.Foreign exchange administration

U.S. foreign-exchange-market intervention during the Volcker-Greenspan era

The Federal Reserve abandoned foreign-exchange-market intervention because it conflicted with the System’s commitment to price stability. By the early 1980s, economists generally concluded that, absent a portfolio-balance channel, sterilized foreign-exchange-market intervention did not provide central banks with a mechanism for systematically influencing exchange rates independent of their monetary policies. If intervention were to have anything other than a fleeting, hit-or-miss effect on exchange rates, monetary policy had to support it. Exchange rates, however, often responded to U.S. monetary-policy initiatives, so intervention to offset or reverse those exchange-rate responses can seem a contrary policy move and can create uncertainty about the strength of the System's commitment to price stability. That the U.S. Treasury maintained primary responsibility for foreign-exchange intervention only compounded this uncertainty. In addition, many FOMC participants feared that swap drawings and warehousing could contravene the Congressional appropriations process and, therefore, potentially pose a threat to System independence, a necessary condition for monetary-policy credibility.Banks and banking, Central ; Foreign exchange administration ; Monetary policy ; Federal Open Market Committee

U.S. monetary-policy evolution and U.S. intervention

The United States all but abandoned its foreign-exchange-market intervention operations in late 1995, when they proved corrosive to the credibility of the Federal Reserve?s commitment to price stability. We view this decision as the culmination of the evolution of U.S. monetary policy over the past century from a gold standard to a fiat money regime. The abandonment of intervention was necessary to secure monetary policy credibility.Foreign exchange market ; Monetary policy - United States ; Federal Open Market Committee

Evaluation of flow quality in two large NASA wind tunnels at transonic speeds

Wind tunnel testing of low drag airfoils and basic transition studies at transonic speeds are designed to provide high quality aerodynamic data at high Reynolds numbers. This requires that the flow quality in facilities used for such research be excellent. To obtain a better understanding of the characteristics of facility disturbances and identification of their sources for possible facility modification, detailed flow quality measurements were made in two prospective NASA wind tunnels. Experimental results are presented of an extensive and systematic flow quality study of the settling chamber, test section, and diffuser in the Langley 8 foot transonic pressure tunnel and the Ames 12 foot pressure wind tunnel. Results indicate that the free stream velocity and pressure fluctuation levels in both facilities are low at subsonic speeds and are so high as to make it difficult to conduct meaningful boundary layer control and transition studies at transonic speeds